Post-Harvest Physiology of Horticultural Produce: Water Loss, Respiration, and Ethylene Role

Post-Harvest Physiology of Horticultural Produce: Water Loss, Respiration, and Ethylene Role

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  Post-Harvest Physiology ofHorticulture produce (Fruits, Vegetables and Flowers)- Water loss, Ripening, Respiration and Role of Ethylene) Prepared by Umesh Timilsina Assistant Professor CNRM, Bardibas Agriculture and Forestry University
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  PHYSIOLOGY OF FRUITAND VEGETABLES • Fruit development usually start after anthesis. • Entire process of fruit development is divided into three major physiological stages: 1. Growth 2. Maturation 3. Senescence
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  • Growth -involves cell division and subsequent cell enlargement, which accounts for the final size of the produce. 1. Phase I or Lag Phase 2. Phase II or exponential phase 3. Phase III or Plateau phase • Maturation - usually commences before growth ceases and includes different activities in different commodities. Growth and maturation are often collectively referred to as the development phase. • Senescence - is defined as the period when synthetic (anabolic) biochemical process gives way to degradative (catabolic) process, leading to ageing and finally death of the tissue.
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  Type of growthcurves in fruit crops: 1. Single Sigmoid curve Double sigmoid Triple Sigmoid Example: Apple, pear, pineapple, banana, avocado, almond, strawberry, loquat, date palm, papaya, mango and lemon Example: Peach, plum, apricot, ber, raspberries, fig, blackberry, blueberry, cherry, pecanut, persimmon, guava, grapes, olives, Example: Kiwi fruit
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  Fruit Growth patternof Tomato
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  FRUIT AND VEGETABLESARE ALIVE AFTER HARVEST • Horticultural Produce respire by taking up O2, giving off CO2 and heat and also transpire. • While attached to plants, losses due to transpiration and respiration are replaced by flow of sap, which contain water, photosynthates and minerals. • These functions continue even after harvest, and since the produce is now removed from the its normal source of H2O, photosynthates and minerals, the produce entirely depend on their own food reserves and moisture content. • Therefore, losses of repairable substrates and moisture are not made up and deterioration has commenced hence, produce are perishable.
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  Difference between attachedand detached plant organs Attached organ Detached organ Photosynthesis Transpiration Translocation Respiration Absorption/ Uptake Senescence Respiration Sprouting Transpiration Ethylene production
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  Basic Physiological differencebetween Attached and Detached organs Physiological Process Attached organ Detached Organ Absorption/Uptake Roots absorb water and minerals from soil and translocation take place. Does not have root to absorb water and minerals. So, there will not be translocation Translocation There will be the connection of roots with the vascular bundles and there will be translocation to full fill the demands. There will not be the connection of roots with the vascular bundles and there will be not be translocation to full fill the demands. Photosynthesis Photosynthesis takes place and translocation of food materials to other organs Generally, no photosynthesis occurs, no translocation to other organs Transpiration Transpiration loss is supported by absorption which is means of temperature management No any supported means and cause weight loss and shriveling Respiration Break down of substrate and release of energy; loss of substrate is supported by photosynthesis Breakdown of substrate and release of energy, loss of substrate is not supported by photosynthesis Ripening and Senescence Presence or regular supply of Co factors or ripening inhibitors in/by the plants. So, there will be delay in ripening and senescence Absence or disrupt supply of co-factors or ripening inhibitors. So, there will be faster ripening and senescence.
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  1. Transpiration • Mostfresh produce contain 80-90 % of water when harvested. • Transpiration is a physical process in which high amount of water is lost from the produce, which is the main cause of deterioration. • This exchange of water vapour in produce is carried through the cuticle, epidermis cells, stomata and hairs of the produce. • Produce stored at high temperature will have high transpiration rate. • When the harvested produce loses 5 % or more of its fresh weight, it begins to wilt and soon becomes unusable. • Water loss also causes loss in quality, such as reduced crispness and other undesirable changes in colour, weight loss, shrinkage, changes in the flavor, texture, palatability and also loss of nutritional quality.
