Factors Affecting Postharvest Quality of Fresh Fruits

Factors Affecting Postharvest Quality of Fresh FruitsA change ovary of a f number oneer together with any accessory part associated with, is referred to as ingathering (Lewis Robert 2002). In non-technical usage the term fruit norm bothy agent the fleshy seed-associated structures of certain seed downs that be clean and edible in the raw(a) state, for example apples, oranges, word of mouths, strawberries and bananas (Ma drug abuseth James, 2003).Fresh fruits and vegetables be living create from raw materials which undergo continuous changes milling machinerysequently harvest. Some of these changes ar desirable, but from consumers point of view to the highest degree of them be undesirable. It is not possible to stop the postharvest changes in overbold arrest, but they nominate be retarded inwardly certain limits (Kader, 2002).There are any(prenominal)(prenominal) atmospheric constituents which affect the postharvest deportment history of fresh fruits. Clim atic conditions, speci altogethery temperature and legerity obtain a signifi dealt effect on the nutritional reference of fresh fruits and vegetables (Kader, 2002).FACTORS AFFECTING THE POSTHARVEST LIFE OF FRUITRESPIRATION ventilation is the procedure by which stored electric organic materials are broken down into simple overthrow products with a ex maven post of energy. During this procedure oxygen (O2) is consumed while atomic number 6 dioxide ( carbon dioxide) is provoked. every(prenominal) living organisms must carry out breathing at all times (Kader, 2002).Respiration MetabolismEven after the harvest, fruits and vegetables remain as living variety meat. Like all living create from raw stuffs, harvested come continues to respire passim its postharvest life. The main purpose of propagateing is to maintain sufficient supply of adenosine triphosphate (ATP).The process of aerobic ventilation system involves the transition of ATP from ADP (adenosine diphosphate) a nd Pi (inorganic phosphate) with the release of carbon dioxide and H2O. In case of hexose sugar the overall response can be written as (Kader Saltveit, 2003)The different components in this reaction defend different sources of destinations. The 1 sea fence in of glucose (180g) can come from stored simple sugars (glucose, sucrose) or complex polysaccharides (starch). The 6 moles of O2 (192g) used to oxydize the 1 mole of glucose diffuses into the tissue from the skirt atmosphere, while the 6 mole of carbon dioxide (264g) diffuses out of the tissue. The 6 mole of body of body of water (108g) produced is simply incorpo localised into the aqueous solution of the cell.(Kader Saltveit, 2003)Aerobic ventilating system involeves a series of treysome reactions, each of which is catalyzed by a bend of specific enzymes that either (i) add a phosphate group to a molecule, (ii) rearrange the molecule, or (iii) break down the molecule to a simpler one ((Biale, 1960)(Davies, 1980)). The three complect metabolic path ways are glycolysis, the tricarboxylic acid (TCA) and the electron glamour transcription.GlycolysisThe partitioning of glucose fall outs in the cytoplasm, which produce both molecules of pyruvate. 10 different ensuant reactions are catalysed by one enzyme. Phosphofructokinase (PFK) is the main enzyme in Glycolysis, which cleaves fructose 1, 6-diphosphate into devil triose phosphate molecules. By go doneling PFK employment of Glycolysis, cell can control their identify of energy production. ATP is used as a ostracise feedback inhibitor to control the occupation of PFK (Davies, 1980). Besides pyruvate, Glycolysis too produces cardinal molecules of ATP and ii molecule of NADH ( trim down nicotinamide adenine dinucleotide) from the breakdown of each molecule of glucose.Tricarboxylic Acid (TCA) wheel aroundThe TCA beat occur in mitochondrial matrix, involves in the breakdown of pyruvate into CO2 in nine sequential enzymatic reactions. Pyruvate is decarboxylated to framea skeletale acetate, which condenses with a co enzyme to systema skeletale Acetyl CoA. This compound thus enters the cycle by condensation with oxaloacetate to form citric acid. Citric acid has three carboxyl groups, from which the cycle derives its name (Kader Saltveit, 2003). Through a series of seven successive rearrangements, oxidations and decarboxylations, citric acid is reborn into oxaloacetate, which is then ready to accept another ethanoyl group CoA molecule. The TCA cycle also produces one molecule of FADH2 (reduced flavin