New Star Software Collection/NSS_Collection.iso/3-251 oo2 english program/1.ima/RR.ZIP/PSPOILAG.SEQ

Text File | 1991-06-30 | 3.4 KB | 64 lines

In order to maintain our health, we all need a regular intake of
food, and this diet should be balanced. A balanced diet has
vitamins obtained from fruit and vegetables, protein from meat,
milk and fish and carbohydrates from grain crops. Ideally, all
the food we consume should be fresh, since fresh food has a high
nutrient value, but obviously there are problems in doing this.
The growing and gathering of crops, for example, is a seasonal
occurrence, whereas our food requirements are continuous. In
addition, food must often be transported for days or even weeks
before it reaches the markets where it is sold. If there were no
effective methods of preservation, much of the food produced
throughout the world would spoil. The consequences of so much
spoilage would be unbalanced diets, food shortages, and hunger
on a massive scale.

Spoilage is a natural process. It occurs in animal and vegetable
tissues almost as soon as their life source has been cut off. In
normal conditions, meat and some fruits decay within hours,
whereas grain and nuts may last considerably longer. The process
of decay is accelerated not only by certain protein-like enzymes
already present in the food tissues, but also by the arrival and
subsequent growth of microorganisms such as moulds, yeasts and
bacteria.

These microorganisms are foreign to the animal and plant tissues
which they enter. They live in the air, soil and water of our
environment. There are probably billions of them on your hands
and on the page of the book you are now reading. In order to
live, grow and multiply successfully on our food, these
microorganisms have certain environmental and nutrient
requirements. They need moisture, warmth and, in most cases,
oxygen. In addition, the food cells they enter must be able to
offer them some source of energy, for example sugar, without
which these microorganisms cannot develop.

We can illustrate the activity of moulds, yeasts and bacteria by
describing what happens to an apple that falls to the ground.
The fall damages the apple's skin and causes slight cuts in its
cells. Through these tiny openings, the millions of
microorganisms in the soil now enter to feed on the plant
tissues. The moulds and yeasts are well suited to the slightly
acidic, juice of apples. While the moulds slowly spread from
cell to cell, using the sugar they consume to grow new tissues,
the yeasts enter the damaged part of the apple, converting the
sugar there into alcohol. This alcohol then attracts certain
varieties of fruit-fly which are carriers of bacteria. The
bacteria begin to develop in the decaying tissues, using up the
alcohol as they do so.

Within days, the main structure of the apple is gone. It has
been consumed to generate new mould, yeast and bacteria cells.
All that remain are seeds, from which a new apple tree may
eventually grow, and cellulose (C6HlOO5). Rain gradually pushes
the cellulose down into the soil where anaerobic bacteria, those
not requiring oxygen, convert It into other substances, such as
carbon dioxide, ammonia (NH3) and mineral elements. This same
process of decay occurs in animal tissues as well, although the
microorganisms involved are different.

Food that is spoilt cannot give us all the nutrients we need for
a healthy life. Worse, it can make us ill or even kill us. Our
food preservation methods either prevent the further growth of,
or destroy, the micro organisms which cause food spoilage.