Comparison of soluble sugar degradation in soybean seed under simulated tropical storage conditions

Storage of soybean [Glycine max (L.) Merr.] seed under tropical conditions can lead to deterioration that affects product taste and color. A study was designed to assess the effect of extreme storage conditions on the degradation of soluble sugars and to relate these changes to seed deterioration. Seed of six cultivars of soybean were stored for 9 mo. under control (4 degrees C, 45% RH) and simulated tropical (30 degrees C, 82% RH) conditions. Soluble sugar metabolism was monitored by high performance anion exchange chromatography coupled to pulsed amperometric detection (HPAE-PAD). Soluble sugar content was constant or only slightly affected under control conditions. However, substantial hydrolysis of stachyose, raffinose, and verbascose occurred under simulated tropical conditions. The resulting release of glucose and galactose, combined with the degree of hydrolysis of oligosaccharides, appears to be strongly linked to soybean seed quality as indicated by seed germination. Storage behavior was cultivar dependent, pointing to the importance of selecting cultivars for storability in tropical countries. Determination of glucose seems to be a sensitive analytical and practical tool for monitoring soybean seed quality and deterioration under extreme climatic conditions.