Food Biochemistry and Food Processing (Simpson/Food Biochemistry and Food Processing) || Biochemistry of Fruit Processing

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28Biochemistry of Fruit Processing

Moustapha Oke, Jissy K. Jacob, and Gopinadhan Paliyath

IntroductionFruit ClassificationChemical Composition of Fruits

CarbohydratesVitaminsMineralsDietary FiberProteinsLipidsVolatilesWaterOrganic AcidsPigmentsPhenolicsCell Structure

Fruit ProcessingHarvesting and Processing of FruitsFreezing and Canning of FruitsNonenzymatic BrowningFruit Juice Processing

Apple Juice ProcessingEnzyme ApplicationsApple Juice Preservation

Processed Apple ProductsApple SauceSliced ApplesDried Apple Products

Quality ControlBiochemical Composition and Nutritional Value of

Processed ApplesFlavanonesFlavonolsAnthocyaninsFlavans

Further ReadingReferences

Abstract: Processing of fruits is an important segment of food in-dustry. As fruits are highly perishable, processing is an efficient wayof ensuring their year-round availability. Fruits are processed intojuice, sauce, infused and dried products. Several standardized tech-niques are available to preserve the quality of processed products,still, there are nutrient losses associated with processing. Commonfruits processed include grape, orange, apples, pears, peach, and soon. Processed fruits can be enriched with the addition of nutraceu-tical components.

INTRODUCTIONOverall, the food and beverage processing industry is an impor-tant manufacturing sector all across the world. The United Statesis among the top producers and consumers of fruits and tree nutsin the world. Each year, fruit and tree nut production generatesabout 13% of US farm cash receipts for all agricultural crops.Annual US per capita use of fruit and tree nuts totals nearly300 pounds fresh-weight equivalent. Oranges, apples, grapes,and bananas are the most popular fruits. The consumption offruits and processed products has enjoyed an unprecedentedgrowth during the past decade. Many factors motivate this in-crease, including consumers’ awareness of the health benefits offruit constituents such as the importance of dietary fiber, antiox-idants, vitamins, minerals, and phytochemicals present in fruits.In food stores, one can buy fresh and processed exotic fooditems, either canned, frozen, dehydrated, fermented, pickled,or made into jams, jellies, and marmalades year-round. Sev-eral varieties of fruits are sold throughout the year in developedcountries, and with the increase in international trade of fruits,even tropical fruits are available at a reasonable cost. The foodprocessing industry uses fruits as ingredients in juice blends,snacks, baby foods, and many other processed food items. As a

Food Biochemistry and Food Processing, Second Edition. Edited by Benjamin K. Simpson, Leo M.L. Nollet, Fidel Toldra, Soottawat Benjakul, Gopinadhan Paliyath and Y.H. Hui.C© 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.

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28 Biochemistry of Fruit Processing 555

Table 28.1. World Production of Fruit in 2002 in Metric Tons

Production(Metric Tons) Africa Asia Europe America

Australia andNew Zealand World

Primary fruits 61,934,001 204,640,809 73,435,847 129,642,621 4,438,090 475,503,880Apples 1,696,109 30,870,497 15,820,454 7,875,880 831,999 57,094,939Bananas 7,140,629 35,766,134 446,600 15,372,622 250,000 69,832,378Grapes 3,113,940 14,761,974 28,739,848 12,529,900 1,872,588 61,018,250Mangoes 2,535,781 19,841,469 – 3,343,697 28,000 25,748,947Oranges 4,920,544 14,177,590 6,180,846 38,402,953 444,500 64,128,523Pears 530,547 10,996,503 3,626,020 1,759,538 202,597 17,115,205Plums 173,946 5,385,634 2,661,194 1,069,953 24,000 9,314,727Strawberries 171,132 325,670 1,276,192 1,157,540 21,300 3,237,533

Source: Calculated from FAOSTAT database. http://faostat.fao.org/default.aspx. Accessed on December 07, 2011.

result, the world production of primary fruits has increased from384 million metric tons in 1992 to 475 million metric tons in2002 (FAO). The world production of fruits in 2002 by regionsis shown in Table 28.1.

Advances in fruit processing technologies mostly occur in re-sponse to consumer demands or improvement in the efficiencyof technology. Traditional methods of canning, freezing, and de-hydration are progressively being replaced by fresh-cut, ready-to-eat fruit preparations. The use of modified atmosphere andirradiation also helps in extending the shelf life of produce.

Fruits are essential source of minerals, vitamins, and dietaryfiber. In addition to these components, they provide carbohy-drates, and to a lesser extent, proteins. Fruits play an importantrole in the digestion of meat, cheese, and other high-energyfoods by neutralizing the acids produced by the hydrolysisof lipids.

FRUIT CLASSIFICATIONFruits can be broadly grouped into three categories according totheir growth latitude, whether it is in temperate, subtropical, ortropical regions.

1. Temperate zone fruits: Four subgroups can be distin-guished among temperate zone fruits that include smallfruits and berries (e.g., grape, strawberry, blueberry, black-berry, cranberry), stone fruits (e.g., peach, plum, cherry,apricot, nectarine) and pome fruits, (e.g., apple, pear,Asian pear or Nashi, and European pear or quince).

2. Subtropical fruits: Two subgroups can be differentiatedamong subtropical fruits and include citrus fruits (e.g.,orange, grapefruit, lemon, tangerine, mandarin, lime,and pummelo), and noncitrus fruits (e.g., avocado, fig,kiwifruit, olive, pomegranate, and cherimoya).

3. Tropical fruits: Major tropical fruits include banana,mango, papaya, and pineapple. Minor tropical fruit in-clude passion fruit, cashew apple, guava, longan, lychee,mangosteen, carambola, rambutan, sapota, and so on.

CHEMICAL COMPOSITION OF FRUITSCarbohydrates

Fruits typically contain between 10% and 25% carbohydrates,less than 1% of protein and less than 0.5% of fat (Somogyiet al. 1996b). Carbohydrates, sugars, and starches are brokendown into CO2, water, and energy during catabolism. The ma-jor sources of carbohydrates are banana, plantain, date, raisin,breadfruit, and jackfruit. Proteins and amino acids are containedin dried apricot and fig, whereas fats are the major componentsof avocado and olives. Sugars are the major carbohydrate com-ponents of fruits and their composition vary from fruit to fruit.In general, sucrose, glucose, and fructose are the major sugarcomponents present in fruits (Table 28.2). Several fruits alsocontain sugar alcohols such as sorbitol.

Vitamins

Fruits and vegetables are major contributors to our daily vitaminrequirements. The nutrient contribution from a specific fruit orvegetable is dependent on the amount of vitamins present in thefruit or vegetable, as well as the amount consumed. The approx-imate percentage contribution to daily vitamin intake from fruitsand vegetables is: vitamin A, 50%; thiamine, 60%; riboflavin,30%; niacin, 50%; and vitamin C, 100% (Somogyi et al. 1996b).Vitamins are sensitive to different processing conditions such asexposure to heat, cold, reduced and high levels of oxygen, light,free water, and mineral ions. Trimming, washing, blanching, andcanning can also cause the loss in vitamin content of fruits andvegetables.

