Chemical structure and gelation characteristics of a purified gel derived from sword beans ().

Herein, a new method was developed to obtain a crude extract from sword beans at a higher extraction efficiency. The crude extract formed a gel at 8 °C, which melted at 70 °C, and lyophilization of the purified gel produced a powder that could be dissolved in distilled water at a concentration of 7 % (w/w) or less. A 3 % powder solution gelled at 12 °C and melted at 60 °C. The infrared spectrum of the gel powder was consistent with that of starch. Furthermore, a 4-aminobenzoic acid ethyl ester-labeling analysis revealed that glucose was the constituent sugar in the powder, and the powder solution reacted strongly in a starch-iodine test. These observations confirmed that the gelling substance was starch. However, the melting and gelling temperatures were dissimilar to those of other starches frequently used in the food industry. Thus, our results provide valuable information for using sword bean starch as a novel food material.