Hironori Masui

Subunit Structure and Functional Properties of the Predominant Globulin of Perilla (Perilla frutescens var. frutescens) Seeds

Approximately 40% of defatted perilla seeds consists of proteins which are primarily composed of globulin (84%). The amino acid profile of perilla proteins demonstrated balanced amounts of all essential amino acids, except for lysine. The molecular mass of the predominant globulin was estimated to be 340 kDa by gel filtration. This globulin was separated into three intermediary subunits (54, 57 and 59 kDa) by SDS–PAGE. It is suggested from these results that the globulin exists as a hexamer. A treatment with 50 mM dithiothreitol enabled the intermediary subunits to be separated into three acidic subunits (31–34 kDa) and four basic subunits (23–25 kDa). It is interesting that this subunit structure is the same as that of sesame α-globulin, despite them coming from different families. Compared to sesame α-globulin, the heat-induced gel of perilla globulin had better water-holding ability, despite it displaying the same degree of gel hardness.

Reducing-agents-mediated Solubilization and Activation of Debranching Enzyme (Pullulanase) in Rice Flour

The effects of reducing agents on solubilization and activation of the debranching enzyme (pullulanase) were examined using rice flour. The activity of the debranching enzyme was observed in a buffer solution (pH 7.5) in which rice flour was incubated together with thiol-reducing reagents, (dithiothreitol, 2-mercaptoethanol etc.), but there was only low activity in the absence of reducing agents. Immunochemical measurement and the specific activity of the enzyme showed that the activation caused by the reductant was due to solubilization of the enzyme protein besides the enzyme activation.

Precipitation of sword bean proteins by heating and addition of magnesium chloride in a crude extract.

Sword bean (Canavalia gladiata) seeds are a traditional food in Asian countries. In this study, we aimed to determine the optimal methods for the precipitation of sword bean proteins useful for the food development. The soaking time for sword beans was determined by comparing it with that for soybeans. Sword bean proteins were extracted from dried seeds in distilled water using novel methods. We found that most proteins could be precipitated by heating the extract at more than 90 °C. Interestingly, adding magnesium chloride to the extract at lower temperatures induced specific precipitation of a single protein with a molecular weight of approximately 48 kDa. The molecular weight and N-terminal sequence of the precipitated protein was identical to that of canavalin. These data suggested that canavalin was precipitated by the addition of magnesium chloride to the extract. Our results provide important insights into the production of processed foods from sword bean. Graphical abstract

Network structure and forces involved in perilla globulin gelation: comparison with sesame globulin.

Scanning electron micrographs show that perilla globulin gel had a finer network structure than sesame α-globulin gel. The effects of various reagents on the gel formation and solubility of perilla and sesame gels were compared. The contribution of disulfide bonds to the formation and stability of perilla gel was greater than to sesame gel, despite having the same subunit structure.