Dimensional changes in milled rice (Oryza sativa L.) kernel during cooking in relation to its physicochemical properties by image analysis Original Research Article

The present study was aimed to develop model for describing the changes in dimensions of milled whole kernels during cooking in excess water. Samples of ten Thai rice varieties ranging from low to high amylose content (16–29% d.b.) with three initial moisture levels (approximately, 8%, 12% and 16% d.b.) were used to investigate the influence of initial moisture content and variety manifested by the physicochemical properties such as amylose content (AC), alkali spreading value (AS), gel consistency (GC) and protein content (PC) on the kernel dimensional changes. It was found that the kernel initial moisture content did not affect the dimensional changes during cooking. The changes in kernel dimensions during cooking could be best expressed by either an exponential relationship with the R2 for fitting ranging, respectively, from 0.969 to 0.997, 0.921 to 0.973, 0.936 to 0.997 and 0.968 to 0.995 or by a Peleg model with the R2 for fitting ranging, respectively, from 0.969 to 0.997, 0.921 to 0.977, 0.937 to 0.997 and 0.968 to 0.995 for kernel length, width, perimeter and projected area for all rice varieties. The regression coefficients of the fitted relationship for describing changes in kernel dimensions during cooking were found to be the function of physicochemical properties, namely, AC, AS and PC of rice varieties and could be estimated within ±5% of actual values. It was observed that the regression coefficients of the power model describing kernel expansions in terms of water absorbed during cooking were the function of the physicochemical properties of the milled rice. It was concluded that the kernel expansions due to water uptake could be estimated from the physicochemical properties, namely, AC and AS during cooking.