- April 13, 2020
The Impact of Postharvest Storage Practices on the Aroma Profile of Fleshy Fruits
TheImpact of Postharvest Storage Practices on the Aroma Profile ofFleshy Fruits
TheImpact of Postharvest Storage Practices on the Aroma Profile ofFleshy Fruits
Inthe best scenario, farmers should grow vegetables and fruits underoptimal conditions, harvest them at the peak of their maturity orripening, and avail the commodities for consumption within a fewdays. These would be the ideal conditions to enjoy the full nutritionand flavor in fruits and vegetables. However, in contemporaryeconomies, this scenario is impossible, owing to a number of factors.First, there is an increased emphasis on large-scale fruit andvegetable production. Leading horticultural regions are known fortheir large-scale production, which provides economies of scale(Whitakeret.al, 2011).In this regard, it is likely that not all vegetables and fruitsharvested will get to the market within the required time, thereforenecessitating storage. Secondly, horticultural trade has assumed atranscontinental and global scale. Vegetables and fruits areincreasingly being shipped across continents, some staying in transitfor weeks (Valero& Serrano, 2012).Therefore, these delays require efficient storage practices topreserve the nutritious and taste properties in fruits. Internationalmarkets reject fruits that do not meet the set standards. Fruitscontaining unauthorized pesticides as well as pesticide residuesabove the recommended limits are not allowed into the market.Consequently, the manner of post-harvest handling determines theattractiveness and sellability of fruits in the international market(Valero& Serrano, 2012).
Theeffect of Post-harvest Practices on the Aroma of Fleshy Fruits
Thechanging pattern of Agriculture, as well as horticultural trade, hasnecessitated the development of advanced post-harvest technologiesthat preserve the traditional properties of fruits. The majority ofthis technology focus on preserving the natural quality andsalability of fruits beyond their shelf life (Whitakeret.al, 2011).In many cases, farmers and traders focus on preserving the appearanceas well as the texture of fruits, with little consideration towardspreserving their aroma and flavor. To add to this challenge, geneticenhancements in horticulture seek to boost attributes that promotethe endurance of fruits to survive the lengthy shipping durations,sometimes at the expense of the aroma and flavor of these fruits. Thefocus on the visual appeal (i.e. large size and bright color) limitsthe richness of the fruits in terms of aroma and flavor (Rizzoloet al., 2012).
Theimportance of post-storage activities stems from the fact thatharvested fruits are living despite their detachment from theirmother plant. Therefore, they are separated from their source ofnutrition and water, hence the likelihood of deterioration.Stress-induced or natural senescence causes the deterioration ofleafy or fleshy commodities (Whitakeret.al, 2011).Post-harvest activities limit the effect of the senescenceresponsible for fruit deterioration however, the trick is inpreserving the flavor of the fruits. The first line of defenseagainst the loss of fruit flavor is the limitation of water loss aswell as the respiration rates. These interventions limit thelikelihood of loss because of bacterial and fungal infection offruits. The preservation of respiration and water loss is achievedthrough refrigeration, which again plays a significant role inlimiting bacterial and fungal infections in fruits (Whitakeret.al, 2011).
Theeffect of post-harvest practices on the flavor of fruits dependslargely on the type of fruit in question. Fruits are grouped into twocategories i.e. the non-climacteric and climacteric fruits. Theclassification is determined by the fruits’ physiological regimeduring ripening (Whitakeret.al, 2011).Organic acids and sugars are the principal respiratory substancesassociated with fruits. The accumulation of these compounds afterharvest determines the flavor of fruits. Excess accumulation oforganic acids and fruits reduced the flavor of fruits as well aslimit their shelf life. Modern post-harvest practices work bylimiting the production of these components beyond the required level(Valero& Serrano, 2012).
