Abstract
To make clear the mechanism of natural removal of astringency in the fruits of pollination constant non-astringent (PCNA) type cultivars of Japanese persimmon, which is assumed quite different from that of pollination variant non-astringent (PVNA) and astringent (PVA) type cultivars, and pollination constant astringent (PCA) type cultivars, we studied preliminarily whether there exist any qualitative differences of tannins among the 4 types of Japanese persimmon fruits.
1. Catechin and gallic acid were major components of phenolics in ethyl acetate extract of fruits and their contents changed remarkably with time and fruit types. In PCNA cultivars, catechin was detected throughout the growing period of fruit, while gallic acid was detected only at the earlier stage. On the contrary, in PVNA, PVA, and PCA cultivars, catechin disappeared rapidly in June, whereas gallic acid increased greatly reaching the peak in late June, then declined toward late July to a very low level.
2. Exclusion chromatography using controlled-pore glass media (CPG-10 120Å and 2000Å) was applied to the separation of tannin fractions in aqueous acetone extracts of fruits. CPG-10 2000Å chromatography separated the tannins into two fractions with any cultivars, however, the comparative peak weights of the fractions of PCNA cultivars were quite different from those of PVNA, PVA, and PCA cultivars. In PVNA, PVA, and PCA cultivars, the high molecular fraction of tannins was predominant at an earlier stage of growth, whereas the low molecular fraction was predominant in PCNA cultivars, and its conversion to high molecular fraction seemed to be very slow. Moreover, this low molecular fraction of PCNA cultivars was detected throughout the course of natural removal of astringency.