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  Main sites ofwater loss in harvested organs 1. Epidermal layer  Cuticles and wax are continuously deposited on the epidermal cells  Mature fruits and leaves have thicker cuticles and wax, so lose less water than immature ones 2. Stomata  Immature organs have a greater number of stomata than the matured ones 3. Lenticels:  Circular groups of protruding air-filled cells with central opening which often takes the place of stomata.  Present in leaves and roots  Continuously open and allow exchange of gases and water 4. Emergences and Trichomes  These appendages increase the surface areas and increases water loss 5. Detached sites
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  Consequences of WaterLoss  Loss in weight of all commodities  Softening of fruits and vegetables  Wilting of leaves and flowers  Shriveling of fruits and root crops  Stem end rind breakdown of oranges  Discoloration of rambutan and lanzones
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  Implication:  The fasterwater is lost from the commodity, the faster it loses its freshness.  Therefore, transpiration should be slowed down to keep the commodity fresh.
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  Factors influencing therate of transpiration in various commodities 1.Surface of the commodity - Commodities having greater surface area in relation to their weight will lose water more rapidly. It is clearly visible in leafy vegetables where the water loss is much faster than a fruit as they have more surface area to volume ratio. 2.Surface injuries - Mechanical damages accelerate the rate of water loss from the harvested produce. Bruising and abrasion injuries will damage the protective surface layer and directly expose the underlying tissues to the atmosphere allowing greater transpiration. 3.Maturity stage - less matured fruits lose more moisture then matured fruits/vegetables 4.Skin texture - Fresh produce having thin skin with many more spores lose water quickly than those having thick skin with fewer spores. 5.Temperature - Water loss is high with increase in storage temperature. The loss will be further enhanced when high temperature is combined with low relative humidity.
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  6. Relative humidity- The rate at which water is lost from fresh produce also depends on the water vapour pressure difference between the produce and the surrounding air. • So water loss from fresh produce will be low when the relative humidity i.e. moisture content of the air is high. • Further, the faster the surrounding air moves over fresh produce the quicker will be the water loss. • Transpiration results in following type of deterioration: Loss in weight Loss in appearance (wilting and shriveling) Textural quality (softening, loss of crispiness and juiciness)
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  Vapour Pressure Deficit(VPD) • VPD is the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated. or • Vapor Pressure Deficit (VPD) is a measure of the difference between the amount of moisture in the air and the maximum amount of moisture the air can hold at a given temperature.
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  How VPD Works?? SaturationVapor Pressure (SVP):  This is the maximum amount of water vapor the air can hold at a specific temperature.  Warmer air can hold more moisture. Actual Vapor Pressure (AVP):  This is the actual amount of water vapor present in the air. VPD Formula: VPD=SVP−AVP  It is typically measured in kilopascals (kPa).
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  Why VPD Matters? PlantTranspiration: • A higher VPD means the air is drier, increasing the rate of transpiration (water loss) from plants. • Conversely, a lower VPD indicates more humid air, which reduces transpiration.
