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Kinetics of texture change during cooking and frying of potatoes were evaluated in this study. Potatoes were cut into cylinders (diameter × height: 20 mm × 20 mm for cooking, and 10 mm × 20 mm for frying) and cooked in a temperature controlled water bath at 80–100C or fried in a commercial fryer at 160–190C for selected times. the cooked samples were water cooled while the fried samples were air cooled immediately after the treatment. Test samples were then subjected to a single cycle compression test in a computer interfaced Universal Testing Machine and three textural properties (hardness, stiffness and firmness) were derived from the resulting force‐deformation curves. Texture parameters of cooked potatoes decreased with progress of cooking time and the rate of texture changes associated with each temperature was found to be consistent with two pseudo first‐order kinetic mechanisms, one more rapid than the other. Textural values of fried potatoes were found to increase with frying time and also followed a first order kinetic model. Temperature sensitivity of rate constants was adequately described by Arrhenius and z‐value models.

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Color, as a quality attribute of cooked and fried potatoes, is affected by the extent and nature of heat during thermal processing. Improvement of color parameters has been made possible by the increase in knowledge of kinetics of color change. Analysis of kinetic data allows processors to minimize undesirable changes and optimize color retention. the objective of this study was to evaluate kinetics of color change during cooking and frying of potatoes. Potatoes were cut into cylinders (diameter × height: 20 mm × 20 mm for cooking and 10 mm × 20 mm for frying) and cooked in a temperature controlled water bath at 80–100C or fried in a commercial fryer at 160–190C for selected times. Color changes associated with cooked and fried potatoes were evaluated using a tristiumulus colorimeter in the L, a, b mode. For cooked potatoes, L and b values decreased while ΔE and a values increased with time at each cooking temperature. For fried potatoes, L value decreased while a, b and ΔE values increased as frying time increased. A modified first order model was used to characterize color change kinetics of both cooked and fried potatoes based on changes occurring between the initial and a maximum or minimum value. Temperature sensitivity of rate constants was adequately described by the Arrhenius and z‐value models.

Bacterial soft rot, caused by Erwinia carotovora ssp. carotovora (Ecc), is a major disease in stored potatoes. The pathogen causes different physical, physiological and chemical changes in potatoes, which may affect the acceptability of raw and processed products. This study was carried out to evaluate the effect of disease severity on different physico‐chemical and physiological properties of raw and cooked potatoes and to select the parameters most responsive to disease severity. Potatoes were inoculated with bacteria and incubated at 20C for different lengths of time to produce different levels of disease. As incubation time increased the volume of disease (VDS) increased, which in turn influenced the respiration rate (RR). In both raw and cooked potatoes, the physical changes (texture and color) associated with the progress of disease were reduced hardness, firmness and L value, and increased a and b values and total color difference (ΔE). The chemical changes were reduced ascorbic acid and pH, and increased reducing sugars, total sugars and titrable acidity along with the activities of peroxidase and polyphenol oxidase. The changes in physical and chemical parameters of raw and cooked potatoes during storage were described by fractional conversion equation models. All parameters were quite sensitive to disease except reducing sugars, peroxidase and PPO activity. The correlation matrix indicated that several of the quality parameters were related and thus most of them could be successfully used to predict tuber quality from disease.