Factors responsible for deterioration of harvested fruits and vegetables

 Factors responsible for the deterioration of harvested fruits and vegetables

Soon after harvesting the degradation process starts in the fruit or vegetables. The degradation might be due to the fact that the biochemical changes occurring inside the highly perishable products and a few associated environmental changes make them more susceptible to losing their shelf life more rapidly. In this context here are given a few important factors that are responsible for the deterioration of harvested products. 

The factors that are responsible for the deterioration of Horticultural produce can be divided into three broad categories.

        A. Biological factors

1.      Respiration rate

2.      Ethylene production

3.      Compositional changes

4.      Growth and development

5.      Transpiration

6.      Physiological breakdown

7.      Physical damage (injuries)

8.      Pathological breakdown (Microbial)

9.      Surface area to volume

10.  Membrane permeability

B. Environmental factors

1.      Temperature

2.      Relative humidity

3.      Atmospheric gas compositions

4.      Light

C.  Other factors

1.       Packaging

2.      Storage

3.      Transportation

The major factors responsible for the deterioration of fruits and vegetables during their post-harvest life are:

1. Respiration

2. Transpiration

3. Ethylene

4. Mechanical damage to the harvested produce

5. Pests and diseases

I. RESPIRATION:

It is the most deteriorating biological process of the harvested fruits and vegetables which leads to the oxidative breakdown of complex material (Carbohydrates/acids) into simpler molecules (CO₂, H₂O) with the production of energy. Since the products are still alive and with plenty of moisture content, after harvest, their living cells respire to secure energy. The equation for respiration is as follows.

Stored foods + H₂O →  soluble foods + O₂    →  CO₂ + H₂O + Heat and useful energy.

[This is a biochemical reaction catalyzed by enzymes]

            The rate of respiration is again influenced by a  no of factors during storage. These factors are divided into two groups.

(A)  Plant factors

(B)   Environmental factors.

(A) Plant Factors:

(i) Soluble Sugars: Soluble sugars particularly glucose are chief sugars used in respiration. Hence, the greater the concentration of soluble sugars within the living tissues, the greater the rate of respiration.

(ii) Proportion of living cells: Living cells require a constant supply of energy. Respiration liberation the necessary energy. So the rate of respiration will be directly proportional to the number of living cells.

(iii) Water content of the product: The rate of respiration varies directly with the water content of the product. Generally, succulent products respire more rapidly than non-succulent products. Thus lettuce heads respire (deteriorate) more rapidly than potatoes or sweet potatoes or even peppers.

(B) Environmental factors:

(i) Concentration of O₂ + CO₂: More O₂ concentration more will be the respiration rate and vice versa.

(ii) Temperature: Higher the temperature greater will be the respiration rate.

II. TRANSPIRATION:

            It is the main cause of deterioration because it results in not only direct quantitative losses (loss of salable weight) but also in loss in appearance (wilting and shriveling), textural quality loss (softening loss of crispness) and loss in nutritional quality. Transpiration is also influenced by both plant factors as well as environmental factors.

Plant factors:-

1) Differentiation of tissues: Plant products differ in the degree of differentiation of their tissues and hence they differ in the rate of transpiration under the same conditions. In general, non-differentiated very succulent tissues contain more water than highly differentiated, non-succulent tissues. Under the same conditions, tissues with high water content lose water more rapidly than tissues with low water content.

Ex: Highly succulent –Asparagus spears, spinach leaves highly differentiated products mature cabbage heads, onions, celery etc.

2) Outer cover: Two kinds of tissues constitute the outer cover of plant products. These are epidermis and periderm. The epidermis consists of a single layer of living cells on the outer walls a layer of wax on epidermis retards transpiration, plant products with cutinized epidermis will shrink less rapidly in storage than those with non-cutinized epidermis.

            The plant products with a well-developed and non-injured periderm lose water less rapidly and keep longer in storage than those products with a poorly developed (or) badly injured or bruised periderm. Plant products that possess a periderm as the outer cover are apples, pears, citrus fruits, root crop vegetables, potatoes and sweet potatoes.

Environmental factors:-

1) Temperature: High storage temperature induces a greater rate of transpiration and greater shrinkage than comparatively low temperature.

2) Relative humidity: The rate of transpiration is inversely proportional to the relative humidity. In other words, low relative humidity induces a high rate of transpiration and high RH induces a low rate of transpiration.

III. ETHYLENE:

            All living cells are capable of producing ethylene. Moreover, ripening fruits are rich source of ethylene production. The cuticle on the fruit surface acts as a resistant barrier through which it is dissipated. This is one of the reasons, why the internal concentration of ethylene within the fruit is greater than the external concentration in the atmosphere.

            Ethylene causes degreening in oranges and bananas, it bleaches the green colour of leafy vegetables, celery, cabbage, broccoli etc. In fruits and vegetables degreening is related to ripening process. The most obvious and studies effect of ethylene is an initiator of fruit ripening or, as contributor to ripening.

IV. MECHANICAL DAMAGE:

            The various mechanical injuries that can occur to a product are:-

Roller bruising: Fruits can severely damage by vibration or transit bruising sometimes called ‘roller bruising’. Usually, the damage occurs on the fruit surface as a result of rubbing (or) vibration against another surface during handling transportation.

Impact bruising: It is another injury that can affect fresh produce. This happens when the product drops onto a hard surface during the filling of the package or from the dropping of individual packages or even pallet loads of produce. The impact bruising may not be seen on the product surface, since the symptoms appear as internal damage.

Compression bruising: It also causes losses and deterioration of fresh commodities. It occurs from simply ‘squeezing ‘the product into too small a space.

V. PESTS AND DISEASES:

            Fruits and vegetables are attacked by a variety of insect pests which render them unfit for human consumption (or) reduce their market value. In all cases, infestation starts in the field. In most cases, the damage is visible in the field itself and such fruits and vegetables are discarded during harvesting. However, in many cases, the infestation is internal and not visible at the time of harvesting. It is only during post-harvest storage/handling that the infestation becomes visible.