Correlation of Polyphenols, Pectin Substances and Antioxidant Activity of Persimmon Fruits (Diospyros kaki L.) According to Ripening Stage and Processing Conditions

Abstract

Persimmon (Diospyros kaki), a member of the Ebenaceae family, has been cultivated in Georgia since the 1950s, with an annual production of approximately 50,000 tons. Among the commercially important cultivars, the astringent 'Hachiya' and the non-astringent 'Hyakume' are predominant. Persimmon fruits are characterized by high nutritional value and are rich in bioactive compounds, particularly phenolic compounds and dietary fiber. The present study investigated the chemical composition and antioxidant capacity of 'Hachiya' and 'Hyakume' fruits at different stages of ripeness and after various pre-treatments (CO₂ exposure, freezing, and thermal treatment). The quantitative determination included sugars, total polyphenols, pectin substances, titratable acidity, vitamin C, carotenoids, cellulose, total nitrogen, and protein content. Significant variability in phenolic compounds and pectin fractions was observed during ripening and following pre-treatment. A correlation between pectin content and tannin-related astringency was established. During ripening, the formation of insoluble pectin–tannin complexes reduced the level of soluble tannins and consequently decreased bitterness. Antioxidant activity, evaluated by DPPH and ABTS assays, was strongly correlated with total polyphenol content. Overall, both ripening stage and pre-treatment significantly affect the chemical composition and antioxidant potential of persimmon fruits. Fruits at the technical ripeness stage represent a particularly rich source of polyphenolic compounds, especially tannins, which may largely determine the health-promoting properties of persimmon