46780638 Post Harvest Tech for Leafy Veg

7/22/2019 46780638 Post Harvest Tech for Leafy Veg

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Postharvest Technology for Leafy Vegetables

AVRDC The World Vegetable CenterShanhua, Taiwan


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Postharvest Technologyfor Leafy Vegetables

AVRDC-ADB Postharvest ProjectsRETA 6208/6376

Antonio L. Acedo, Jr.


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AVRDC - The World Vegetable CenterThe leading international nonprofit organization committed to alleviating povertyand malnutrition in the developing world through the increased production andconsumption of safe vegetables.

AVRDC - The World Vegetable CenterP.O. Box 42Shanhua, Tainan 74199TAIWAN

Tel: +886 6 583 7801Fax: +886 6 583 0009

Email: [email protected]: www.avrdc.org

AVRDC Publication No: 10-733

Editor: Maureen MecozziAVRDC Publication Team: Kathy Chen, Vanna Liu, Chen Ming-che, Shiu-luan Lu

2010 AVRDC - The World Vegetable Center

Project partner

CitationAcedo AL Jr. 2010. Postharvest technology for leafy vegetables. AVRDC-ADB Postharvest ProjectsRETA 6208/6376. AVRDC Publication No. 10-733. AVRDC - The World Vegetable Center, Taiwan. 67 p.


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Contents

Contents ..................................................................................................................................... iTables.........................................................................................................................................iiFigures........................................................................................................................................

iiiForeword.....................................................................................................................................iv

1 INTRODUCTION...................................................................................................................1

2 PRODUCT QUALITY AND POSTHARVEST LOSS.............................................................2Quality Factors .......................................................................................................................2Quality Deterioration ..............................................................................................................2

Physiological deterioration.................................................................................................2Pathological decay.............................................................................................................5Mechanical injury ...............................................................................................................5

Postharvest Loss....................................................................................................................5

3 POSTHARVEST TECHNOLOGIES FOR FRESH LEAFY VEGETABLES............................6Improved Crop Variety ...........................................................................................................6Production Factors .................................................................................................................6Harvesting ..............................................................................................................................7

Harvest maturity.................................................................................................................7Time of harvesting .............................................................................................................7Harvesting method.............................................................................................................8

Field Handling ........................................................................................................................8Packinghouse Operations ......................................................................................................9

Trimming............................................................................................................................9Sorting/Grading................................................................................................................10Washing and sanitizing....................................................................................................10Other commodity treatments ...........................................................................................11

Packaging.............................................................................................................................12Produce packages ...........................................................................................................12Reinforcing and handling packages.................................................................................12Modified atmosphere packaging (MAP)...........................................................................14

Cooling and Storage ............................................................................................................15Precooling ........................................................................................................................17Optimum storage conditions............................................................................................17Cooling methods in developing countries........................................................................18

Transport Techniques .......................................................................................................... 21Market Handling ...................................................................................................................22Other PHT Developments.................................................................................................... 22

Ethylene removal from postharvest chain ....................................................................... 22Cold chain system............................................................................................................23Supply chain management .............................................................................................. 24Economic Analysis of Postharvest Technologies ................................................................ 26Example 1: postharvest technical advice ........................................................................ 27Example 2: postharvest technique from exploratory investigation .................................. 27Example 3: introduction of better postharvest material ................................................... 27

4 PROCESSING TECHNOLOGIES FOR LEAFY VEGETABLES......................................... 30Importance of Processing .................................................................................................... 30Commodity Considerations .................................................................................................. 30Preprocessing Operations.................................................................................................... 30

Washing........................................................................................................................... 30Cutting.............................................................................................................................. 31Blanching ......................................................................................................................... 31

Salting Technology............................................................................................................... 31Fermentation Technologies.................................................................................................. 32

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Basic information ............................................................................................................. 32Sauerkraut processing..................................................................................................... 33Kimchi processing............................................................................................................ 35Fermented mustards and cabbage.................................................................................. 35

Pickling Technologies .......................................................................................................... 46Drying/Dehydration Technologies........................................................................................ 46

Basic principles................................................................................................................ 46

Pre-drying operations ...................................................................................................... 47Simple dryers................................................................................................................... 47Producing dehydrated cabbage....................................................................................... 48Producing dehydrated Kangkong .................................................................................... 48Dehydrated leafy vegetables in China............................................................................. 50Packaging dried vegetables ............................................................................................ 50

Canning Technologies ......................................................................................................... 53Cabbage canning............................................................................................................. 53Canning techniques for other leafy vegetables ............................................................... 54

5 SUMMARY......................................................................................................................... 55

References............................................................................................................................... 56

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Tables

Table 1. Chinese cabbage grade standards in Yunnan, China................................................ 18Table 2. Postharvest cooling methods and suitable commodities. .......................................... 16Table 3. Cost benefit analysis of keeping 2-3 outer leaves of Chinese cabbage duringtransport compared to removing all outer leaves. .................................................................... 28Table 4. Potential cost and benefit of using guava leaf extract and alum for bacterial soft rotcontrol in common cabbage. .................................................................................................... 28Table 5. Cost-benefit analysis of using poly sacks and plastic crates for transportingvegetables from the collecting center, Keppetipola to the central (Manning) market in Colombo,Sri Lanka................................................................................................................................... 29Table 7. Sample recipe for Kimchi production.......................................................................... 36Table 8. Desired fresh and dry weight ratio after drying for some vegetables........................ 59

Figures

Figure 1. Ethylene-induced cabbage yellowing and culinary herbs epinasty, abscission andyellowing................................................................................................................................... 11Figure 2. Chilling injury development in sweet basil leaves. ...................................................... 4Figure 3. Trimming, cleaning, and bundling leafy vegetables. ................................................... 9Figure 4. Packaging containers for leafy vegetables. .............................................................. 13Figure 5. Protective packaging practices. ................................................................................ 14Figure 6. MAP practices for leafy vegetables........................................................................... 16Figure 7. Ice packing and use of ice bottles for cooling leafy vegetables. ............................... 19Figure 8. Simple refrigeration equipment for the storage of leafy vegetables.......................... 19Figure 9. Low-cost evaporative cooler developed in Sri Lanka................................................ 28Figure 10. Application of evaporative cooling and/or modified atmosphere in packing andtransport of leafy vegetables. ................................................................................................... 29Figure 11. Traditional and innovative stacking procedures for containers of leafy vegetables 23Figure 12. Traditional supply chain system for leafy vegetables.............................................. 25Figure 13. Corporate supply chain system for leafy vegetables. ............................................. 26Figure 14. Cooperative system of supply chain management. ................................................ 26Figure 15. Myanmar government-initiated supply chain for export vegetables produced bycontract farmers and brought to the packinghouse for sorting, hydrocooling, packing in cartonbox, cold storage, and transport in refrigerated trucks for cargo flight..................................... 27Figure 16. Process flow for sauerkraut production................................................................... 42Figure 17. Process flow for Kimchi production.........................................................................36Figure 18. Flow chart of fermented leaf mustard processing. .................................................. 45Figure 19. Process flow for producing fermented mustard leaves........................................... 39Figure 20. Lao process for producing fermented Chinese mustard. ........................................ 39Figure 21. Fermentation pond/plastic barrel and earthen jar for fermented product................ 48Figure 22. General flow chart of fermented leaf mustard processing. ..................................... 48Figure 23. Company processing operation for fermented mustards in Thailand. .................... 49Figure 24. Process flow for Chinese mustard fermentation technique ................................... 42Figure 25. Process flow for Chinese mustard and cabbage fermentation . ............................ 43Figure 26. Process flow for fermented cabbage and mustard canning................................... 45Figure 27. Process flow for producing pickled cabbage........................................................... 46Figure 28. Different commercial solar dryers in Thailand......................................................... 49Figure 29. Gas- and electric-powered cabinet dryers. ............................................................. 49Figure 30. Washing, cutting, blanching and removal of excess water in leafy vegetable forprocessing to dehydrated product. ........................................................................................... 51Figure 31. Drying leafy vegetable with or without pre-drying dextrose treatment................... 52Figure 32. Sorting, packing and storage of dehydrated leafy vegetable................................. 53

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1 INTRODUCTION

Leafy vegetables are important crops in Greater Mekong Subregion (GMS) countries,providing income to many small farmers, processors, and other entrepreneurs, and serving ashealth foods for the rural and urban populace. They are rich sources of vitamins, minerals, anddietary fiber. Leafy vegetables also play a vital role in the global drive to end hiddenhungermicronutrient deficiency (Buyckx, undated). Deficiency in vitamin A is a majorproblem in 37 countries, mostly in Southeast Asia and Africa, with 250,000-500,000 people,mostly children, becoming partially or totally blind yearly. More than 2 billion people worldwideare anemic or have insufficient iron intake. Green leafy vegetables are rich in both vitamin Aand iron. Sustainable and reliable food supply systems are needed to ensure global foodavailability, access to food at the household level, and more opportunities for development ofpeoples well-being. A vital strategy is to reduce postharvest losses, especially highlyperishable leafy vegetables.