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  2. Respiration • Respirationis the metabolic process in which oxidative breakdown of complex materials such as starch, sugars and organic acids into simpler molecules (CO2, H2O) takes place along with the production of energy. Types of respiration 1. Aerobic Respiration Most of the energy required by fruits and vegetable is supplied by aerobic respiration. The most normal substrate for respiration is glucose. C6H12O6 +6O2 6CO2 + (Glucose) (Carbondioxide) 6H2O+ Energy (Kcal) (Water) Aerobic respiration completes in two processes: i. Glycolysis or Embedon Mayerhoff Paranas (EMP) pathway: Cytoplasm ii. Kreb cycle or TCA cycle or Citric Acid cycle- Mitrochondria
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  1.Hexokinase 2. Phosphofructoisomerase 3. Phosphofructokinase 4.Aldolase 5. Triose Phosphate isomerase 6. Glyceraldehyde-3-phosphate dehydrogenase 7. Phosphoglycerokinase 8. Phosphoglyceromutase 9. Enolase 10.Pyruvatekinase HE PUT THE PHONE AND TriED TO GET PLASTIC PLATE TO EAT PIE
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  GREAT GRAND MOTHERTHROWS FRESH FRUIT IN DISH AND GO BY PICKING PUMPKINS TO PREPARE PIES Glucose Glucose-6-Phosphate Fructose-6- Phosphate Fructose 1,6-Bi phosphate Dihydroxyacetone Phosphate Glyceraldheyde-3-Phosphate 1,3- Biphosphoglycerate 3-Phosphoglycerate 2-Phosphoglycerate Phosphoenolpyruvate Pyruvate
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  Electron Transport System •Electronsfrom NADH and FADH₂ (produced during glycolysis, the citric acid cycle, and beta-oxidation) are transferred through a series of protein complexes (Complex I–IV). •As electrons move along the chain, protons (H ) ⁺ are pumped from the mitochondrial matrix to the intermembrane space, creating a proton gradient.
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   Oxidative phosphorylationor electron transport-linked phosphorylation or terminal oxidation is the final stage of cellular respiration, where the energy from nutrients is used to produce ATP (adenosine triphosphate), the energy currency of the cell.  It occurs in the inner mitochondrial membrane in eukaryotic cells. Key Points: Produces about 32–38 ATP molecules per glucose. Highly efficient compared to anaerobic respiration. Generates heat as a byproduct, helping maintain body temperature.
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  • Considering glycolysisand TCA cycle, when one molecule of glucose is oxidized completely it will produce 38 ATP molecules in the presence of oxygen .
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  2. Anaerobic Respiration •In the absence of oxygen, the pyruvic acid will not yield Acetyl COA. So there will not be TCA cycle. • It will produce either lactic acid or ethanol depending upon the presence of predominant enzyme. • Glucose Pruvate Lactate Lactate dehydrogenase Pyruvate Carboxylase CO2 Acetaldehyde NADH +H Alcohol Dehydrogenasse NAD Ethanol
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  What is Q10?? •Q10 is defined as for every 10 °C rise in temperature the rate of reaction will be increase by 2-3 folds. Until up to 30°C, the enzymatic activities doubles but when it reaches to 40°C, metabolic activities slow down. • The formula to calculate the Q10 value related to respiration is: where R1 is the respiration rate at temperature T1, and R2 is the respiration rate at temperature T2, with the temperature difference (T2 - T1) always being 10 degrees Celsius. Explanation: Q10: •Represents the "temperature coefficient," which indicates how much a biological process, like respiration, increases in rate for every 10 degree Celsius rise in temperature. R1 and R2: •These are the measured respiration rates at two different temperatures, where R2 is the rate at the higher temperature. T1 and T2: •These are the corresponding temperatures at which R1 and R2 were measured, respectively.
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  • The rateof deterioration of horticultural commodities is directly proportion to the respiration rate. • On the basis of their respiration rate we can classify different fruit and vegetables in following way:
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  Respiration Quotient (RQ) RQ=Release of CO2 Consume of O2 • RQ gives an idea of what substance is being metabolized for energy produced in the plant. • For e.g. Glucose = 1 Protein: 0.8 Malate =1.3 Fat= 0.7 • Measurement of RQ itself can given some guide to the type of substrate that is being respired. • As low RQ suggests some fat metabolism while high metabolism (RQ) suggest of organic acids. • Fats require more oxygen for complete oxidation from outside and produce less CO per ₂ oxygen consumed compared to carbohydrates. This results in a lower RQ value for fats (~0.7) compared to carbohydrates (~1.0).
