Nondestructive Method for Measuring Fruit Ripening of ‘La France’ Pears Using a Laser Doppler Vibrometer

Abstract

The elastic index of ‘La France’ pears was measured during ripening by a laser Doppler vibrometer (LDV). Fruit were harvested thrice during the 1999 season. After harvest, samples of fruit were just allowed to ripen at 20°C. A portion of optimum-harvested fruit was stored at 1°C for 2 weeks or 1, 2 or 4 months and transferred to 20°C for ripening. The value for the elastic index of early-harvested fruit was 36.4 × 10⁵ Hz²·g^2/3 just after harvest; the values declined with a function of time. The elastic index of optimum-harvested pear showed a bi-phasic decrease, whereas that of late-harvested fruit exhibited a sharp decrease with a single-phase pattern as the fruit ripened. Storage reduced the elastic index and modified the decreasing pattern. Optimum-harvested fruit that were stored at 1°C for 2 weeks showed a slight bi-phasic decrease in the elastic index, whereas fruit stored for 1 or 2 months did not. Fruit stored at 1°C for 4 months showed the lowest initial value (4.3 × 10⁵ Hz²·g^2/3) and little decrease. The correlation coefficients between flesh firmness, measured by a conventional probe method and the elastic index, was significantly high, independent of harvest date or storage periods. The only exception was with fruit stored at 1°C for 4 months. These results indicate that ‘La France’ pear fruit exhibit bi-phasic decreases in the elastic index when they were harvested at optimum period and stored for periods up to 2 weeks; furthermore, fruit firmness of ‘La France’ pears is amenable to analysis by an LDV.