Factors responsible for deterioration

Factors responsible for deterioration
    The factors that are responsible for the deterioration of Horticultural produce are:
    I. Biological factors
    II. Environmental factors

    I. Biological factors

    1. Respiration rate - being living entities fruits , vegetables, flowers respire actively after harvest. Detailed quantities an qualitative occurring due life of horticultural to this factors
    is detailed in lecture - 3 (Physiology and Biochemistry of Horticultural Produce)

    2. Ethylene production - ethylene plays a vital role in postharvest produce. Its detailed physiological changes are described in lecture - 4

    3. Compositional changes
    Many pigment changes also takes place even after harvest in some commodities.
    These changes are:
    a. Loss of chlorophyll (green color) – In vegetables
    b. Loss of carotenoids (yellow and orange color) – In apricot, peaches, citrus fruits and tomato
    c. Loss of anthocyanins (red and blue color) – In apples, cherries and strawberries
    d. Change in carbohydrates
    i. Starch to sugar conversion – potato
    ii. Sugar to starch conversion – peas, sweet corn
    e. Breakdown of pectin and other polysaccharides – causes softening of fruit
    f. Change in organic acids, proteins, amino acids and lipids. – can influence flavor
    g. Loss in vitamins – effects nutritional quality
    4. Growth and development
    In some commodity growth and development continue even after harvest which accelerates deterioration. For example
    • Sprouting of potato, onion and garlic
    • Fresh rooting of onions
    • Harvested corps continues to grows even after harvest but is very much evident in Asparagus
    • Increase of volume in lettuce

    5. Transpiration
    Most fresh 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, palatability and loss of nutritional quality.

    Factors influence the transpiration rate in various commodities:
    • 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.
    • 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.
    • Maturity stage - less matured fruits lose more moisture then matured fruits/vegetables
    • Skin texture - Fresh produce having thin skin with many more spores lose water quickly than those having thick skin with fewer spores.
    • 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
    • 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)
    6. Physiological breakdown
    When produce is exposed to an undesirable temperature physiological breakdown takes place. Following physiological breakdowns are common in various commodities:
    • Freezing injury - when commodity stored at below their freezing temperature
    • Chilling injury - when commodity stored at below their desired storage temperature
    • Heat injury - when commodity exposed to direct sunlight or at excessively high temperature. It causes defects like sunburn, bleaching, scalding, uneven ripening and excessive softening.
    • Very low O2 (<1%) and high CO2 (>20%) atmosphere during storage can cause physiological problems
    • Loss of texture, structure and microbial damage

    7. Physical damage
    Various types of physical damages responsible for deterioration are
    • Mechanical injury/cut - during harvesting, handling, storage, transportation etc.
    • Bruising due to vibration (during transportation), impact (dropping) and compression (overfilling)

    8. Pathological breakdown
    This is the most common symptom of deterioration where it is mainly caused by the activities of bacteria and fungi (yeast and mould). Succulent nature of fruits and vegetables make them easily invaded by these organisms. The common pathogens causing rots in fruits and vegetables are fungi such as Alternaria, Botrytis, Diplodia, Phomopsis, Rhizopus, Penicillium and Fusarium and among bacteria, Erwinia and Pseudomonas cause extensive damage
    Microorganisms usually directly consume small amounts of the food but they damage the produce to the point that it becomes unacceptable because of rotting or other defects. Losses from post-harvest disease in fresh produce can be both quantitative and qualitative. Loss in quantity occurs where deep penetration of decay makes the infected produce unusable. Loss in quality occurs when the disease affects only the surface of produce causing skin blemishes that can lower the value of a commercial crop.

    9. Surface area to volume - grater surface leads to more weight and respiratory loss
    10. Membrane permeability - fluctuation in storage temperature and physiological injuries like chilling injury leads to membrane damage resulting in electrolyte leakage.

Last modified: Thursday, 1 December 2011, 5:39 AM