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  Respiratory behavior offruits and vegetables • If the respiration rate of a fruit or vegetable is measured as their O2 consumed or CO2 evolved during the course of the development, maturation, ripening and senescent period, a characteristic respiratory pattern is observed. • The respiratory pattern also impacts the pattern of evolution of ethylene. • Based on this pattern, fruits can be classified into ‘climacteric’ and ‘non-climacteric’. • Few fruits exhibit the pronounced increase in the respiration (increase in CO2 and C2H4) coincident with the ripening, such increase in the respiration is known as respiratory climacteric, and this group of fruits is called climacteric.
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  Features Climacteric FruitsNon-Climacteric Fruits Definition Fruits that continue to ripen after being harvested. Fruits that do not ripen further once harvested. Ripening Process Undergo a distinct ripening phase after harvest, involving biochemical and physiological changes. Remain in the same state as when harvested, with minimal biochemical changes. Ethylene Production Produce a large amount of ethylene, which triggers ripening. Produce very little or no ethylene, so ripening does not continue after harvest. Respiration Rate Exhibits a spike in respiration (climacteric rise) during ripening. Respiration rate remains steady, without a significant increase. Harvesting Considerations Can be harvested before full ripeness and will ripen off the plant. Must be harvested at peak ripeness because they do not improve in quality after picking. Storage & Transport Can be stored and transported unripe, then ripened later (e.g., in storage rooms with ethylene exposure). Need to be transported carefully when fully ripe to avoid spoilage. Shelf Life Longer shelf life since they can be harvested unripe and ripened when needed. Shorter shelf life as they must be consumed soon after harvesting. Texture & Flavor Development Becomes softer, sweeter, and more aromatic over time after harvesting. Flavor and texture do not improve significantly after harvest. Examples Banana, mango, apple, pear, avocado, tomato, peach, papaya, plum, guava, passionfruit. Strawberry, orange, grape, watermelon, cherry, pineapple, cucumber, raspberry, lemon, bell pepper.
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  Factors responsible forthe respiration (external and internal) A. Internal Factors 1. Type of Commodity • Different crops have different natural respiration rates:  High respiration rate – leafy vegetables (spinach, lettuce), broccoli  Moderate respiration rate – mango, tomato  Low respiration rate – nuts, dried seeds • Higher respiration = shorter shelf life. 2. Stage of Maturity and Ripeness  Immature fruits → high respiration  Mature-green → moderate  Ripening stage → respiration increases (climacteric rise in some fruits)  Example: Mango and banana show a climacteric rise in respiration.
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  3. Climacteric vsNon-Climacteric Nature Climacteric fruits (show sharp rise in respiration & ethylene during ripening): Mango, banana, apple, tomato Non-climacteric fruits (no sharp rise): Citrus, grapes, litchi Climacteric fruits respire faster during ripening. 4. Chemical Composition High sugar/starch content → higher respiration High moisture content → higher metabolic activity High fat content (nuts) → lower respiration
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  5. Physiological Condition •Injury or bruising → increases respiration • Disease or infection → increases respiration • Sprouting in potatoes/onions → increases respiration 6. Genetic Factors (Variety/Cultivar) • Different cultivars of the same crop may have different respiration rates. • Example: Some mango varieties respire faster and soften earlier than others.
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  B. External Factors 1.Temperature (Most Important Factor) • High temperature → increases respiration rate • Low temperature → reduces respiration • Every 10°C rise approximately doubles respiration (Q concept) ₁₀ • Example: Mango stored at 30°C deteriorates faster than at 13°C. 2. Oxygen (O ) Concentration ₂ • High O → higher respiration ₂ • Low O → reduced respiration ₂ • Very low O → anaerobic respiration (causes off-flavor) ₂ • Controlled atmosphere storage reduces O to slow respiration. ₂ 3. Carbon Dioxide (CO ) Concentration ₂ • Moderate increase in CO → reduces respiration ₂ • Excess CO → physiological injury ₂
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  4. Ethylene • Ethylenestimulates respiration, especially in climacteric fruits. • Example: Ethylene exposure accelerates ripening in mango and banana. 5. Relative Humidity • Low RH → water loss → stress → increased respiration • High RH (optimum) → maintains quality 6. Mechanical Injury • Cutting, bruising, or peeling increases respiration • Example: Fresh-cut vegetables respire faster than whole vegetables 7. Light • Some vegetables may respire differently under light • Light may influence chlorophyll and metabolic activity
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  3. Ripening • Ripeningis a phase of qualitative change which occurs in particularly, fruits after completion of maturation, during which the fruit becomes acceptable for consumption in terms of taste and flavour. • Ripening occur during the later stages of maturation and is the first stage of senescence.
