Maximizing The Nutritional Value Of Fruits And Vegetables
BY Diane M. BarrettMaximizing the Nutritional Value ofFruits & VegetablesReview of literature on nutritional value of produce compares fresh,frozen, and canned products and indicates areas for further research.Interest in the nutritional valueof fruits and vegetables has beenincreasing, in part because ofrecent findings on the high levelof obesity and other diet-relatedhealth problems in children and inpart because of increased federalsupport of programs fundingconsumption of fresh and processedfruit and vegetable products.The following discussionis based in part on a review byRickman et al. (2007a, b) of recentliterature on the nutritional valuethiamin, riboflavin, B-6, niacin,folate, A, and E. Phytochemicalsin fruits and vegetables, such aspolyphenolics, carotenoids, andglucosinolates, may also havenutritional value. While manyfruits and vegetables are consumedprimarily in their fresh state, someproduce such as tomatoes, snapbeans, corn, peaches, nectarines,and pineapples are also consumedto a significant degree in theirprocessed state. Table 1 lists percapita consumption of selectedof providing the recommended 5–13 daily servings year round. In theU.S., fruits and vegetables grownin North America may spend up to5 days in transit following harvestbefore arriving at a distributioncenter. Transportation time forfruits and vegetables grown in thesouthern hemisphere for winterand spring consumption in theU.S. ranges from as little as a fewdays if transported by air freight toseveral weeks if sent by refrigeratedship. At the retail store, fruits andFresh fruits and vegetables may not be consumed for a significant length oftime following harvest, during which time nutrient degradation may occur.of fresh, canned, and frozen fruitsand vegetables. The review wascommissioned by the Canned FoodAlliance and prepared by faculty ofthe University of California Centerfor Excellence in Fruit & VegetableQuality (see sidebar).Fresh Fruits and VegetablesFruits and vegetables are a majorsource of macronutrients such asfiber and micronutrients such asminerals and vitamins C,pg4004.07 www.ift.orgfresh, frozen, and canned fruitsand vegetables in the United States(ERS, 2004).Fruits and vegetables are oftenthe most attractive and healthpromoting when harvested at theirpeak maturity, but most Americansdo not have home gardens capablevegetables may spend 1–3 days ondisplay prior to being purchasedby the consumer, who may storethem for up to 7 days prior toconsumption. This means thatfresh fruits and vegetables maynot be consumed for a significantlength of time following harvest,during which time nutrientdegradation may occur.Most fruits and vegetablesare composed of 70–90%water and once separated
from their source of nutrients(tree, plant, or vine) undergohigher rates of respiration,resulting in moisture loss, qualityand nutrient degradation, andpotential microbial spoilage.In some instances, fruits andvegetables may be harvestedimmature to reduce mechanicaldamage during harvesting andtransportation. Because intactfruits and vegetables are still aliveand respiring, temperature andrelative humidity must be carefullycontrolled to maintain low rates ofrespiration, prevent moisture loss,and maintain eating quality.Changes in nutrientcomposition from harvestto consumption depend to acertain degree on the particularnutrient, the commodity, and thepostharvest handling, storage,and home cooking conditions. Inaddition, initial nutrient contentis affected by the particularcultivar (e.g., Red Delicious andFuji apples), soil type, productionsystem (conventional, organic,etc.), and weather conditions(temperature, humidity, daylighthours, etc.) during growth.Fruits and vegetables forthe fresh market are generallyharvested by hand, with theexception of roots and tubers,while many commodities destinedfor processing are mechanicallyharvested. Mechanical harvestinggenerally causes more stressto the plant tissue and mayresult in more damage thanhand harvesting. Nutrientretention isoptimizedif fruits and vegetables are gentlyhandled and stored at high relativehumidity and refrigerated. Somecommodities, such as applesand pears, are stored for up to12 months under controlledatmosphere conditions that utilizelow oxygen and high carbondioxide levels to slow downrespiration. Most perishablecommodities, however, are storedunder refrigerated conditions, andstorage life may range from 8–10days for highly perishable fruitslike berries to 8–10 weeks forless-perishable commodities likesquash, pumpkin, apples, grapes,and pears.Processed Fruits and VegetablesMany fruits and vegetables onlygrow in specific regions of theworld, in a particular type ofsoil, under certain temperatureand humidity environments, andat limited times of year, and inmany