Chemical Characteristics of Tannins from Non-Astringent and Astringent Type Fruits of Japanese Persimmon (Diospyros kaki) with Particular Reference to Ultracentrifugal Behavior

Abstract

Schlieren pattern in analytical ultracentrifugation and reactivity to acetaldehyde of tannins of Japanese persimmon fruit (Diospros kaki) were investigated using cvs. ‘Fuyu’, pollination constant non-astringent (PCNA) type, and‘Hiratanenashi’, pollination variant astringent (PVA) type.
1) To study the schlieren pattern, tannins extracted from both cultivars with aqueous acetone were separated into two fractions (F-I and F-II) by size exclusion chromatography on CPG-10 2000Å. After the tannin concentrations were equalised, these fractions were incubated at 40°C and subjected to ultracentrifugation at pre-incubation (0 day), 1 and 3 days of incubation. The schlieren patterns revealed that F-I and F-II fractions from both cultivars contained three or four tannin components, and that the sedimentation coefficient of each component from‘Hiratanenashi’ was larger than the corresponding component from‘Fuyu’. Moreover, the components of the F-I fraction from‘Hiratanenashi’changed or shifted remarkably during incubation; two faster components (26S and 23S) disappeared and one slower component (6S) appeared. Conversely, the components of both fractions (F-I and F-II) from‘Fuyu’and F-II fraction from‘Hiratanenashi’were stable.
2) To characterize the reactivity of tannins to acetaldehyde, coagulation times of the fruit juice bathed in acetaldehyde vapor were compared between‘Fuyu’and ‘Hiratanenashi’at different tannin concentrations and pHs. A longer time was needed for coagulation as the tannin concentration became lower and when the pH value was between 3.0 and 5.0. The fruit juice from‘Fuyu’coagulated more slowly than that from‘Hiratanenashi’.
The present results suggest that tannin substances from‘Fuyu’distribute mainly in a lower molecular weight range and have a milder chemical property compared with those from‘Hiratanenashi’.