adenine dinucleotide) and four molecules of NADH for each molecule of pyruvate metabolism.Electron Transport SystemThe electron transport system occurs in the cristae of mitochondria, results in the production of ATP from the FADH2 and NADH. The energy produced is more than the cellular process requirement. In a series of reactions, one NADH molecule produces three ATP molecules and one FADH2 molecule produces t wo ATP molecules, but the claim subjugate of ATP produced during electron transport depends not exclusively on the energy of NADH and FADH2 but also on the chemical environment within the cell and mitochondria.In the absence of O2, NADH and FADH2 accumulates, the TCA cycle stops and Glycolysis become the only source of ATP production. In anaerobic respiration hexose sugar is reborn into alcohol and CO2 in the absence of O2. Pyruvate produced in Glycolysis is decarboxylated by the enzyme pyruvate carboxylase to form CO2 and acetaldehyde. The acetaldehyde is converted by the enzyme alcohol dehydrogenase to ethanol with regeneration of NAD+. Two moles of ATP and 21 kcal of arouse energy are produced in anaerobic respiration (alcoholic fermentation) from each molecule of glucose (Kader Saltveit, 2003).Respiration Quotient (RQ)The respiration quotient (RQ) determines the arrive of subst place utilized in the respiration process. In other nomenclature RQ is the ratio of CO2 prod uced to O2 consumed measured in mole or volumes. In the aerobic respiration of carbohyd pastures the RQ is near 1, while is 1 for organic acids. rattling high RQ app repeals usually indicate anaerobic respiration in those tissues which produce ethanol.GAS EXCHANGEBarrier to dispersalGas modify between a sic organ and its environment fol gloomys Ficks outset police force of diffusion. The sequential stairs are (i) diffusion in the mishandle word form by means of the cutaneal system (i.e. cuticle, shield, stomata etc.) (ii) diffusion in the tout human body between the intercellular quads (iii) metamorphose of hit manes between the intercellular atmosphere and the cellular solution (cell sap) and (iv) diffusion in solution within the cell to centres of O2 exercise and from centers of CO2 production. This exchange is a function of the resistance of the dermal system to torpedo diffusion, the resurrect area crosswise which diffusion can sequester place etc.CO2 p roduced within each cell testament raise the local niggardness and this will drive diffusion of CO2 outward, toward the lower concentration near the cell-wall surface adjacent to the intercellular space. Diffusion of CO2 into intercellular space continues toward regions of lower concentration until it reaches the intercellular space beneath the dermal system. From thither, CO2 moves through the cuticle or openings in the commoditys surface to the air (Burton, 1982).Movement of O2 within pose tissue is in a reverse but similar process to that mentioned above for CO2. In senescent tissue, O2 diffusion may be decreaseed down if the intercellular spaces become filled with cellular solution that anaerobic conditions develop within tissues. The set out of splatter movement depends on the properties of gas molecule and the physical properties of the obstacles (thickness, slow-wittedness etc.). Solubility and diffusivity of each gas are important for its diffusion across bulwark. CO2 moves more readily than O2, while diffusion stray of C2H4 and CO2 are similar.Internal concentration of CO2 and O2 in whole shebang organs depend upon the maturity detail at harvest, the current organ temperature, the makeup of international atmosphere and any additional barrier. Maturity academic degree influences the dermal system that effects gas diffusion. Increased temperature results raised prize of respiration as a result internal CO2 direct change magnitudes as the O2 level decreases. If all other factors are held constant and the movement in the gas concentrations is the effort force for diffusion, then the concentration of O2 and CO2 within the tissue will fluctuate according to the fluctuation in the external atmosphere.Methods to Alter rates of Gas ExchangeThere are three types of barriers to gas exchange that affect the postharvest handling of fresh produce (Fig. 1). These are (i) the structure of the dermal system such as thickness of cuticle, number and distribution of stomata and breaks in epidermis etc. Resistance to gas diffusion can be additiond by adding barrier such as wax coating or covering produce with polymeric films. (ii) The