Theextent of the respiratory climacterics have considerable variationsamong fruits and are inversely correlated with their shelf life(Whitakeret.al, 2011).On the other hand, a high basal rate of respiration is associatedwith a short shelf life in non-climacteric fruits. Post-harveststorage limits the transient rise in respiration among climactericfruits. Rising respiration levels in climacteric fruits leads toconcurrent bursts in the production of autocatalytic ethylene(Rizzoloet al., 2012).Ethylene plays an important role in the metabolic changes andprocesses that happen during ripening in climacteric fruits.Therefore, the regulation of ethylene through controlling therespiration rates in climacteric fruits is an essential role ofpost-harvest storage. Although ethylene has no significant role inthe ripening of non-climacteric fruits, it may influence lateelements of the fruits such as carotenogenesis and de-greening(Rizzoloet al., 2012).
Thereare significant differences in the two categories of fruits when itcomes to post-harvest handling. Climacteric fruits will continue withthe ripening process after harvesting while the non-climactericfruits will not ripen further after harvesting. Therefore, inclimacteric fruits, the post-harvest processes can influence theflavor of fruits, unlike the case of non-climacteric fruits (Whitakeret.al, 2011).In both types, delayed harvesting optimizes the color of fruits aswell as the sugar content development. In commercial situations, asignificant proportion of the desirable changes in aroma and flavoroccur after harvest, for the case if the climacteric fruits (Karamanet al., 2013).Therefore, post-harvest interventions should aim at maintaining thefresh-like state in fruits for long periods, delay the loss of flavoras well as prevent the development of other off-flavors and aromathat reduce the desirability of fruits. Storage conditions should befree from chemicals and other agents that may contaminate theripening process (Rizzoloet al., 2012).The development of off-flavors may occur during congestions oraccidental and an intentional mixture of different types of fruitsduring harvest and storage.
Manyfruits produce more than 100 volatile compounds that determine theiraroma (Karamanet al., 2013).However, the production of relatively smaller amounts of thecompounds may contribute significantly to the enhancement of uniquearomas n fruits. Metabolites of amino acids, fatty acids andcarbohydrates are the sources of aroma profiles in fruits (Karamanet al., 2013).Therefore, poor post-harvest practices may influence the developmentof these aromas, especially when harvesting is done beforematuration. In the last ten years, there have been increased effortsin molecular biology towards the characterization and elucidation ofcritical enzymes and genes responsible for the generation of fruitaroma volatiles. Examples of these efforts include hydroperoxidelyases (HPLs), lipoxygenases (LOXs), alcohol acyl-transferases(AATs), terpene synthasis (TPSs), alcohol dehydrogenases (ADHs) andcarotenoid cleavage dioxygenases (Whitakeret.al, 2011).
Withvariations in the degree of product and substrate specificity, thesequential action of HPL and LOX on the linolenic and linoleic acidsmay yield unsaturated and saturated acids. Consequently, the effectsof ADH to the resulting alcohols can reduce these properties (Valero& Serrano, 2012).Regarding fruit aroma, mono- and sesquiterpene synthases are the TPSsthat are of major interest. They yield carbon isopentenoids that canhave a major impact on the fruit flavor. Therefore, molecular biologyfocuses on augmenting the beneficial properties of these elements topromote fruit flavor. In this regard, post-harvest activitiescontinue to play an increasingly reduced role in influencing thearoma of fruits (Cordeiroet al., 2013).
Althoughstudies on the enzymes and genes responsible for the biosynthesis ofnorisoprenoids, sesquiterpenes, and monoterpenes during fruitripening are still in their infancy, sesquiterpene and mono volatilesappear to be critical contributors in the aroma of fleshy fruits(Whitakeret.al, 2011).This is more evident in climacteric fruits that non-climactericfruits. Citrus fruits are the best example in this case since theyowe the majority of their distinctive aroma profiles to theseterpenes. Regarding the relevance of post-harvest changes in theflavor and aroma of fruits, evidence shows that ethylene stimulatesthe synthesis of some compounds. Terpenoids have been found to besignificant contributors to the flavor of wines and fruit juices(Whitakeret.al, 2011).Additionally, mono- and sesquiterpene alcohols can release impressivearoma volatiles when cleaved by exogenous or endogenous glycosidases.Mangoes are the best characteristic fruits in which terpenes dominatethe aroma and flavor compounds. Therefore, exogenous or endogenousglycosidases can influence greatly the quality of mango fruits aswell as other related fruits during storage (Valero& Serrano, 2012).