Reducing postharvest losses through appropriate postharvest technologies for fresh andprocessed produce would not only increase food availability to the growing world populationbut also decrease the area needed for production and conserve natural resources (Kader,

2006). While there are many postharvest technologies that extend the market availability ofvegetables, the appropriateness of these technologies has to be ascertained through site-specific and commodity-specific studies. A technology proven effective and commercially usedelsewhere is not necessarily the best for use under conditions of another country.Technologies developed in a developing country may better suit the need of anotherdeveloping country, as they typically are much simpler and less costly than technologiescreated in developed countries.

In recent years, reducing postharvest losses has become only part of efforts to improve foodavailability; assuring food quality and safety are increasingly important as well. Marketdemand is responding to consumers' rising nutritional expectations and awareness of foodsafety. Maintaining product quality and safety can greatly determine marketing success(Sullivan et al., 1991). Countries can increase their competitiveness and world market shares

by providing higher quality, safe products and promoting lower prices through technologicalinnovation.

Leafy vegetables given emphasis in this report include the leafy brassicas, such as commoncabbage, which is also known as round cabbage or head cabbage (Brassica oleracea varcapitata); Chinese cabbage (Brassica rapa. var.pekinensis); bok choy or pak choi (Brassicarapa. var. chinensis), a non-heading form of Chinese cabbage; Chinese mustard (Brassicajuncea var. rugosa); and other priority vegetables of the partners in Cambodia, Laos, andVietnam (e.g. amaranth, kangkong).

This report consolidates the literature search results and relevant information from paperspresented during the RETA 6376 Workshop on Best Practices in Postharvest Management ofLeafy Vegetables in GMS Countries held on 25-27 October 2007 in Hanoi, Vietnam.

Information and actual observations during country visits and study missions in some GMScountries are also included. This report has three main sections. The first section providessome basic information on leafy vegetable quality and postharvest loss, for betterunderstanding of the underlying reasons for the technological recommendations in freshproduce handling and processing described in the second and third sections. The focusthroughout is on simple, low-cost methods. Other techniques and information that can beconsidered in future initiatives are incorporated. In addition, sample cost-benefit analyses ofselected techniques is introduced in preparation for training on this topic, and for similaranalyses to be done for the techniques developed in the AVRDC-ADB postharvest projects.

Postharvest Technology of Leafy Vegetables 1


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2 PRODUCT QUALITY AND POSTHARVEST LOSS

Quality Factors

Leafy vegetable quality is mainly based on appearance (e.g. fresh-looking, well-formed or

well-shaped, right size, right maturity, right color, turgid or not wilted, free of defects such asrot, physical damage, yellowing, or wilting) and to a certain extent, other attributes that cannotbe seen but can be discerned by the other human senses, such as firmness, tenderness, andtaste. For common cabbage and Chinese cabbage, the heads should be light green, compactbut not overmature (no seed stalk), right size, and free of defects. Freshness of cabbages canbe tested by rubbing two heads together; if they are fresh, they will make a squeaking sound.For other leafy vegetables, consumers seek similar visual quality attributes (freshness,uniformity of size, shape and typical color, and free of defects). Chinese mustard should havethe typical flavor or aroma.

Concerns about food safety and nutritional value have made quality definition more complex.Safety factors include pesticide residues (the most important safety issue among consumers),microbial contamination (the number one safety concern among health authorities and

scientists), natural toxicants (antinutrients), natural contaminants (mycotoxins, bacterial toxins,and heavy metals such as cadmium, lead, mercury), and environmental pollutants (Kader andRolle, 2004). These safety concerns, particularly microbial contamination, are the basis for theworldwide promotion of safety standards in production (Good Agricultural Practices or GAP),postharvest handling (Good Hygienic Practices or GHP) and processing (Good ManufacturingPractices or GMP), which incorporate principles and recommendations from Hazard Analysis& Critical Control Points (HACCP) and Codex Alimentarius. Quality standards compliancewould greatly raise market competitiveness and consumer confidence in the produce and itssource.

Quality Deterioration

Wilting due to water loss, senescence-associated discoloration (yellowing or browning),mechanical injury, high respiration rate, and decay or rotting are the main causes of qualitydeterioration and postharvest loss of leafy vegetables. These causes of quality loss arephysiological, pathological, and mechanical in nature.

Physiological deterioration

Water loss and wilting. Leafy vegetables are mostly water (>90%) and have the propensity tolose water through transpiration (evaporation of water from plant tissues). Water loss is themain cause of weight loss (loss in saleable weight) and wilting (Fig. 1). A loss of 5-10% offresh weight would make leafy vegetables to appear wilted and become unusable(Kanlayanarat, 2007). Water loss also induces degradation of nutritional components (e.g.vitamin C loss) and imposes stress (i.e. water stress) that increases respiration and ethyleneproduction. In pak choi, wilting is primarily due to water loss through the stomata (OHare etal., 2001). Water loss was measured at 2.8% per hour at 35C. Complete closure of allstomata occurs between 10-15% moisture loss. Wilting occurred more rapidly in leaves withlower initial water potential. Water potential in pak choi was highest when harvested at 0400and 2200h.

Respiration and ethylene production. Leafy vegetables are non-climacteric, that is, they do notexhibit a final surge in respiration and ethylene production during senescence (Jobling,undated). Cabbages generally have lower respiration and ethylene production rates, partlydue to their morphology, in which the young inner leaves are fully covered by the more matureouter leaves compared with Chinese kale or green mustards. However, cabbage is sensitiveto ethylene (senescence hormone), which causes yellowing, epinasty (leaf curving), and

abscission (Fig. 1) (Cantwell and Suslow, 2006; Cantwell and Reid, 2006; Jobling, undated).In lettuce, ethylene induces russet spotting manifested as dark brown spotting of the midribs.

2 AVRDC-ADB Postharvest Projects RETA 6208/6376


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A. Ethylene-induced disorders B. Bacterial soft rot, wilting and yellowing in cabbages

Figure 1. Ethylene-induced cabbage yellowing and culinary herbs epinasty, abscissionand yellowing (Cantwell & Suslow, 2006; Cantwell & Reid, 2006); bacterial soft rot incommon cabbage and Chinese cabbage; and out leaf wilting and yellowing in Chinesecabbage (Acedo et al., 1999; Acedo et al., 2003).



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Figure 2. Chilling injury development in sweet basil leaves (Cantwell & Reid, 2006).

(Score: 0 = no injury, 8 = severe. Score of 3: limit of commercial acceptability.)

Prolonged exposure to ethylene, as low as 0.01 ppm, could cause significant losses of freshproduce. Ethylene easily accumulates in packages, packinghouses, storage areas, and evenmarkets. All plant tissues produce ethylene, although at varying levels. In markets (wholesale,retail, distribution centers), the main sources of ethylene, in addition to the fresh produce,include ripening fruit, decaying produce, and exhaust gases of vehicles; concentration couldreach 0.02-0.06 ppm, which can cause a 10-30% loss in product shelf life (Wills et al., 2000).The effect of ethylene is cumulative, so continuous exposure to a low concentrationthroughout marketing can cause significant harm. The loss of shelf life will be most frustratingfor the final consumer, as the loss of quality will not be obvious during marketing and retail.Aside from accelerating aging, ethylene increases product susceptibility to decay.

In pak choi, leaf yellowing was found to be controlled by the sugar level (the main energysubstrate) rather than ethylene, which explains the poor performance of anti-ethylene agents(e.g. 1-methylcyclopropene) in extending shelf life (OHare et al., 2001). Understanding thismechanism also avoided the potentially expensive error of designing genetically modified pakchoi through manipulation of ethylene metabolism. Sugars tend to be highest in youngerleaves and lowest in leaves toward the base of stem even though the leaves may look similarin size and appearance. As a result, shelf life was longer in younger leaves than older leaves.

Leaf yellowing may also be related to genetics (i.e. cultivars), exposure to temperature abuse(i.e. high temperatures), and the level of stress tolerance inherent in the leaf tissue(Kanlayanarat, 2007).

