In order to enrich the apple quality evaluation system, TPA mechanical tests were carried out on Fuji, Guoguang and Golden delicious apple pulp at 10 loading speeds of 0.01, 0.1, 0.5, 1, 2, 5, 9, 13 and 17mm/s, and the mechanical characteristic parameters of pulp were obtained. The effects of loading speed on pulp hardness, elasticity, cohesiveness, chewiness and resilience were analyzed. The microstructure of pulp of different varieties pulp was observed by laser confocal microscope. Based on the Voronoi model of pulp tissue structure, the compression test was simulated to construct the relationship between microstructure and mechanical properties. The results showed that the loading speeds had a certain effect on the cohesiveness and chewiness, and had a linear relationship with the cohesiveness of Guoguang variety and the chewiness of Golden delicious. The microstructure of pulp directly determines its mechanical properties, the smaller the roundness of cells and pores, the greater the hardness, cohesiveness, chewiness and resilience. Using Abaqus for compression test simulation, the maximum deviation of stress is 4.3%, which proves that the model is effective and the accuracy is improved. The results provides technical parameters for mechanical system improvements for apple during harvesting, storing and transporting and perfect evaluation system of apple texture.

Fruit and vegetable peels exert a protective effect on fruits as constituent parts of the outermost tissue and their properties are of great importance to reducing fruit and vegetable mechanical injury. Four kinds of fruit and vegetable peels such as Nagafu apple, Crisp pear, Tainong mango and long eggplant were chosen to perform longitudinal and transverse tests of tensile property by means of electronic universal testing machine. Stress-strain curve, tensile strength, elastic modulus and fracture strain of peels were obtained; and the microstructures of four kinds of peels were scanned using an electron microscope (SEM). The results indicated that cubic polynomials proved superior for quantifying the stress-strain non-linear relationship of peels and the fitting error of tensile strength is less than 10 parts per thousand. Tensile strength, elastic modulus and fracture strain of peels were different in the case of different fruits and vegetables cultivated and different parts of the same peel; fruit and vegetable peels belong to anisotropic heterogeneous materials and have certain strength. The mean values of tensile strength and fracture strain of the long eggplant peel are the biggest in four kinds of peels and that of elastic modulus of Nagafu apple peel is the largest; long eggplant and Nagafu apple peels had better resistance to damage sensibility than Crisp pear peel. The bearing capacity of the peels depends on the number, width and distribution of microcracks on the surface, and the shape of the epidermal cells and fruit dot on peels; the number of microcracks is bigger and the width of microcracks is wider, the tensile strength is smaller and the elastic modulus of peel is bigger with the slippage increase of epidermis cells. This study provides basic technical parameters for mechanical equipment design for fruit and vegetable during harvesting, processing, packaging, storing and transporting and builds the correlations between macro-mechanics properties and microstructures of fruit and vegetable peels.

The texture of apple peel, as an important quality attribute of the fruit, is directly relevant to a fruit’s ability to resist mechanical injury. In order to explore the variations in texture of two apple peels under different puncture test conditions and evaluate the relation of apple peel puncture force to whole fruit firmness percentage, at 0.1, 1, 5, 11, and 17 mm/s loading speeds, puncture mechanical measurements were performed using an electronic testing machine mounted with 2, 3.5, 7.9 or 11 mm-diameter probes. For the same probe, the mean values of peel puncture force and stiffness, as well as the fruit puncture force, for Danxia and Fuji cultivars increased firstly and then changed a little with the increase of loading speed. Moreover, at the same loading speed, the puncture measurements of each cultivar increased significantly ( ) with increasing probe diameter and the peel puncture force has a significant linear correlation with probe diameter. Among the different cultivars, under the same loading speed, the Fuji peel and fruit samples had the greater puncture force; the Fuji peel contribution change was relatively big with the increasing of loading speed, and Fuji cultivar was more likely to be injured than the other cultivar. The results were expected to serve as a reference for investigating the puncture injury sensitivity of different apple varieties during transportation and storage and to enrich the texture evaluation index of apple peel.