Themaintenance of the cold chain from handling, storage, shipping, andmarketing is the most important rule of post-harvest practice. Theaim of maintaining this chain is to ensure that the produce stays innon-injurious low temperature to retard ripening, general metabolismand senescence (Karamanet al., 2013).However, the majority of horticultural crops, particularly fruitsfrom the subtropical and tropical regions are prone to chillinginjuries when the storage temperatures range just above zero degreesCelsius to a high of 10 to 15 degrees Celsius (Valero& Serrano, 2012). Some of the commodities that may be affected by this temperaturerange include mangoes, bananas, breadfruits, and jicama. Injuriouslow temperatures, which last for considerable durations may alter themetabolism of commodities that are sensitive to chilling. This mayresult in loss of flavor or the development of off-flavors in fruits.Along with the widely studied loss of the wooly texture and juice inchill-injured nectarines and peaches, there is significant evidenceindicating the loss of the ‘peachy’ aroma and distinct sweetnessderived from δ-decalactones and ­γ-decalactones (Whitakeret.al, 2011).In mangoes, chilling adversely alters aroma, which causes generaldecreases in the production of all ripening-associated volatilities.
Evenas post-harvest interventions seek to maintain the flavor as well assellability of fruits, it becomes increasingly challenging to upholdthe natural aroma of various fruits using the most widely knownpost-harvest activities (Valero& Serrano, 2012).Low-temperature storage remains the most prominent and effectivemeans of maintaining the sellability of fruits but often comes at aprice regarding fruits that have little endurance for significantvariations in optimum storage temperatures. Therefore, temperatureinterventions need to take into consideration the sensitivity offruits to such measures. This is especially important for productssuch as bananas, jicama, breadfruit, and mangoes (Cordeiroet al., 2013).
Acombination of high carbon dioxide, low oxygen, and low temperaturescreate controlled atmospheres (CAs) that are used in limitingrespiration. Modified atmosphere packaging (MAP) reduces ethyleneproduction and fruit responses to the present ethylene (Valero& Serrano, 2012).Therefore, this results in the induction of senescence and ripening.Moreover, the MAP reduces/inhibits the growth of post-harvestpathogens, which may cause the destruction of the competitiveprofiles in fruits. In other cases, coatings of wax, and othersubstances are applied on fruit surfaces before storage to maintain aglossy appearance by reducing water loss (Cordeiroet al., 2013).Consequently, the application of these waxes modifies the internalatmosphere in fruits. Therefore, this modification has the potentialto influence the aroma and flavor of fleshy fruits, depending on thefruit’s response to the interventions.
Althoughtechnologies such as waxing are effective in maintaining the qualityfruits as well as extending the shelf life of fruits, under certaincircumstances, there can be unintended consequences of thesepost-harvest practices (Cordeiroet al., 2013).For example, there is a likelihood of the development of carbondioxide-induced disorders such as the production of offensive odors. The response of individual fruits to controlled atmospheres ormodified atmosphere packaging and low temperature variesconsiderably. The responses depend on the maturity of fruits at thetime of harvest, the cultivar as well as pre-harvest factors.Therefore, it is impossible to determine the resulting variations inthe flavors and aromas of fruits based on experiences (Cordeiroet al., 2013).