Minerals

Minerals found in fruits in general may not be fully nutrition-ally available (e.g., calcium, found as calcium oxalate in certainproduce is not nutritionally available). Major minerals in fruitsare base-forming elements (K, Ca, Mg, Na) and acid-formingelements (P, Cl, S). Minerals often present in microquantities areMn, Zn, Fe, Cu, Co, Mo, and I. Potassium is the most abundantmineral in fruits, followed by calcium and magnesium. Highpotassium is often associated with increased acidity and

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556 Part 5: Fruits, Vegetables, and Cereals

Table 28.2. Sugar Composition of Selected Fruits

Sugar, g/100 mL of Juice

Fruit Sucrose Glucose Fructose Sorbitol

Apple 0.82±0.13 2.14±0.43 5.31±0.94 0.20±0.04Cherry 0.08±0.02 7.50±0.81 6.83±0.74 2.95±0.33Grape 0.29±0.08 9.59±1.03 10.53±1.04 NDNectarine 8.38±0.73 0.85±0.04 0.59±0.02 0.27±0.04Peach 5.68±0.52 0.67±0.06 0.49±0.01 0.09±0.02Pear 0.55±0.12 1.68±0.36 8.12±1.56 4.08±0.79Plum 0.51±0.36 4.28±1.18 4.86±1.30 6.29±1.97Kiwifruit 1.81±0.72 6.94±2.85 8.24±3.43 NDStrawberry 0.17±0.06 1.80±0.16 2.18±0.19 ND

Source: Reprinted with permission from Van Gorsel et al. 1992. Copyright, American Chemical Society.ND, not detected (<0.05 g/100 mL).

improved color, whereas high calcium content reduces the inci-dence of physiological disorders and improves quality of fruits.Phosphorus is a constituent of several metabolites and nucleicacids and plays an important role in carbohydrate metabolismand energy transfer.

Dietary Fiber

Dietary fiber consists of cellulose, hemicellulose, lignin, andpectic substances, which are derived from fruit cell walls andskins. The dietary fiber content of fruits ranges from 0.5% to1.5% by fresh weight. Because of its properties that include ahigh water-holding capacity, dietary fiber plays a major role inthe movement of digested food and reducing the incidence ofcolon cancer and cardiovascular disease.

Proteins

Fruits contain less than 1% protein (as opposed to 9–20% proteinin nuts). In general, plant protein sources provide a significantportion of dietary protein requirement in countries where ani-mal proteins are in short supply. Plant proteins, unlike animalproteins, are often deficient or limiting in one or more essentialamino acids. The green fruits are important sources of proteinsas they contain enzymes and proteins associated with the pho-tosynthetic apparatus. Enzymes, which catalyze metabolic pro-cesses in fruits, are important in the reactions involved in fruitripening and senescence. Some of the enzymes important to fruitquality are:

� Ascorbic acid oxidase: Catalyzes oxidation of ascorbic acidand results in loss of nutritional quality.

� Chlorophyllase: Catalyzes removal of phytol ring fromchlorophyll; results in loss of green color.

� Polyphenol oxidase: Catalyzes oxidation of phenolics, re-sulting in the formation of brown colored polymers.

� Lipoxygenase: Catalyzes oxidation of unsaturated fattyacids; results in off-odor and off-flavor production.

� Polygalacturonase: Catalyzes hydrolysis of glycosidicbonds between adjacent polygalacturonic acid residuesin pectin; results in tissue softening.

� Pectinesterase: Catalyzes deesterification of methyl groupsin pectin; Act in conjunction with polygalacturonases, lead-ing to tissue softening.

� Cellulase: Catalyzes hydrolysis of cellulose polymers in thecell wall and therefore is involved in fruit softening.

� Phospholipase D: Initiates the degradation of cellmembrane.

Lipids

In general, the lipid content of fruits is very small amountingto 0.1–0.2%. Avocado, olive, and nuts are exceptions. Despitethe relatively small amount of storage lipids in fresh fruits, theystill possess cell membrane lipids. Lipids make up the surfacewax, which contributes to the shiny appearance of fruits, andcuticle, which protects fruits against water loss and pathogens.The degree of fatty acid saturation establishes membrane flu-idity with greater saturation, resulting in less fluidity. Lipidsplay a significant role in the characteristic aroma and flavor offruits. For example, the characteristic aroma and flavor of cutfruits result from the action of the enzyme lipoxygenase on fattyacids (linoleic and linolenic acids), eventually leading to theproduction of volatile compounds. The action of lipoxygenaseis increased after the fruit is cut because there is a greater chancefor the enzyme and substrate to mix together. Lipoxygenase canalso be responsible for the off-flavor and off-aroma in certainplant products (soybean oil).

Volatiles

The specific aroma of fruits is due to the amount and diversity ofvolatiles they contain. Volatiles are present in extremely smallquantities (<100 ug/g fresh wt). Ethylene is the most abundantvolatile in fruit, but has no typical fruit aroma. Characteristicflavors and aromas are a combination of various character im-pact compounds, mainly esters, terpenes, short chain aldehydes,

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Table 28.3. Organic Acids of Selected Fruits

Organic Acid, mg/100 mL of Juice

Fruit Citric Ascorbic Malic Quinic Tartaric

Apple ND Tr 518±32 ND NDCherry ND Tr 727±20 ND NDGrape Tr Tr 285±58 ND 162±24Nectarine 730±92 114±6 501±42 774±57 TrPeach 140±39 Tr 383±67 136±28 NDPear 109±16 Tr 358±72 121±11 TrPlum ND Tr 371±16 220±2 NDKiwifruit ND Tr 294±24 214±68 NDStrawberry 207±35 56±4 199±26 ND ND

Source: Reprinted with permission from Van Gorsel et al. 1992. Copyright, American Chemical Society.ND, not detected; Tr, <10 mg/100 mL.

ketones, organic acids, and so on. Their relative importance de-pends upon the threshold concentration (sometimes, <1 ppb)and interaction with other compounds. For some fruits such asapple and bananas, the specific aroma is determined by the pres-ence of a single compound, ethyl-2-methylbutyrate in apples,and isoamylacetate in bananas.

Water

Water is the most abundant single component of fruits and veg-etables (up to 90% of total weight). The maximum water contentof fruits varies due to structural differences. Agricultural con-ditions also influence the water content of plants. As a majorcomponent of fruits, water has an impact on both the quality andthe deterioration. Turgidity is a major quality determinant factorin fruits. Loss of turgor is associated with loss of quality, and isa major problem during postharvest storage and transportation.Harvest should be done during the cool part of the day in orderto keep the turgidity at its optimum.

Organic Acids

The role of organic acids in fruits is twofold.

