β-galactosidase and its significance in ripening of "Saijyo" Japanese Persimmon fruit

The fruit extracts of ripening cv. Japanese Persimmon, "Saijyo", contained a number of glycosidases and glycanases. Among them, beta-galactosidase appeared to be the most significant, and the activity increased in parallel with tissue ripening. Persimmon beta-galactosidase was presented in at least three isoforms, beta-galactosidase-I (pI = 4.88), beta-galactosidase-II (pI = 6.76), and beta-galactosidase-III (pI = 7.05). beta-Galactosidase-III had exo-type galactanase activity, while the others did not. The activity of endo-type glycanases was a maximum in immature green or yellow fruits. The firmness of the pulp tissue decreased dramatically, and the amount of water-soluble polysaccharide (WSS) increased. The enzyme activities of exo-type glycosidases, especially beta-galactosidase, appeared maximal in mature red fruits. The amount of extractable pectin remained unchanged, although the galactose content of the high-molecularweight fraction in WSS decreased dramatically. These results suggest that the ripening of persimmon was caused by the solubilization of pectic polysaccharide by endo-type glycanases and digestion by exo-type glycosidases. beta-Galactosidase, in particular, seemed to play a major role in ripening the fruit.