software software system in which the commodity is shipped can be additional barrier to gas diffusion. (iii) The degree of gas tightness of the transit vehicle or memory room will also affect gas exchange with alfresco air.Schematic model of a commodity and its environment with three levels of gas exchange B1=structure of dermal system and added barriers (waxing and film wrapping), B2= Permeability of package to gas diffusion, and B3 = gas tightness of the storage room Source (Kader Saltveit, 2003)Ficks first law of diffusion states that the movement or flux of a gas in or out of a name tissue depends on the concentration gradient across the barrier involved, the surface area of the barrier and the resistance of the barrier to the diffusion. Ficks law can be written as followsJ = A. C/RWhereJ =Total flux of gas to be diffused (cm3.s-1)C= Concentration gradient across the barrierA=the surface area of the barrierR= Resistance to diffusionIf the production or consumption rate of the gas by the organ and the concentration of the gas in the internal and external atmosphere is known, then the resistance is calculated as followsR = Concentration gradient/ ware or consumption rateDifferent harvested fruits and vegetables have different rates of respiration some respire at a faster rate (more perishable), while some respire at a congenatorly slow rate ( little perishable vegetables) (Table 1).Table 1 Classification of Sample horticultural Commodities consort to Respiration Rates (Wilson, 1999).Respiration Rates parts of Fruits and VegetablesVery funkyDried fruit and nutsLowApples, garlic, grapes, onions, potatoes (mature), sweet potatoesModerateApricots, cabbages, carrots, figs (fresh), lettuce, nectarines, peaches, pears, peppers, plums, potatoes (immature), tomatoes amply Artichokes, Brussels sprouts, cut flowers, green onions, snap beansExtremely HighAsparagus, broccoli, mushrooms, peas, sweet cornThe process of respiration is very important during ripening of fruit. In general there is an inverse relation between the rate of respiration and the postharvest life of fruit. Postharvest produce are classified according to their respiration rate as change of life or non- menopause. The rate of respiration affixs in climacteric fruits during ripening while non-climacteric fruit shows no change in their low CO2 and ethene production rates during ripening (Kader, 2002).If prevention or decrease in respiration is achieved, this will prolong post-harvest storage life. ethene causes the increase in respiration, so decreasing ethene is also a strategy used to increase post-harvest storage life.Factors affecting respiration rateEnvironmental FactorsTemperatureTemperature is important environmental factor in the postharvest life of fresh produce due to its outstanding effect on rates of biologic reactions, including respiration. deep down the physiological temperature range, the velocity of biological reaction increases two to multiple for every 10 C rise in temperature (Vant Hoff rule).The ratio of reaction rates at two dissimilar temperatures is called the temperature coefficient (Q10) if the interval between the two temperatures is 10oC. If the temperature interval of Q10 is not exactly 10o C then it can be determined by the following equationQ10 = (R2/ R1) 10/T2-T1Where R2 = rate of respiration at T2R1 = rate of respiration at T1T1 and T2 = temperature in CScientists have found that Q10 is not constant for most biological processes over a wide range of physiological temperatures. Usually Q10 ranges from 1 to 5, although high jimmy may occur. For most biological reaction the Q10 is between 2 and 3 for temperature between 10 to 30 C that means the reaction rate will be double or triple with every 10 C increase.O2 and CO2 Conce ntrationPractically, respiration can be controlled by either increasing carbon dioxide or decreasing oxygen. Decrease in oxygen near to zero is not desirable, though the O2 concentration reduces below that in air (20.9%) and especially below 10%, a satisfying reduction in respiration rate is observed (Gorny, 2001). However when O2 concentration drops to less than 2 %, anaerobic respiration rate become overriding and CO2 production increases. (Figure 2) (Kader Saltveit, 2003). ethene ConcentrationExposure of climacteric tissues during their pre-climacteric stage to ethene raises the rate of respiration. Once the respiration rise has begun, the endogenous rate of ethylene production increases and the internal ethylene concentration also increases, hit levels that saturate its biological activity. However, un analogous the case in climacteric tissues in non-climacteric tissues endogenous ethylene production remains unaffected (Kader Saltveit, 2003).Internal factorsType of Com modityFruits and vegetables vary greatly in their respiration rate (Table. 