Detection and Cryoprotective Activity of Dehydrin Proteins from Rice Bran and Soybean Whey

Dehydrin proteins, group2 LEA proteins in rice bran and soybean whey were analyzed by two-dimensional (2D) electrophoresis, and the cryoprotective activity on freeze/thaw inactivation of lactate dehydrogenase was examined as a criterion of its function. Dehydrins in rice bran were detected by immunoblotting using antibody raised against a conserved lysine-rich motif sequence. In the water-soluble fraction of rice bran, 10 spots of 44 kDa and 23 kDa dehydrin-like polypeptides were detected on the immunoblotted membrane. Isoelectric points of the polypeptides were between 6.6 and 7.4. The 23 kDa dehydrin polypeptide was partially purified by ammonium sulfate fractionation and ion exchange column chromatography. CP₅₀ value, protein amount necessary to keep 50% of enzyme activity, of the 23 kDa dehydrin was 0.78 μM (15.6 μg/mL), slightly lower than that of bovine serum albumin. Heat-soluble soybean whey proteins were analyzed by SDS-PAGE and 2D-electrophoresis. Dehydrin appeared to be the most abundant protein in the fraction. CP₅₀ value for heat-soluble whey protein was estimated to be 15.8 μg/mL, while that of total whey was 355 μg/mL. The result indicated that simple heat fractionation is efficient to concentrate cryoprotective protein from soybean whey.