Influence of ultrasonication on functional components and tissue structures of seed coat powder of adzuki beans

Abstract

For the purpose of utilizing the seed coat, a by-product of Adzuki bean jam production, as a food material, the drying and milling of the seed coat, then the seed coat refined with or without ultrasonication (pastes), their respective color tone, proximate component, dietary fiber, mineral components, free amino acids, polyphenols and tissue structures were compared and discussed.
The average yield of the seed coat powder was 31.2%. The capacity for water-holding and oil absorption of the seed coat powder was 3 times and 1.6 times higher than soft wheat flour, respectively. The protein, lipid and ash of the seed coat powder refined by ultrasonication slightly decreased, but the carbohydrate and total dietary fiber relatively increased. There was no significant difference among the 9 kinds of minerals, free amino acids and polyphenols. The tissue observation by scanning electron microscopy indicated clearer depressions and winkles on the surface of the seed coat powder treated by ultrasonication compared the unrefined seed coat powder, proving the refining effect of ultrasonication. As a result of a sensory evaluation, a 15-minute ultrasonic cleaning removed any unpleasant odors from the seed coat powder, and the red tint became even darker.