EFFECT OF PRECOOLING ON

STORAGE LIFE OF VEGETABLES

SUBMITTED BYSHALINI JHINKWANG.B.P.U.A&TPANTNAGAR

VEGETABLES IN FIELD PRIOR TO HARVEST

CONCEPT Temperature plays a very critical role in life of

vegetables. In the field, plant can regulate its temperature by

altering stomatal opening and water absorption. Once the vegetable is harvested, it ceases to function

as before and is not able to regulate the temperature anymore.

Quality loss after harvest occurs as a result of physiological and biological processes, the rates of which are influenced primarily by product temperature.

FIELD HEAT. The heat contained in a crop immediately after harvest. Field heat is a combination of the heat absorbed by the plant tissues from the environment prior to harvest and the heat resulting from the relatively rapid respiration occuring in the still-warm plant tissues.

OUR PRIME FOCUS :- TO AVOID QUALITY LOSS OF PRODUCT ONCE ITS HARVESTED

BUT HOW?

PRECOOLING First introduced by Powell and his coworkers in the US Department of Agriculture in 1904. It is the key component in the preservation of quality for perishable fresh produce in post-harvest systems. Precooling is defined as the removal of field heat from freshly harvested produce in order to slow down metabolism and reduce deterioration prior to transport or storage. It is done to retard ripening and senescence process.Pre-cooling rapidly lowers the temperature of freshly harvested produce and is done immediately following harvest to minimize spoilage.Generally vegetables are precooled to their storage temperatures.

METHODS OF PRECOOLING ?

1. Room cooling.2. Forced-air cooling.3. Hydro-cooling.4. Ice cooling.5. Vacuum cooling.

1.ROOM COOLINGHorticultural produce is placed in a room and allowed to cool by cold air. Room is insulated and air is cooled by refrigeration unit.It is a slow method ,cold air does not circulate readily through the produce and is only appropriate for very small amounts of produce or produce that does not deteriorate rapidly. Its cost is relatively low

2.FORCED AIR COOLING

Forced air cooling is used mainly for bulk produce and palletized produce.It is the most versatile and widely used of all cooling methods. In this ,chilled air is forced to flow around each piece of produce. This close contact of chilled air with the produce results in rapid, even cooling throughout the mass of produce.This method is faster than room cooling because a flow of chilled air is in direct contact with the produce.

3.HYDRO COOLINGProduce is cooled by cold water either by immersion in a tank of circulating cold water or showering the cold water over the produce.Heat transfer is faster than forced air cooling because water is in direct contact with the produce and has a higher heat removal capacity than air.It is more expensive method than room cooling.

4.ICE COOLINGCrushed or fine granular ice is used to cool the produce. The ice is either packed around produce in cartons or sacks, or it is made into a slurry with water and injected into waxed cartons packed with produce. The ice then fills the voids around the produce. Its faster than hydrocooling because contact with the produce is good, and ice has a higher heat removal capacity than water.

5.VACCUM COOLINGIn this, containers of produce are put in a vacuum chamber. Air is drawn out of the chamber creating a high vacuum. Under the high vacuum, the boiling temperature of water is substantially lowered.Vacuum cooling is the fastest and most uniform method of pre-cooling because of the high amount of heat required for evaporating the water.Most expensive system to set up.

VEGETABLE TEMP.(°F)

%RH STORAGE LIFE(IN DAYS)

PRECOOLING METHOD

ASPARAGUS 32-35 95-100 14-21 H,IBEANS,LIMA 37-41 95 7-10 R,F,HBEETS,ROOTS 32 98-100 90-150 RBROCCOLI 32 95-100 10-14 I,F,HBRUSSEL SPROUTS 32 95-100 21-35 H,V,ICABBAGE 32 98-100 90-180 R,FCAULIFLOWER 32 90-98 20-30 H,VCELERY 32 98-100 20-30 IBRINJAL 46-54 90-95 10-14 R,FLEEK 32 95-100 60-90 H,ILETTUCE 32 85-90 14-21 H,IOKRA 45-50 90-95 7-14 R,FONION BULB 32 65-70 30-180 NONION GREEN 32 95-100 7-10 H,IPOTATOES 50-60 90 56-140 R,FRADISHES 32 95-100 21-28 IPEAS,IN PODS 32 95-98 7-10 F,H,I

EFFECT OF PRECOOLING ON

QUALITY AND SHELF LIFE OF

BROCOLI SCIENTISTS Vandana Kochhar and Satish Kumar Department of Processing and Food Engineering, Punjab Agricultural University, Ludhiana, Punjab, India

Scientific name - Brassica oleracea var. italica Variety – Punjab Broccoli 1 Quality parameters:-a. Colour.b. Weight. c. Shrivelling and decay.d. Texture(firmness of head). The compression force

(compactness of head) was higher in room/forced air cooled samples especially in broccoli with stalk compared to other two methods. Further broccoli with stalk had higher compression force compared to broccoli without stalk.

Thus (YI) value was highest for room cooled and least for package iced samples. It was further observed that broccoli without stalk showed higher ‘YI’ values compared to broccoli with stalk (Figure 6) respectively especially in hydro/package iced broccoli while in other two methods there was no difference.

Thus PLW (%) was highest for room cooled and least for package iced samples. It was further observed that broccoli without stalk showed higher PLW compared to broccoli with stalk

Thus shriveling values was higher in room/forced air cooled samples compared to other two methods both in broccoli with and without stalk. Moreover broccoli without stalk had higher values than broccoli with stalk .

CONCLUSIONBased on these observations, it was concluded that package icing and hydrocooling were better methods of cooling compared to forced air cooling and hydrocooling.. The shelf-life and quality of broccoli could be maintained up to 18 days in broccoli with stalk and 15 days in broccoli without stalk respectively under cold storage conditions.

SOURCE : Journal of Food Processing $ Technology

Overall effects and benefits of precooling

Reduce respiration in vegetables after harvest so minimise weight loss too.

Reduce metabolic changes so enzyme activity too. Reducing the production and sensitivity of the produce

to ethylene that accelerates ripening and senescence. Inhibits the growth of decay producing microorganisms Inhibits water loss. Increases shelf life of produce. Minimize losses during marketing. Improved utilization by consumer. Expanded market opportunities. Lowering the required workload of a cold storage since

optimum storage temperature is reached more quickly.

PRECAUTIONS Use suitable precooling method depending

upon type of produce.Ex.potatoes should not be washed with water.

Cooling time should be based on initial product temperature and coolant temperature.

Takecare of the temperature and precoling method for chilling sensitive commodities.

According to the  FAo, Precooling is “amongst the most efficient

quality enhancements available” and is regarded “as one of the most value-adding activities in the horticultural chain”.

References www.extension.org International Journal of Environmental &

Agriculture Research (IJOEAR) ,May 2015 United States Department of Agriculture. Journal of Food Processing and Technology,Feb

2015. Post harvest management of horticultural

crops(S.saraswathy,T.L.Preethy,S.Balasubramanium,J.Suresh,N.Revathy,S.Natrajan)

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