Internal hollows in cooked rice grains (Oryza sativa cv. Koshihikari) observed by NMR micro imaging

Nondestructive analysis of water distribution and structural changes in cooked rice grains, Oryza sativa cv Koshihikari, was performed with Nuclear Magnetic Resonance (NMR) Micro imaging of protons (H-1). Using a specially designed holder, high quality images of cooked rice grains were obtained, even when up to 10 grains were studied simultaneously. Internal hollows were observed in all examined cooked rice grains, and we propose a mechanism to explain their formation. The origin of these hollows was hypothesized to be cracks or fissures, and hollows resulted from sealing of such lacerations by gelatinized starch in the peripheral layer in combination with expansion of the grain during cooking.