Theprimary cause of the development of off-flavors during storage or theshelf life of fruits is the accumulation of significant fermentativemetabolites. The most destructive fermentative metabolites includeethanol and acetaldehyde. These metabolites develop because of theexistence of several types of stress including high levels of carbondioxide, high or low oxygen concentration, injurious chilling as wellas hypoxia induced by coatings such as wax. The production ofacetaldehyde occurs during ripening in all fruits. However, theproduction rates increase rapidly when post-harvest practices utilizecoatings, MAP and CA storage (Whitakeret.al, 2011).Post-harvest intervention/treatment with ethanol or acetaldehyde canbe used to enhance the synthesis of volatiles, which improve thearoma of fruits. However, the threshold for the utilization ofacetaldehyde or ethanol in improving fruit aroma is quite lowregarding tropical fruits. In many cases, phytotoxicity emerges asthe major problem when these compounds are utilized for the abovepurposes.
Controlledatmospheres with short-term low oxygen levels induces off-flavors inpapayas, strawberries, and mangoes. The combination of these gasseswith ethylene, ethanol, and acetaldehyde induce off-flavors instrawberry fruits (Whitakeret.al, 2011).Moreover, insecticidal treatment of fruits after harvest may alsocause significant variation is the fruit flavors. For example,insecticidal quarantine treatment of fruits such as papaya forperiods exceeding three days in oxygen level below 0.4% results inthe development of off-flavors (Petriccioneet al., 2015).The off-flavors result from the accumulation ethanol after longperiods under the conditions. However, these conditions are notuniversally harmful to fruits each fruit has its ideal post-harvestthriving conditions. Contrary to the above examples, certain fruitssuch as avocados and apples can tolerate and benefit from the aboveconditions. Additionally, these conditions can boost the aroma andflavors of the fruits that thrive under these conditions (Petriccioneet al., 2015).The use of certain fruit coatings on guavas, mandarin, and mangoesinduce anaerobic respiration as well as elevated levels ofacetaldehyde and ethanol production. The application of the leastpermeable coatings in mandarin results to poor flavor and aromascores. Increased acetaldehyde and ethanol concentrations infungicide-treated and waxed fruits does not significantly alter theflavor of mandarin fruits. However, this may not apply to commoditiesthat are sensitive to acetaldehyde (Whitakeret.al, 2011).
Thechallenges presented by existing postharvest procedures have led tothe development of modern storage and preservation technologies, somestill in their experimental phases. Radio frequency (RF) heating iscurrently under development as a possible alternative to methylbromide to be used for the quarantine treatments in the eradicationof medfly larvae (Petriccioneet al., 2015).Moreover, RF heating can also be used in the eradication of otherinsect pests that affect the attractive properties of fruits.However, RF heating still presents challenges regarding thealteration of the aroma and flavor of fruits. For example, althoughthe method results in less accumulation of ethanol and acetaldehydethan other conventional methods in mangoes, leads to substantialaroma variations. More specifically, the method alters the aromaprofiles of hexanal and mono-sesquiterpenes (Whitakeret.al, 2011).Again, such aggressive methods require the acceptance of consumersowing to their untested results as well as the resulting alterationsin the fruit flavor. All kinds of artificial interventions appear tobe detrimental to the aroma profiles of fruits. Despite theprocedural differences, the results often lead to the accumulation ofunwanted properties in fruits. Another problem with RF heatingoriginates from the fact that consumers are unaware of the long-termeffects constantly consuming fruits that have been subjected to suchaggressive post-harvest procedures to maintain their shelf life.
Bothcontrolled atmosphere, which works by suppressing the production ofethylene, and post-storage treatment using 1-methylcyclopropene,which works by blocking the action of ethylene, can have profoundalterations/effects on the aroma of fruits (Passamet al., 2011).This is especially the case in aroma volatile production mostlyduring the ripening of climacteric fruits. When stored in controlledenvironments for ten days, apples loses their fruity and floral notesand retains citrus and vegetative characteristics. Consequently, thecontrolled environments lead to the development of higher levels ofsourness and astringency. Therefore, the sweetness levels dropdramatically. The aroma and flavor of the fruit fall by 15-fold(Whitakeret.al, 2011).
