Postharvest quality evaluation of “Fuyu” and “Taishuu” persimmons using a nondestructive vibrational method and an acoustic vibration technique

We investigated time-course changes in the elasticity index (EI) and texture index (TI) of two persimmon (Diospyros kaki   Thunb.) cultivars (“Fuyu” and “Taishuu”) during the postharvest period. EI was determined using the formula EI=f22m2/3, where f2 is the second resonance frequency of a sample, and m is the mass of the sample. A nondestructive vibrational method employing a laser Doppler vibrometer (LDV) was used for measuring the second resonance frequency (f2) of the persimmon samples. The changes in the EI of both cultivars showed quasi-exponential decays. An improved texture measurement device was used for measuring the TI of the cultivars. The TI was defined by (1/T)∑|Vi|(1/T)∑|Vi|, where T (s) is the sampling period and Vi (V), the amplitude of each data point. The pattern of time-course changes in TI differed between “Taishuu” and “Fuyu” persimmons; a sharp decline was observed in the TI of “Fuyu.” Along with the sensory test, we determined the optimum eating ripeness of persimmons in terms of their EI to be 2.9–6.0 × 104 kg2/3 Hz2 (“Taishuu”) and 4.8–6.4 × 104 kg2/3 Hz2 (“Fuyu”).