Hiroko Kimura

Comparative nutritional value for amino acids, oligopeptides and soybean protein

In recent years our view on the absorption of protein digestion products has undergone a radical change. We now believe that intralumen hydrolysis of intake proteins to free amino acids is only partial. It has thus been hypothesized that partial protein hydrolysates or oligopeptide mixtures are nutritionally superior to corresponding amino acid mixtures. With this consideration for a background, we developed a sophisticated technique of protease-catalyzed modification of soy protein to produce enzymatically modified proteins (EMP) having different levels of covalently attached methionine. We also carried out feeding tests with protein-malnourished rats, with the result that for their recovery from a state of malnutrition, an EMP containing peptide-bound methionine at 3% was significantly more effective than the corresponding amino acid mixture and even the soy protein itself. Discussions stress the importance of applying such a technique to production of an oligopeptide rather than a free amino acid nitrogen source as a foodstuff for therapeutic use.

Time-course characteristics for the digestion of endogenous as well as exogenous protein in the small intestine: a case study with rats fed a [15N]-soy protein isolate.

A study was conducted to evaluate a net value of exogenous (dietary) protein nutrition in rats fed a [15N]-labeled soy protein isolate (SPI). Although [15N]-SPI-derived nitrogen reached a plateau 2 hr after feeding, it accounted for only a half of the total nitrogen in the small intestine. 15N was confirmed that was normally transported to liver, kidney, spleen, and brain. The present study reveals the large degree of participation of endogenous proteins in dietary SPI during small-intestinal digestion.