Studiescontinue to show that controlled environments have profound effectson the flavor and aroma of fruits. However, some studies such as oneconducted by Sinhaet al (2012) reportedthat despite the substantial decline in the production of esters forexample butyl acetate when fruits are stores under controlledatmospheres, the storage of “Pacific Rose” apples in CA showslittle effect on the natural flavor of the fruit. However, anincreased storage duration leads to the development of off-flavorsthat may alter the aroma of fruits but after a lengthy period ofstorage (Whitakeret.al, 2011).Therefore, the degree of responsiveness to controlled environmentsdepends very much on the adaptability of the fruit to the atmosphericchanges. Fruits such as the “Pacific apples” have higherresistance to the damaging effects of controlled environments, whilegrapes and mangoes have little resistance to the injurious conditionspresent in controlled environments (Sinhaet al., 2012).Post-harvest practices are significant determinants of the quality offruits as this study shows. The degrees of their impact vary widelydepending on the variations in the characteristics of fruits.
Thechanging pattern of Agriculture, as well as horticultural trade,continues to force farmers and retailers to develop advancedpost-harvest technologies that preserve the traditional and desirableproperties of fruits. In the past, the majority of the post-storagetechnology focused on preserving the natural quality and salabilityof fruits beyond their shelf life. In many cases, farmers and tradersfocused on preserving the appearance as well as the texture offruits, with little consideration towards preserving their aroma andflavor. However, in the contemporary horticultural market, consumersand regulatory authorities are now focusing on the need to retain thearoma and flavor of fruits, therefore, presenting a new challenge tofarmers and retailers. To add to this challenge, genetic enhancementsin horticulture always seek to boost attributes that promote theendurance of fruits to survive the lengthy shipping duration,sometimes at the expense of the aroma and flavor of these fruits.However, growing consumer and regulatory concerns have forcedstakeholders to consider the need to preserve the original aroma andflavor in fruits.
Post-harvestactivities limit the effect of the senescence responsible for fruitdeterioration however, the trick now lies in preserving the flavorof the fruits. Traditionally, the first line of defense against theloss of fruit flavor has always been the limitation of water loss aswell as the respiration rates. These interventions have helped limitthe likelihood of loss because of bacterial and fungal infection offruits. The preservation of respiration and water loss has beenachieved through refrigeration, which again has played a significantrole in limiting bacterial and fungal infections in fruits. However,the changing times demand the development of non-chillingpost-harvest preservation methods to protect fruits that cannotendure the injurious effects of chilling.
Thisresearch has shown that the effect of post-harvest practices on theflavor of fruits depends largely on the type of fruit in question.The choice of post-harvest intervention should be made after acareful consideration of the fruit type i.e. either non-climactericor climacteric. The classification is determined by the fruits’physiological regime during ripening. Organic acids and sugars arethe principal respiratory substances associated with fruits. Theaccumulation of these compounds after harvest determines the flavorof fruits. Excess accumulation of organic acids and fruits reducedthe flavor of fruits as well as limit their shelf life. Modernpost-harvest practices should work by limiting the production ofthese components beyond the required level. Technologicaladvancements in post-harvest activities should consider these aspectsduring their development to reduce the injurious effects of otherstorage methods on the aroma of fruits. Even as post-harvestinterventions seek to maintain the flavor as well as sellability offruits, the activities should also aim at upholding the natural aromaof various fruits using the most widely known post-harvestactivities. Low-temperature storage remains the most prominent andeffective means of maintaining the attractiveness of fruits but oftencomes at a price regarding fruits that have little endurance forsignificant variations in optimum storage temperatures. Therefore,temperature interventions need to take into consideration thesensitivity of fruits to such measures. This is especially importantfor products such as bananas, jicama, breadfruit, and mangoes.
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