Amino Acid Profiles of 44 Soybean Lines and ACE-I Inhibitory Activities of Peptide Fractions from Selected Lines

Soybeans are cultivated in the United States chiefly for cooking oil, while the residue after oil extraction (soybean meal) is mostly used in animal feed formulations. High protein content in the defatted soybean meals led to the extraction of pure protein and its application in food products. We selected 44 soybean lines to determine their moisture and protein contents, and their amino acid composition was investigated. Soybean lines with high protein content, one high yielding (R95-1705), and two high oleic acid (N98-4445A, S03-543CR), were selected for protein isolate preparation, hydrolysis using alcalase and gastro-intestinal (GI) resistance. Furthermore, the GI resistant hydrolysates were fractionated and tested for angiotensin-I-converting enzyme (ACE-I) inhibition activity. The amino acid analysis showed high methionine in the high protein and fatty acid lines (R05-4494 and R05-5491), and high cysteine content in one of the high oleic acid soybean line CRR05-188 in comparison to the check lines (UA-4805 and 5601-T). The protein isolate with the highest purity (90-93 %) was derived from the selected lines N98-4445A and S03-543CR, and hydrolyzed using alcalase enzyme. The protein hydrolysates (500 A mu g/mL) showed inhibition of the ACE-I by 49 %. The results from this study will promote the use of high oleic acid soybeans as a source of protein and peptides with functional activities.