Lecture 2: Biological Aspect of Postharvest Handling of Crops
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This document provides an overview of the biological aspects of postharvest handling of crops. It begins with learning objectives focused on classifying fruits and vegetables based on their structures and postharvest life, and understanding the physiological processes that affect quality after harvest. The document then outlines topics that will be covered, including classification, morphological structures, chemical properties, postharvest physiology, and factors affecting quality. It provides details on these topics, such as how cuticle thickness, stomata, and other structures influence water loss and susceptibility to damage. The goal is to understand how crop structure relates to perishability and how to properly handle crops after harvesting.
Lecture 2: Biological Aspect of Postharvest Handling of Crops
- 1. Lecture 2 BIOLOGICAL ASPECT OF POSTHARVEST HANDLING OF CROPS
- 2. LEARNING OBJECTIVES At the end of the lesson, the learners are expected to: 1. Classify fruits and vegetable based on their morpho- anatomical structures and length of postharvest life; 2. Relate the morpho-anatomical structures of fruits and vegetables on the length of their postharvest life; 3. Determine the chemical bases for handling common fruits and vegetables; 4. Explain important physiological processes that affect the postharvest life of fruits and vegetables; and 5. Determine the factors affecting the physiological processes of fruits and vegetables after harvest.
- 3. LESSON OUTLINE 1 Classification of Crop Produce 2 Structure of Fruits and Vegetables 3 Chemical Basis for Handling Fruits and Vegetables 4 Post harvest Physiology 5. Factors affecting Physiological Processes in Fruits and Vegetables After Harvest
- 4. CLASSIFICATION OF CROP PRODUCE • FRUITS: Botanically, are mature ovaries and seed bearing parts of plants • Include: grains, legumes, nuts, cucumbers, coffee , mangoes, peppers, tomatoes, citrus, bananas, grapes, strawberry, pineapple, lanzones, rambutan, dragon fruit, kaong, etc.
- 5. The succulent, high moisture and generally sweet fruits and consumed raw as dessert rather than main meals.
- 6. Vegetables are all other parts of plant which are edible. Include: roots, stems, tubers , leaves etc. These are generally consumed, processed in one form or the other and part of main meal.
- 7. Harvested fruits and vegetables have the following characteristics: high moisture content highly perishable
- 8. MORPHO- ANATOMICAL BASIS FOR PERISHABILITY OF FRUITS AND VEGETABLES The response of a commodity to its surroundings and to the method of handling depends on what organ it is. 1. Plant part or organ utilized
- 9. Leaves and flowers wilt easily, flower buds open, fruits ripen, bulbs, tubers and storage roots sprout and shoot tips elongate.
- 10. Fruits and fruit vegetables vary in the nature of their fruit walls. The fruit wall consists of both the peel and the edible portion excluding the seed. 2. Nature of the fruit wall
- 11. Some terminologies in relation to fruit wall: Rind – the tough and leathery peel of citrus and watermelon. Pulp – the edible portion of citrus. Aril – the edible portion of rambutan, mangosteen, durian and lanzones.
- 12. The nature of the fruit wall greatly influences the effect of the environment on the organ and its susceptibility to mechanical damages. The thin outer part of the fruitwall and succulent pulp of some fruits like tomatoes make them susceptible to damage. Fruits with leathery peel are less susceptible to bruises as in starfruit and apple.
- 13. Fruits with thick and hard fruit wall like cucumbers, melons and squash are better able to withstand damage than those with soft fruit walls like tomatoes and bananas. Squash Cucumber Melon Bananas
- 14. It determines the reactive area for respiration, transpiration penetration of chemicals and microorganisms. 3. Surface area to volume ratio
- 15. The greater the surface area to volume ratio, the faster the diffusion of gases involved in respiration, exit of water through transpiration and entry of microorganisms and chemicals. These result to shorter postharvest life.
- 16. The cuticle is the non-cellular waxy layer above the epidermal cells of the commodity. The epidermal cells comprise the first layer of the cells exposed to the environment. 4. Nature of the cuticle
- 17. The thicker and more complex the cuticle, the greater is its protective capacity for: moisture loss penetration of microorganism and chemicals mechanical damage temperature changes escape of flavor components
- 18. Immature fruits deteriorate at a faster rate than mature ones. Mature fruits have thick, complex and waxy cuticles whereas immature ones have thin, irregular and less waxy cuticle. In winged beans, the wing portion has thinner cuticle hence it wilts at a faster rate than the other parts of the pod.