1. Organic acids are an integral part of many metabolicpathways, especially Krebs (TCA) cycle. Tricarboxylicacid cycle (respiration) is the main channel for the oxi-dation of organic acids, serving as an important energysource for the cells. Organic acids are metabolized intomany constituents including amino acids. Major organicacids present in fruits include citric acid, malic acid, andquinic acid.

2. Organic acids are important contributors to the taste andflavor of many fruits and vegetables. Total titratable acid-ity, the quantity and specificity of organic acids present infruits and so one influence the buffering system and thepH. Acid content decreases during ripening, because partof it is used for respiration and another part is transformed

into sugars (gluconeogenesis). The composition of organicacids in some fruits is given in (Table 28.3).

Pigments

Pigments are mainly responsible for the skin and flesh colors infruits and vegetables. They undergo changes during maturationand ripening of the fruits including, loss of chlorophyll (greencolor), synthesis and/or revelation of carotenoids (yellow andorange), and biosynthesis of anthocyanins (red, blue, and purple)(Table 28.4.). Anthocyanins occur as glycosides and are watersoluble, unstable, and easily hydrolyzed by enzymes to free

Table 28.4. Anthocyanins of Selected Fruits

Anthocyanin

Fruit Identification Peak Area

Apple Cyanidin 3-arabinoside 22±6Cyanidin 7-arabinoside or

Cyanidin 3-glucoside27±15

Cyanidin 3-galactoside 260±69Cherry Cyanidin 3-glucoside 189±40

Cyanidin 3-rutinoside 1320±109Peonidin 3 rutinoside 47±36

Grape Cyanidin 3-glucoside 121±33Delphinidin 3-glucoside 586±110Malvidin 3-glucoside 2157±375Peonidin 3-glucoside 478±92

Nectarine Cyanidin 3-glucoside 322±51Peach Cyanidin 3-glucoside 180±43Plum Cyanidin 3-glucoside 42±5Strawberry Cyanidin 3-glucoside 70±18

Pelargonidin 3-glucoside 1302±29Pelargonidin 3-glycoside 78±9

Source: Reprinted with permission from Van Gorsel et al. 1992.Copyright, American Chemical Society.

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anthocyanins. The latter may be oxidized to brown products byphenoloxidases after wounding.

Phenolics

Fruit phenolics include chlorogenic acid, catechin, epicatechin,leucoanthocyanidins and anthocyanins, flavonoids, cinnamicacid derivatives, and simple phenols. The total phenolic contentof fruits varies from 1 to 2 g/100 g fresh weight. Chlorogenicacid is the main substrate responsible for the enzymatic brown-ing of damaged fruit tissue. Phenolic components are oxidizedby polyphenol oxidase enzyme in the presence of O2 to brownproducts according to the following reactions.

Monophenol + O2Polyphenol oxidase→ quinone + H2O

1,4 diphenol + O2Polyphenol oxidase→ 1,4 quinone + H2O

Phenolic components are responsible for the astringency infruits and decrease with maturity because of their conversionfrom soluble to insoluble forms, and metabolic conversions.

Cell Structure

The fruit is composed of three kinds of cells that includeparenchyma, collenchyma, and sclerenchyma.

1. Parenchyma cells: Parenchyma cells are the most abundantcells found in fruits. These cells are mostly responsible forthe texture resulting from turgor pressure.

2. Collenchyma cells: Collenchyma cells contribute tothe plasticity of fruit material. The collenchyma cellsare located usually closer to the periphery of fruits.Collenchyma cells have thickened lignified cell walls andare elongated in their form.

3. Sclerenchyma cells: Also called stone cells, forexample, in pears, sclerenchyma cells are responsible forthe gritty/sandy texture of pears. They have very thicklignified cell walls and are also responsible for the stringytexture in such commodities as asparagus. For somecommodities such as asparagus, the number ofsclerenchyma cells increases after harvest and duringhandling, and storage.

FRUIT PROCESSINGHarvesting and Processing of Fruits

Harvesting is one of the most important of fruit-growing ac-tivities. It represents about half of the cost involved in fruitproduction because most fruit crops are still harvested by hand.Improvement needs to be done for the development of mechan-ical harvesters. Production of fruits of nearly equal size, andresistant to mechanical damage during harvest, is another areaaddressed by breeding technology. Certain fruits that are not tobe processed are harvested with stems in order to avoid microbialinvasion. Examples of this include cherries and apples.

Harvested fruit is washed to remove soil, microorganisms andpesticide residues, and then sorted according to their size and

quality. Fruit sorting can be done by hand or mechanically. Thereare two ways of mechanical sorting of fruits, sorting with wa-ter, which takes advantage of changes in density with ripening;and automatic high-speed sorting, in which compressed air jetsseparate fruit in response to differences in color and ripenessas measured by light reflectance or transmittance. When notmarketed as fresh, fruits are processed in many ways including:canning, freezing, concentration, and drying.

Freezing and Canning of Fruits

For freezing and canning of fruits, the general sequence of oper-ations includes (1) washing; (2) peeling; (3) cutting, trimming,coring; (4) blanching; (5) packaging and sealing; and (6) heatprocessing or freezing.

Freezing is generally superior to canning for preserving thefirmness of fruits. In order to minimize postharvest changes,freezing process is done at the harvest site for certain fruits.Fruit to be frozen must be stabilized against enzymatic changesduring frozen storage and on thawing. The principal enzymaticchanges are oxidations, causing darkening of color and the pro-duction of off-flavor. An important color change is enzymaticbrowning in apples, peaches, and bananas. This is due to the oxi-dation of pigment precursors such as o-diphenols and tannins byenzymes of the group known as phenol oxidases and polyphenoloxidases. Frozen fruits are produced for home use, restaurants,baking manufacturers, and other food industries. Depending onthe intended end use, various techniques are employed to preventoxidation.

The objective of blanching is to inhibit various enzyme reac-tions that reduce the quality of fruits. Fruits generally are notheat blanched because the heat causes loss of turgor, resulting insogginess and juice drainage after thawing. An exception to thisis when the frozen fruit is to receive heating during the bakingoperation, in which case calcium salts are added to the blanch-ing water or after blanching. Calcium salts increase the firmnessof the fruit by forming calcium pectates. For the same purpose,pectin, carboxymethyl cellulose, alginates, and other colloidalthickeners can also be added to fruit prior to freezing. Insteadof heat treatments, certain chemicals can be used in order to in-activate oxidative enzymes or to act as antioxidants. The majorantioxidant treatments include ascorbic acid dip and treatmentwith sulfites. Other methods for the prevention of contact withoxygen using physical barriers (sugar syrup) can be used.

Commonly dissolved in sugar syrup, vitamin C acts as anantioxidant and protects the fruit from darkening by subjectingitself to oxidation. A concentration of 0.05–0.2% ascorbic acidin syrup is effective for apple and peach. Peaches subjected tothis treatment may not darken during frozen storage at −18◦C forup to 2 years. Because low pH also helps in delaying oxidativeprocesses, vitamin C and citric acid may be used in combination.Furthermore, citric acid removes cofactors of oxidative enzymessuch as copper ions in polyphenol oxidase.