Physiological disorders. Chilling injury is induced by storage below the recommended lowtemperature requirement but above the freezing point of tissues, usually between -2C to 0C.In Chinese cabbage, chilling sensitivity varies with cultivar and the injury symptom is mainlymidrib discoloration, especially on outer leaves (Cantwell and Suslow, 2006). Chinesecabbage developed patchy papery necrosis more severely at 0C and 2C, while none wasnoted at 20C. For tropical leafy vegetables such as kangkong and some mustard greens,chilling injury is induced at 10C and lower. This was shown in sweet basil leaves, whichdeveloped chilling injury symptoms (browning of leaves and growing tip, bronzing of leaf veins,and loss of glossy appearance of leaves) more rapidly at lower chilling temperatures (Fig. 2)(Cantwell and Reid, 2006). For common cabbage, physiological deterioration during storage isassociated with stem or seed stalk growth (bolting), root growth, internal breakdown, leafabscission, discoloration, and black speck (Cantwell and Suslow, 2006).

Chilling injury score

Days of storage



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Pathological decay

Leafy vegetables are susceptible to postharvest diseases that render the produce unfit to sell.Postharvest diseases can be spread through field boxes contaminated by soil or decayingproduce or both, contaminated water used to wash produce before packing, decaying rejectedproduce left lying around the packinghouse, and contaminated healthy produce in packages.

Microbial infection can occur both before and after harvest. The infection after harvest can befound at any time between the field and final consumer (Kanlayanarat, 2007).

Among postharvest diseases, bacterial soft rot is the most important problem, particularly inbrassicas such as cabbages and Chinese kale (Fig. 1). It is caused by various bacterialspecies including Erwinia, Pseudomonas, andXanthomonas and is characterized by slimybreakdown of infected tissue with offensive foul odor. The disease usually develops at the cutportion (butt end) and injured leaves of cabbages. Other common decays in cabbage arewatery soft rot (Sclerotinia), gray mold rot (Botrytis cinerea), and alternaria leaf spot (Alternariaspp.) (Cantwell and Suslow, 2006).

Mechanical injury

Leafy vegetables are very susceptible to mechanical injury (physical damage). Leaf tearingand crushing, midrib breakage, and head cracking or bursting are common forms of damage.Physical injuries increase physiological deterioration through browning as a result of oxidationof phenolics substances, and susceptibility to decay. Postharvest rots have been found to bemore prevalent in bruised or damaged produce (Bachmann and Earles, 2000). Mechanicaldamage also increases moisture loss by as much as 3-4 times more than that of undamagedproduce.

Postharvest Loss

Quality deterioration results in partial or total loss of fresh produce. It is predisposed by anumber of interacting factors, which may be preharvest, harvest and/or postharvest in origin,

such as poor crop variety, unfavorable climate, inadequate cultural practices, lack ofharvesting techniques, improper handling, and poor storage conditions. Non-technologicalfactors also contribute to postharvest loss, such as lack of capable human resources, lack ofknowledge about technical and scientific technologies, inefficient commercialization andmarketing systems, lack of logistical support, and lack of enabling policy for the use andadministration of human, economic, technical, and scientific resources.

Postharvest losses of leafy vegetables vary with commodity, location, growing season, andother factors such as standards of quality and consumer preferences and purchasing power,which differ greatly among countries and across cultures (Kader and Rolle, 2004). Postharvestloss estimates in developing countries are alarming (e.g. 20-50% of production) but efforts arelacking to establish the seriousness of the problem and the interventions needed.

In the AVRDC-ADB postharvest projects, postharvest losses were determined at specificstages in the supply chain in Cambodia, Laos, and Vietnam and outright volume loss ofspecific vegetables including the leafy types (e.g. Chinese cabbage) was estimated at anaverage of 17% (Weinberger et al., 2007). The loss situation maybe more serious if qualitativelosses (e.g. loss in price due to reduced quality, loss in nutritional quality, edibility or caloricvalue) were factored in. Contributing factors to these losses were identified and prioritized forR&D interventions. In the RETA 6376 initiative, more specific assessment of postharvest lossis being pursued, covering selected leafy vegetables in two upland areas of each country atthe farmer and processor levels.



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3 POSTHARVEST TECHNOLOGIES FOR FRESHLEAFY VEGETABLES

The farm-to-table approach (other terms: system approach, whole chain approach, supply

chain approach) is increasingly used to grow and market fresh produce. With this approach,factors before and after harvest are taken into account to obtain the desired product quantityand quality, reduce postharvest loss, and ensure delivery of good quality, safe produce toconsumers. Any intervention that manipulates postharvest quality and shelf life could beconsidered under postharvest technology (PHT). This section introduces some productionfactors that influence product quality and shelf life, and discusses PHT innovations andrecommendations, from harvesting to market handling.

Improved Crop Variety

Leafy vegetables have limited storage life even under optimum storage conditions. Thepotential shelf life is partly under genetic control and can be manipulated by breeding.

Breeding leafy vegetables for long shelf life and desired shipping quality is a particular need indeveloping countries with hot and humid climates where refrigerated facilities are lacking dueto the high cost. Some specific shelf-life attributes that can be manipulated through breedinginclude green color retention and resistance to postharvest stress such as high temperatureand microbial infection.

More effort is now being exerted to develop vegetable varieties with desired shelf life, shippingand processing attributes, and high levels of nutrients. Breeding leafy vegetables with highcarotenoids content has been reported and results in lettuce were promising due to observedgenetic variations in B-carotene and lutein contents (Fonseca, 2004). B-carotene and luteinwere observed to be higher in leaves with higher chlorophyll content. Other nutrients invegetables include those with therapeutic or pharmaceutical uses, hence the termnutraceuticals (e.g. glucosinolates). A growing concern is placed on the possibility ofaccidentally lowering beneficial non-target components while enhancing targeted ones withnew technologies.

Production Factors

Environmental conditions and cultural practices during production have tremendous effects onproduce quality, safety, and shelf life. For example, lettuce harvested during a period of raindoes not ship well and product losses are increased.

Produce stressed by too much or too little water (by irrigation or rainfall), high rates of nitrogenfertilization, or mechanical injury (scrapes, bruises, abrasions) is susceptible to postharvestdiseases. Brassicas are prone to bacterial soft rotif nitrogen is applied as foliar feed, thus

nitrogen should be applied to the soil. This effect was not observed in pak choi (Jiang andPearce, 2005); nitrogen above the optimal level did not result in reduced shelf life, whilespraying nutrient solution appeared to be beneficial as it retarded yellowing. Potassium sulfateapplication also enhanced chlorophyll content and extended shelf life of pak choi.

Stress during growth has different effects on produce quality and shelf life. Sustained andintermittent water stress had mostly negative effects for pak choi (Jiang and Pearce, 2005).Although shelf life of pak choi could be extended by these stresses, the plant fresh and dryweights were reduced. In Chinese cabbage, water stress did not affect the water content andweight loss during nine weeks of storage at 0C. On the other hand, low light stress (shading)before harvest resulted in more rapid yellowing and wilting in pak choi, and lowered the leafsugar, organic acids, and chlorophyll content. Increasing the period of shading before harvestfurther reduced sugar content and increased moisture loss during storage.



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Ensuring safety of fresh leafy vegetables also begins in the field. Outbreaks of food-borneillnesses have been traced to contamination of produce in the field (Bachmann and Earles,2000). Some preventive measures include (1) avoiding application of fresh animal manure orslurries to a field or to an area immediately adjacent to a field nearing harvest maturity, (2)cleaning equipment that has been used to apply manure on one field before moving it toanother field, (3) avoiding using irrigation water from a farm pond used by livestock, and (4)

avoiding contact of produce with soil during growth (by mulching) or harvest.

Harvesting

Harvest maturity

Quality cannot be improved after harvest, only maintained; therefore, it is important to harvestat the proper maturity stage and at peak quality. Immature or overmature produce may not lastas long in storage as that picked at proper maturity. Common cabbage and Chinese cabbageheads are harvested when firm and mature (Bautista and Acedo, 1987; Boyette et al., 1992;Stephens, 2003; Cantwell and Suslow, 2006). Compactness (firmness, hardness, solidity) ofheads may be determined by hand pressure. A compact head can be only slightly

compressed with moderate hand pressure. Delaying harvest even a few days beyond maturitycan result in split or cracked heads and increased incidence of rots. Immature heads are puffyor have hollow spaces because the inner leaves are not fully developed and hence, looselyarranged, which make them susceptible to damage (Bautista and Acedo, 1987). Whenharvested immature, yield decreases and shelf life is shorter than that of mature heads. Incertain cases, some sample heads of common cabbage or Chinese cabbage are cutlongitudinally to observe the internal stem; if the stem is too long, the head is alreadyovermature (Chen, 2007). Harvest maturity of other vegetables such as leafy mustards,amaranth, and kangkong is based on plant size, number of days after planting (usually 25-30days) and/or tenderness of leaves. They are harvested when they have developed to thefullest size, yet not so advanced in age that the leaves are tough and the flavor is bitter.