countries refrigeration isnot available. Processing allowsfruits and vegetables producedin remote regions of the world,such as coconuts, durian, mango,and papaya, to be stabilized andtransported to distant locations forconsumption. In many instances,fruits and vegetables such aspumpkin, clingstone peaches, andsome leafy greens and squashes maybe too tough or bitter to consumeCenters Address Fruitand Vegetable QualityCalifornia is the primary producer offruits and vegetables in the UnitedStates, and in January 2006, the University of California established a Centerfor Excellence in Fruit & Vegetable Qualitywithin the Robert Mondavi Institute ofWine & Food Science (http://robertmondaviinstitute.ucdavis.edu/).More than 30 scientists—rangingfrom economists to consumer scientists,sensory scientists, molecular biologists,chemists, biochemists, postharvestphysiologists, nutritionists, and processengineers—are involved in the Center,which will form an integral part of a newFoods for Health Initiative.The long-term goal is to develop andpromote science-based information andtechnology that increases consumption offruits and vegetables by enhancing botheating quality and health. To accomplishthis, the scientists will focus on threeshort- to medium-term objectives: definedesirable sensory parameters thatdescribe consumer perception of fruitand vegetable quality; correlate sensoryparameters with objective measurementsof quality (color, texture, flavor, andnutritional quality); and identify optimalgenetic, preharvest, postharvest, andprocessing practices that maximizequality and nutritional value of fruits andvegetables.Other interdisciplinary centersfocusing on foods for health are beingdeveloped at many other universities inthe United States, Canada, Europe, andthe rest of the world, including Texas A&MUniversity, Iowa State University, theUniversity of Illinois, Purdue University,and the University of Minnesota. There is aneed to encourage collaboration betweenscientists at these various universities andidentify strengths specific to individualprograms which need not be duplicated atother locations.04.07 www.ift.org41pg
Table 1. Per-capita consumption of fruits and vegetables in 2004. From ERS (2006).CommodityAsparagusBeans, snapCarrotsCornGreen peasMushroomsPeaches and 6—2.65.14.42.119.3Amount 28.21.21.63.64.80.93a—70.4Total for all processing varieties.aunless they undergo thermaltreatment, either during homecooking or, in the case where thegrowing location is distant, duringthe canning process. Canning,freezing, dehydration, pickling,fermentation, and other methodsof preservation are carried out withthe goal of delivering processedproducts that are safe and retaindesirable quality attributes similarto those of fresh products.Processing, however, changesthe color, texture, flavor, andnutritional quality of many freshfruits and vegetables. Surprisinglyfew published studies compare thenutritional quality of fresh, frozen,and canned fruits and vegetables.Freezing is typically precededby blanching (a short-time heatingstep) to inactivate enzymes, andthis pretreatment may resultin some relatively limited lossof quality components. Frozenproducts should not be stored forlong periods in “frost-free” homefreezers, because these go throughwarming cycles to defrost coils andinherently warm products stored inthem. Storage in warehouses wheretemperature is well maintainedmay be for up to one year.In general, water-solublepg4204.07 www.ift.orgnutrients such as vitamins Cand B and the polyphenolicsare degraded by processingtreatments and may be leachedinto cooking water or the canningmedium. Fat-soluble nutrientssuch as vitamins A and E and thecarotenoids may be released fromtheir cellular matrices by thermal,freezing, high-pressure, or otherpreservation treatments. Becausethey have been extracted to agreater degree by the treatment,it is possible to analyze themmore readily, and it may appearthat there is an increase. It is notlikely that processing methodsper se will cause a real increasein nutrient concentration, butthey may make nutrients moredetectable instrumentally andperhaps more available biologically.Scientists are still investigating therelationship between what maybe detected in the laboratory andthe “bioavailability” or amount ofmaterial that is absorbed into ourbodies. In the determination ofantioxidant activity, for example,a growing number of researchersare investigating antioxidant effectsusing human, animal, or cell-linemodels rather than relying merelyon instrumental determinationof model systems that may or notsimulate what happens in the body.Fresh vs Canned and FrozenVitamin C is water soluble andsensitive to heat, light, and oxygen,making it susceptible to lossduring both home cooking of freshfruits and vegetables and thermalprocessing. For that