Study On Mechanical Damage Mechanism And Effect Evaluation On Storage Of Korla Fragrant Pear

Korla fragrant pear is the pillar fruit industry in the southern Xinjiang area.The mechanical damage caused by the various processes in the post-harvest processing of fragrant pears will aggravate the deterioration of fragrant pears,cause fragrant pears to rot,and reduce the commercial value of fragrant pears.Reducing the mechanical damage of fragrant pear and the loss of storage rot has become an important problem to be solved urgently in the fragrant pear industry.Investigating the cause of mechanical damage of fragrant pears and its influence on the storage of fragrant pear can provide guidance for the loss of post-harvest processing and the reasonable regulation of post-harvest processing conditions,and promote the development of fragrant pear industry.The objective is to study the mechanism of mechanical damage and the effect of damage on storage of Korla fragrant pear.Mechanical damage test bed is built.The maturity quantitative model of Korla fragrant pear is established.The damage area change law of fragrant pears under static pressure,impact,vibration and combined loads are studied,and the external characteristics and microcosmic characteristics of damaged fragrant pears are analyzed.Effects of maturity and loading on mechanical damage of fragrant pear are revealed.Non-destructive testing techniques based on electrical characteristics is used,studying the changing laws of the electrical parameters of pear under different loads,constructing a mathematical model of the relationship between electrical parameters and damage area,and using the Critic objective weighting method to determine the optimal electrical parameters combination to evaluate of the damage degree.To clarify the impact of fragrant pear damage on storage,three modeling methods of BPNN,GRNN and ANFIS are used to predict the shelf life of Korla fragrant pear.The main conclusions of this study are given as follows:(1)The maturity quantitative evaluation model of Korla fragrant pear is established.The quality comprehensive index and accumulated temperature of Korla fragrant pear have a stable change rule,and the relationship between quality comprehensive index and accumulated temperature conforms to Sigmoidal model.The maturity quantitative model was determined based on Sigmoidal model,and the RMSE is 2.28 between the predicted maturity and the true maturity.The results showed that the maturity quantitative model could accurately evaluate the maturity of fragrant pear.(2)The influence mechanism of maturity and loads on mechanical damage of Korla fragrant pear is clarified.The interaction between vibration and impact can inhibit the damage of Korla fragrant pear.The mathematical relationship between the magnitude of loads and the damage area of Korla fragrant pear is consistent with the quadratic function,and the established models can describe the law of the influence of maturity and load action on the damage degree.Scanning electron microscopy is used to confirm that whatever the type of loads,the damage mechanism of fragrant pear is characterized by collapse and folding of microscopic tissue cell structure,and the relationship between the damage degree and collapse and folding of the cells microstructure is direct proportion.(3)A quantitative evaluation method for damage degree of Korla fragrant pear based on electrical characteristics is proposed.The mathematical relationship between electrical parameters and damage area of Korla fragrant pear under different loads is consistent with the quadratic function.The established models can describe the laws of parallel equivalent capacitance(Cp),parallel equivalent resistance(Rp)and complex impedance(Z)with damage area.Rp at the frequency of 100 Hz has the best effect on evaluating the damage area under static pressure,Z at 1kHz has the best effect on evaluating impact damage area,Rp at the frequency of 1 kHz has the best effect on evaluating the damage area of vibration.Cp at 1 MHz is the best for evaluating reloading damage.The radiographic detection technology combined with the electrical characteristic technology can realize the quantitative evaluation of the damage degree of Korla fragrant pear and identify the damage site.(4)The effects of damage degree,storage temperature and maturity on the shelf life of fragrant pear are revealed.The shelf life prediction model of fragrant pear is established based on neural network modeling method.The ANFIS model with input membership function of psigmf is used to predict the shelf life of Korla fragrant pear,and its prediction performance is the best(RMSE=3.56;R~2=0.9912).