Physiological age of the vegetable or the leaves within a plant could affect the rate of

postharvest quality loss. In pak choi, young leaves (2025 days after emergence) are moreprone to moisture loss and subsequent wilting than older ones (40 days) (OHare et al., 2001).However, older leaves turned yellow more quickly than younger leaves. This response wasrelated to initial sugar content, which was higher in younger leaves. In Chinese cabbageheads, intact mature leaves had a greater tendency to yellow than the same leaves, butdetached from the head. Young leaves in intact heads began to swell and expand after onemonth of storage, causing some heads to crack, leading to rapid senescence of whole heads.

Time of harvesting

The time of the day when harvesting is done also affects produce quality and shelf life. Ingeneral, harvesting during the coolest time of the day (e.g. early morning) is desirable; theproduce is not be exposed to the heat of the sun and the work efficiency of the harvesters is

higher. If harvesting during the hotter part of the day cannot be avoided, the produce shouldbe kept shaded in the field to minimize product heat, weight loss, and wilting.

Research showed that harvest time of day could affect quality of pak choi but not Chinesecabbage. Pak choi harvested at 0400h and 2000h contained the highest initial and final watercontent. Leaves harvested at these times maintained highest water potential, resulting in aslower rate of wilting than those with lower water potential (Jiang and Pearce, 2005). However,harvesting later in the day has an added advantage because sugar levels were found to behigher as a result of photosynthesis during the day (OHare et al., 2001). This could slow downleaf yellowing in pak choi, which has been associated with sugar depletion.



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Harvesting method

Harvesting is done manually, hence the harvesters have a major influence on produce quality.They should be made aware of the importance of good sanitation practices, proper maturityselection, and careful handling to avoid mechanical injuries.

A cabbage head is harvested by bending it to one side and cutting it with a knife, which shouldbe sharpened frequently to reduce effort and lessen picker fatigue. In Yunnan, China,cabbages and other leafy vegetables are harvested and trimmed using a special knife (Fig. 3)(Chen, 2007). The head should not be snapped or twisted, as this method damages the headand results in inconsistent stalk length and trim. Broken stalks are also more susceptible todecay. The stalk should be cut flat and as close to the head as possible, yet long enough toretain two to four wrapper leaves. Extra leaves act as a cushion during handling and may bedesired in certain markets. Yellowed, damaged, or diseased wrapper leaves should beremoved. Heads with insect damage and other defects should be discarded. It is essential thatheads not harvested be left undamaged because fields may be harvested as many as threetimes for maximum yield. Harvested cabbage can be placed in bags, boxes, wagons, or palletbins. Harvesting aids can significantly reduce labor costs, improve harvest efficiency andcabbage quality, and speed the harvest and field handling operation.

Mustards and Chinese kale are harvested as single leaves or whole plants. Fields are usuallyharvested several times, so care is needed to prevent damage to the plants. The producemust be handled gently during harvesting and field handling to avoid physical damage.

Field Handling

The harvested produce is usually placed in collection containers, which may be plastic cratesor bamboo baskets with cotton or paper cushioning or padding (Chen, 2007). Throwingharvested produce into the collection container or vehicle should be avoided to preventphysical injuries. Handling aids such as boxes, farm trailer, or a simple conveyer can be used.

Exposure of harvested produce to the heat of the sun is detrimental except in a few cases.Leafy vegetables left in the sun after harvest may reach temperatures as high as 50

oC(Kanlayanarat, 2007). High product temperature accelerates quality deterioration due toincreased water loss and respiration. If packed and transported without cooling, wilting andother deteriorative processes rapidly set in.

Purposive water loss (23% water loss) may be imposed on harvested produce. In pak choi,this can be done by laying plants under the sun for 30 minutes immediately after harvest(Jiang and Pearce, 2005). This was found to significantly reduce mechanical damage(snapping of turgid outer leaves) when the produce was packed into bamboo baskets.Subsequent washing to remove dirt was able to rehydrate the produce. Wilted pak choi couldbe re-hydrated (and cooled) by dipping in water and the general appearance, color, andoriginal weight could be restored if moisture loss was less than 10%. Rehydration andcontrolled water loss led to a reduction in losses of 14.5%.

In Cambodia, the practice of leaving cabbage heads in the field for an hour or two with the cutbutt end exposed to the sun may also work for the above purpose (Vanndy and Buntong,2007). Additionally, this practice would dry out the cut butt end of the cabbage head, therebydepriving soft rot pathogens of water needed for their growth and development. However, theproblem of heat accumulation within the produce has to be addressed. After the treatment,prompt transport to the packing shed should be done to dissipate field heat without the use ofwater for cooling. Washing is not advisable in common cabbage. Other leafy vegetablesshould be transported to the packing shed as soon as possible as they are particularlysusceptible to wilting and other damage from high temperatures.



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Table 1. Chinese cabbage grade standards in Yunnan, China (Chen, 2007)

Grade Quality SpecificationsHeadSize/Weight (kg)

Tolerance

First

Same variety; head tight or firm,of natural color and luster, fresh,clean,

and without rot, old stem, yellowleaf, peculiar smell, bolting,wormhole and physical defect

Rotting within 1%;

other defects notover 5%

Second

Same variety; head tight or firm,of natural color and luster, fresh,clean, and without rot, old stem,yellow leaf, peculiar smell,bolting, wormhole and physicaldefect

Rotting within 1%;weight differenceswithin 10%; otherdefects not over10%

Third

Same variety; head loose, ofnatural color and luster, fresh,clean, andwithout rot, old stem, yellow leaf,

peculiar smell, bolting, wormholeand physical defect

Extra big 4.0Big 3.5Medium 2.5Small 1.5Extra small 1.0

Rotting within 1%;weight differenceswithin 10%; otherdefects not over

10%

In Yunnan, China, leafy vegetables are usually trimmed using a special knife (Fig. 3) (Chen2007). Damaged and senescent leaves are removed and for some vegetables (e.g. cabbage,Chinese cabbage), the butt is trimmed. For leaf mustards, the roots are usually retained andcleaned by washing together with the leaves. The cleaned produce is wrapped or bundledbefore packaging (Fig. 3).

Sorting/Grading

Systematic sorting or grading coupled with appropriate packaging and storage, will extendshelf life, maintain wholesomeness, freshness, and quality, and substantially reduce lossesand marketing costs. Sorting is done to separate poor produce from good produce, and furtherclassify the good produce based on other quality parameters, such size (Bautista and Acedo,1987). If this is done following quality standards set by product standards agencies or industryrequirements, the process is referred to as grading. Leafy vegetables are usually sorted orgraded based on maturity, size, shape, color, weight, and freedom from defects such as insect,disease and mechanical damage. Table 1 shows sample grade standards for Chinesecabbage in Yunnan, China.

In many developing countries, implementation of grade standards as well as safety standardsfor leafy vegetables and other fresh horticultural produce faces formidable difficulties thatcontribute to the lingering problem of high postharvest losses. Grade standards, if enforcedproperly, are essential tools of quality assurance during marketing. They provide a common

language for trade among farmers, handlers, processors, and marketers; maintain orderlymarketing and equity in the marketplace; and protect consumers from inedible and poorquality produce (Kader, 2006).

Washing and sanitizing

Most leafy vegetables are washed in clean water to remove dirt and other debris and surfacecontaminants. This is especially important during rainy weather as the produce often iscontaminated with soil. In heading type of cabbages, washing is not advisable as it could favorbacterial soft rot if the heads are not properly dried. The wrapper leaves also keep the inneredible part clean.

Sanitation is essential to control the spread of diseases from one item to another and limit the

pathogen load in wash water or in the packinghouse air. Waterborne microorganisms,including postharvest plant pathogens and agents of human illness, can be rapidly acquiredand taken up on plant surfaces (Kader, 2006). Natural plant surface contours, natural



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openings, harvest and trimming wounds can be points of entry and provide safe harbor formicrobes.

