Changes in anthocyanins, polyphenols and β-carotene in the manufacture of colored sweet potato miso

Abstract

Changes in anthocyanins, polyphenols and β-carotene in colored (purple or orange) sweet potato miso during production were investigated by HPLC. Acylated anthocyanins (YGM) of purple-fleshed sweet potato decreased after aging, while nonacylated and monoacylated anthocyanins, which were presumed to be the deacylated products of acylated anthocyanins, were increased. For the change in polyphenols, the disappearance of chlorogenic acid and the accumulation of caffeic acid was observed in both misos. Therefore, deacylation caused by koji-mold seems be the main change in anthocyanins and polyphenols during colored sweet potato miso production. β-carotene content of orange-fleshed sweet potato remained at 94.6% after aging, and appears to be relatively stable. In addition, DPPH radical scavenging activity of colored sweet potato miso and commercial miso was assayed and compared. Among the miso samples, the radical scavenging activity of purple-fleshed sweet potato miso was especially high, and its activity became slightly higher compared with the mixture of the ingredients. However, the composition of elements with radical scavenging activity was greatly changed, and the proportion of caffeic acid in total radical scavenging activity increased. These results suggest that the absorption of colored sweet potato miso compounds after ingestion is changed by fermentation and aging.