Distribution of Trypsin Inhibitors in Green Soybean(Edamame)during Cultivation

Abstract

Green soybean is widely consumed as "Edamame" (boiled green soybean)in Japan because of its characteristic taste and nutritional value. It is well known that mature soybean contains several kinds of trypsin inhibitors(TI), but a few paper were available about TI in green soybean. In order to know the changes of TI activities in green soybean during maturation, soybeans were harvested periodically from the plants cultivated for 111 days to 165 days. The results are as follows; (1)TI activity was not observed within 116 days of cultivation. TI activity was found in the soybeans harvested from 123 day-old plants. TI activity in the soybeans was measured during cultivation from 123 to 165 days periodically. The maximum TI activity was determined to be 17.9mg/g of fresh weight and specific activity was 168 in green soybean picked from 137 day-old plants seed length, 1.2-1.4cm. TI activity in green soybean increased with the growth of seeds; TI activity of green soybean of seed length 0.8-1.0cm was only 6.9mg/g of fresh weight, whereas, that of seeds of 1.0-1.2cm length was 14.7mg/g of fresh weight. (2)TI in soybean was fractionated by chromatography on columns of Sephadex G-75 and DEAE-cellulose. (i)TI in green soybean of seed length 1.2-1.4cm was separated into 4-6 TI peaks on Sephadex G-75 and main inhibitors were No.3 and No.4 peaks. TI activity ratio of No.3 and No.4 to total TI activity increased with cultivation period. TI in green soybean of short length(less than 1.2cm)was fractionated into six peaks and main inhibitors were also No.3 and No.4 peaks. (ii)TI of No.3 and No.4 peaks obtained by gel-filtration were further fractionated with a DEAE-cellulose column, The number of TI peaks in same length seeds tended to decrease with cultivation days. TI in the seeds of same size(1.2-1.4cm length)picked from 123, 159 and 165 day-old plants had 7, 5 and 4 peaks by column chromatography on DEAE-cellulose, respectively. (3)Changes of TI activity in green soybean by heating were also investigated. TI activity in green soybean obtained from local market was 19.7mg/g of fresh weight and decreased slightly to 13mg/g of fresh weight by the heat treatment at 100°C for 5min. TI in this heat-treated green soybean was fractionated into 9 peaks on Sephadex G-75.