Microstructural, dehydration and rehydration properties of rice starch granules in noodles as affected by water and oil addition using vacuum impregnation

Abstract The objective was to understand the vacuum impregnation/infusion (VI) for the impregnation of water and oil into rice starch granules using different sequences to influence the granule structure and the mass transfer properties during noodle drying and rehydration. The proposed type of distribution of the oil and water inside the granules was discussed. Confocal micrographs of the raw starch granules revealed that VI forced water and oil into the granules. Without VI, a portion of water was impregnated while none of the oil was. Polarized‐light micrographs showed that the addition of water into the flour prior to the oil created large, long crystals in the dried noodles. However, when the oil was added first, the crystals were small and spherical. The dehydration rate of the cooked noodles was strongly affected by oil addition using VI. The rehydration rate of the dried, cooked noodles was governed more by the drying rate than the characteristics of the noodle components. The cooking quality [cooking time (330 s), cooking loss (1.40%) and water absorption (163.64%)] of the noodles was good following the addition of oil using VI prior to adding water. VI is a powerful tool for impregnating oil and water into rice starch granules. Practical Applications Consumers are increasingly adopting more informed lifestyle habits, including eating healthy food. Rice is a main carbohydrate source and staple food in many countries. Lowering the glycemic index of rice products while maintaining their good quality is an ongoing challenge. The addition of water and oil into starch granules are likely stimulate starch gelatinization and oil‐starch complex formation which reduces starch digestibility. This study proved that vacuum impregnation/infusion is a powerful technique to impregnate liquids (e.g., water and oil) into rice starch granules and significantly alters the rice product properties (crystal properties, drying rate, rehydration rate, cooking time, cooking loss and water gain) in ways beneficial to the product quality. Similar benefits may apply to other starch sources, and other liquids can also be vacuum‐impregnated into starch granules. Industries using cereal‐based products can take advantage of these findings.