Sulfite is a multiple function antioxidant. Bisulfites of sodiumor calcium are used to stabilize the color of fresh fruits. Likevitamin C, sulfite is an oxygen acceptor and inhibits the ac-tivity of oxidizing enzymes. Furthermore, sulfite reduces the

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nonenzymatic Maillard-type browning reactions by reactingwith aldehyde groups of sugars so that they are no longer free tocombine with amino acids. Inhibition of browning is especiallyimportant in dried fruits such as apples, apricots, and pears.Sulfite also exhibits antimicrobial properties. The disadvantageof sulfite is that some people are allergic to this chemical, whichmakes its use restricted, for example, FDA prohibited the useof sulfite in fresh produce and limited the residual in processedproducts to 10 ppm, with appropriate label.

Sugar syrup has long been used to minimize oxidation beforethe mechanisms of browning reactions were understood, andstill remains as a common practice today. Application of sugarsyrup provides a coating to the fruit and thus prevents the contactof the cut surface and oxidizable components from contact withatmospheric oxygen. Sugar syrup also increases the sensory at-tributes of fruits, by reducing the loss of volatiles and improvingthe taste.

Vacuum treatment is used in combination with the chemicaldips in order to improve their effects. While fruits are submergedin the dip, vacuum is applied to draw air from the fruit tissue,allowing better penetration.

In order to reduce the cost of handling and shipping, somehigh-moisture fruits are pureed and concentrated to two or threetimes their natural solids content. Many others are dried forvarious purposes to different moisture levels. The majority offruit including apricot, apple, figs, pears, prunes, and raisins aresun dried. Sulfite is commonly used to preserve the color whenfruits are dried under high temperature that does not inactivatethe oxidative enzymes.

Nonenzymatic Browning

Also called Maillard reaction, the nonenzymatic browning is ofgreat importance in fruit processing. During Maillard reaction,the amino groups of amino acids, peptides, or proteins, react withaldehyde groups of sugars resulting in the formation of brownnitrogenous polymers called melanoidins (Ellis 1959, deMan1999). The velocity and pattern of the reaction depend on thenature of the reacting compounds, the pH of the medium, andthe temperature. Each kind of food shows a different browningpattern. Lysine is the most reactive amino acid because it con-tains a free amino group. The destruction of lysine reduces thenutritional value of a food since it is a limiting essential aminoacid. The major steps involved in the Maillard reaction are:

1. An aldose or ketose reacts with a primary amino group ofamino acid, peptide or protein, to produce an N-substitutedglycosylamine;

2. The Amadori reaction, which rearranges the glycosy-lamine to yield ketosamine or aldoseamine;

3. Rearrangement of the ketosamine with a second moleculeof aldose to yield diketosamine, whereas the rearrange-ment of the aldoseamine with a second molecule of aminoacid leads to a diamino sugar;

4. Amino sugars are degraded by losing water to give rise toamino or nonamino compounds;

5. The condensation of the obtained products with amino acidor with each other.

In Maillard reaction, the basic amino group is the reactivecomponent and therefore, the browning is dependent on theinitial pH, or the presence of a buffer system. Low pH resultsin the protonation of the basic amino group, and therefore itinhibits the reaction. The effect of pH is also heavily dependenton the moisture content of the product. When the moisture ishigh, the browning is caused by caramelization, whereas at lowwater content and pH of about 6, the Maillard reaction prevails.The flavors produced by the Maillard reaction in some cases arereminiscent of caramelization.

The nonenzymic browning can be prevented by closely mon-itoring the factors leading to its occurrence, including temper-ature, pH, and moisture content. The use of inhibitors such assulfite is an effective way of controlling nonenzymic brown-ing. It is believed that sulfite reacts with the degradation prod-ucts of the amino sugars to prevent the condensation of theseproducts into melanoidins. However, sulfite can react with thi-amine, which prohibits its use in foods containing this vitamin(Figs. 28.1 and 28.2).

Fruit Juice Processing

The quality of the juice depends on the quality of the raw ma-terial, regardless of the process. Often, the quality of the fruitis dependent on the stage of maturity or the stage of ripening.The major physicochemical parameters used in assessing fruitripening are sugar content, acidity, starch content, and firmness(Somogyi 1996a, 1996b).

The main steps involved in the processing of most type ofjuice include the extraction of the juice, clarification, juice de-aeration, pasteurization, concentration, essence add-back, can-ning or bottling, and freezing (less frequent). Juice extractorsfor oranges and grapefruits, whose peel contain bitter oils, aredesigned to cause the peel oil to run down the outside of thefruit and not enter the juice stream. Since apples do not containbitter oil, the whole apples are pressed. Juice extraction shouldbe done as quickly as possible, in order to minimize oxidation ofphenolic compounds in fruit juice by naturally present enzymes.

Apple Juice Processing

Apple juice is processed and sold in many forms includingAmerican apple cider, European apple cider, and shelf-stableapple juice. American apple cider is the product of sound, ripefruit that has been pressed and bottled or packaged with noform of preservatives added and stored under refrigeration. Thisis a sweet type of cider, which has not been fermented. Be-cause of an increased number of food-borne outbreaks of E. coli0157:H7 and Cryptosporidium parvum in apple cider, many ju-risdictions are working toward implementation of a kill step inthe processing of apple cider. Several pathogen outbreaks makeunpasteurized apple cider not suitable for general consumption,and especially for children, elderly, and immunocompromisedpeople.

European type of apple cider is a naturally fermented ap-ple juice, usually fermented to a specific gravity of one or less(Anonymous 1980). Shelf-stable apple juice includes clarified

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Unsaturatedcarbonyl compounds

Polymer

H+

Diketose-amino compound

Monoketose-amino compound

–H2O

Deoxyosones + othercarbonyl compounds

N-containingcompounds

Aldose-amino compound

Unsaturated osones

FurfuralsAldosylaminocompounds

MELANOIDINS

Copolymer Polymer

Figure 28.1. Mechanism of browning reaction.

and crushed apple juice and concentrates. The most populartype of apple juice is the one that has been clarified and fil-tered before pasteurization and bottling. Natural juice is a juicethat comes from the press. Up to 2% of ascorbic acid canbe added before pasteurization and bottling in order to pre-serve the color. Crushed apple juice is produced by passingcoarsely ground apples through a pulper and desecrator beforepasteurization.

Juice concentrates can be two types: frozen, when the Brixis about 42◦, or regular (commercial) concentrate with a Brixof 70◦ or more. Regardless of the type of apple product that isto be produced, the quality of the apple juice is directly relatedto the quality of the raw material used in its production. Onlysound ripe fruits should be used in the processing of apple juice.“Windfalls” or apples that are fallen and picked from the ground,should not be used for the juice due to the risk of contaminationby pathogens such as E. coli O157:H7, C. parvum, Penicilliumexpansium (producing the mycotoxin patulin) and also the risk ofpronounced musty or earthy off-flavor of the juice. Overmatureapples are very difficult to process, whereas immature applesgive a starchy and astringent juice with poor flavor.