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  Changes during ripening 1.Seed maturation 2. Changes in pigmentation or peel color • Involves the loss of chlorophyll and either the synthesis of other pigments (Carotenoids, anthocyanin, lycopene etc.) • The rate of color change varies widely. • Some with a slower rate and some at a faster rate. • At the early stage of development, it is the chlorophyll that gives the green color. Chlorophyll Chlorophyllase Other pigments • The pigments in the peel of banana are chlorophyll, carotenoids and xanthophylls. • The change in color of ripening fruits is associated with the breakdown
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  3. Changes infirmness or softening • The breaking down of cell wall is the consequences of the action of hydrolases synthesized during ripening and which leads to the destruction of cells and tissues. • In banana, polygalacturonase activity increases as the flesh softens. • This enzyme is found to be responsible for softening. • During ripening protopectin breaks downs to polygalactouronic acid in series of reaction and causes softening of fruits.
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  4. Changes inaroma and flavor • Flavor is the subtle and complex perception that combines taste, smell and mouth feel. • Ripening usually brings about an increase in simple sugars to increase sweetness, a decrease in organic acids and phenolics to minimize astringency and increase in volatiles to produce the characteristic flavor. • The volatile compounds of highly diverse nature (alcohols, aldehydes, esters, ketones and terpenes participate in this aromatic perceptions. • At least 350 volatile compounds haven been shown to occur in ripe banana. • The overall flavor of the fruit is influenced by organic acids, particularly on the desirable sugar acid balance necessary for the pleasant taste. • Flavour is the result of the sugar/acid balance and the astringent compound content. • The astringency of the fruit is attributed to phenolic compounds which are partly polyphenols (tanins and condensed tanins).
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  Fruit Flavouring compound Apple( ripe) Ethyl 2- methylbutyrate Apple ( green) Hexanal, 2- hexanal Banana ( ripe) Eugenol Banana ( green) 2- hexanal Banana ( overripe) Isopentanol Grapefruit Nootakatone Lemon Citral Orange Valencene Pineapple Methyl Propionate Ester Carambola Methyl Anthranilate Durian Hydrogen Sulphide Tamarind 2-acetyl furan Raspberry 1- (α– hydroxyphenyl)- 3- butanone Cherry Methyl Salicylate and Methyl Anthranilate
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  5. Change incarbohydrate composition: • During ripening, fruits undergo significant changes in their storage form of carbon. • Starch in many fruits is prevalent carbon storage compound and it undergoes hydrolytic conversion during ripening yielding free sugar. • During ripening, the starch concentration decreases while concentration of sugar increases to a varying degrees in different cultivars. • During ripening of banana, there is dramatic conversion of starch to sugar and this conversion generally occurs over a relatively short period of time. • Banana thus represent an excellent example of hydrolytic alternations of carbohydrate during ripening. • During ripening of banana, a reduction in starch content from around 15-25% to less than 5 % in the ripe pulp.
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  6. Change inorganic acid: •In most of the fruits, there is decrease in acidity during ripening, while in some it gets increased gradually during ripening. • As the banana fruit approach towards its climacteric peak, the acidity of fruit is increased and then continuously decreases. •The decrease in acidity of banana during post climacteric phase is due to increase in Malic enzymes and pyruvate decarboxylation. •The increase in acidity during ripening is due to result of two factors i.e. organic acid assimilation and the rate of its oxidation to carbonic acid and water.
