Abstract
Green soybeans (Glycine max merr.) are harvested in the pod stage and the somewhat still immature seeds are eaten as a snack or vegetable. The taste of the beans deteriorates very rapidly after harvest, which preceeds the loss of visual quality.
This study was carried out to clarify the optimum harvest maturity, and to find the practical measures of maintaining high quality after harvest. The quality of green soybeans available in the market was also surveyed.
Since the contents of sugar, free amino acids and ascorbic acid decrease rapidly at the late stage of maturity of soybeans, the optimum harvest period was estimated to be 30-36 days after anthesis, a little before the maximum growth of beans.
When the soybeans were picked at the optimum period and stored at 20°C, total ascorbic acid content decreased rapidly in 3-4 days after harvest. The contents of total sugar and free amino acids, the main taste constituents, decreased more rapidly and showed a marked reduction even 1 day after harvest. These changes were considerably retarded when the beans were stored at 1°C.
The effect of hydro-cooling immediately after harvest was examined. The pods were im-mersed in ice water for 2 hr, and then stored at 20°C. The effect of the treatment for keeping quality was not obvious in the materials harvested at the optimum maturity. In the soybeans harvested at a later stage, however, a marked effect was found in keeping the total ascorbic acids, total sugar and free amino acid contents.
Among the soybeans purchased from various retail stores, wide differences were found in external appearance, contents of constituents and price. According to the constituents in all the materials tested, it was supposed that a number of days had elapsed since the soybeans were harvested so their taste had already deteriorated markedly.