The processing of apple juice starts with washing and sortingof the fruit in order to remove soil and other foreign material aswell as decayed fruits. Any damaged or decayed fruit should be

removed or trimmed in order to keep down the level of patulin inthe finished juice. Patulin is an indicator, which tells if the juicewas produced from windfalls or spoiled apples. The acceptablelevel of patulin in most countries is less than 50 ppb. Patulinis carcinogenic and teratogenic. Various methods are currentlyused to reduce the levels of patulin in apple juice, namely, char-coal treatment, chemical preservation (sulfur dioxide), gammairradiation, fermentation, and trimming of fungus-infected ap-ples. A recent study shows that pressing followed by centrifuga-tion resulted in an average toxin reduction of 89%. Total toxinreduction using filtration, enzyme treatment, and fining were 70,73, and 77%, respectively, in the finished juice. (Bissessur et al.2001). Patulin reduction was due to the binding of the toxin tosolid substrates such as the filter cake, pellet, and sediment.

Prior to pressing, apples are ground using disintegrators, ham-mers, or grating mills. The effectiveness of the pressing oper-ation depends on the maturity level of the fruits, as more ma-ture fruits are often difficult to press. A wide range of pressesis used in juice extraction including hydraulic, pneumatic, andscrew/basket type. The vertical hydraulic is a batch-type pressand requires no press aid. The main disadvantage is that thepress is labor intensive and produces juice with low solids con-tent. Hydraulic presses are the oldest type of press and are stillused worldwide. The newer versions are automated and require

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HCNH2

OHH

HHO

OHH

OH

CH2OH

HC

OHH

HHO

OHH

OH

CH2OH

NH3 CH

OHH

HHO

OHH

OHH

CH2OH

NH2

HC

O

HHO

OHH

OHH

CH2OH

–H

NH2

CH2NH2

OH

HHO

OHH

OHH

CH2ÖH

H2NCH 2COH

HHO

OHH

OHH

CH2O

alpha-D-Glucopyranosylamine

1-Amino-1-deoxy-alpha-D-fructopyranose

+ H

H

Figure 28.2. Amadori rearrangement in amino sugars.

press aid such as up to 1–2% paper pulp or rice hulls or bothin order to reduce spillage and increase juice channel in themash. The apple mash has many natural enzymes. Pectinolyticenzyme products contain the primary types of pectinases, pect-inmethylesterase (PME), polygalacturonase (PG), pectin lyase,and pectin transeliminase (PTE). PME deesterifies methylatedcarboxylic acid moieties of pectin, liberating methanol fromthe side chain, after which PG can hydrolyze the long pectinchains (Fig. 28.3). Enzymatic mash treatment has been devel-oped to improve the pressabiliy of the mash and, therefore thethroughput and yield. An amount of 80–120 mL of enzyme perton is added to the apple mash in order to break down the cellstructure. High-molecular weight constituents of cell walls, likeprotopectin, are insoluble and inhibit the extraction of the juice

from the fruit and keep solid particles suspended in the juice.Pectinase used in the apple juice processing is extracted from thefungus Aspergillus niger. Pectinase developed for apple mashpretreatment acts mainly on the cell wall, breaking the structureand freeing the juice. Also, the viscosity of the juice is lowered,and it can emerge more easily from the mash. The high content ofpectin esterase (PE) causes the formation of deesterified pectinfragments, which has a low water-binding capacity and reducesthe slipperiness. These pectins consist of chains of galacturonicacid joined by alpha-glycoside linkage. In addition, polymersof xylose, galactose, and arabinose (hemicelluloses) form a linkwith the cellulose. The entire system forms a gel that retains thejuice in the mash. The extraction is easier, even if the pectinsare partially broken by pectinesterase. The pomace acts like a

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OO

O OOO O O

HOOC H3COOC H3COOCH3COOC

Pectin-methyl-esterase___________________________________________________________

OOOO

OOOO

HOOC HOOCHOOCHOOC

_____________________________________________________Polygalacturonase

HOHHOHO

HOOC

(n)

OO

OO

OO

OO

H3COOC HOOC H3COOC H3COOC

_____________________________________________________Pectin-transeliminase

O

H3COOC

O OO

HOOC H3COOC

OO

H3COOC

HOHO

O

HOOC

HOHO

HOHHOHO

HOOCH3COOC

(n) (n)

Figure 28.3. Diagrammatic representation of the site of action of various pectinolytic enzymes.

pressing aid, when used with mash predraining. The applica-tion of enzyme treatment can increase the press throughput by30–40% and the juice yield by over 20%. Mash pretreatmentalso increases the flux rate of ultrafiltered apple juice by up to50%. An important by-product of apple juice industry is pectin.Therefore, overtreatment of mash with pectinolytic enzymescould render the pomace unsuitable for the production of pectin.Inactivation of the enzyme after reaching the appropriate levelof pectin degradation is an important step in the production ofapple juice. Residual pectic enzymes in apple juice concentratecould cause setup problems, when used for making apple jelly.There is a recent development in apple juice extraction with theprocess of liquefaction. Liquefaction is a process of completelybreaking down the mash by using an enzyme preparation, tem-

perature, and time combination. The liquefied juice is extractedfrom the residual solid by the use of decanter centrifuges and ro-tary vacuum filters. It is a common practice, with the addition ofcellulose enzyme to the mash to further degrade the cellulose tosoluble solids, increasing the juice Brix nearly by 5◦. The com-mercially available enzyme preparations contain more than 120substrate specific enzyme components. Another popular extrac-tion method is the countercurrent extraction method, developedin South Africa and refined in Europe in the 1970s. The principleof the system is as follows: the mash is heated, predrained, andcounterwashed with water and recycled hot juice. A 90–95%recovery is possible when the throughput is about 3 tons perhour. The main disadvantage of the system is the lower solu-ble solids content of the obtained juice (6–8 vs. 11–12 from

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Washing and sorting

Disintegrator

Juice extraction

Enzyme treatment

Filtration

Evaporation

Standardization

Storage

Raw apple

Figure 28.4. Apple juice and concentrate flow chart.

other methods). Juice yield from different types of extractionvaries from 75% to 95%, and depends on many factors includ-ing the cultivar and maturity of the fruit, the type of extraction,the equipment and press aids, the time, temperature, and theaddition and concentration of the enzyme to the apple mash(Fig. 28.4).

