Soybean peptide: optimal preparatory conditions, chemical and amino acid constituents

Abstract

The study investigated the optimal condition for preparing soybean peptide from soybean isolates using digestive enzyme systems, comprising pepsin, trypsin and α-chymotrypsin set at differentpH and temperatures. It was evaluated for closeness of characteristics to the control peptide (a TEK® oligopeptide, designated MSBP for the purpose of this study) which was a biotechnologically produced, sold and used in China. The study also investigated the nutrient and amino acidprofiles of the possible peptides produced. This study has demonstrated that peptides of biological activity could be prepared from unconventional sources and protocols. Based on the results of the sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) as well as the amino acid analysis carried out on all the 97 peptide samples prepared, including the control, the peptide, H8 was adjudged to have characteristics that were closest to that of the control peptide,MSBP. The peptide fractionation, molecular weight determination of the resolved bands, coupled with amino acid profiles, all supported the similarity of peptide H8 to MSBP. The sample H8 was prepared from protein isolate from dehulled, defatted soybean (DHSB) at the temperature setting of 42.5 o C and pH of 2.0 (pepsin), 7.5 (trypsin) and 8.5 (α-chymotrypsin). The residual moisture levels in the prepared peptides were far below the critical level above which samplesare most likely to undergo fungal attack, leading to unwholesomeness. In terms of the crude protein (CP) content, 60% of the peptides prepared from DHSB contained more than 90%, in CP values, compared to only 3% of the total sample size from defatted soybean (DFSB) with similarCP values. The amino acid analyses indicated that the sulphur-containing amino acids, namely methionine and cysteine were the most limiting amino acids relative to all the others.