Changes in Mechanical and Microscopic Properties of a Soybean Seed during Experimental Natto Making Process

Abstract

Changes in mechanical properties of a sample soybean seed during experimental Natto making process were studied from a histological standpoint. The process for Natto making was partitioned into soaking, autoclaving, fermenting and aging operations by which physical structures of a soybean seed were influenced. The hardness of the sample soybean was drastically changed by the autoclaving operation in which decrease of autofluorescent brightness of the soybean tissue was observed by autofluorescent stereo microscopy. However, the tissue microstructure visualized by the SEM was not obviously changed in the autoclaving process. As a result, it seemed that some compositions, which should influence hardness and autofluorescent properties of a soybean seed, were eluted from the tissue by the autoclaving operation. Shrinkage of an internal structure in a cell matrix, which should be resulted from protein decompositions by a protease reaction, was observed during fermenting and aging processes. As a result, a gap in a cell matrix increased and it was thought that the gap should also have relations with a slight decrease of hardness of sample soybeans. An observation of microscopic structures of a soybean seed during Natto making process has potential for studying manufacture of Natto.