Chlorine in the form of sodium hypochlorite (NaOCl) solution (e.g. Chlorox or commercialbleach) or as a dry, powdered calcium hypochlorite, can be used in wash water as adisinfectant. For the majority of vegetables, chlorine in wash water should be maintained in

the range of 75150 ppm (Suslow, 1997; Bachmann and Earles, 2000). The antimicrobialform, hypochlorous acid, is most available in water with a neutral pH (6.5 to 7.5).Concentrations above 200 ppm may injure some vegetables (e.g. leafy greens and celery) orleave undesirable off-flavors. A 100 ppm chlorine solution can be prepared by mixing 4tablespoons of commercial bleach (5.25% NaOCl) per gallon of water (Bautista and Acedo,1987). Chlorine is routinely used as a sanitizer in wash, spray, and flume waters used in thefresh fruit and vegetable industry (Beuchat and Ryu, 1997). Antimicrobial activity depends onthe amount of free available chlorine (as hypochlorous acid) in water that comes in contactwith microbial cells.

Chlorinated water can also be used during hydrocooling, and to disinfect packinghouse,packaging and transport facilities. Furthermore, use of sanitized wash water can help toprevent postharvest diseases and food-borne illnesses. E. coli0157:H7, Salmonella,

Cryptosporidium, Hepatitis, and Cyclospera are among the disease-causing organisms thathave been transferred via fresh fruits and vegetables.

A standard procedure for washing lettuce leaves in tap water was reported to remove 92.4%of the microflora (Adams et al., 1989). Including 100 ppm available free chlorine in wash waterreduced the count by 97.8%. Adjusting the pH from 9 to 4.5-5.0 with inorganic and organicacids resulted in a 1.5- to 4.0-fold increase in microbiocidal effect. Increasing the washing timein hypochlorite solution from 5 to 30 minutes did not decrease microbial levels further,whereas extended washing in tap water produced a reduction comparable to hypochlorite.The addition of 100 ppm of a surfactant (Tween 80) to a hypochlorite washing solutionenhanced lethality but adversely affected sensory qualities of lettuce.

Hydrogen peroxide (food grade) also can be used as a disinfectant. Concentrations of 0.5% or

less are effective for inhibiting development of postharvest decay caused by a number of fungi(Bachmann and Earles, 2000). Hydrogen peroxide has a low toxicity rating and is generallyrecognized as having little potential for environmental damage. Ozone as a sanitizer may notbe practical in developing countries because of its high cost.

Other commodity treatments

Rehydration by dipping in clean water or water added with chlorine can be done to restore thefresh and turgid appearance of some leafy vegetables such as Chinese kale, kangkong, andmustards.

Common cabbage and Chinese cabbage can be applied with antibacterial treatments tocontrol bacterial soft rot. The use of saturated alum solution and lime paste has been foundvery effective in controlling soft rot in common cabbage (Bautista and Acedo, 1987). Alum hasa two-fold function to control bacterial soft rot: as an antimicrobial agent by direct kill, and as amoisture-withdrawing substance that deprives the bacterial pathogens of water. However,alum is phytotoxic and causes black spotting on affected leaf tissues, thus care must be takento apply alum only on the butt end of cabbage. On the other hand, lime is only moisture-withdrawing and usually cannot control soft rot if the pathogen already has entered into thetissues through wounds. The use of alum is now a commercial practice of common cabbagegrowers in the Philippines. Lime paste is used by commercial cabbage growers in Indonesia.In Thailand, lime (CaCO3) paste is used in commercial packinghouses for Chinese cabbage(Kanlayanarat, 2007). The paste is applied at the butt end and allowed to dry before packing.

Other potential low-cost techniques to control bacterial soft rot in cabbages include the use ofbotanicals or leaf extracts from plants that are known to be edible or consumed as medicinalplants. One effective treatment is the use of guava leaf extract, the effect of which in commoncabbage and Chinese cabbage was comparable to alum treatment (Acedo et al., 1999, 2003;



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Acedo and Capuno, 2004). Cabbages treated with guava leaf extract were free of bacterialsoft rot, while untreated heads all developed soft rot symptoms after pathogen inoculation,which resulted in trimming losses of more than 30%. Other plants known to be edible ormedicinal, such as oregano, milkweed (local medicinal plant used to contain dengue fever)and lemon grass were less effective. After treatment, the applied extract or substance (alum orlime) requires proper drying before packing.

Packaging

Proper packing is essential to maintain the freshness of leafy vegetables. Packaging shouldbe designed to prevent premature deterioration in product quality, in addition to serving as ahandling unit (Bautista and Acedo, 1987). Packages should prevent or reduce physical injuryduring transit and handling, provide ventilation to hasten cooling and escape of heat causedby respiration, and reduce water loss from the produce (Gast, 1991). Some packages promotesale of the produce.

Produce packages

Different kinds of containers are used for leafy vegetables, depending on the market andvalue of the produce. For export and high-value leafy vegetables, more rigid and presentablebut expensive containers are used, such as foam box and cartons (Fig. 4). For the localmarkets, bamboo baskets of different sizes and shapes are used.

Rigid containers (plastic or wooden crates, cartons) are far much better than non-rigidcontainers (mesh bags, plastic bags) for protection of produce from damage during handlingand transport. Rigid packages are also easier to stack or palletize. The different packages aredescribed as follows:

Basket: Usually refers to containers made of woven materials, which may be bamboo,rattan or plastic strips.

Box: Usually refers to containers made of corrugated fiberboard or Styrofoam. It maybe a two-piece telescoping box, or a carton that closes with top flaps. The contentscan be place-packed with liners and layer dividers, or bulk-filled.

Crate: Usually refers to a wooden or plastic container. Wooden crates are usuallywire-bound and may be collapsible.

Plastic containers, a relatively new type of container, have good stacking strength and arewater-resistant. Plastic crates for handling and transportation of vegetables wer introducedrecently in some developing countries. In Nepal, plastic crates are increasingly used byfarmers and traders, particularly in situations where their return and reuse can be guaranteed;the crates have been reported to reduce postharvest losses and improve quality and safety ofvegetables (Adhikari, 2006). In Sri Lanka, losses of vegetables were reduced from 30% with

the use of poly sacks to 5% with the use of plastic crates (Fernando, 2006).

Reinforcing and handling packages

Telescoping construction, dividers, and corner reinforcement are ways that boxes have beenmade stronger. Container liners and cushions minimize physical injuries. Containers need tobe vented to effectively lower and maintain produce temperature for storage (Gast, 1991).Vents allow cold air to be forced more quickly through the containers and produce. Vents alsoallow the heat built up by respiration to escape. Produce exposed to high temperatures inunvented containers will usually have a shorter shelf life. A well-made container has uniformventing, so when it is stacked the vents will match other containers. Matching is important socold air can be pulled through a whole stack of containers. Too much venting weakens acontainer, while too little venting restricts the airflow through it. A good rule of thumb is to have5% of the container sides and/or ends vented. A few large vertical vents are better than manysmall round ones.



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Figure 5. Protective packaging practices.

In GMS countries, some techniques to reduce damage and improve shelf life of packed leafyvegetables include the use of newsprint or sack liners and cotton-cloth covers, use of paperand stretchable foam cups to wrap cabbages individually or in groups, and special

arrangements of Chinese kale or mustard inside the container to protect the leaves fromdamage and water loss (Fig. 5) (Buntong and Vanndy, 2007; Chen, 2007; Thanh, 2007).

Modified atmosphere packaging (MAP)

MAP is very effective in retaining freshness and extending shelf life of fresh produce bymaintaining the green color, inhibiting water loss, reducing loss due to product respiratory heat,and maintaining the natural fresh taste of produce. MAP is exemplified by the use of polymericfilm as packing material, which can be employed during transport and storage. Plastic filmscan be used to pack specific volumes of produce, as individual wrapping, or as containerliners (Fig. 6).

Low density polyethylene (PE) film is generally used for packing fresh vegetables and fruitowing to its high permeability and softness compared with high density PE (Somjate, 2006).PE can be sealed easily, has good O2 and CO2 permeability, low temperature durability, good



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tear resistance, and good appearance. It is therefore used for the production of MAP, whichcan be manipulated to match the characteristic respiration of produce by reducing O2 levels toslow down the rates of respiration and senescence. However, high-density PE also has beenfound to markedly reduce water loss of produce (Ben Yehoshua, 1978).

Since PE bags are non-rigid, product volume per bag should be limited. In a study on packing

5, 10, and 15 kg Chinese kale per PE bag, it was found that losses due to weight loss,bruising and trimming increased with increasing product volume and were about 5.6%, 6.9%and 13.1%, respectively (Amuttiratana and Passornsiri, 1992).

