Effect of Sun Exposure on the Color of Salted Ume Fruit

Abstract

Ume fruit was brined with 0, 0.3, 0.6 and 0.9% (based on fruit weight) calcium hydroxide for 36 days and subsequently exposed to the sun for 8 days. The water content and titratable acidity decreased, and the sodium chloride concentration increased in the fruit from all lots during brining. During exposure to the sun while immersed in water with a film package, the sodium chloride concentration and titratable acidity both decreased, and the water content increased in the fruit from all lots. The L- and b-values of the fruit surface decreased, the a-value increased, and the chlorophyll content decreased markedly in the first 3 days in the fruit from all lots during brining. The L- and a-values increased after sun exposure, these values being larger with increasing calcium hydroxide concentration. The ‘lightness’ and ‘redness’ of the sun-exposed ume samples were evaluated according to a 7-level numerical scale in comparison with the brined ume samples with the same calcium hydroxide concentration, and the result was subjected to the t-test. A significant difference between these two groups was at the level of p<0.001 with every calcium hydroxide concentration. The sun-exposed ume samples were lighter and redder than the brined ume samples. The ‘redness’ could be discriminated at the significance level of p<0.01 between paired samples, except with a 0.6-0.9% calcium hydroxide concentration in the brined ume sample and 0.3-0.6% in the sun-exposed ume sample. A coefficient of correlation between the scale of ‘redness’ and the hue value was recognized with r=−0.915 and r=−0.947 (both p<0.05) for the brined and sun-exposed ume samples, respectively. It was confirmed that the ‘redness’ was increased by sun exposure after brining and, furthermore, the hardness was unchanged by sun exposure. Consequently, it is suggested that the sun-exposure step can be introduced into the salted ume processing in order to intensify the red coloring.