Enzyme Applications

Enzyme applications in the apple juice processing follow theextraction, especially when producing a clarified type of juice.The main objective is to remove the suspended particles fromthe juice (Smock and Neubert 1950). The soluble pectin in thejuice has colloidal properties and inhibits the separation of theundissolved cloud particles from the clear juice. Pectinase hy-drolyzes the pectin molecule so it can no longer hold juice. Thetreatment dosage of pectinase depends on the enzyme strengthand varies from one manufacturer to another. A typical ‘3X’enzyme dosage is about 100 mL per 4000 liters of raw juice.Depectinization is important for the viscosity reduction and theformation of galacturonic acid groups that helps flocculate the

suspended matter. This material, if not removed, binds to the fil-ters, reduces the production, and can result in a haze formationin the final product. There are two methods of enzyme treatmentcommonly used in the juice industry including (1) hot treatmentwhere the enzymes are added to 54◦C juice, mixed, and heldfor 1–2 hours; and (2) cold treatment where the enzymes areadded to the juice at reduced temperature (20◦C) and held for6–8 hours. The complete breakdown of the pectin is monitoredby means of an acidified alcohol test. Five milliliters of juiceare added to 15 mL of HCl-acidified, ethyl alcohol. Pectin ispresent if a gel develops in 3–5 minutes after mixing the juicewith the ethanol solution. The absence of gel formation meansthe juice depectination is complete. In the cloud of the postpro-cessed juice, other polymers such as starch, and arabinans canbe present and therefore, the clear juice is treated with alpha-amylase and hemicellulase enzymes, in order to partially orcompletely degrade them. Gelatin can be used to remove frag-mented pectin chains and tannins from the juice. Best resultsare obtained when hydrating 1% gelatin in warm 60◦C water.Gelatin can be added in combination with the enzyme treatment,bentonite, or by adding midway through the enzyme treatmentperiod. The positively charged gelatin facilitates the removal ofthe negatively charged suspended colloidal material from thejuice. Bentonite can be added in the range of 1.25–2.5 kg of re-hydrated bentonite per 4000 L of juice. Bentonite is also added toincrease the efficiency of settling, protein removal, and preven-tion of cloudiness caused by metal ions. For cloudy and naturalapple juice, enzymes are usually not used. The enzyme-treated,refined, and settled apple juice is then pumped from the settledmaterial (lees) and further clarified by filtration.

The filtration of apple juice is done with or without a filteraid. The major types of filters are pressure leaf, rotary vacuum,frame, belt, and Millipore filters. To obtain the desired productcolor and clarity, most juice manufacturers use a filter mediumor filter aid in the filtration process. The filter media includediatomaceous earth, paper pulp pads, cloth pads or socks, andceramic membranes to name a few. The filter aid helps to pre-vent the blinding of the filters and increase throughput. As thefruit matures, more filter aid will be required. Several types offilter aids are available, in which the most commonly used isdiatomaceous earth or cellulose-type materials. Additional juicecan be recovered from the tank bottoms or “lees” by centrifuga-tion or filtration. This recovered juice can be added to the rawjuice before filtration.

Diatomaceous earth, or kieselguhr, is a form of hydrated silica.It has also been called fossil silica or infusorial earth. Diatoma-ceous earth is made up of the skeletal remains of prehistoricdiatoms that were single-cell plant life and is related to the algaethat grow in the lakes and oceans. Diatomaceous earth filtrationis a three-step operation: (1) first, a firm thin protective precoatlayer of filter aid, usually of cellulose, is built up on the filterseptum (which is usually a fine wire screen, synthetic cloth,or felt); (2) the use of the correct amount of a diatomite bodyfeed or admix (about 4.54 kg per 3000 cm2 of filter screen);and (3) the separation of the spent filter cake from the septumprior to the next filter cycle. Prior to the filtration, centrifugationmay be used to remove high-molecular weight suspended solids.

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RO

1 µ = 1000 nm

Mic

ropa

rtic

les

Col

loid

sIo

ns a

nd m

olec

ules

10 µ

0.1 nm

2 nm

0.3 µ MF

F

UF

Figure 28.5. Membrane filtration. RO, reverse osmosis; UF,ultrafiltration; MF, microfiltration; F, filtration.

In some juice plants, high-speed centrifugation is used prior tothe filtration. This centrifugation step reduces the solids by about50%, thus minimizing the amount of filter aid required. The fil-tration process is critical, not only from the point of view ofproduction, but also for the quality of the end product. Bothpressure and vacuum filters have been used with success injuice production (Nelson and Tresler 1980). A recent develop-ment in the juice industry is the membrane ultrafiltration. Ul-trafiltration, based on membrane separation, has been used withgood results to separate, clarify, and concentrate various foodproducts. Ultrafiltration of apple juice will not only clarify theproducts, but depending on the size of the membrane, will alsoremove the yeast and mold microorganisms common in applejuice (Fig. 28.5).

Apple Juice Preservation

Preservation of apple juice can be achieved by refrigeration, pas-teurization, concentration, chemical treatment, membrane filtra-tion, or irradiation. The most common method is pasteurizationbased on temperature and time of exposure. The juice is heatedto over 83◦C, held for 3 minutes, filled hot into the container(cans or bottles), and hermetically sealed. The apple juice is heldfor 1 minute at 83◦C and then cooled to less than 37◦C. Whencontainers are closed hot and then cooled, vacuum develops,reducing the available oxygen that also aids in the prevention ofmicrobial growth. After the heat treatment, the juice may also

be stored in bulk containers. Aseptic packaging is another com-mon process where, after pasteurization, the juice is cooled andpacked in a closed, commercially sterile system under asepticconditions. This process provides shelf-stable juice in laminated,soft-sided consumer cartons, bag-in-box cartons, or aseptic bagsin 200–250 liter drums.

Apple juice concentration is another common method ofpreservation. The single-strength apple juice is concentratedby evaporation, preferably to 70◦ or 71◦ Brix. By an alternatemethod, the single-strength juice is preconcentrated by reverseosmosis to about 40◦ Brix, then further concentrated by evapo-ration methods. The reduced water content and natural aciditymake the final concentrated apple juice shelf stable at roomtemperature. There are several evaporators used in apple juiceproduction including rising film evaporators, falling film evap-orators, and multiple effect tubular and plate evaporators. Dueto the heat sensitivity of the apple juice, the multiple-effectevaporator with aroma recovery is the most commonly used.The general method in a multiple-effect evaporator is to heat thejuice to about 90◦C and capture the volatile (aroma) componentsby cooling and condensation. This is followed by reheating the20–25◦ Brix juice concentrate in the first stage to about 100◦Cand then concentrate it to about 40–45◦ Brix. Another stage ofheating and evaporation at about 50◦C to 60◦ Brix, and final heat-ing and concentration in the fourth stage to 71◦ Brix providesfully concentrated juice. The warm concentrate is then chilledto 4–5◦C prior to adjusting the Brix to 70◦ before barreling orbulk storage.

Chemicals such as benzoic acid, sorbic acid, and sulfite aresometimes used to reduce spoilage of unpasteurized apple juice,either in bulk or as an aid in helping to preserve refrigeratedproducts. Application of irradiation and ultrasonic sound arenew emerging methods of preservation with high potential eventhough not fully accepted by consumers at this time.

Apple essence is recovered during the concentration of ap-ple juice. The identification of volatile apple constituents, com-monly known as essence or aroma, has been the subject ofconsiderable research. In 1967, researchers at the USDA iden-tified 56 separate compounds from apple essence. These com-pounds were further refined by organoleptic identification, usinga trained panel of sensory specialists. These laboratory eval-uations revealed 18 threshold compounds identified as “De-licious” apple compounds consisting of alcohols, aldehydes,and esters. Three of the eighteen compounds had “apple-likearomas” according to the taste panel. These were 1-hexanal,trans-2-hexenal, and ethyl, 2-methyl butyrate (Flath et al. 1967,Somogyi et al. 1996b).