Plastic film packaging in pak choi effectively reduced moisture loss and wilting and wasconsiderably more effective than manual misting or treating leaves with anti-transpirantchemical (OHare et al., 2001). Plastic packaging maintains a very high RH, whichnecessitates sanitary washing before packing to avoid bacterial rot. In another MAP trial undersupermarket conditions (ambient temperature of 28C) using plastic film wrap (clingwrap), itwas found that semi-packed pak choi (two-thirds of leaves exposed) performed better thanfully packed and non-packed pak choi (Jiang and Pearce, 2005). Although the fully packedproduce had less water loss, it tended to have more rot. Supermarkets preferred the semi-pack option from an aesthetic standpoint, as the fully packed produce tended to fog due to

moisture condensation. In Chinese cabbage, plastic film wrap was similarly effective inreducing moisture loss from outer leaves. However, rot develops if the heads are mechanicallydamaged.

In Thailand, commercial supermarket MAP practice for cabbage and Chinese cabbageincludes the use of perforated plastic bags (4-8 holes at 5 mm diameter) or individualwrapping with polyvinyl chloride (PVC) film at shelf temperature of 7

oC (Kanlayanarat, 2007).

For Chinese kale, perforated plastic bags (4-8 holes) or PE bags with one open end are used.If perforated plastic bags are used, the number of holes should not be excessive, as the leafyvegetable will still easily wilt. If the number of perforations is too few, water will condense atthe surface of the plastic bag, favoring disease development.

Cooling and Storage

Cooling is the foundation of produce quality protection. It extends shelf life by reducing therate of physiological change (i.e. rate of respiration and transpiration) and retarding the growthof spoilage microorganisms. Because every degree of reduction from ambient temperatureincreases storage life, every form of cooling is beneficial, even if it is not optimum; simple low-cost cooling or refreshing the product is better than no cooling at all. Ways of cooling freshproduce include (1) keeping out of direct sun; (2) using natural cooling, such as harvestingduring the cool early morning hours, opening stores for ventilation during the cool of the night,using the cool temperature of high altitudes or a natural source of cold water when available;(3) evaporative cooling obtained by drawing dry air over a moist surface; (4) mechanicalrefrigeration; and (5) cooling promptly after harvest by appropriate precooling methods. Somecooling and storage recommendations and simple techniques are described by Kitinoja and

Kader (2003).



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Figure 6. MAP practices for leafy vegetables.

Table 2. Postharvest cooling methods and suitable commodities (Sullivan et al., 1996).

Cooling

method

Commodities Comments

Hydrocooling Most leafy vegetables, fruitsand fruit-type vegetables,sweet corn, snap beans

Very fast cooling; uniform cooling in bulk if properly used,but may vary extensively in packed shipping containers;daily cleaning and sanitation measures essential; productmust tolerate wetting; need water-tolerant shippingcontainers

Forced-aircooling(pressurecooling)

Most fruits, berries, fruit-type vegetables, tubers,and vegetables notsusceptible to chilling injury

Much faster than room cooling; cooling rates uniform ifproperly used. Container venting and stackingrequirements are critical to effective cooling. Economicaland efficient.

Package icing Most vegetables Fast cooling; limited to commodities that can toleratewater-ice contact; water-tolerant shipping containers areessential. Economical and efficient.

Room cooling All commodities Too slow for many perishable commodities. Cooling ratesvary extensively within loads, pallets, and containers.

Vacuum cooling Leafy vegetables, iceberglettuce

Commodities must have a favorable surface-to-massratio for effective cooling. Causes about 1% weight lossfor each 6C cooled. A procedure that adds water duringcooling prevents this weight loss, but equipment is moreexpensive, and water-tolerant shipping containersneeded.

Transit cooling

Mechanicalrefrigeration

All commodities Cooling in most available equipment is too slow andvariable; generally not effective for field heat removal.

Top-icing andchannel-icing

Most vegetables Slow and irregular, top-ice weight reduced net payload;water-tolerant shipping containers needed.



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Exposure to alternating cold and warm temperatures may result in moisture accumulation onthe surface of produce (sweating), which may hasten decay. Different commodities storedtogether should be capable of tolerating the same temperature, RH and level of ethylene inthe storage environment. High ethylene producers, such as ripe bananas, apples, cantaloupe,can stimulate undesirable physiological changes in color, flavor, and texture in ethylenesensitive commodities, such as leafy vegetables.

A farmer who can cool and store produce has greater market flexibility because the need tomarket immediately after harvest is eliminated. The challenge, especially for small farmers, isthe set-up cost.

Cooling methods in developing countries

Use of ice. In developing countries, ice packing or top icing is increasingly used for leafyvegetables due to increasing availability of ice (Fig. 7). Ice packing can be used to coolvegetables during transport, distribution and storage. In tropical climates, the temperature in abox of leafy vegetables may increase to 35-40C when sealed in the afternoon andtransported the following morning. Ice packing can lower the temperature to 20-25C (Huang,2006). It was also found effective in reducing leaf yellowing, wilting, and trim loss. For

vegetables sensitive to chilling injury or that are damaged when in direct contact with ice, suchas amaranth, a layer of newspaper can be placed between layers of vegetables and ice.Thickness of the alternating layers of vegetables and ice depends on the type of vegetable,ambient temperature, and distance or the time to the market. During transport and sale at themarket, the ice melts. Leafy vegetables are sprayed repeatedly with water, especially atdestination markets, to maintain low temperatures and prevent wilting or softening.

In Yunnan, China, ice bottles are used by commercial growers as a simple technique forcooling produce in containers and preventing direct contact of produce with the ice (Fig. 7)(Chen, 2007). A simple refrigerating unit also has been developed for fresh vegetables (Fig. 8).

Evaporative cooling storage. Refrigerated facilities are expensive in terms of set-up andoperational cost. Alternative storage methods are therefore important in developing countries

and one of these is evaporative cooling storage. An evaporative cooler (EC) developed inIndia, the Zero Energy Cool Chamber, is an on-farm, low-cost, environmentally friendly coolchamber, was made from locally available material (Ahsan, 2006). Temperatures within thechamber were reduced by as much as 1718C, with more than 90% RH during peak summerperiods. It increased shelf life and reduced wastage of fruit (banana, mango, oranges, limes,and grapes) and vegetables (tomato and potato). A similar zero-energy storage structure wasdeveloped in Nepal (Adhikari, 2006). The structure is constructed using brick and sand,rectangular in shape, and has dimensions of 75 cm x 50 cm x 75 cm. Its outer and inner wallsmade of bricks are separated by a 10 cm space filled with sand, which is frequently watered tomaintain a temperature of 710C and RH of >85%. It increased shelf life and reduced lossesof vegetables including leafy type such as cabbage, capsicum, and leafy vegetables. In SriLanka, a low cost evaporative cooler was also developed (Fig. 9) and introduced to retailtraders (Fernando, 2006). Temperatures inside the cooler are 5-7

oC lower than ambient and

RH ranges from 9095%. It has a capacity of 100 kg vegetables and can be used fortemporary storage of unsold produce. It reduced losses from 20% to 5%.



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Figure 7. Ice packing and use of ice bottles for cooling leafy vegetables.

Figure 8. Simple refrigeration equipment for the storage of leafy vegetables.



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Figure 9. Low-cost evaporative cooler developed in Sri Lanka (Fernando, 2006).

Other simple and low-cost evaporative cooling structures were described previously (Acedoand Thanh, 2006), some of which were tested by partners in Cambodia, Laos, and Vietnamfor tomato and chilli storage. The box-type evaporative coolers with moist jute sack wallingand the other with moist rice hull wall inserts, as described in this report, were found to beequally effective in inhibiting wilting and reducing weight loss, resulting in doubling of shelf lifeof pechay (Brassica napus var. chinensis) (Acedo, 1997). Intermittent exposure to light wasfound to reduce leafy yellowing, which is a problem of continuous holding inside the

evaporative cooler. Later, postharvest lighting also was found to affect the shelf life of pak choi(Jiang and Pearce, 2005). Leaves stored at 10C under normal fluorescent lighting had a shelflife of 10 days, compared with 8.2 days for leaves stored in the dark. However, high intensitylighting (metal halide and high-pressure sodium) reduced shelf life to about 6 days due to heatdamage.