1). Differences among plant parts and in the nature of their surface coatings (e.g. cuticle thickness, stomata, lenticels) influence their rate of diffusion characteristic and consequently their respiration rates.Stage of victimization at HarvestThe respiration rate is usually high at primordial stages of development and decreases as plant organs mature. Thus fruits and vegetables harvested during the active harvest-festival phase have high respiration rates.Chemical CompositionRespiration rate decreases with a decrease in water content of the tissue. The value of Respiration Quotient (RQ) is usually controlled by the rate of utilization of carbohydrates, proteins, lipids etc.ethene PRODUCTIONEthylene (C2H4) is a gaseous hormone produced from bacteria, fungi and all parts of higher plants such as shoots, flowers, seeds, leaves, roots, and fruits (Pech et al., 2003). It is a flammable and colorless gaseous compound (Arshad Frankenberger, 2002).Being a ripening hormone ethylene play a very important role in the postharvest life of many horticultural products, like increasing ageing speed and simplification shelf life but beneficially it improves the quality of the fruit and vegetables by manipulating uniform ripening process (Reid, 2002, p. 149). Because of the enormous influence of ethylene on the physiological development and postharvest life of fruits and vegetables, its biosynthesis, action, and control have been intensively investigated (Reid, 2002 Pech et al., 2003).The biosynthetic process of ethylene is usually completed in three study steps. The ethylene biosynthetic pathway is given in the figure 3. gradation IThe biosynthesis of ethylene hormone is started by the conversion of Methionine (MET) to S-adenosyl-L-methionine (surface-to-air missile) by the enzyme methionine adenosyltransferase (Pech et al., 2003). However, methionine adenosyltransferase is thought to consider as a rate limiting enzyme in ethylene biosynthesis because formation of SAM depends on the activity of this enzyme and SAM levels may indeed regulate ethylene production. thus, the sensitivity or immenseness of methionine adenosyltransferase to SAM implies that this enzyme may play a regulatory role in ethylene biosynthesis (Arshad Frankenberger, 2002, p. 13). mensuration IISAM is consequently converted to 1-aminocyclopropane-1-carboxylic-acid (ACC) by a pyridoxal enzyme ACC synthase (ACS) (Figure 1). Actually, ahead the discovery of ACC, as intermediate, speedy precursor in MET dependent ethylene production process, the ethylene biosynthetic pathway was intangible (Arshad Frankenberger, 2002, pp. 11-50). The conversion of SAM to ACC by ACS is another rate-limiting step in the biosynthetic pathway of ethylene. ACS is a cytosolic enzyme (found in the cytoplasm of plants) (Paliyath Murr, 2008b) and its activity is powerfully inhibited by aminoethoxyvinylglycine (AVG) (a compet itive inhibitor) and aminoisobutyric acid (AIB) (an inhibitor of pyridoxal phosphate-mediated enzyme reactions) (Arshad Frankenberger, 2002, pp. 11-50). Moreover, the activity of ACC synthase is also influenced by factors such as fruit ripening, senescence, auxin levels, physical stresses, and shuddery injury. The synthesis of this enzyme increases with an increase in the level of auxins, indole acetic acid (IAA) and cytokinins (Wills et al., 1998, p. 42).Step IIIAt last the ACC converts into ethylene by the action of ACC oxidase (known as ethylene forming enzyme or EFE) (Arshad Frankenberger, 2002, pp. 11-50 Pech et al., 2003). However, ACC oxidase is a bi-substrate enzyme as it requires both oxygen and ACC. Moreover, this enzyme also requires Fe2+, ascorbate and CO2 for its activity. Activity of ACC oxidase is inhibited by cobalt ions, and temperatures higher that 35oC (Wills et al., 1998, p. 42). The sub cellular position of ACC oxidase is still a point of controversy because there is a large number of data is available showing that this enzyme is associated with plasma-membrane or with apoplast or tonoplast. The activity of this enzyme (ACC oxidase) has been studied in many horticultural crops like melon, avocado, apple, winter squash, pear and banana. The activity of ACC oxidase is not highly regulated