Research Of Apple Texture Based On Microstructure And Modal Analysis

The apple texture features are always used as basis for classification,processing,transportation and package,and are an important quality standard to determine the commercial values.The apple texture features are affected by the microstructure which is different among the variable apple cultivars.So,the morphology indices of the cell and pore in the mesocarp of Fuji,Golden Delicious and Jonagold were studied to analyze the difference of the microstructure,in order to explore the factors influencing the texture features in microstructure.In addition,the apple texture features are also affected by the vibration characteristics which could be used for texture evaluation.The experimental modal analysis was used to identify the dynamic properties of the Golden Delicious apples like natural frequencies to predict the texture features.The major contents and results of the studies are listed as follow:(1)The mesocarp microstructure of Fuji,Golden Delicious and Jonagold apples.The fluorescence images were acquired by confocal laser scanning microscopy(CLSM)for the mesocarp located at the equator of Fuji,Golden Delicious and Jonagold apples.It was found that the mesocarp cell area,circumference and feret diameter of the Fuji and Jonagold apples were not different significantly(p>0.05),but both of the Fuji and Jonagold were markably higher than the Golden Delicious apple(p<0.05).For cell solidity,it was shown that Fuji(0.9±0.0)= Golden Delicious(0.9±0.0)< Jonagold(1.0±0.0),reflecting that the cell of the Jonagold were the most circular and the connection between the cells in the Jonagold mesocarp was least.The area,circumference and feret diameter of the mesocarp pore of the Fuji apple was significantly lower than both of the Golden Delicious and Jonagold(p<0.05),while there were no pronominantly differences for the pore area,circumference and feret diameter of the latter two(p>0.05).Fuji apple(0.8±0.0)and Golden Delicious apple(0.8±0.0)were both signally higher than Jonagold apple(0.7±0.0)(p<0.05)for the solidity of the mesocarp pore.When the principal components analysis(PCA)was performed to reduce the dimensions of the morphology parameters,it could effectively classify the Fuji,Golden Delicious and Jonagold apples.(2)The relationship between the texture and microstructure of Fuji,Golden Delicious and Jonagold apples.The cylinder mesocarp samples were obtained from the equator location of the apple to be performed the puncture test and texture profile analysis(TPA)test.There were no observably differences in fracture force,fracture total work,crispness,cohesiveness,chewiness,resilience and initial elastic modulus between Fuji and Golden Delicious apple(p>0.05),but both of Fuji and Golden Dilicious apple were higher than the Jonagold(p<0.05).There were comprehensive influences of the cell and pore on the apple texture: the mesocarp became soft with bigger cells and pores;if there was no difference in cell size,the mesocarp became soft with bigger pores or plenty of bigger cells;when there was no difference in pore size,the mesocarp tended to be more hard with density distribution of cells.It was shown that the unary linear regression models for fracture force,hardness and initial elastic modulus with the pore solidity were performed better(R2>0.9,p<0.001).(3)The changes of the dynamic characteristics for Golden Delicious apples during storage.The impact modal analysis system was build to identify the dynamic parameters of Golden Delicious apples.During the storage in room temperature,the natural frequencies of the Golden Delicious apple changed from 103.2±25.3 Hz to 989.5±1.1 Hz,showing multiply natural frequencies and intensive modalities.It increased from 103.2±25.3 Hz to 146.7±14.1 Hz(p<0.05)and from 222.6±12.9 Hz to 250.5±13.9 Hz(p<0.05)for the 1st order and the 2nd order natural frequencies during the storage,respectively;while the natural frequencies from the 3rd order to the 11 th order all decreased during the storage,such as the natural frequency in the 3rd order decreased from 371.0±8.1 Hz to 346.3±15.7 Hz(p<0.05);lastly,the 12 th order natural frequency did not change during storage(p>0.05).Most natural frequencies were notably related with the apple sample mass and density,but not with the shape index from the Pearson comparison.Besides,the 1st order vibration mode was the flexural modality,the 2nd was the spherical modality,while the vibration modes from the 3rd to the 12 th were all compound modalities for the Golden Delicious apples.(4)The changes of the texture for the different tissues of Golden Delicious apples during storage.The puncture test was performed for the texture of the calyx,equator and stem part of the apple exocarp,and the compression test was used for the calyx,equator and stem of the mesocarp,respectively.The texture of the calyx,equator and stem location of the exocarp tissue of the apple samples changed dramatically(p<0.05),of which the yield gradient and the elastic modulus were all reduced by 50%,and the yield gradient was more sensitive to time evolution than the elastic modulus.The mesocarp texture varied in unconspicuous trends.Through the Pearson comparison,the yield gradient and elastic modulus of the apple exocarp dramatically correlated with multiply natural frequencies(p<0.01).(5)The regression prediction for the texture features of the different tissues for Golden Delicious apples.The natural frequencies,mass and density were used as interpretation variables,while the apple texture parameters(yield gradient and elastic modulus)were as response variables for multivariate regression models.It was shown that the partial least squares regression models and the support vector regression models were suitable for predicting the exocarp texture features but not for the mesocarp texture characteristics.The partial least squares regression models including natural frequencies,mass and density for exocarp tissue yield gradient and elastic modulus were the best regression models with all residual prediction deviation(RPD)more than 1.5.In this study,the microstructure parameters of the apple mesocarp were used to interpret the differences in texture features among Fuji,Golden Delicious and Jonagold apple,and providing the technology support for explaining the fruit texture quality from the microstructure perspective and for exploring the constitutive relation of the biomaterials.Moreover,the modal parameters of the Golden Delicious apples were identified by experimental modal analysis system to build the partial least squares regression models and support vector regression models to predict the texture parameters of the different tissues of the apple samples.It realized the connection between the statics and the dynamics for apples,made it approach to the practical operating conditions in the fruit industry,and provided a method to evaluate the fruit texture according to the dynamic properties.