Evaporative cooling principle can also be employed during packaging and transport. Forexample, Chinese kale dipped in water for rehydration is packed right away in the containerwhile still wet to provide water for evaporation and cooling (Fig. 10). This technique can beused during transport of produce and after arrival at the destination market; however, theproduce has to be taken out from the container because prolonged exposure to wet conditionfavors decay development. Covering the container with wet cloth (Fig. 10) can also cool theproduce. In addition, the transport load can be transformed into an evaporative cooling and/or

modified atmosphere chamber by lining it with wet cloth and/or plastic film (Fig. 10) (Chen,2007).



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Figure 10. Application of evaporative cooling and/or modified atmosphere in packingand transport of leafy vegetables.

Transport Techniques

Minimizing losses during transport necessitates special attention to vehicles, equipment,infrastructure, and handling. Fresh produce is transported using both refrigerated and non-refrigerated vehicles. Non-refrigerated vehicles are generally open-sided trucks, with wiremesh frames. This type of transport is inexpensive and convenient, and usually is used indeveloping countries. Fresh produce must not be watered prior to loading, as this will lead todecay, rotting, and extensive losses. Major causes of losses are improper handling duringloading and unloading; over loading without separation of produce, which leads to overheatingand mechanical injury to produce at the bottom of the stack; rough roads; and lack of



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ventilation of the produce. Postharvest operations must address these problems. Refrigeratedtransport facilities become necessary for fresh produce destined for niche and internationalmarkets.

For maximum shelf life and quality, leafy vegetables should not be stored or transported intrucks where there are mixed loads containing ripening fruit such as apples, pears, mangoes,

tomatoes, or bananas. Because of their soft and delicate texture, leafy vegetables should behandled gently to minimize mechanical injury.

Stacking of containers in the transport load provides one of the major challenges to reducemechanical injury. This is a particular problem for vegetables such as cabbages packed inbaskets or big plastic bags (Fig. 11). An innovative but very simple technique to reducedamage due to compression of produce is the provision of wooden dividers separating thelayers of containers in the transport load (Fig. 11).

Market Handling

At destination markets, the produce may again undergo cleaning, sorting, packing and storage.

Most postharvest measures described above could be applied at this stage.

Other PHT Developments

Ethylene removal from postharvest chain

Ethylene, being a senescence hormone, is destructive to the quality of leafy vegetables as itaccelerates different deteriorative processes. Ethylene removal from the postharvest chain,therefore, has far-reaching benefits. Preventing ethylene buildup around the product inpackages and during storage, transport, and marketing is often the simplest method ofreducing the damaging effects of ethylene. For ethylene-sensitive products such as leafyvegetables, it is important to avoid storing them with products that produce high levels of

ethylene. Increasing the ventilation rate of the storage area is another way of reducingethylene around fresh produce.

Ethylene can be removed through different chemical processes. Potassium permanganate isusually used because it reacts with ethylene to produce carbon dioxide and water. To scrubthe air efficiently, it is best to spread the potassium permanganate over as large a surfacearea as possible, either in trays or within highly permeable bags.

An ethylene scrubber made of potassium permanganate impregnated onto clay-ash chip (apropriety Philippine product) has been developed. Ayoub et al (1987) also tested ethylene-absorbing blankets containing alumina coated with potassium permanganate in two mixedloads of fruits and vegetables in two marine containers shipped from California to South Korea.The total produce lost in the container without ethylene scrubbing was 2,645 lbs (out of 16,070

lbs) valued at $928, which is much higher than the $160 cost of the ethylene scrubbers. Thetechnical and economic feasibility of preventing ethylene damage was similarly demonstratedin lettuce using ethylene scrubber (Thompson et al., 1989) and by separating ethylene-generating produce from ethylene-sensitive produce during transport (Jordan et al., 1987).



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Figure 11. Traditional and innovative stacking proceduresfor containers of leafy vegetables.

Cold chain system

As with refrigerated storage, the cold chain system is not a low-cost technology, but isintroduced here for future consideration as a joint government-private sector initiative. Coldchain systems preserve the freshness of produce from harvesting through marketing anddelivery to the consumer and have a tremendous impact on fresh produce marketing (Ho,2006). The economic impact of cold-chain systems is due to (1) increased consumersatisfaction as a result of improved freshness and keeping quality of produce; (2) pricestabilization and continuity of supply; (3) reduced total marketing expenses due to reducedproduct losses; increased net quantities of fresh produce and reduced unit marketing andgarbage disposal costs; and (4) improved quality and competitiveness of farm produce,thereby contributing to increased farmer income.

Some developing countries, such as Indonesia and Philippines, are starting to adopt the coldchain approach and adapt it to their needs. In the Philippines, small vegetable growers in

different villages of a highland province in Bukidnon (located in the southern islandscollectively called Mindanao) penetrated institutional markets (e.g. a fast-food chain) in Cebu



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(one of the islands in the central part collectively called Visayas) and Manila (the countryscenter located in the northern part collectively called Luzon) through clustering and applicationof the cold chain system (Rapusas, 2006). Previously, selling lettuce to local traders wasdifficult because of low prices and 25% of the weight deducted as an allowance for trimmings,despite the fact that the lettuce was of good quality. An alternative market was sought by thegrower, who began supplying 200 kg of lettuce on a weekly basis to fast-food outlets in Cebu,

and later, in Manilathe latter requiring air transport of 400 kg lettuce weekly. Apart from thehigh cost of air freight, lettuce delivered to the processor did not meet the 61% yield specifiedin the marketing contract, owing to the need for 16-20% trimming.

Attaining the high quality standards of the fast-food processor was a formidable challenge forthe grower. A further challenge was that of supplying a 20-foot refrigerated van with 3.5 metrictons of lettuce on a weekly basis. Clusters of lettuce growers were then formed and sharedproduction technologies and quality standards. With the use of refrigerated transport, thetrimmings were significantly reduced to a maximum of 10% and the processors yield recoveryspecification of 61% was successfully met. To further improve the lettuce supply chain,government agencies provided assistance in terms of equipment supporta 10-footrefrigerated truck, a 20-foot refrigerated van or container, and a precoolerto complete thecold chain system.

Operational steps are as follows: (1) harvested lettuce heads are immediately brought to thepackinghouse for cleaning (wiping with a cloth to remove soil and other dirt particles), sorting,air drying (about 2 hours) and anti-browning treatment (using citrus or calamansi juice, alum,or ascorbic acid applied to the cut portion of the lettuce); (2) selected heads are carefullyarranged into nestable and vented plastic crates (11.5 kg capacity) with a brown paper liningfor every two layers with each layer consisting of 12 heads; (3) cluster growers transport thepacked produce to a consolidation area using a rented 20-foot refrigerated van, especially forgrowers located far from this area; (4) the consolidated packed produce is transported inrefrigerated containers to a city pier for loading into the ship en route to Manila (shipping timefrom the consolidation area up to the buyer/processor takes 40 hours). The achievements ofthe five-grower lettuce cluster have provided the impetus for other independent, small lettucegrowers to join the cluster. This development has given the cluster a window of opportunity to

expand its production volume and, in turn, its captive market.

Supply chain management

A system approach to producing and marketing fresh leafy vegetables is essential to raisefarm productivity and profitability and ensure the sustainability and reliability of supply chains.Different supply chain systems exist in developing countries, and in general, they can begrouped into traditional and progressive supply chains.

Traditional supply chain. Many supply chains that involve small farmers in rural areas fallunder this category. Farmers are at the mercy of middlemen who usually dictate productprices and who may have contract-like agreements with the farmers. The middleman receivesthe crop and sells it in a wholesale market to wet markets and to supermarkets (Fig. 12)

(Kanlayanarat, 2007). The farmer also may sell the crop directly to the market. This supplychain is a low-technology system, usually with no temperature control, and relies on selling theproduce within one day after harvest. Product losses may be very high, particularly duringadverse weather conditions.

Progressive supply chain. The cold chain system described above is one example ofprogressive supply chains, which harness technological developments and marketrequirements to create marketing advantage and opportunities.

Food corporations (e.g. supermarket chains) and multinational companies develop their ownsupply chain system to serve better the needs of their customers and therefore ensureprofitability of their business ventures. In Thailand, for example, a food corporation suppliesvegetables to its chain of supermarkets by getting supplies from its contract farmers, who

grow vegetables following recommended production practices (Fig. 13) (Kanlayanarat, 2007).Pricing of farmers produce depends on prevailing market price. Depending on the crop, the



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harvested produce is sorted and packed on-farm and brought to the companys headquartersfor subsequent distribution. Other crops are brought to the companys packinghouse forgrading using the companys quality standards, packing, and holding or storage. Thepackinghouse is located near the companys headquarters and distribution center. Ifdistribution cannot be done on the same day of arrival, storage is done in the companyscentral cold room. The produce is distributed to supermarket outlets in refrigerated trucks and

displayed on refrigerated shelves.

