Characterization of biochemical and functional properties of water-soluble tempe flour

Characteristics of water-soluble flours from soy (SF), soy tempe (STF), and germinated-soy tempe (GTF) were compared with those of commercial soy protein isolate (SPI). Defatted flour of soy, soy tempe, and germinated soy tempe were extracted in alkaline water (pH 9) and freeze dried to produce water-soluble flours. Protein contents of SF, STF, and GTF were 49%, 47%, and 51%, respectively, and lower than that of SPI (84%). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles showed that STF and GTF contained lower molecular size of proteins compared to SF and SPI. Trypsin inhibitor activity was detected only in SPI. The most abundant phytic acid was contained in SF, followed in order of decreasing abundance, by SPI, STF, and GTF. Antiradical activities measured by DPPH assay also showed significant variations, and the activity was highest in GTF, followed in order of decreasing activities, by STF, SF, and SPI. The foaming and emulsion capacities of STF and GTF were significantly lower than SPI, but higher than SF. These data strongly suggest that STF and GTF have better functional characteristics than commercial SPI. However, optimization of the extraction process is needed to improve the yield and protein content.