Study On Correlation Between The Starch Content Of Potato And Its Mechanical Rheological Characteristics

Potato is a kind of agricultural viscoelastic material, both biological mechanics characteristics and starch content of potatoes are related to its biological tissues. The starch mainly exists in the cells of potato biological tissues. when the material suffers the exogenic action, the force loads on the cell wall by the water and starch granule, so the starch content probably has an obvious effect on the biological mechanics characteristics of potatoes. The compression and stress relaxation tests were accomplished for Zi Huabai and Desiree potatoes in our study. The correlation between mechanical properties and starch content of potatoes were acquired, and the method would be found to predict the starch content of potatoes by mechanical tests. In the study, the compression and stress relaxation models were established by the virtual prototyping technology. The compression and stress relaxation processes of the potato were simulated with ADAMS technology.(1) The compression tests were completed in different loading rates for cylindrical samples and tubers of the potato. The compression curves were measured and compression characteristic parameters were determined by regression analysis, and no obvious biological yield point appeared on the curve. When the tuber was compressed in different loading rates, the initial stage of compression curve was approximatively superposed. There was insignificant difference for parameters which were acquired in different loading rates. Meanwhlie, the difference of compression characteristics between samples and tubers was discovered in the test results. When the sample was compressed by flat indenter, the water in cell tissue ran off, and the density, elastic modulus of the sample increased as the strain grew. When the tuber was compressed by cylindrical probe, the tissue of potato appeared viscous flow, and the stiffness of the tuber decreased as the deformation increased.When the tuber was compressed to the rupture point by cylindrical probe, the tuber had showed a minor strain, and the viscoelastic deformation process can be described by the Maxwell model. The viscoelastic deformation process were analysed, and the constitutive equation of the tuber compression was obtained. The elastic modulus and viscosity coefficient in the model were determined.(2) The stress relaxation tests were completed under two constant deformations with cylindrical samples and tubers of the potato. The stress relaxation model was established and the parameters in the model were determined. The study results showed that the residual elastic behavior was quite different under two constant deformations for tubers. According to the test results, the difference of stress relaxation characteristics between samples and tubers was discovered. During the relaxation process, the sample had a heavy respiration and water loss, and its relaxation time was longer than that of the tuber.(3) In order to get the correlation between the starch content of potato and its mechanical rheological characteristics, the starch content of samples and tubers were measured in the study by using IODINE-STARCH colorimetric method. The mechanical property parameters which correlate closely with the starch content were determined. For cylindrical samples of two potato cultivars, the elastic modulus which was obtained in compression and relaxation tests correlates closely with the starch content and water ratio. For tubers of two cultivars, the stiffness, energy at rupture point, and viscosity coefficient correlate closely with the starch content. The regression equations were established for starch content and mechanical parameters.(4) Virtual prototyping technology was introduced to the study. According to the results of compression and relaxation tests, the virtual prototype models of compression and relaxation were established for potato tubers with ADAMS technology. By comparing the simulation curve with the experiment curve, the validity of models were verified. When models were running, the stress and strain of elements in models were detected, and the rules were analysed. At the same time, the compression in different loading rates and the stress relaxation in different time spans were simulated, and the simulation results showed the effects of loading rates and time spans for potato's compression and stress relaxation.