The assay for the total activity of peptidase (TPase activity) in Sake koji using rice protein as a substrate

Abstract

We examined the assay for the total activity of peptidase (TPase activity) in Sake koji using rice protein which mainly contained glutelin as a substrate.
The rice protein used as a substrate was prepared from polished rice powder by extraction with 0.1 M lactic acid and isoelectric point precipitation. In this method, amino acid produced from the substrate by the total activities of peptidase was measured by a ninhydrine method as arginine content.
A positive correlation was recognized between TPase activities and amino acid produced from steamed rice digestion by the Koji enzyme extract. This correlation was higher than that between acid carboxy peptidase (ACPase) activity as the standard method. Because the substrate of ACPase activity was Cbz-Glu-Tyr, the assay for ACPase was evaluated as amino acids produced by specific peptidase hydrolyzing the synthetic substrate. On the other hand, because the substrate of TPase activity was rice protein, it was indicated that the assay of TPase precisely evaluated total amino acid produced by the proteolytic digest of rice during Sake production.