Changes Occurring in the Proteins as a Result of Processing Groundnuts under Selected Industrial Conditions

With increasing production of edible groundnuts, conservation of the nutritive value of the meal gains in importance.Much information is available concerning the optimal conditions for producing meals of good quality from soya beans and cottonseeds but, hitherto, comparable experiments on groundnuts have not been reported.Soya beans and cottonseeds contain only about 20 "/b of oil and can therefore be efficiently expelled, pressed or solvent-extracted in one operation.This is not so with groundnuts, which contain about 50 7; of oil and must therefore be expelled in at least two stages.In each of these a 'cooking' operation is followed by pressing or solvent extraction.Thus groundnut meal is usually subjected to much more severe heat treatment than soyabean meal or cottonseed meal.The fundamental issue is the effect of the treatment applied to extract the groundnut oil on the nutritive value of the protein-rich residue.Some heat treatment is beneficial because sulphur-containing amino-acids are made available and bound biotin is set free.Furthermore, it is very probable that a trypsin inhibitor present in the untreated nuts is destroyed by heating.Exposure to higher temperatures (especially in the presence of steam) significantly reduces the nutritive value of groundnut protein.The purpose of the present paper is to give evidence in support of the above statements. Previous work on the effect of heat on proteinsSeegers & Mattill (1935) and Fixsen (1934-5) reported decided decreases in nutritive value when casein, meat, liver, kidney, heart, cereals and fish meals were heated to high cooking temperatures for a long time.On the other hand, Osborne & Mendel (1917) and Shrewsbury, Vestal & Hauge (1932) found that heated soya beans brought about a definite improvement in the grow-th of animals previously given a similar diet containing 'raw' soya beans.Both groups of workers showed by experiments on rats that heating increased the palatability and the nitrogen absorption.The true digestibility coefficient was raised by about 4y0.Johnson, Parsons & Steenbock (1939) observed that the amount of nitrogen absorbed by the rats was almost the same from raw and from heated soya beans but the nitrogen retention was higher with heated beans.Only I I yo of sulphur was retained from the raw beans as compared with 25 "/o from the heated beans.The difference led the authors to conclude that cystine exists in the raw soya beans in a bound form but, after heat treatment, becomes available to the animal.