A thesis submitted in partial fulfilment of the requirement for the degree of Master of Science, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 1982

The firmness of potatoes was evaluated in terms of the elasticity modulus based on axial compression, radial compression and Hertz contact stress analysis using an Instron testing machine. Cylindrical test specimens (1. 5 cm in diameter and 3. 0 cm long), whole potatoes and their flat surface were tested under compression at the loading rate of 50mm/min. The changes in firmness of potatoes were monitored over a period of 8 weeks when stored at 5, 10, 20 and 30°C. Potatoes exhibited nonlinear force-deformation behavior in axial compression tests requiring the calculation of tangent elasticity modulus values as a function of percent compression. In .radial compression tests, there was marked deviation of experimental force-deformation relationships from the theory. Therefore, the computed values of elasticity modulus were expressed as a function of percent compression. In compression tests with whole potatoes and their flat surface, the force-deformation relationship conformed to Hertz analysis only at low compression values and could be used to calculate elasticity modulus independent of percent compression. The experimental elasticity modulus values showed a wide variation in their magnitudes primarily .due to the characteristics of each test method used. The firmness of potatoes appeared to decrease exponentially with storage period at all temperatures. Since the elasticity modulus values .as determined in various compression tests were different, it was necessary to express change in their magnitude during storage on percentage basis for making relative comparisons. The radial compression test showed maximum percentage decrease in the elasticity modulus values with storage time. The axial compression test values were next. The compression of whole potatoes and their flat surface followed very closely to each other and showed minimum decrease in the elasticity modulus values during the storage at all temperature.