ANALYSIS OF VIBRATION CHARACTERISTIC OF 'HUANGGUAN' PEARS AND ITS RELATION TO FIRMNESS DURING STORAGE

Vibration characteristics of fruits are correlated with their mechanical and structural properties. In this article, the vibration characteristics of Huangguan' pears after a long period of low-temperature storage were detected by a laser Doppler vibrometer (LDV), and their relationship to firmness was investigated. A fast Fourier transform (FFT) algorithm was used to extract the vibration parameters, including second resonance frequency (f(2)), amplitude at f(2), and phase shift at 400, 800, 1200, and 1600 Hz' Pear firmness near the skin, in the middle, and near the core was measured by puncture test. In addition, the elasticity index (El), defined as f(2)(2).m(2/3), was calculated. The results showed that firmness maintained a relatively stable level, while f(2), El, and the amplitude at f(2) decreased and the phase shift at all selected frequencies increased gradually before day 24. None of the vibration parameters showed obvious relationships with pear firmness in the first 24 days. After day 24, pear firmness near the skin and in the middle declined gradually, while the vibration parameters exhibited a trend opposite to that which appeared before day 24, except for amplitude at f(2). In this period, pear firmness was correlated with vibration parameters, except amplitude at f(2), at the 0.01 level, and the highest correlation coefficient (r) was observed between f(2) and firmness near the skin (r = -0.7656). During the entire test period, no good relationships could be established between the vibration parameters and firmness. The results indicate that the LDV method might not be promising for measuring the penetration firmness of 'Huangguan' pears, but it was more sensitive to storage time than the puncture test.