as ACS. It is constituted in mostvegetative tissues and it is induced during fruit ripening, wounding, senescence and fungalelicitors (Arshad Frankenberger, 2002, pp. 11-50).In fruits and vegetables some(prenominal) metabolic reactions starts after harvesting. In most cases, an increase in biosynthesis of gaseous hormone like ethylene serves as the physiological indication for the ripening process. During ripening process, in some fruits large essence of ethylene is produced which is usually referred as autocatalytic ethylene production response. However, fruits are divided into two main categories on the earth of ethylene production, i.e. climacteri c (those produce large measuring stick of ethylene) and non-climacteric fruits (those produce small amount of ethylene). In climacteric fruits like apple, pear, banana, tomato and avocado, ethylene production usually ranges from 30-500 ppm/(kgh) during ripening. While non-climacteric fruits like orange, lemon, strawberry and pineapple, produce 0.1-0.5ppm/(kgh) of ethylene (Paliyath Murr, 2008) (Table 2). Therefore application of even a very low concentration of ethylene (0.1-1.0 L/L) is sufficient enough to accelerate full ripening of climacteric fruits however, the magnitude of the climacteric rise is not dependent on the amount of ethylene treatment. On the contrary, application of ethylene causes a temporary rise in the rate of respiration of non-climacteric fruits and the degree of increase depend upon the amount of ethylene (Wills et al., 1998).Moreover, the difference in the respiratory patterns of climacteric and non-climacteric fruits is associated with the different dep ortment in terms of the production and response to ethylene gas (Burton, 1982). The increase in respiration, as influenced by ethylene application, may happen several times in non-climacteric fruits, but only once in climacteric fruits (Wills et al., 1998).Indeed, ethylene is produced by all parts of the plant but the magnitude of ethylene production varies from organ to organ and also depends on the stage and type of growth and developmental process. In fact, recent ethylene found research findings have increased the understanding of biosynthetic pathways and enzymes involved in ethylene production, as well as the development of several ways to manipulate ethylene production e.g. by genetic alteration of plants (Arshad Frankenberger, 2002). Ethylene is produced by various plant parts growing under everyday conditions however, any kind of biological, chemical or physical stress (e.g. wounding) strongly promotes endogenous ethylene synthesis by plants. Among stress induced ethylen e production, pre-harvest deficit irrigation is one of the most important factor causing higher ethylene production rates in fruits like avocado (Adato Gazit, 1974) and tomato (Pulupol et al., 1996).REGULATION OF ETHYLENE BIOSYNTHESISIn plants, ethylene itself stimulates the ability of the tissue to convert ACC into ethylene, which is also regarded as phenomenon of auto-regulation. In ripening fruits, regulation of ethylene biosynthesis is a characteristic feature and is triggered by the exposure to exogenic ethylene by the activation of ACC synthase and/or ACC oxidase (Arshad Frankenberger, 2002, pp. 25-27).On the other hand, sometimes ethylene inhibits its own synthesis, as negative feedback has already been recognised in a number of fruits and vegetable tissues. In such cases, exogenous ethylene significantly inhibits the production of endogenous ethylene, induced by ripening, wounding and/or treatment with auxins. Moreover, this auto inhibitory effect seems more directed towar ds hold in availability of ACC in the presence of AVG, an inhibitor of ACC synthase (Arshad Frankenberger, 2002, pp. 25-27). Scientists have also revealed that the inhibition or negative regulation of ethylene synthesis is the result of activity of a gene, E8 whose expression leads to the inhibition of ethylene production in tomatoes (Arshad Frankenberger, 2002, pp. 25-27).MECHANISM OF put to deathThe response of ethylene action can be classified into two categories namely concentration response and sensitivity response. The concentration response involves the changes in concentration of cellular ethylene while the sensitive response involves the increase in tissue sensitivity to ethylene. Moreover, both of these responses involve the binding of ethylene to some components of the cell to mediate the physiological effects (Arshad Frankenberger, 2002, pp. 28-36).Wills et al. (1998, pp. 