reason, loss ofvitamin C is often used as an indexof nutrient degradation.Research indicates that as longas fresh products undergo minimalstorage and are handled at propertemperatures, they are superiorto processed products in termsof vitamin C content. However,vitamin C degrades rapidly afterharvest, and this degradationcontinues during storage. VitaminC losses in vegetables stored at4 C for 7 days range from 15% forgreen peas to 77% for green beans.Refrigeration slows deteriorationof vitamin C, as demonstrated inthe case of broccoli, where lossesafter 7 days of storage were 0 at0 C but 56% at 20 C. It should benoted, however, that 20 C storageof broccoli for 7 days is atypical andwould result in a wilted, yellowedproduct that would in all likelihoodnot be consumed.Losses of vitamin C duringhome cooking of fresh vegetablesrange from 15 to 55%, dependingon the cooking method. Additionalvitamin C loss due to cookingcanned products is minimal, sincelittle if any added water is neededand heating time is generally lessthan the cooking time neededfor fresh or frozen products.Table 2 compares vitamin
Table 2. Cumulative losses in vitamin C due to fresh storage or processing and storage, followed by home cooking in all cases. Adapted from Rickman et al. (2007a).VegetableBroccoliaCarrotsaGreen beansGreen Refrigerated storage timebefore processing andcooking (days)21217721001–20.28d0Initial concentration(g/kg)Authors repeated analysis in two consecutive years, results indicated separately.Stored for 12 mo prior to cooking.cAuthors reported increase in vitamin C with fresh storage.Loss after cooking (% wet weight)FrozenCanned53842 68e77e85fHoward et al. (1999)Howard et al. (1999)Howard et al. (1999)Howard et al. (1999)Howard et al. (1999)Weits et al. (1970)Weits et al. (1970)Fellers and Stepat (1935)6481e67eWeits et al. (1970)Authors did not provide values. Values taken from USDA (2005).Stored for 6 mo prior to cooking.fAuthors did not indicate storage time before cooking.adbeC content in fresh, frozen, andcanned vegetables that are furtherstored and then home cooked.Canning exposes fruits andvegetables to high temperatures,which degrade vitamin C and maycause leaching into the canningmedium. Vitamin C decreased by10–90% during the canning ofvarious vegetables, but there waslittle change in content duringstorage of canned products.Vitamin C losses duringfreezing were slightly lower, butwere strongly influenced by theparticular commodity and theblanching and freezing conditionsused. Frozen fruit and vegetableproducts showed little change innutrient content if the storagetemperature was well maintained.Losses in B vitamins also occurduring transportation and storageof fresh fruits and vegetables, butless literature is available on thesenutrients. The B vitamins, thiaminand vitamin B-6 in particular, arequite sensitive to heat and light,and reported losses as a result ofcanning range from 7 to 70%for various vegetables. The Bvitamins were also sensitiveReferenceFreshto blanching and freezing, withlosses in the range of 20–60%.The water-soluble polyphenoliccompounds are found primarilyin the skins of commodities suchas peaches, pears, and apples.Therefore, removal of the skin willsignificantly change the levels ofthese compounds. Polyphenolicsgenerally decline with storage offresh fruits and vegetables and asa result of canning and blanching(Howard et al., 1999). Mineraland fiber content was foundto be similar in fresh, canned,and frozen fruit and vegetableproducts; this is expected, sincethese nutrients are relatively inertand are not sensitive to degradationby thermal processes used in foodpreservation.Fat-soluble nutrients suchas vitamins A and E and thecarotenoids (including lycopene)are sensitive to heat, light, oxygen,and pH. However, because thesecompounds are fat soluble, there islittle leaching into cooking wateror canning medium. Refrigeratedstorage for 14–16 days resultedin a 10% increase in the betacarotene content of carrots and a10% loss in green beans (Howardet al., 1999). Processed tomatoproducts have higher lycopenecontent than fresh, most likelydue to the heat-induced releaseof this nutrient from its cellularmatrix (Nagarajan and Hotchkiss,1999). Therefore, processing doesnot cause the synthesis of morecarotenoid compounds but merelyallows scientists to detect greateramounts of them due to theirincreased extraction. Comparedto the water-soluble vitamins, thecarotenoids and lycopene appearto be relatively stable duringprocessing, storage, and cooking,but there is a lack of informationon these components.Fiber is relatively insensitiveto thermal processing or freezing,so the fiber content is very similarin fresh and processed fruits andvegetables. Brassica crops, suchas cabbage and broccoli, havea naturally occurring enzymecalled myrosinase that04.07 www.ift.org43pg
