Study On Acoustic Vibration Nondestructive Testing Method For Internal Quality Of Kiwifruit

Kiwifruit is a very important part of fruit industry in China,with the largest planting area and output in the world.However,the rapid detection and classification ability of Kiwifruit in China is backward,fruit quality is uneven,value-added space is low,market competitiveness is weak.Therefore,it is necessary to find a fast and accurate nondestructive testing method to realize the quality inspection of Kiwifruit.Kiwifruit is a kind of respiratory climacteric fruit.As the fruit matures,the hardness of fruit decreases and the content of internal quality index changes.Acoustic nondestructive testing technology is used in this paper.Through testing the internal quality of Kiwifruit,the change rule was explored,the dynamic model of quality index was built.A non-destructive testing platform based on acoustic vibration characteristics was built,to study the impact of different test points and fruit weights on Kiwifruit vibration signal acquisition.The prediction model of hardness based on resonance frequency and elastic index was built,compare the results of different prediction models after correct and optimize,the better prediction model of hardness was obtained.The research results are as follows:(1)The construction of indexes quality changes by dynamic modelUnder room temperature and 8?,there is a very significant linear relationship between the storage time and each index.The higher the storage temperature is,the faster the change rate of each index is.The hardness,Vitamin C content,L~*value and cellulose content of Kiwifruit decreased with the increase of storage time,while the weight loss rate,a~*value,b~*value,?E value and C value increased with the increase of storage time.The internal quality indexes of Kiwifruit were fitted by zero-order and first kinetic model and Weibull model,the results show that Weibull model has the best fitting effect.The R~2 of weight loss rate,hardness,a~*value,b~*value,L~*value,?E value,C value and cellulose content is 0.980?0.997?0.983?0.975?0.986?0.969?0.990?0.992 under room temperature;0.974?0.979?0.979?0.910?0.998?0.840?0.988?0.990 under 8?.According to sensory evaluation and Weibull model,when the hardness of Kiwifruit pulp is 2.58 N at room temperature,and 4.26N at 8?,it is not recommended to eat.(2)The construction of a non-destructive testing platform by acoustic vibrationA non-destructive testing platform based on acoustic vibration characteristics of Kiwifruit was built to collect vibration response signals of Kiwifruit by use DFT5004 and DFT6000.During the test,adopt Fast fourier transform,sampling frequency is 2000 Hz,data length is 2048,spectral lines is 800,overlap rate is 20,the average method is linear average,20 on average.Different weight and different test points had no significant effect on vibration response frequency.(3)Establishment of prediction model of Kiwifruit hardnessUnder different storage conditions,taking the vibration frequency and elastic index of Kiwifruit as independent variables,hardness as dependent variable by using SMLR,Single linear regression and PLSR method to construct Kiwifruit hardness prediction model.Optimize and determine the number of characteristic frequency to participate in the modeling.The model by PLSR and SMLR got the same better results.r_c=0.983,REMSEC=0.664 N;r_p=0.929,REMSEP=1.412 N,REMSE is decreased under the room temperature.r_c=0.980,REMSEC=0.681 N;r_p=0.961,REMSEP=0.904 N,r decreased by1.94%,REMSE is also decreased under 8?.The results show that it is feasible to use acoustic vibration non-destructive testing technology to judge the internal quality of Kiwifruit.