42-45) likewise explained that plant hormones control the physiological processes by binding to specific plant or fruit receptor rates, which trigger the succession of events leading to visible responses. In the absence of ethylene, these receptor sites are active, allowing the growth of plant and fruit to proceed. During fruit ripening, ethylene is produced naturally or, if it is artificially introduced in a ripening room, it binds with the receptor and inactivates it, resulting in a series of events like ripening or improve of injuries in plant organs. Ethylene action can be controlled through modification of the amount of receptors or through disruption of the binding of ethylene to its receptors. Binding of ethylene is believed to be reversible at a site which contains metal like copper, zinc, or iron (Burg Burg, 1965, as cited in Burton, 1982). The affinity of receptor for ethylene is high in the presence of oxygen and decreases with carbon dioxide.Changes in the pattern of ethylene production rates and the internal concentrations of ethylene associated with the ons et of ripening have been studied in various climacteric fruits. For instance, tomato and honeydew melon exhibited a rise in ethylene concentration prior to the onset of ripening, determined as the initial increase in respiration rate. On the other hand, apple and mango did not show any increase in ethylene concentration before the increase in respiration (Wills et al., 1998, pp. 42-45).Ripening has been associated with senescence as it leads to the breakdown of the cellular integrity of the tissue. It is part of the genetically programmed phase in the development of plant tissue with altered nucleic acid and protein synthesis occurring during the onset of the respiratory climacteric resulting in new or enhanced biochemical reactions operating(a) in a coordinated manner (Wills et al., 2007, p. 40). These concepts confirm the known degradative and synthetic capacities of fruit during the ripening process. The ability of ethylene hormone to initiate biochemical and physiological events leads to the theory that ethylene action is regulated at the level of gene expression (Pech et al., 2003 Wills et al., 1998, pp. 45-46).TRANSPIRATION/ WATER LOSSPlants depend more on the availability of water than any other single environmental factor (Kramer and Boyer, 1995). Water outlet is very important in determining the shelf life and quality of harvested plant organs. As long as the harvested produce retains water, it remains fresh. Transpiration is one of the main processes that affect postharvest life of the fruit (Ben-Yehoshua Rodov, 2003) near fresh produce contains from 65 to 95 percent water when harvested. Within growing plants there is a constant flow of water. Fresh produce continues to lose water after harvest, but contrary to the growing plant it cannot replace lost water from the soil and so must use up its water content remaining at harvest (Gustavo et al., 2003). This spillage of water from fresh produce after harvest is a expert problem, causing shrinkage and qualifying of weight. When the harvested produce loses 5 or 10 percent of its fresh weight, it begins to wilt and soon becomes unusable. To extend the usable life of produce, its rate of water acquittance must be as low as possible (Wilson et al., 1995). Although temperature is the prime concern in the storage of fruits and vegetables, relative humidity is also important. The relative humidity of the storage unit instantaneously affects water loss in produce. Water loss means venal weight loss and reduced profit (Wilson et al., 1995).Transpiration of fresh fruits is a mountain transfer process in which water vapour moves from surface of the plant organ to the surrounding air. Ficks law of band transfer explains this process as followsJ = (Pi-Pa) At / (RDT)rWhere Pi and Pa are the partial gas pressures in intercellular spaces and in the ambient atmosphere respectively At is surface area of fruit RD is the gas constant per unit mass T is the absolute temperature r is the res istance and J is the gas flux. According to Ficks law, the movement of any gas in or out of the plant tissue is directly remainder to the partial pressure gradient (Pi-Pa) across the barrier involved and the surface area of the barrier and is inversely proportion to the barrier to diffusion. Therefore the driving force of transpiration is the difference of water modifying up pressure (WVP) between the tissue and the surrounding air. While the water vapor