Birds Eye Steamfresh and other brands of frozen vegetables provideboth preparation convenience and extended shelf life. Although freezingand canning may reduce the nutritive value of fruits and vegetables toa degree, they extend the length of time they are available. Once theproducts are processed, nutritive losses in the canned or frozen productsare minimal if the products are stored and handled appropriately.produces nutritious isothiocyanatecompounds. Processing destroysthis enzyme, but it exists inthe intestine as well, so thesame nutritious compounds areproduced there when cookedbroccoli is eaten.Research and Education NeedsResearch shows that by the timea fruit or vegetable is consumed,fresh, frozen, and canned versionsmay be nutritionally similar,depending on the postharvesthandling and processing treatments.However, since most studies haveonly evaluated changes in vitaminsand perhaps total phenolics, littleis known about the effects ofprocessing on some of the morenutritionally significant compoundsin fruits and vegetables. Futureresearch should focus on specificnutrients known to be bioavailableand utilizable by the body, andpg4404.07 www.ift.orgon the effects of fresh storage andcooking, as well as processing,storage, and cooking.Loss of nutrients during freshstorage may be more substantialthan consumers realize, soconsumers should be educatedabout proper storage. Fruits andvegetables should be consumedsoon after harvest, or postharvesthandling conditions must becontrolled such that nutrientdegradation does not occur. Agood diet should include a varietyof fruits and vegetables, whetherthey are fresh, frozen, canned,dried, or otherwise preserved. TheNutrition Facts label on processedproducts accurately reflects thenutritional content and should beconsulted by consumers interestedin healthy diets. FTDiane M. Barrett, Ph.D., a Professional Memberof IFT, is Fruit & Vegetable Products Specialist,Dept. of Food Science & Technology, and Directorof the Center for Excellence in Fruit and VegetableQuality, University of California, Davis, CA 95616(dmbarrett@ucdavis.edu).The author thanks Christine Bruhn, Jim Thompson,Alyson Mitchell, Dan Kliebenstein, Beth Mitcham,Clare Hasler, and Andy Waterhouse from theCenter for Excellence in Fruit and VegetableQuality for their assistance in preparation of thismanuscript and her coauthors on the literaturereview, Joy Rickman and Christine Bruhn, forallowing some of the information presented inthe more comprehensive review to be cited here.R EF ER ENCESERS. 2006. Food consumption (percapita) data system. Econ. Res. Service,U.S. Dept. of Agriculture. www.ers.usda.gov/data/foodconsumption.Accessed July 26.Fellers, C.R. and Stepat, W. 1935.Effect of shipping, freezing and canningon the ascorbic acid (vitamin C)content of peas. Proc. Am. Soc. Hort.Sci. 32: 627-633.Howard, L., Wong, A., Perry, A.,and Klein, B. 1999. β-carotene andascorbic acid retention in fresh andprocessed vegetables. J. Food Sci. 64:929-936.Hunter, K.J. and Fletcher, J.M. 2002.The antioxidant activity and composition of fresh, frozen, jarred and cannedvegetables. Innovative Food Sci.Emerg. Technol. 3: 399-406.Nagarajan, N. and Hotchkiss, J. 1999.In vitro inhibition of N-nitrosomorpholine formation by fresh and processedtomatoes. J. Food Sci. 64: 964-967.Rickman, J.C., Barrett, D.M., andBruhn, C.M. 2007a. Nutritionalcomparison of fresh, frozen and cannedfruits and vegetables. Part 1. VitaminsC and B and phenolic compounds. J.Sci. Food Agric. (in press).Rickman, J.C., Bruhn, C.M., andBarrett, D.M. 2007b. Nutritional comparison of fresh, frozen, and cannedfruits and vegetables. II. Vitamin A andcarotenoids, vitamin E, minerals andfiber. J. Sci. Food Agric. (in press).USDA. 2005. USDA nutrient databasefor standard reference, Release 18.U.S. Dept. of Agriculture, AgriculturalResearch Service, Washington, D.C.Weits, J., van der Meer, M.A.,Lassche, J.B., Meyer, J.C., Steinbuch,E., and Gersons, L. 1970. Nutritivevalue and organoleptic properties ofthree vegetables fresh and preserved insix different ways. Intl. J. Vit. Res. 40:648-658.
(temperature, humidity, daylight hours, etc.) during growth. Fruits and vegetables for the fresh market are generally harvested by hand, with the exception of roots and tubers, while many commodities destined for processing are mechanically harvested. Mechanical harvesting generally causes more stress to the plant tissue and may
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Le genou de Lucy. Odile Jacob. 1999. Coppens Y. Pré-textes. L’homme préhistorique en morceaux. Eds Odile Jacob. 2011. Costentin J., Delaveau P. Café, thé, chocolat, les bons effets sur le cerveau et pour le corps. Editions Odile Jacob. 2010. 3 Crawford M., Marsh D. The driving force : food in human evolution and the future.
