Effect of processing on high-protein feedstuffs: A review

Abstract

Many potentially useful protein sources for animal feeding would remain unused if appropriate processing was not possible. One often-used process for plant and animal protein modifications is heat treatment. Although the usefulness of heat processing is unquestioned, it may be detrimental to protein utilization in simple-stomached animals. Feed proteins are highly reactive and during processing may undergo several types of changes. Of these changes the protein-reducing carbohydrates reactions and protein-protein interactions are the most important. These modifications in the chemical nature of feed proteins lead to losses in their nutritional value due to the combined effect of the destruction of certain essential amino acids and the reduction in amino acid availability, lysine being the most sensitive amino acid to nutritive damage. The loss of amino acid availability is due to the formation of cross-linkages which reduces the rate of protein digestion, possibly by preventing enzyme penetration or by blocking the sites of enzyme attack. The extent of heat damage to protein nutritional quality is a function of different processing conditions such as time, temperature, moisture content and presence of reducing substance; time being the most significant factor. The required information on the value of processed proteins can be better provided by direct measurements of the bioavailability of individual amino acids. It was concluded that changes in amino acid availability due to processing may have great nutritional importance, especially when the limiting amino acid in the protein in question, being the significant dietary source, may be limiting in the diet as a whole.