Processed Apple Products

The popularity of blended traditional/tropical juice products haspushed the consumption of traditional fruit juices such as apple,orange, and grape juices to 25 liters in 2002, an increase of morethan 24% from 1992 (Statistics Canada 2003). Apples are nor-mally processed into a variety of products, although apple juiceis the most popular processed apple product. With a produc-tion of 465,418 metric tons of apple in 2001, Canada exported

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18,538 metric tons of concentrated apple juice. For the sameyear, United States exported 25,170 metric tons of concentratedapple juice (FAO 2003). Apples for processing should be ofhigh quality, proper maturity, of medium size, and uniform inshape. Apples are processed into frozen, canned, dehydrated ap-ple slices and dices, and different kinds of applesauce. Applesthat are unsuitable for peeling are diverted to juice processing.

Apple Sauce

Diced or chopped apples with added sugar, preferably a sugarconcentrate, are cooked at 93–98◦C for 4–5 minutes in order to

soften the fruit and inactivate polyphenol oxidase. Sauce witha good texture, color, and consistency is produced with highquality raw apples and a good combination of time and temper-ature treatment. Cooked applesauce is passed through a pulperof 1.65–3.2 mm finishing screen to remove unwanted debrisand improve the texture. Applesauce is then heated to 90◦C andimmediately filled in glass jars or metal cans. The filled apple-sauce are seamed or capped at 88◦C and cooled to 35–40◦Cafter 1–2 minutes (Fig. 28.6). There are various types of apple-sauce that include natural, no sugar added, “chunky”, cinnamonapplesauce, and mixture of applesauce and other fruits such asapricot, peach, or cherry.

Raw apple

Washing and sorting

Dicing/chopping

First inspection

Cooking

Pulping/finishing

Second inspection

Preheating/filling

Holding/cooking

Cooling

Seaming

Labeling/storage

Peeling and coring

Vacuuming

Blanching/filing

Cooking

Cooling

Seaming

Labeling/storage

Apple

sauce

Canned

apple

slices

Figure 28.6. A flow chart depicting steps in apple processing.

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Sliced Apples

Sliced apples have multiple uses and are preserved by manydifferent methods such as canned, refrigerated, frozen, or dehy-drated states. About 85% of sliced apples are processed, whereasonly 15% are refrigerated, frozen or dehydrated and frozen. Ap-ple slice texture is very important, as well as the consistency ofthe slice size, therefore, apples with firm flesh and high-quality,falling within a specified size range are desirable. Apples aresliced into 12–16 slices and blanched after inspection for even-tual defects. The blanched apple slices are hot filled into cans andclosed under steam vacuum after addition of hot water or sugarsyrup. The canned apples are heated at 82.2◦C and immediatelycooled to 37–40◦C.

When bulk frozen, apple slices are vacuum treated andblanched and filled into 13–15 kg tins or poly-lined boxes. Thetins or boxes are then sealed, frozen, and stored at −17◦C.

Individual quick frozen apple slices (IQF) are usually treatedwith sodium bisulfite after inspection. Nitrogen (N2) and carbondioxide (CO2) are the most popular freezing media. From thevacuum tank, the apple slices pass through an IQF unit wherethe slices are individually frozen. From the freezing unit, theslices are filled into tins or poly-lined boxes and stored frozen at−17◦C or below.

Dehydrofrozen apple slices are dehydrated to less than 50% oftheir original weight and then frozen. The dehydrofrozen slicesare packed in cardboard containers or large metal cans withpolyethylene liners and rapidly frozen before storing. Frozenslices are thawed and then soaked in a combined solution ofsugar, CaCl2, and ascorbic acid, or bisulfite. For fresh and re-frigerated apple slices, the use of 0.1–0.2% calcium chloride,and ascorbate protects apple slices from browning and micro-bial spoilage. Blanched slices resist browning for approximately2 days, but lose flavor, sugar, and acid. This type of product has avery short shelf life. Recently, the use of natural protein polymercoatings (NatureSeal) has shown promise in enhancing the shelflife and quality of fresh-cut apple products.

Dried Apple Products

Most processing cultivars are used for drying, but the best qual-ity dried apple slices are obtained from “Red Delicious” and

“Golden Delicious” apples. A desirable quality attribute of ap-ples used for drying is a high sugar/water ratio. Color preserva-tion and reduction in undesirable enzyme activities are achievedby the use of bisulfite. There are two types of dried apple prod-ucts including evaporated and dehydrated apples. Evaporatedapples are cut into rings, pie pieces, or dices and then dried toless than 24% moisture by weight. The dehydrated apples, onthe other hand, are cut into dices, pie pieces, granules, and flakesprior to drying to 3–0.5% moisture content. Up to 300 ppm ofbisulfite is used to prevent color deterioration. The maximumallowed SO2 in dried apples in Europe is 500 ppm, whereas inUnited States, the limit is 1000 ppm.

Quality Control

Apples contain several organic acids and as such, only a limitednumber of microorganisms can grow in them. The most com-mon microbes are molds, yeasts, aciduric bacteria, and certainpathogens such as E. coli O157:H7, capable of growing at lowpH (Swanson 1989). Several approaches to quality managementare available today including total quality management (TQM),statistical quality control (SQC), and hazard analysis criticalcontrol points (HACCP).

Biochemical Composition and NutritionalValue of Processed Apples

The nutritive value of most processed apple products is similar tothe fresh raw product. Apple products are sources of potassium,phosphorus, calcium, vitamin A, and ascorbic acid. Glucose,sucrose, and fructose are the most abundant sugars. Dried ordehydrated apples have a higher energy value per gram tissuedue to the concentration of sugars (Tables 28.4 and 28.5).

The nutritional value of apples, and fruits in general, is en-hanced by the presence of flavonoids. More than 4000 flavonoidshave been identified to date. There are many classes of flavonoidsof which flavanones, flavones, flavonols, isoflavonoids, antho-cyanins, and flavans are of interest. Flavanones occur predom-inantly in citrus fruits, anthocyanins, catechins, and flavonolsare widely distributed in fruits, and isoflavonoids are present in

Table 28.5. Nutrients in Fruits and Processed Products (454 g)

Apples Food Energy (kcal) Protein (g) Fat (g) Carbohydrate (g) Calcium (mg) Phosphorus (mg) Iron (mg)

Raw fresh 242 0.8 2.5 60.5 29 42 1.3Applesaucea 413 0.9 0.5 108.0 18 23 2.3Unsweetened Juice 186 0.9 0.9 49.0 18 23 2.3Apple juice 213 0.5 0.1 54.0 27 41 2.7Frozen sliceda 422 0.9 0.5 110.2 23 27 2.3Apple buttera 844 1.8 3.6 212.3 64 163 3.2Dried, 24% 1247 4.5 7.3 325.7 141 236 7.3Dehydrated, 2% 1601 6.4 9.1 417.8 181 299 9.1

Source: Composition of foods. Agriculture Handbook No 8.aWith sugar.

