Observation of moisture distribution affecting texture of food by MRI

Abstract

Water is a principle factor determining the texture and quality of food. Water distribution in spaghetti during cooking and standing, and in rice grains during water soaking, were investigated using MRI. Formation of a moisture gradient was observed in a cross-section of boiled spaghetti strands, as a result of water diffusion from the surface to the core with starch gelatinization. Homogenization of water distribution was observed during standing of the boiled spaghetti. Water distribution in five types of cooked spaghetti was compared using MR images and water distribution profiles, enabling quantitative analysis of water diffusion. As for milled rice grains, water first penetrated the embryo attachment site and the surface of the ventral side of the endosperm, then migrated along the central line and transverse cracks, and finally diffused to all parts of the endosperm. The central part of the endosperm allowed more water to penetrate. In milled rice grains of the cultivar Yamadanishiki, which has a white core, water quickly infiltrated into the cracks or chalky parts on the dorsiventral line and then diffused to the lateral side of the grain. The route, pattern and speed of water penetration are determined by the morphological structure, crack formation and hardness distribution associated with the filling of starch granules in the grains.