Fundamental Study on Citrus Fruit Juice

IV. Changes in Viscosity of Juice during Fruit Development

Abstract

This study was conducted for two seasons in 1974 and 1975 during Satuma mandarin (Citrus unshiu MARC.) development to determine changes in the viscosity of the fruit juice, the relation between such changes and the morphological and the histological changes and the correlation between those variables for the fruit sampling dates.
(1) A certain pattern in the changes in viscosity of fruit juice was recognized during fruit development. This pattern was divided into three stages. Stage-1 was period of rapid increase in viscosity from early July to early August. This period corresponded with the first half of enlargment of fruit cells. Stage-2 was characterized by a period of considerable decrease in the viscosity of the fruit juice. This period agreed closely with the latter part of enlargment of cell in the fruit from early in August to the second part of September with Wase unshiu or to the second part of October with Futsu unshiu. The viscosity of the fruit juice was increased again slowly in stage-3 by the accumlation of sugar and the other materials. This period was regarded as the maturation period.
(2) The viscosity of fruit juice of Futsu unshiu was higher than Wase unshiu through the whole period. The viscosity of fruit juice with Wase unshiu and Futsu unshiu in the 1974 season was higher value than for the 1975 season. The difference in viscosity of fruit juice seemed to correspond with changes in meterological and the other enviromental conditions.
(3) In this experiment, the higher the viscosity of juice in the sampled fruit at the first date, the more its value was on the second date. Therefore, the correlation between the viscosity of juice in the sampled fruit on each date was analyzed. There was a high positive correlation between the viscosity of juice in the sampled fruit at the preceeding time and the latter time, for example the first time and the second time, the second time and the third time. The correlation coefficient of Wase unshiu and Futsu unshiu was above 0.8 through the whole period. The juice viscosity for sampled fruit at the end date of stages 1, 2 and 3 was positively correlated with the viscosity of juice in the sampled fruit on the respective preceeding date for a time internal in each stage and the greater the sampling period from the preceeding date to the end date was a shorter period of days, the higher their correlation coefficient was. Their correlation coefficent was significant at the 1% level.
From the experimental results described above, the changes in viscosity of fruit juice during fruit development was considered to be a useful index for determing fruit taste taste and producing sweet fruit.