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O

OH

OH

A C

B

O

OH

OH

OH

OH+

OH

OH

O

OH

OH

OH

O

OH

O

OH

OH

OH

OH

OH

OH

OH

OH

OH

OOH

Biflavan

Flavans

Flavonone

BlueberriesCherriesWine

Anthocyanin

Catechin

ApplesPeachesTea

Citrus

Figure 28.7. Chemical structures of fruit flavonoids. The propanoid structure consists of two fused rings. “A” is aromatic ring and “C” is aheterocyclic ring attached by carbon–carbon bond to “B” ring. The flavonoids differ in their structure at the “B” and “C” rings.

legumes. Structurally, flavonoids are characterized by a C6-C3-C6 carbon skeleton (Fig. 28.7). They occur as aglycones (withoutsugar moieties) and as glycosides (with sugar moieties). Process-ing may decrease the content of flavonoids by up to 50%, due toleaching into water or removal of portions of the fruit such as theskin, that are rich in flavonoids and anthocyanins. It is estimatedthat the dietary intake of flavonoids may vary from 23 mg/d to1000 mg/d in various populations (Peterson and Dwyer 1998).Flavonoids are increasingly recognized as playing potentiallyimportant roles in health including but not limited to their rolesas antioxidants. Epidemiological studies suggest that flavonoidsmay reduce the risk of developing cardiovascular diseasesand stroke.

Flavanones

The major source of flavanones is citrus fruits and juices.Flavanones contribute to the flavor of citrus, for example,naringin found in grapefruit provides the bitter taste, whereashesperidin, found in oranges is tasteless.

Flavonols

The best-known flavonols are quercetin and kaempferol.Quercetin is ubiquitous in fruits and vegetables. Kaempferolis most common among fruits and leafy vegetables. In fruits,flavonols and their glycosides are found predominantly in theskin. Myricetin is found most often in berries.

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Table 28.6. Nutrients in Fruit and Processed Products (454 g)

ApplesSodium

(mg)Potassium

(mg)Vitamin A

(IU)Thiamin

(mg)Riboflavin

(mg)Niacin(mg)

Vitamin C(mg)

Raw fresh 4 459 380 0.12 0.08 0.3 16Applesaucea 9 295 180 0.08 0.05 0.2 5Unsweetened juice 9 354 180 0.08 0.05 0.2 5Apple juice 5 458 – 0.03 0.07 0.4 4Frozen sliceda 64 308 80 0.05 0.014 1.0 33Apple buttera 9 1143 0 0.05 0.09 0.7 9Dried, 24% 23 22,581 – 0.26 0.053 2.3 48Dehydrated, 2% 32 3311 – 0.02 0.026 2.9 47

Source: Composition of foods. Agriculture Handbook No 8.aWith sugar.

Anthocyanins

Anthocyanins often occur as a complex mixture. Grape extractscan have glucosides, acetyl glucosides, and coumaryl glucosidesof delphinidin, cyanidin, petunidin, peonidin, and malvidin. Thecolor of anthocyanins is pH dependent. An anthocyanin is usu-ally red at a pH of 3.5, becoming colorless and then shiftingto blue as the pH increases. Fruit anthocyanin content increaseswith maturity. In stone fruits (peaches and plums) and pomefruits (apple and pears), anthocyanins are restricted to the skin,whereas in soft fruits (berries), they are present both in skin andflesh. Anthocyanins are used as coloring agents for beveragesand other food products.

Flavans

Flavans are what was once called catechins, leucoanthocyanins,proanthocyanins, and tannins. They occur as monoflavans, bi-flavans, and triflavans. Monoflavans are found in ripe fruits andfresh leaves. Biflavans and triflavans are found in fruits such asapples, blackberries, blackcurrants, cranberries, grapes, peaches,and strawberries (Table 28.6).

FURTHER READING

Arthey D, Ashwurst PR. 2001. Fruit Processing: Nutrition, Productsand Quality Management. Aspen Publishers, Gaithersburg, MD,p. 312.

Enachescu DM. 1995. Fruit and Vegetable Processing. FAO Agri-cultural Services Bulletin 119, FAO, p. 382.

Jongen WMF. 2002. Fruit and Vegetable Processing: ImprovingQuality. (Electronic Resource). CRC Press, Boca Raton, FL.

Salunkhe DK, Kadam SS. 1998. Handbook of Vegetable Science andTechnology: Production, Composition, storage and Processing.Marcel Dekker, New York, p. 721.

REFERENCES

Anonymous. 1980. Cider. In: National Association of Cider Makers.NACM, Dorchester, Dorset.

Bissessur J et al. 2001. Reduction of patulin during apple juiceclarification. J Food Protection 64: 1216–1222.

deMan JM. 1999. Principles of food chemistry, 3rd edn. AspenPublishers, Gaithersburg, MD, pp. 120–137.

Ellis GP. 1959. The Maillard reaction. In: ML Wolfram, RS Tip-son (eds.) Advances in Carbohydrates Chemistry, Volume 14.Academic Press, New York.

Flath RA et al. 1967. J Agric Food Chem 15: 29–38.Canadian apple industry. http://www.ats.agr.gc.ca/can/4480-eng

.htm. Accessed on December 06, 2011.FAO. 2003. http://www.statcan.gc.ca/pub/82-003-x/2008004/

article/6500821-eng.pdf. Accessed on December 06, 2011.Statistics Canada. 2003. http://www.statcan.ca/english/ads/23F0001

XCB/highlight.htm. Accessed on December 07, 2011.Nelson PE, Tresler DK. 1980. Fruit and Vegetable Juice Production

Technology, 3rd edn. AVI Co., Westport, CT.Peterson J, Dwyer J. 1998. Flavonoids: dietary occurrence and bio-

chemical activity. Nutrition Research 18: 1995–2018.Somogyi LP et al. 1996a. Processing Fruits: Science and Technol-

ogy, Volume 2, Major Processed Products. Technomic PublishingCo., Lancaster, PA, pp. 9–35.

Somogyi LP et al. 1996b. Processing Fruits: Science and Technol-ogy, Volume 1, Biology, Principles and Applications. TechnomicPublishing Co., Lancaster, PA, pp. 1–24.

Smock RM, Neubert AM. 1950. Apples and Apple Products. Inter-science Publishers, New York.

Swanson KMJ. 1989. Microbiology and preservation. In: DL Down-ing (ed.) Processed Apple Products. Van Nostrand Reinhold/AVI,New York, pp. 343–363.

Van Gorsel H et al. 1992. Compositional characterisation of prunejuice. J Agric Food Chem 40: 784–789.

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Food Biochemistry and Food Processing (Simpson/Food Biochemistry and Food Processing) || Biochemistry of Fruit Processing