Compression Damage And Quality Deterioration Mechanism Of ‘Fuji’ Apple Fruit

In recent years,the production of apples has been increasing year by year,and apple picking is mainly done by hand.The post-harvest cleaning,grading,packaging and other processes have initially achieved mechanized operations,but in the above process,whether it is manual or mechanized processing,apples are inevitable The ground will be subject to different degrees of mechanical damage caused by extrusion,drop and vibration.In order to solve the mechanical damage of apple fruit caused by static compression during post-harvest processing.Firstly,the mechanical properties of apple fruit were studied,the physical and mechanical properties parameters of apple fruit were measured,and the elastic modulus,Poisson’s ratio,and breaking stress of apple pulp and peel were obtained.Through static compression and creep tests on apples,the compressive damage factors,the optimum creep model,and the relationship between creep parameters and time were determined.With the help of Ansys Workbench finite element analysis software,the apples with different degrees of compression damage were simulated to quantitatively evaluate and predict the mechanical damage degree of apples.The effects of different compression damage on apple fruit quality during storage were studied by static compression test.This study can provide a theoretical reference for the mechanical damage protection and equipment optimization design of apple fruit in the mechanized post-harvest treatment process.The main research contents and conclusions of this paper are as follows:（1）Physical and mechanical properties of Apple fruit were studied.In this paper,the geometric mean diameter,surface area,sphericity,density and fresh fruit quality of Shaanxi Fuji apple fruit during picking period were determined and the difference was analyzed.The compression tests of apple pulp under three different loads were carried out by using texture analyzer.The force-displacement curves were measured under three loads,and the force and displacement of apple pulp rupture point were obtained.The tearing force,instantaneous breaking force and absolute elongation length of apple peel were obtained by tensile test of apple peel using electronic tensile machine.Based on relevant formulas,the elastic modulus,Poisson’s ratio and failure stress of apple pulp and peel were determined respectively.（2）Compressive mechanical behavior and creep properties of apple were studied.Taking storage time,loading speed and compression position as experimental factors,orthogonal compression test was carried out on apple pulp samples,and the corresponding destructive force F,stiffness K and deformation energy U_swere obtained by analyzing the deformation-pressure curve.Three component Kelvin creep model,four component Burgers creep model and six component Generalized Kelvin-Voigt creep model were established respectively.The variation of creep parameters with storage time was analyzed,and the correlation of creep parameters was analyzed.The results showed that loading speed,storage time and compression position were the main and secondary factors affecting the damage,stiffness and deformation energy of apple pulp.The loading speed and storage time had significant effects on the compressive force and stiffness of apple flesh,and on the deformation energy.The loading position has significant effect on the compressive damage and stiffness of apple pulp,but has no significant effect on the deformation energy.The four-component Burgers model is most suitable for describing the creep characteristics of apple pulp.During storage,the initial elastic coefficient E₀,delay elastic coefficient E₁and viscosity coefficientηof creep parameters had the same variation pattern,and showed a decreasing trend with the increase of storage time.The delay time T₁increases with storage time（3）Finite element simulation of apple fruit compression characteristics.The finite element model of apple compression was established and the simulation calculation of apple fruit compression characteristics was carried out.The results showed that when the compression loading force was 20N,apple fruit was not damaged.When the compressive loading force was 40N,apple fruit might be damaged.When the compressive loading force was 60N,apple fruit was slightly damaged.When the compressive loading force was 80N,apple fruit was obviously damaged and deformed.The regression analysis of the maximum equivalent stress of peel and pulp-core during apple fruit compression was carried out.The results showed that there was a positive correlation between the maximum equivalent stress and the compressive force of peel and pulp-core of apple fruit.（4）Effects of compression damage on mechanical properties and storage quality of Apple fruits.Five experimental groups and a blank control group were designed.The damage mechanical behavior,damage volume,mass damage rate,ethylene yield,respiration rate,hardness,browning degree,titratable acid（TA）,soluble solid（TSS）,TSS/TA ratio,malondialdehyde（MDA）,cell membrane permeability,ascorbic acid,total phenol,total flavonoids,pectin and soluble pectin of apple fruit were investigated.The results showed that apple fruit would not be damaged when the compression force reached40N.Compared with 0N and 40N groups,fruit weight loss,browning degree,MDA,cell membrane permeability and soluble pectin contents in 80N,160N,320N and 640N groups were significantly increased,while hardness,ascorbic acid,total phenol,total flavonoids and pectin contents were significantly decreased.