Microbiology Of Fresh Fruits, Vegetables And Their Products

Spoilage of Fruits and Vegetables

In general, fruits and vegetables are bulky, easily damaged mechanically,
consist largely of water which is readily lost and above all, are living
entities and must be kept so for their longivity. Thus, they are sensitive to
their environment viz., temperature, level of oxygen, carbon dioxide and
ethylene etc. Spoilage of fresh fruits and vegetables usually occurs during
storage and transport and while waiting to be processed into various

Microbiology Of Fresh Fruits, Vegetables And Their Products

These also get contaminated with spoilage organsims either from
each other or when they are laid into the baskets, lugs, boxes etc. during
harvesting. Mechanical injuries during transportation further aggravate the
deterioration process. The decay of perishables may occur due to the physical
factors, action of their own hydrolytic enzymes or microbial contaminants
etc as discussed earlier. 

Since fruits and vegetables after picking are alive for
certain time thus, are sensitive to their environment, their rate of metabolism
is temperature dependent and they may be damaged by heat or cold or even by
levels of different gases in the atmosphere. Oxygen is taken in during
respiration and CO2 heat and water vapours are given-off. 

As fruits or
vegetables are detached from the mother plant, the continuity of the flow of sap
is totally disrupted but the respiration and water loss continues leading to
exhaustion of food reserve and moisture. The irreparable losses are caused
leading to deterioration and eventually spoilage. Spoilage is mainly of 2 types:
Abiotic spoilage and Biotic spoilage.

Abiotic spoilage: It is due to the different physical (wilting, caking and
melting etc.) and chemical changes in the product (hydrolytic action of
enzymes, oxidation of fats, putrefaction of proteins, browning reaction between
proteins and sugars). Temperature control is the major factor to provide
longevity to the fruits and vegetables.

Biotic spoilage: This includes the microbial action associated with bacteria,
yeasts and molds on vegetables and fruits and the normal processes of aging.
The species of microorganisms causing food spoilage largely depend upon
different factors e.g. kind and variety of fruits/vegetables, environmental
condition e.g. storage, temperature, relative humidity of the atmosphere and
various gas contents of the atmosphere etc. 

There are two types of microbial
spoilage: (a) Spoilage caused by plant pathogens which attack various parts of
the plant used as foods, (b) Spoilage caused by saprophytes. The most common
and general type of spoilage in fruits and vegetables are mildew are listed in
Table 4.4. Dry rots often lead to darkening and discoloring, and hardening of
the surface of vegetables and fruits. In microbial spoilage, the vegetables often
develop water soaked musky areas while the fruits generally have brown or
white colored patches.

The chief market diseases of some vegetables and fruits

The composition of the fruit/vegetable, its pH and moisture content affect their
type of spoilage. Moisture content is usually expressed in terms of water
activity ‘aw’. Various microorganisms have different requirements for
moisture level (Figure 4.2). Amongst the microorganisms, spoilage can be
caused by bacteria, molds/yeasts etc. depending upon the pH of food. 

Bacteria: Various groups of bacteria can attack different fruits and vegetables,
depending upon their composition such as lactic acid bacteria, acetic acid
bacteria, coliform bacteria and sporeforming bacteria. The food can be
preserved for longer time by prolonging the lag phase. 

This can be obtained by
avoiding the contamination of the food and turning the environmental
conditions e.g. temperature, moisture and pH unfavourable for the growth of
contaminants (microorganism). 

Thus, by lowering the storage temperature of
the fruits/vegetables, filling up the storage chamber with the inert gases will
definitely lead to longer shelf- life of the vegetables and fruits. pH is another
important factor governing the bacterial growth which range between pH 4-8.
Growth rate is lowered by a decrease in pH.

Yeasts: Yeasts are widely found in the environment. The yeast growth depends
largely upon the nature of fruit product. These are generally fermentative in

Molds: Molds are frequently associated with food products. Some of the molds
secrete toxic compounds (mycotoxins) like aflatoxins, patulin etc. Aflatoxin
has been detected in dried figs and fig paste while patulin is the most common
mycotoxin detected in the processed fruits. 

The mold Penicillium expansum
which causes apple rot and some other molds produce patulin. The mycotoxins
are deleterious to various animals and presumably the human beings also.

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