Another Thailand initiative to improve leafy vegetable supply chain management in thenorthern highlands of Chiang Mai capitalizes on the cooperative system with outside support(Royal Project Foundation) (Kanlayanarat, 2007). The vegetables include cabbages and othertemperate types produced following research-based recommendations. The farmers harvesttheir own vegetables and deliver them to 37 fully equipped collection centers (Fig. 14). Thevegetables then go through the following processes: checking for quantity and quality;cleaning, trimming, checking for chemical residues such as fertilizer and pesticides (if found tobe unsafe, the produce is rejected); packing; pre-cooling (if needed); and storage in coldrooms. Each postharvest center has fairly extensive infrastructure and equipment, such asconveyors, carts, crates, measuring devices, displays showing quality guidelines, and cuttingand trimming devices. At least one pre-cooling facility is used.

Crops are cooled in different ways. The center has also a cold room for storing perishablecrops before transport. Small refrigerated trucks then collect the produce from each centerand take it to the packinghouse in Chiang Mai. This is a large, central collection point usuallyemploying more than a hundred people. Produce is processed and packed to a high standardof efficiency and hygiene. At the packinghouse, produce is checked for quality, trimmed,washed, checked for all chemical residues, and then packed again. Low grade or excessproduce is usually sent for food processing. The packed produce is transported to Chiang Mai,Bangkok, or regional markets.

Like the local postharvest centers, the packinghouse is fully equipped and has cold storagefacilities. The packinghouse itself is temperature and humidity controlled to reduce cropwastage. Whether the produce is destined for Chiang Mai, Bangkok or regional markets, the

produce is transported by large refrigerated trucks. When the produce arrives at the BangkokDistribution Center, the delivery is again checked for quantity and quality, as some producemay have been damaged in transit. After quality check up, the produce is stored in cold rooms.From there, the produce is transported to Doi Kham Stores or to third-party retailers andwholesalers.

Figure 12. Traditional supply chain system for leafy vegetables.



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Figure 13. Corporate supply chain system for leafy vegetables.

Figure 14. Cooperative system of supply chain management.

In Myanmar, a government initiated and owned corporation operates a supply chain forvegetables for export (Kyaw, 2007). It has a packinghouse equipped with three cold roomseach with 10-ton capacity, hydrocooling facility and other postharvest equipment includingpackaging area (Fig. 15). Packaging containers, such as cartons are fabricated and suppliedby a contracted company. Upon arrival in the packinghouse, the vegetables produced bycontract growers, such as lettuce and broccoli, are sorted, precooled with 1oC watercontaining a disinfectant, air-dried, packed in air-tight plastic bags before putting into cartons,stored in the cold room (if delivery within the day could not be done), and transported inrefrigerated trucks for cargo flights.

Economic Analysis of Postharvest Technologies

The development, introduction, and use of a certain technology have economic,environmental and social impacts (Jiang and Pearce, 2005). Economic impacts are usuallychanges in profitability due to higher demand and/or bigger markets, lower costs, higher yields,and/or better quality. Environmental impacts are effects on the natural system, such asreduced waste and pollution or improved environmental quality. Social impacts may includeenhanced networking, empowerment of the most disadvantaged groups, recognition of gendercontributions, and the development of human and social capital. Environmental and socialimpacts may be quantified in monetary terms, but in many cases they do not have marketvalues. Some impacts cannot be realized immediately after an intervention has been

developed or introduced. Only potential impacts can be evaluated and so, certainassumptions and projections have to be made.



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For postharvest technologies developed or technological recommendations introduced,economic impacts are mainly longer shelf life, better quality and/or lower losses of the produce,which lead to higher profitability. For these techniques, cost-benefit analysis can be performedand from this, the return on investment or the cost/benefit ratio can be estimated. Threeexamples are given below.

Example 1: postharvest technical advice

The postharvest intervention was given as simple advice to retain 2-3 wrapper leaves inChinese cabbage instead of removing all outer leaves as traditionally practiced. Thetechnique reduced losses from 28.5% for the traditional practice to 6.3% for the introducedtechnique, which resulted to a net profit that far exceeded the additional cost (Table 3).

Example 2: postharvest technique from exploratory investigation

The use of botanical extracts as alternative to alum for cabbage soft rot control was explored.Experiments were conducted and the most effective treatment (guava leaf extract, 1:1extract:water ratio) showed complete control of the disease in contrast to 100% infection of

untreated heads that resulted in trimming losses of 34.8%. (The cost and benefit are onlypotential.) The potential net benefit again far exceeded the cost of the technique (Table 4).

Example 3: introduction of better postharvest material

The use of plastic crates as packaging material for vegetables was introduced and reducedlosses to 5%, down from 30% for the usual practice of using polyethylene sacks (Fernando,2006). Cost benefit analysis is shown in Table 5, which illustrates that using plastic crates canincrease profitability.

Figure 15. Myanmar government-initiated supply chain for export vegetables producedby contract farmers and brought to the packinghouse for sorting, hydrocooling,packing in carton box, cold storage, and transport in refrigerated trucks for cargo flight.



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Table 3. Cost benefit analysis of keeping 2-3 outer leaves of Chinese cabbage duringtransport compared to removing all outer leaves (modified from Jiang and Pearce,2005).

Particulars Unit Traditional practice Keeping 2-3 outer leaves

Losses-2nd day % 28.5 6.2-3rd day % 28.6 6.4-Average % 28.5 6.3Weight of Chinese cabbage kg 1000.00 1000.00 (1156 kg shipped)-Wasted kg 285.35 62.00-Sold kg 714.65 938.00-Revenues @ 0.60 yuan/kg yuan 428.79 562.80Cost-Transportation cost yuan 33.00 37.50-Additional labor (loading etc.) yuan 6.00 6.00-Total costs yuan 39.00 43.50Net profit (revenues-total cost) yuan 389.79 519.30

1 USD = 8 Chinese yuan or RMB (Renminbi)

Table 4. Potential cost and benefit of using guava leaf extract and alum for bacterialsoft rot control in common cabbage (Acedo et al., 1999).

Particulars No treatment Guava leaf extract Alum treatment

% Trimming losses due soft rot-Trial 1 30.9 0 0-Trial 2 38.6 0 0-Average 34.8 0 0Weight of Chinese cabbage, kg 1000 1000 1000-Wasted 348 0 0-Sold 652 1000 1000-Revenues @ 30 pesos/kg 19,560 30,000 30,000Cost, pesos-Treatment cost (materials, labor) 0 100 120-Trimming cost (labor) 150 0 0-Total costs, pesos 150 100 120Net profit (revenues-total cost), pesos 19,410 29,900 29.880

1 USD = 52 Philippine peso (PHP)



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Table 5. Cost-benefit analysis of using poly sacks and plastic crates for transportingvegetables from the collecting center, Keppetipola to the central (Manning) market inColombo, Sri Lanka (Fernando, 2006).

Particulars Use of poly sacks Use of plastic crates

1) Capacity per truck load- Number of units transported 80 bags 125 crates- Average weight of vegetables per unit 50 kg 20 kg- Total capacity 4,000 kg 2,500 kg2) Unit price of a package LKR 30.00/bag 527.00/crate3) Lifespan of package 2 journeys 240 journeys4) Farm-gate purchasing price, LKR 25.00/kg 27.00/kg5) Transport cost LKR- Keppettipola to central market LKR 2,500.00 2,500.00- Return journey LKR 625.00*6) Handling charges LKR 6.00 6.007) Selling price of vegetables LKR 30.00 37.00

Capital cost-Total cost of packages LKR 2,400.00 65,876.00Fixed cost-Depreciation of packages LKR 1,200.00 274.00Variable-Total transport cost LKR 2,500.00 3,125.00-Loading and unloading cost LKR 960.00 1,500.00-Cost of vegetables LKR 100,000.00 67,500.00

Total cost LKR 104,660.00 72,399.00Total revenue LKR 120,000.00 92,500.00

Net profit LKR 15,340.00 20,100.00

* Empty crates occupy 1/4 of the total truck capacity 1USD = 100 LKR.Losses of vegetables were reduced from 30% with poly sacks to 5% with plastic sacks.



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4 PROCESSING TECHNOLOGIES FOR LEAFYVEGETABLES

Importance of Processing

Processing is an important value-added activity that stabilizes and diversifies food

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46780638 Post Harvest Tech for Leafy Veg