Non-destructive Testing Of Ripeness Of Hami Melon Based On Acoustic Property

Melon is one of the characteristic fruits of xinjiang.Recently,the larger difference exists in internal quality because farmers occupy the market by cultivating early and using ripening agent.This situation had led a serious decline in commodity rate and reputation of pear.Therefore,there is a highly required to non-destructively detect ripeness of melon.For this situation,an acoustic setup constructed with a hammer and a microphone,respectively operated as exciter and sensor,was developed.Meanwhile,the stabilities of experimental device were test and investigated the influence on response parameters to melon under different excitation conditions.Then,the optimum testing conditions was determined.Frequency response parameters were extracted to calculate elastic index and damping ratio of melon.Detection model of melon ripeness based on index calculated by frequency response parameters and band magnitude parameters was constructed.The results proved that it could provide theoretical support for non-destructively detecting of ripeness of melon using acoustic response method.The main contributions of this research are as follows:(1)The differences of the resonance frequency measured from same point with repeated excitation and different sensing points at the melon equator were not significant(P>0.05).The results of test condition showed that the resonance frequency was not affected by the material of hammer and exciting force(P>0.05).While a test condition with a rubber hammer at 8 to 12 N indicated that the acquired response signal was stronger and more easily extracted.(2)Melon firmness can be assessed by elastic index combined with damping ratio and the correlation coefficient(r)of constructed detection model reached 0.913.The sensitivity of this model was 68.99%,and was very similar to that of M-T test(69.79%).The soluble solids content of melon can be estimated by damping ratio and the correlation coefficient(r)of constructed detection model was 0.834.The sensitivity of this model was 46.43%,and was very similar to that of refractometer test(69.79%).(3)Seven band magnitude parameters and sum of these could be extracted in40~200 Hz of frequency domain response signal.These eight band magnitude parameters not related to the soluble solids content of melon analyzed by PCR,while related to melon firmness.The PCR ripeness detection model based on eight band magnitude parameters and mass of melon was established.The correlation coefficient for calibration set(rc)and validation set(rv)of model were 0.891 and0.795,respectively.The root mean square error of calibration set(RMSEC)and validation set(RMSEV)were 1.04 N/mm and 1.24 N/mm,respectively.The results showed that this model was stable and reliable.The detection sensitivity of this model was 67.70%,and was suitable for non-destructively detecting of melon firmness.Nonetheless,the results lower than firmness detection model based on elastic index combined with damping ratio.