Measuring Behavior of an Acceleration Measuring Unit Implanted in Potatoes

Abstract

Mechanical harvest and postharvest handling induce numerous mechanical impacts on potato tubers. These impacts may cause damage such as blackspot bruise, resulting in severe economic losses. To obtain reliable data of actual mechanical impacts, a miniaturized triaxial acceleration measuring unit (AMU) was implanted into potato tubers and tested in the laboratory. Tests were carried out with potatoes of two cultivars on several dates during the 2007-2008 season. The potatoes were hand-harvested and stored at 4C. Quasi-static elastic properties of the tubers were determined with a universal testing machine. The dimensions of the AMU were 42 13 13 mm. It was implanted in the tubers by means of a cork borer. A drop simulator was used for free fall tests from heights up to 100 cm. The acquired impact forces closely correlated with the impact acceleration obtained with the AMU. Test samples included both intact tubers and potatoes with the AMU implanted in order to determine the effects of tuber size, position of AMU, tissue thickness between AMU and tuber surface, drop height, and impact material on tissue mechanical properties. The experimental results were compared with data calculated according to Hertz' theory of elastic impact. The implantation procedure caused significant decrease of tuber apparent modulus of elasticity at the location of the drill hole. However, this area comprises less than 5% of the total tuber surface. Impact force and impact acceleration obtained in this study significantly correlated with tuber size, tissue thickness, drop height, and impact material. The dynamic modulus of elasticity of potato tubers calculated from impact force and impact acceleration data declined with increasing impact strength after an intermediate initial increase. This point of decline was similar in intact tubers and in tubers with AMU and may indicate mechanical tissue damage. However, because the AMU was embedded in the cushioning tuber tissue, the AMU peak values of impact were smaller than those obtained with a drop simulator. Furthermore, investigations with the implanted AMU yielded more realistic results of the actual mechanical impacts on potatoes and other susceptible produce than those with comparable electronic fruit.