- 19. Lanzones is not waxy. Hence, Lanzones losses water fast which shows up as browning. Banana deteriorates at a much slower rate. Pomelo has thicker rind hence losses water slower compared to dalandan.
- 20. The stomata are the main passageways for the loss of water and entry of air for respiration. The more stomata , the faster will be the deterioration of the commodities. 5. Number of Stomata
- 21. As the cuticle develops during full development and maturation some of the stomata get covered. Pechay has 13,000 stomates per cm2 in the lower surface of one leaf and possibly twice as much for both surfaces. Immature fruits have more stomata than mature ones which partially explains why immature fruits deteriorate faster.
- 22. Hairs or spines are elongations of the epidermal cells. Visible hairs or spines are known as emergences, while tiny hairs which may not be visible to the naked eye are called trichomes. The special name for the hair of rambutan is spintern. 6. Amount of Hairs and/or Spines
- 23. The more trichomes, the faster is the deterioration since they increase the surface area to volume ratio of the commodities A single rambutan fruit has 200 to 400 spinterns with several trichomes per spintern. Lanzones has trichomes aside from having no wax on the cuticle. Chinese cabbage has more trichomes than mustard while pechay has none.
- 24. Lenticels are circular groups of protruding air-filled cells with a central opening which often takes the place of stomates in fruits, stems and roots. 7. Presence of lenticels
- 25. Laticifers are sap or latex producing ducts surrounding the vascular bundles. When the laticifers are cut open (when harvested or injured) latex is released. Hence the flows of latex on the stem must be avoided or washed off before it hardens. 8. Presence of laticifers
- 26. CLASSIFICATION OF FOOD CROPS BASED ON THEIR POSTHARVEST LIFE Perishables are food crops whose food value is maintained over a short period of time after harvest.
- 27. Durables are food crops which can be maintained as food over a long period of time.
- 30. The Chemical Bases of Handling the Harvested Commodities 1. Carbohydrate Content Fruits and vegetables are complex carbohydrates which supply nutrients, such as vitamins and minerals. Storage organs contain more carbohydrates hence usually last longer. When sugars are being converted to starch, there is a loss of sweetness in commodities such as in corn. The conversion of starch to sugars in potatoes (when stored at a temperature below 10ºC) becomes undesirable for processing. Sugar causes browning during cooking.
- 31. 2. Presence of protopectins Pectic substances are mainly deposited in the cell wall and middle lamella, acting as cementing materials. They occur in the form of: Protopectin Pectinic acids Pectin Pectic acids Total pectic substances increase in amount during the development of fruits. As the fruit ripens, the contents of soluble pectates increase while the total pectic substances decrease.
- 32. Protopectin is one of the substances which form insoluble salts with calcium or magnesium and is found as a cementing substances between cells. Pectin is a carbohydrate in the cell wall of plants. It is a breakdown product from hemicelluloses (protopectins) which is generated during ripening of the fruit. .
- 33. Pectin itself is later broken down to pectinic acid and finally pectic acid. During this chemical breakdown process, the fruit gets softer as the cell walls degenerate Guava, pineapples and oranges contain high pectin, while soft fruits like cherries and strawberries contain few. Under acidic conditions, pectin forms a gel. This effect is used for making jams and jellies.
- 34. 3. Pigment The change of color during ripening is due to changes in the pigments. Color Main Pigment Green, blue green, yellow green in most commodities Red in tomatoes Orange of carrots Red in strawberry Yellow in papaya Purple in eggplant chlorophyll Lycopene Carotene Anthocyanin Cryptoxanthin delphinidine Main Pigments Responsible for specific color of some commodities.
- 35. Pigment Color Found in anthocyanins blue/purple/red berries, grapes, red peppers, beets, eggplant, plums beta-carotene orange/yellow carrots, pumpkin, sweet potatoes, citrus, papaya, melon, squash curcumin yellow turmeric lutein yellow/orange kale, broccoli, spinach lycopene red tomatoes, watermelon, red grapefruits zeaxanthin yellow corn
- 36. 4. Fats and Acids Fats - avocado Malic acid - apple Citric acid - citrus and pineapple, lemons, grapes Ascorbic acid - guava, orange, grapes Tartaric acid - grapes, bananas, tamarind
- 37. Avocado Fat You need not worry about the fat content of avocado, as this fat is not harmful nor does it increase your cholesterol levels. Saturated fats, are those types of fat that are harmful and increase cholesterol levels. However, monounsaturated fats(avocado fat is of this type) and polyunsaturated fats, are not harmful and do not increase cholesterol levels. On the contrary monounsaturated fat and avocado fat help lower cholesterol. Source: www.all-about-lowering- cholesterol.com/avocado..
