CHAPTER 5
Microbiology of Primary Food
Commodities
In this chapter we will examine aspects of the microbiology of some
specific commodity groups describing the microflora with particular
emphasis on spoilage.
5.1 WHAT IS SPOILAGE?
According to the Oxford English Dictionary to spoil is to ‘deprive of
good or effective qualities’. When a food is spoiled its characteristics are
changed so that it is no longer acceptable. Such changes may not always
be microbiological in origin; a product may become unacceptable as a
result of insect damage, drying out, discolouration, staling or rancidity
for instance, but by and large most food spoilage is a result of microbial
activity. Microbiological food spoilage can manifest itself in several
different ways, some of which often occur in combination. Visible
microbial growth may be apparent in the form of surface slime or
colonies, degradation of structural components of the food can cause a
loss of texture, but the most common manifestation will be chemical
products of microbial metabolism, gas, pigments, polysaccharides, off-
odours and flavours.
Spoilage is also a subjective quality; what is spoiled for one person
may be perfectly acceptable to another. The perception of spoilage is
subject to a number of influences, particularly social; foods acceptable in
some cultures are unacceptable in others. Some products such as well
matured cheeses and game birds that have been hung for extended
periods are esteemed by some people and highly objectionable to others.
Affluence is another contributory factor – many are not in the position to
be able to discard food due to some slight sensory defect. In the 18th and
19th century navy, sailors often preferred to eat in dark corners so that
they could not see the weevils and maggots in their food.