Studies on Amino Acid Contents of Processed Soybean

Abstract

Effect of heating on the nutritive value of defatted soybean flour has been investigated by animal experiments. Loss due to heat degradation was evaluated in two ways. In the first method, the amino acids lost during overheating were supplemented by cystine and mixture of lysine, arginine, tryptophan, and serine at dietary levels of 1.6% nitrogen, and cystine and mixture of those amino acids plus histidine at dietary levels of 3.2% nitrogen. The other procedure adopted was the absorbent test used with amino acid mixtures based on the pattern of amino acids released by pancreatic hydrolysis of unheated, properly heated, and overheated defatted soybean flour at 6 and 120 hr hydrolysis.

At 1.6% dietary nitrogen level, the nutritive value of overheated soybean flour increased by supplementation with cystine and amino acid mixture, but at the 3.2% nitrogen level only cystine was effective. Supplementation of lost amino acids to overheated flour did not restore the nutritive value to that of the properly heated flour. Based on the amino acids released by pancreatic hydrolysis of unheated, properly heated, and overheated soybean flour after 6 and 120 hr reaction, amino acid mixtures were prepared and tested for their nutritive value. While the nutritive value of amino acid mixture prepared based on the pattern of amino acid liberated by 6 hr digestion of unheated, properly heated, and overheated flour did not show similar trend to that of 3 kinds of flour itself, the nutritive value of the amino acid mixture prepared after the data obtained by 120 hr digestion agreed well with the trend of unheated or heated soybean flour.

The nutritive value was also measured by the nitrogen balance of test animals.