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  7.Changein amino acidsand proteins • Amino acids generally decrease with ripening in many fruits. • They are reduced towards maturity because of incorporation into proteins required for synthesis of various enzymes. • It is presumed that lowering of amino acids indicates the advancement of maturity. • Aspartic acid, glutamic acids, serine fractions decreases with ripening in muskmelon. • Similarly, in tomato, leucine and iso-leucine decreases with fruit ripening.
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  8. Nutritional Changes: Increasein certain vitamins (e.g., vitamin C) and antioxidants.
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  Factors affecting ripening 1.Temperature
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  2. Radiations Act asboth stimulators or inhibitors of ripening process. Grapes ripe more quickly if treated with infrared radiation. Banana irradiated with X ray exhibited a decrease in softening but an increase in skin blackening.
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  3. Air humidity Therelative humidity and velocity of air in the vicinity of the fruit influenced the maturity, especially in the evolution of the flavor. Saturated air hinders the development of good flavor in Pears. Apple shows blackening of the core.
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  4. Growth substances Treatmentwith growth substances seems effective when the application is made very soon after the picking. Bunch of banana immersed in solution containing 1000 PPM Sodium, 2 4-D, 2 4 5-T showed that ripening is acceralated. Auxin may slow down (generally) or often sometimes acceralate ripening process. Gibberellin inhibits the degradation of chlorophyll so also do Cytokinin. GA also stops color changes in banana. Accumulation of Abscissic Acid is also associated with ripening. ABA markedly increases the degree of ripening of tomatoes in harvested fruits.
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  5. Chemicals Chemicals likeCalcium chloride, Calcium nitrate, 2 4-D and 2 4 5-T have been reported to affect the shelf life of fruits. Pre harvesttreatment with 0.6% Calcium chloride and 1 % Calcium nitrate enhance the storage life of mango and guava. The storage life of citrus fruit was prolonged by spray of 2 4-D and 2 4 5-T.
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  6. 7.
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  Role of Ethylene •Ethylene is naturally occurring odorless, tasteless, gaseous hormone produced by ripening fruits. • It promotes additional ripening of produce expose to it. • It is said that one bad apple spoils the whole bushel is true. • Damaged or diseased apples produce high level of ethylene and stimulates the other apples to ripen too quickly. • As the fruits ripen, they becomes more susceptible to diseases. • Some examples of ethylene effect are: Loss of green color in snap beans Bitterness in carrot Softening and development of off flavor in watermelon Sprouting of potatoes Increased ripening and softening of mature green tomatoes Yellowing and abscission of leaves of broccoli, cabbage and cauliflower
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  History •In 1910, X(?) gas was assumed to be produced from ripening banana and initiated ripening of unripe banana during shipment of banana from Jamaica to Europe. •In 1943, it was identified as Ethylene. •In 1932, Kidd and West recorded the effect of ethylene on climacteric rise of fruits since its ripening effect was not confirmed.
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  BIO SYNTHESIS OFETHYLENE Methionine S- Adenosyl Methionine (SAM) or Adomet ACC Synthase ACC Oxidase O2 ACC (1-Amino Cyclopropane1- Carboxylic acid) Ethylene SAM Synthetase ATP
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  Biosynthesis of Ethylene •Methionine is the precursor molecule for the ethylene synthesis. • It has been found out that 1- Amino-Cyclopropane 1- carboxylic acid (ACC) is the key intermediate in ethylene synthesis. • The conversion of S- Adenosyl Methionine (SAM) to ACC is mediated by ACC synthase. • The synthesis and the activity of this enzyme may be modified by such factors as an aerobiosis, wounding, Indole Acetic Acid (IAA), Cytokinin, Calcium and some exogenous inhibitors. • Moreover, the conversion of ACC to ethylene is enzymatic and this is affected by the nature of external and internal factors. • Conversion of ACC to ethylene requires oxygen and process is inhibited by carbondioxide. In anaerobic condition, there is only accumulation of ACC without production of ethylene.
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  Biosynthesis of Ethylene Methioninecycle or Yang cycle 5-S-Methyl thio Adenine