- 38. At maturation, reducing sugar increases while the acidity decreases, hence the matured/ripe commodities taste sweeter.
- 39. Different practices in PHM Physiological Processes that Occur in Harvested Commodities All fruits and vegetables are living organs. They use oxygen and produce carbon dioxide during respiration, the process by which carbohydrate and other substrates, such as organic acids, proteins and fats, are metabolized.
- 40. Different practices in PHM 1. Respiration is an oxidation process by which organic materials or products of photosynthesis are broken down to simpler forms accompanied by the release of energy and heat. C6H12O6 + O2 CO2 + H2O + energy enzymes
- 41. Different practices in PHM Respiration thereby provides the energy necessary for cells to maintain structure and for ripening processes such as color and flavor development.
- 42. Different practices in PHM The substrates cannot be replenished once the fruit or vegetable has been removed from the plant. Faster respiration rates will result in loss of food nutritional value, loss of saleable weight, poorer flavor, and thus reduced product quality.
- 48. The main organs of a plant are root, stem, leaf, flower and fruit. To keep these organs alive, their organization must be maintained. Once there is a breakdown in this organization even at the cellular level, there is a corresponding change in the metabolism of the commodity which eventually shows in the state of deterioration. To maintain the organization and sustain metabolism, energy is made available through respiration using carbohydrates accumulated before harvest.
- 51. Poor quality of products due improper handling after harvest
- 52. Lengthening of postharvest life, therefore, calls for good production practices in order to have greater energy source at harvest, and respiration should be slowed down after harvest to enable the source of energy to last for a long period of time.
- 53. 2. Transpiration is the loss of water from the plants. Most fruits and vegetables are composed of cells loosely bound together with considerable intercellular spaces which interconnect and lead to lenticels or stomates. .
- 54. Water from cells vaporizes into the intercellular spaces and maintains an essentially saturated atmosphere. Water vapor may then move to the atmosphere through the stomates or lenticels, stem scars or through injured areas or directly through breaks in the cuticle.
- 55. Horticultural products can be regarded as “water inside pleasing packages” or “water with a mechanical structure”. Therefore, water loss or transpiration is a major factor affecting quality of fruits and vegetables.
- 56. Consequences of water loss loss in weight of all commodities softening of fruits and vegetables wilting of leaves and flowers shrivelling of fruits and root crops stem end rind breakdown of oranges discoloration of rambutan and lanzones
- 57. Fresh fruits and vegetables consist mainly of water. It could be as high as 98% by weight in fully turgid leaves. Loss of water can dry up a commodity. A 10% loss in weight may result in 100% commercial loss. The high amount of water in commodities makes them succulent and therefore susceptible to mechanical damage.
- 58. Implication: The faster water is lost from the commodity, the faster it losses its freshness. Therefore, transpiration should be slowed down to keep the commodity fresh.
- 59. 3. Ethylene Production Ethylene (C2H4) is a hormone in gas form which causes the following in harvested crops: hasten ripening promotes sprouting of root, tuber and bulb crops induces abscission of leaves, petals or cutflowers
- 60. Implication: If you want to avoid the ethylene effects, eliminate ethylene from the atmosphere surrounding the commodity. On the other hand, if you want to hasten the ripening process add ethylene or induce it to increase.
- 61. Conditions which will slowdown the rate of respiration and transpiration in plants. 1. Low Temperature The higher the temperature above the optimum temperature, the faster is the rate of respiration and transpiration and consequently shorter postharvest life. Keeping a commodity at a low temperature is thus the most effective way of extending postharvest life.
- 63. 2. Low oxygen in the immediate environment A high concentration of oxygen (21%) will result to faster respiration rate and shorter postharvest life. Oxygen levels below 21% but usually not less than 5% will slow down respiration. Very low oxygen concentration will however result in fermentation which is an abnormal form of respiration resulting in alcoholic odor or undesirable flavor and tissue collapse
- 65. 3. High relative humidity The lower the relative humidity of the air, the faster is the transpiration. Since commodities are considered to have relative humidity close to 100%, it is therefore important to keep them under moist conditions, that is, at high relative humidity even at low temperature.
- 67. Thank You