Abstract
The contents of pectic substances, metal elements, organic acid and the hardness of 'Takada bungo' plums (Prunus mume SIEB. et ZUCC.) were analyzed for about 1 month from the end of May to the beginning of July, 1987, and the results were investigated in relation to harvest time for the processing of the fruit into Ume-Zuke, or pickled plum. The results obtained were as follows: (1) The calcium content of ethanol-insoluble substances prepared from the plums changed little until the middle of June, but decreased gradually with fruit growth. (2) The ratio of HSP (hexametaphosphate-soluble pectin) to TP (total pectin) showed little change with fruit growth, but exhibited a decrease after the middle of June. On the other hand, the ratio of HWSP (hot water-soluble pectin) to TP changed little with fruit growth, but showed an increase after the middle of June. (3) Malic acid content of plums reached a maximum in the middle of June and decreased markedly with fruit growth, whereas the citric acid content of the plums increased gradually with fruit growth, followed by an appreciable increase after the middle of June. (4) Ume-Zuke processed using plums harvested after the last ten days of June had a softer texture. From these results, it was concluded that the increase in citric acid occurring during fruit growth gives rise to chelate binding of divalent cations combined with pectic substances, and that the release of these divalent cations, changing HSP to HWSP to some degree, consequently causes a decrease in the hardness of texture of Ume-Zuke.
