Technology of Forage and By-Products Preservation
2. Principals of food/feed preservation
Actually, there is no basic difference between the technological principals of preservation of food and of feed; the chemical and microbiological principals are the same. To preserve food/feed it is necessary to create conditions (an environment) that preserve the nutritive values and texture of the product that render it suitable for feeding. The longer it is intended to preserve the product, the greater is the necessity to apply special techniques. Preservation technology can minimize losses, but cannot eliminate them.
Basic measures to preserve any kind of a fresh product it is necessary to apply two basic measures:
- To prevent the activity of the enzymes present in the product.
- To protect the product from "external deterioration factors" such as bacteria, molds, yeasts, insects, rodents, etc.
Enzymes
An enzyme is a chemical substance produced by certain living cells (fauna and flora), which, without being changed itself, can elicit or enhance chemical changes in plants or animals. Regarding their relevance to preservation, many of the enzymes found in food cause decomposition, e.g., protease decomposes proteins, amylase decomposes starch, lipase decomposes fats, and respiration enzymes decompose sugars, etc. The common effect of all enzyme activities with respect to preservation is negative.
Enzymes are sensitive materials, and their activity can be eliminated by controlling: temperature, osmotic pressure, pH, and/or moisture content. The following are some examples of food preservation methods based on various technologies for eliminating enzyme activity and so preventing deterioration of the product.
Drying
This changes the osmotic pressure and water activity, suppresses enzyme activity and protects the product against attack by bacteria, yeasts and molds. Examples of applications include grains, seeds, hay, straw, etc.
Salting
This changes the osmotic pressure, suppresses enzyme activity and protects the product against attack by bacteria, yeasts and molds. Examples of applications include fish and meat.
Sweetening
This changes the osmotic pressure, suppresses enzyme activity and protects the product against attack by bacteria, yeasts and molds. Examples of applications include the use of honey, sugar, molasses, jam/jelly making, etc.
Freezing
This reduces enzyme and microorganism activities. Examples of applications include fish, meat, vegetables, etc., which will be safe as long as they remain frozen.
Radiation
Such as radioactivity and microwaves - this suppresses enzyme activity. The products will remain good as long as they are not contaminated again.
Changing the pH
As in pickling and ensiling - this protects the products as long as the pH remains low.
This booklet will focus on the preservation of forages and by-products by the application of ensiling and drying technologies; it will include consideration of dry matter losses related to preservation technology.
