Postharvest

• Classification of crop produce

  • Fruits
  • Vegetables

  
• Fruits


  Botanically, are mature ovaries and seed-bearing parts of plants

  
• Vegetables


  All other parts of plant which are edible, including roots, stems, tubers, leaves etc. These are generally consumed, processed in one form or the other and part of main meal.
• Harvested fruits and vegetables have the following characteristics: high moisture content and highly perishable

  
• Plant part or organ utilized

  • The reaction of a commodity to its environment and how it's treated varies according to its specific organ. Leaves and flowers can easily wilt, flower buds may open, fruits tend to ripen, bulbs, tubers, and storage roots often sprout, and shoot tips typically elongate.
• Fruit wall


  Comprises both the peel and the edible portion, excluding the seed

  
• 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

  
• Nature of the fruit wall

  • The composition of the fruit wall significantly impacts how the environment affects the organ and its vulnerability to mechanical damage. The delicate outer layer of the fruit wall and the juicy pulp of certain fruits, such as tomatoes, render them prone to damage. Fruits with a tougher, leathery peel, like starfruit and apples, are less susceptible to bruising.
• Nature of the fruit wall

  • Fruits with thick and hard fruit walls, such as cucumbers, melons, and squash, are more resilient to damage compared to those with softer fruit walls like tomatoes and bananas.
• Surface area to volume ratio

  • It defines the surface area for respiration, transpiration, and the penetration of chemicals and microorganisms. A higher surface area to volume ratio facilitates quicker diffusion of gases essential for respiration, the release of water during transpiration, and the infiltration of microorganisms and chemicals.
• Cuticle


  The non-cellular waxy layer situated above the epidermal cells of the commodity. These epidermal cells constitute the outermost layer of cells that are in direct contact with the environment.
• Nature of the cuticle

  • 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, and escape of flavor components.
• Immature fruits tend to deteriorate more rapidly than mature ones. Mature fruits typically possess thick, intricate, and waxy cuticles, while immature ones have thinner, irregular, and less waxy cuticles.

  
• Nature of the cuticle

  • In winged beans, the wing portion of the pod has a thinner cuticle, leading to quicker wilting compared to other parts of the pod.
  • Lanzones lacks a waxy coating, resulting in rapid water loss, which manifests as browning.
  • Bananas deteriorate at a much slower rate.
  • Pomelo, with its thicker rind, experiences slower water loss compared to dalandan.

  
• Number of stomata


  • Stomata serve as the primary channels for both water loss and the entry of air for respiration. The greater the number of stomata, the faster the deterioration of commodities is likely to occur.
• During full development and maturation, the cuticle undergoes development, leading to the covering of some stomata. For instance, in one leaf of pechay, there are approximately 13,000 stomata per cm2 on the lower surface, possibly twice as many for both surfaces combined. Immature fruits typically possess more stomata than mature ones, partially accounting for why immature fruits deteriorate faster.

  
• Hairs or spines


  Extensions of the epidermal cells. When these extensions are visible to the naked eye, they are referred to as emergences, while smaller hairs that may not be easily visible are known as trichomes.
• Amount of hairs and/or spines

  • The specific term for the hairs found on rambutan is "spintern". A single rambutan fruit typically contains 200 to 400 spinterns, each with multiple trichomes.
  • Lanzones possesses trichomes in addition to lacking wax on the cuticle.
  • Chinese cabbage has a greater abundance of trichomes compared to mustard, while pechay does not have any trichomes.
• Lenticels


  Circular clusters of protruding air-filled cells with a central opening, frequently substituting for stomata in fruits, stems, and roots.
• Laticifers


  Ducts that produce sap or latex and surround the vascular bundles. When laticifers are cut open, such as during harvesting or when the plant is injured, latex is released.
• Carbohydrate content


  • Fruits and vegetables, rich in complex carbohydrates, provide essential nutrients like vitamins and minerals. Storage organs typically have higher carbohydrate content, resulting in extended shelf life. The transformation of sugars into starch diminishes sweetness, as seen in corn. Conversely, the conversion of starch back to sugars in potatoes, especially when stored below 10°C, is unfavorable for processing. Additionally, sugar induces browning when cooked.
• Protopectins


