TEXTURE DETERMINANTS OF COOKED, PARBOILED RICE .2. PHYSICOCHEMICAL PROPERTIES AND LEACHING BEHAVIOR OF RICE

This paper reports the pasting, gelatinisation and leaching behaviour of 11 cultivars of rice, the starch structural properties of which were determined in the preceding paper. The results show that the contents of leached amylose in the cooking water, as determined by both size exclusion-high performance liquid chromatography (SE-HPLC) and iodine colorimetry, were correlated positively with the texture of cooked rices, which possessed total amylose contents in the range 18.4-29.5%. The amount of leached amylose depended on the total amylose content of the rice. A similar correlation between the conventional 'setback' value, measured using the Viscoamylograph, and the texture of cooked rice may be a result of the leached starch content. The gelatinisation temperatures of rice starches determined by differential scanning calorimetry (DSC) were not correlated with the texture of cooked rice, but were significantly related to the crystallinity of the rice starch. The longest chain population (92-98 DPn), which had been detected previously in the hard rice samples, was not found in their corresponding leached starches. This observation may well support the suggestion in the preceding paper that the longest amylopectin chains could interact with other components in rice, the resultant complexes being retained in the cooked grain and inhibiting softening.