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Mechanism and Pathway of the Water-Soluble Protein Hydrolysis under the Saturated Sub-Critical Water Condition

Wael Abdelmoez and Hiroyuki Yoshida. Center of Excellence Project at the Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Osaka, 599-8531, Japan

In the present work, the hydrolysis of water-soluble protein, bovine serum albumin (BSA), used here as a model protein, under the saturated subcritical condition (SSWC) in the range 200-300 oC was carried out. The products of the reaction were a water-insoluble solid phase and an aqueous phase. The results showed that BSA, under SSWC, passes through aggregation followed by gel formation process which resulting in the formation of insoluble solid aggregates. Then, BSA unfolded with releasing polypeptides as an intermediate product and finally low molecular weigh product such as amino and organic acids. The formed solids were found to be completely water insoluble with having many plastic properties. In our previous work we showed that the aggregation and gelation processes were enhanced dramatically under the SSWC to the limit that we were able to synthesizes a novel-protein based plastic with having a very strong polymer matrix using such formed solid aggregates.1 The present study provided more extensive analysis for the liquid phase for the sake of a primer understanding of the hydrolysis process. The results showed that the yield of the total organic carbon (TOC) in the liquid phase increases by the reaction time and reached a plateau after 10 min. Similarly, the yield of inorganic carbon (IC) increases by the reaction time but with a very high rate at higher temperatures. The time course of the concentration of amino acids in the aqueous phase produced during the SSWC reaction of BSA at four different temperatures, 200, 225, 275, and 300 oC for different interval times were presented. The results showed that there were almost no amino acids produced in the temperature ranges of 200-225 oC within 2 minutes and 275-300 oC within 0.5-minute. Subsequently, the amount of produced amino acids increased with the increase of reaction time with high concentrations at elevated temperatures. As a result of the amino acid decomposition, organic acids were produced and the yield of their productions increases with the increase of both reaction time and temperature. Among all produced organic acid, the pyroglutamic acid was produced with a very high rate up to a relatively long reaction time of about 40 minutes in the temperature range of 200-275 oC. Based on the obtained data it was possible to develop a general mechanism of the water-soluble protein hydrolysis under the saturated subcritical water condition.