Introduction

It is difficult to realize that, of the total amount of energy devoted to agricultural production, only a small fraction is harvested to be used directly or indirectly for animal and human feeding. Most of the energy is left behind, either in the field, in food processing factories, or feed lots. This unused energy has various forms, and is often of complex chemical composition. It may be biologically inert or highly active; it may be tough or very fragile, and susceptible to rapid deterioration. Most of the time these agricultural residues are a nuisance from the human point of view, for indeed, we call them wastes. There are many examples, but one that illustrates how wasteful agricultural systems can be is the growing of coffee. From 100 9 of dried fruit, only 12 g are actually consumed as solids to make about six cups of coffee (1). For most basic food crops, such as grains and food legumes, the harvest index is only about 0.50.

For various reasons, man is now learning to utilize such wastes, imitating the ways of nature to maintain ongoing biological cycles for the continuation of life in harmonious balance.

The term "waste" describes in a broad, non-specific way the raw material to be utilized, and it is because of its complexity, toughness, and general state that its use in bioconversion systems cannot at present, with a few exceptions, yield products that can be readily utilized directly by man. Therefore, it is difficult to talk about biological evaluation of the products of bioconversion for human use in the context of the raw material itself. It must first be processed. The only known exceptions are algae and mushrooms. This paper presents a discussion of methods used for the evaluation of unconventional products.