  Pectic substances that primarily accumulate in the cell wall and middle lamella, serving as binding agents. They manifest in various forms: Protopectin, Pectinic acids, Pectin, Pectic acids.
• The overall quantity of pectic substances rises during fruit maturation. As the fruit ripens, the concentration of soluble pectates escalates while the total pectic substances diminish.
• Protopectin


  A substance that forms insoluble salts with calcium or magnesium and acts as a cementing material between cells.
• Pectin


  A carbohydrate present in the cell wall of plants. It is derived from the breakdown of hemicelluloses (protopectins) and is generated during the ripening of the fruit.
• Function of protopectins


  Pectin undergoes a chemical breakdown process, ultimately transforming into pectinic acid and then pectic acid. As this breakdown occurs, the fruit softens due to the degeneration of cell walls.
• Presence of protopectins


  • Guava, pineapples, and oranges are rich in pectin, whereas softer fruits like cherries and strawberries contain less. In acidic environments, pectin exhibits a gelling effect, which is exploited in the production of jams and jellies.
• Common pigments in crops

  • anthocyanins (blue/purple/red)
  • beta-carotene (orange/yellow)
  • Curcumin (yellow)
  • lutein (yellow/orange)
  • lycopene (red)
  • zeaxanthin (yellow)
• Fats and acids


  • Fats can act as barriers to moisture, potentially accelerating desiccation and shriveling of produce. High-fat content can influence the texture of fruits and vegetables, making them softer or altering their crispness during storage. Fats are susceptible to oxidation, leading to the formation of off-flavors, rancidity, and deterioration of quality in fruits and vegetables. Acids contribute to maintaining an acidic environment, which can help in controlling the growth of spoilage microorganisms and extending the shelf life of fruits and vegetables. Acids can inhibit the activity of enzymes responsible for degrading fruits and vegetables, thus slowing down the ripening process and preserving quality. Acids can help preserve the color of fruits and vegetables by preventing enzymatic browning reactions. Acids can enhance the flavor profile of fruits and vegetables, contributing to their overall sensory appeal.
• Respiration


  An oxidative metabolic process in which organic substances, including products of photosynthesis, are decomposed into simpler compounds, resulting in the liberation of energy and heat. Respiration supplies the essential energy required by cells to uphold the physiological processes necessary for the maintenance of life in harvested commodities.
• Acids


  • Can help preserve the color of fruits and vegetables by preventing enzymatic browning reactions
  • Can enhance the flavor profile of fruits and vegetables, contributing to their overall sensory appeal
• Harvested fruits and vegetables

  • They 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
• Respiration


  1. Organic substances, including products of photosynthesis, are decomposed into simpler compounds, resulting in the liberation of energy and heat

  2. Respiration supplies the essential energy required by cells to uphold their structure and supports ripening processes like the development of color and flavor

  3. Once the fruit or vegetable has been harvested, its substrates cannot be replenished

  4. Accelerated rates of respiration lead to diminished nutritional value, decreased saleable weight, inferior flavor, and consequently, diminished overall product quality
• Respiration rate


  • An excellent gauge for assessing the prospective postharvest lifespan of a commodity
  • Accelerated respiration leads to a quicker release of heat, thereby elevating the surrounding temperature, particularly if the commodity is tightly packed
  • As the energy source diminishes, the accumulation of compounds vital for sustaining tissue and cellular organization ceases
• Respiration rate categories


  • Very low
  • Low
  • Moderate
  • High
  • Very high
  • Extremely high
• Commodities with low respiration rates


  Storage organs (e.g. onions, potato, gabi, sweet potato, yams and ginger)
• Commodities with intermediate respiration rates


  Many fruits at physiological maturity (e.g. lanzones)
• Commodities with high respiration rates


  Organs at immature stage (e.g. asparagus, snap beans, eggplant, cauliflower, okra, young corn, bean sprouts)
• Primary organs of a plant

  • Root, stem, leaf, flower, and fruit
• Even minor disruptions in organization, down to the cellular level, prompt alterations in the metabolism of the commodity, ultimately leading to deterioration