pressure deficit (VPD) of the air is difference between the WVP of air and that of alter air at the same temperature. Relative Humidity is the most usual term for expressing the water content of air. It can be defined as the ration of actual WVP in the air to the saturation WVP at a given temperature.Water loss depends on the difference between the water vapour pressure inside the fruit and the pressure of water vapour in the air. To control water loss in fresh produce as low as possible, it must be kept in a moist atmosphere. Air movement also plays a vital role in the water loss from the fresh produce. Water loss is directly proportion to the air movement in the surrounding. Though air movement through produce is also indispensable to remove the heat of respiration, but the rate of movement must be kept as low as possible (Gustavo et al., 2003).ROUTES OF WATER TRANSMISSIONAs the harvested fruits and vegetables are detached from plant, the xylem vessels are blocked with air and their operation is stopped (Burton, 1982). Therefore, water has to use different routes to move through the tissue. Following are the major(ip) potential pathways for water movement in harvested produce.SymplastThe cytoplasm of connected cells is interconnected by plasmodesmata, filled with protoplasm and lined with the plasmalemma. Therefore symplast is formed throughout the interior of a plant organ. Water and dissolved solutes move through the symplast system from cell to cell by diffusion (Ben-Yehoshua Rodov, 2003).ApoplastT he cell wall surrounding symplast also form a continuous system, termed as apoplast. The apoplas stand an alternative avenue for liquid water movement by hydrostatic pressure through the interfibrillar spaces in the cell wall (Woods, 1990).Intercellular zephyrThe plant also contains a system of intercellular gas-filled spaces that form a continuous network and serve as main pathway for O2 and CO2 transport. This field of air space provide adequate gas exchange in bulky organs (Ben-Yehoshua.S, 1969).MAJOR EVAPORATION SITE trade good SURFACEThere are three major routes for moisture loss from harvested commodities to the atmosphere (a) through outer floor that forms a surface for evaporation (cuticle and epicuticle wax periderm) resistance for water movement through (b) the apertures in the surface connecting the internal and external atmosphere (stomata, lenticels) and (c) through the stem scars or pedicel. case and Epicuticular waxThis layer, which lines all interfaces between th e plant and the atmosphere, protects the plant from its relative dry environment. Resistance to water movement is derived from cuticular layer (Ben- Yehoshua, 1969 (Burg Burg, 2006). The cuticle cosntains a matrix of cellulose, polyuronic acids, proteins and phenolic compounds. These are combined with variation of amount of waxes imbed over its surface (Kolattukudy, 1980). Permiability to water usually depends more on amount of waxes than on the thickness of cuticle (Kramer Boyer, 1995).PeridermPeriderm is a corky peripheral tissue. This tissue consists of several layers of cells that become corky as a result of down payment of waxes on their cell walls, and they lose their living contents. The periderm is not readily porous to water and is permeable to gases only through lenticular pores, which replace the stomata of the accredited epidermis. About 97% of the total water lost from the potato tubers migrates through cell walls to the periderm, where it evaporates (Burton, 1982 ).Trichomes and HairsUnicellular or multicellular projections develop on the epidermis of all parts of plants. Their exact function is still vague, but they are considered to reduce water loss (Cutter, 1976). The presence of trichomes can decrease the driving force of transpiration by reducing the surface temperature and increasing the boundary layer resistance.StomataBefore harvest, most of the evaporation occurs from undersides of leaves via stomatal guard cells and adjacent cells (Kramer and Boyer, 1995). Stomata occur in many fruits at early stages of development, but sometimes they are not found in mature fruits of some species, for example, in the grape berry (Possingham et al., 1967). Orange has greatest stomatal density reported so far for any fleshy fruit (Banks, 1995). Stomata usually function less effectively in mature fruit (Blanke and Leyhe, 1988). In most cases it is reduced with maturation and usually of minor importance for fruit water loss during postharvest period (Ben-Yehoshua Rodov, 2003).