On the preparation of a soluble protein extract from soy beans

Abstract

The average protein content of the soy bean is 36.5 per cent. while that of the soy bean cake is about 41 per cent. The protein of the soy bean has all the amino acids necessary for nutrition and it is claimed to be as valuable as the casein of milk. The proteins of the soy bean, unlike those of other leguminous plants thus far investigated, were found, by Osborne and Mendel, to be adequate for promoting normal growth. In addition to the high protein content, the soy bean is found to contain an adequate amount of water-soluble vitamine and some essential fat-soluble vitamine. These factors combined with low cost make the soy bean of unique significance as a food.

In working with proteolytic enzymes of fungi, the author found some organisms that are able to develop active enzymes which readily hydrolize the soy bean proteins and make them soluble. By using the ground soy bean cake as a substratum for the growth of the proteolytic fungus, then, at the end of the proper incubation period, which is usually about 36 hours, adding water to the mass and allowing the enzyme present in the mycelium to act upon the soy bean proteins, over 50 per cent of the proteins are found to go into solution. This solution when concentrated gives a material containing 45 or more per cent of soluble proteins and protein degradation products and is quite rich in vitamines. This extract can be very cheaply prepared and it may take the place, when properly modified by the addition of necessary salts, of meat extract and other digested meats in infant feeding and, since the soy bean contains very little carbohydrate and even the small amounts present are used up by the fungus, in the process of development, for energy purposes, the extract is practically free from sugars and can be introduced into diabetic cookery.