Study of soybean seed coat components and their relationship to water absorption.

The occurrence of hard or "stone" seeds in shipments of food grade soybeans can cause serious problems in processing, particularly in the preparation of fermented soy products. Climatic conditions during the growing season and as the seed matures may trigger the production of hard seeds. Total water absorption of soybeans is also a significant parameter in assessing quality for export markets. The seed coats of six varieties of soybeans, covering a wide range of water absorption and stone seed content, were analyzed for ash and cations, protein, lignin, and complex carbohydrates. The water absorption characteristics and macrochemical constituents of the whole seed were also determined. The results indicated that there was no correlation between the concentration of any of the cations and the occurrence of hard seeds. The results from analysis of the complex carbohydrates indicated there were differences in hemicellulose content of seed coat fractions, particularly xylans, that correlated with the water uptake ratio and the occurrence of hard seeds.