STUDY OF SOLIDS LEACHED DURING RICE COOKING USING THE TRANSMITTANCE AT 650 NM

Effect of structure evolution of starch in rice on the textural formation of cooked rice

The content and composition of rice kernels are closely related to the textural properties of cooked rice. In this study, the mechanistic explanations of textural changes were linked to proton mobility, leaching behavior, and the molecular features of rice components during cooking. The decreasing trend of hardness and the formation of stickiness was mainly determined by the molecular mobility of components. The molecular weight (Mw) of starch and protein in leached solids increased with the leaching at 70-100 °C. The Mw of rice kernels at different cooking temperatures and times was similar, but the molecular size and volume varied at different stages of cooking. The dismission of the crystalline structure, C1 resonance, and lamellar structures after cooking at 100 °C for 10 min indicated that the structural evolution of starch in rice kernels was time- and temperature-dependent. These results provide a promising foundation for developing strategies to control rice cooking.

Impact of milling and water-to-rice ratio on cooked rice and wastewater properties

Due to the environmental concerns and expense associated with the disposal of wastewater after industrial cooking of rice, the purpose of this study was to evaluate the extent of leaching, water uptake and volumetric expansion of rice during cooking at various milling durations and water-to-rice ratios. Two cultivars of Arkansas rice, a long grain (Francis) and a medium grain (Jupiter), were milled for 10, 20, and 30 s with a laboratory mill. Samples were cooked in aluminum foil covered beakers at water-to-rice ratios of 10:1, 15:1, and 20:1. After 20 min, rice was weighed for water uptake and measured for volumetric expansion using hexane displacement. The excess cooking water was evaluated for total solids, amylose, and protein to determine the extent of leaching. Water uptake and volumetric expansion significantly increased with milling duration in both cultivars. Leached solids increased as the water-to-rice ratio increased in Francis and increased with milling duration in Jupiter; however, the amylose content of leached solids was unaffected by the water-to-rice ratio in both cultivars. Thus, shorter milling durations may limit the extent of leaching during cooking, as observed with Jupiter, while a lower water-to-rice ratio may reduce wastewater contamination for cultivars similar to Francis.