Abstract
We investigated alternative portable methods to the rheometer in fruit firmness evaluation for high functional or aroma components of processed Japanese apricot liqueur (ume liqueur) of ‘Nanko’ Japanese apricot (Prunus mume Sieb. et Zucc.). Fruit firmness using the universal hardness meter showed a difference based on the harvesting time and fruiting position, although there was little difference using the rheometer. The elasticity index (EI) using the portable vibration hardness meter was also able to evaluate these differences as well as the universal hardness meter. EI was more significantly correlated with the rheometer than the universal hardness meter. There was little difference between EIs calculated based on the fruit diameter and mass. EI calculated by f22·d2 (Ed f2), where f2 was the second resonant frequency and d was the fruit diameter, showed a higher correlation with the firmness obtained from the rheometer than EI calculated by f32·d2 (Ed f3), where f3 was the third resonant frequency, in both developing and ripening fruit. Therefore, Ed f2 should be suitable for determining the firmness of Japanese apricot fruit as a substitute for the rheometer. The time of a sharp decrease in fruit firmness, the index of the time when functional components reached high levels in ume liqueur for the rheometer, was not detected by either the universal hardness meter or portable vibration hardness meter. However, the ume liqueur made from fruit with below 10,000 in Ed f2, 17,000 in Ed f3 or 2.2 kg using the universal hardness meter with a 3-mm-diameter cylindrical plunger, contained higher functional components. These results suggest that the portable vibration hardness meter is suitable for the nondestructive measurement of fruit firmness, and might be available for calculating the index of raw material fruit to process ume liqueur with high functional components or aroma components in Japanese apricot ‘Nanko’.
