Effect of Storage Temperature on the Properties of Pectic Polysaccharides in Cotyledons of Adzuki Beans (Vigna angularis)

Abstract

Pectic Polysaccharides (HXSP, from uncooked cotyledons; HWIP, from cooked ones; HWSP, from the cooking soup) and hemicelluloses were prepared from Adzuki beans stored for two years at 5°C and 30°C, and the pectic preparations were fractionated into neutral (I) and acidic (II, III and IV) fractions by DEAE-cellulose chromatography. The acidic fractions from the beans stored at 30°C, as compared with those from the beans stored at 5°C, exhibited some different properties: First, the uronate contents were low in all the acidic fractions. Second, the relative amounts of III and IV considerably increased in HXSP and HWIP. Finally, the molecular sizes of III and IV except those from HWSP decreased to some extent, although the molecular size of II from HWSP greatly decreased even in the beans stored at 5°C when compared to a similar fraction previously prepared from HWSP of fresh Adzuki beans. In addition, the total amount of HWSP in the stored beans at 30°C was somewhat smaller than that in the beans stored at 5°C. Neutral sugar compositions of II, III, IV and hemicelluloses showed no significant difference between the two temperatures of storing the beans. The major neutral sugar constituent was xylose in II-IV and the xylose content increased with increasing their adsorptive activities on the DEAE-cellulose column. In particular, the fraction IV was adsorbed most strongly on the column in spite of its small molecular size and low uronate content, and exhibited the highest xylose content of more than 80%.