Final answer:
The primary difference between regular rice starch and sticky rice starch is the proportion of amylose and amylopectin, where regular rice has more linear amylose leading to a less sticky texture, and sticky rice has more branched amylopectin, which results in a stickier texture when cooked.
Step-by-step explanation:
The difference between the starch in regular rice and the starch in sticky/glutinous rice lies in the composition of two polysaccharides: amylose and amylopectin. Regular rice contains more amylose, which is a linear polymer of glucose with α-1,4 glycosidic linkages, resulting in a firmer, less sticky texture when cooked. Sticky rice, on the other hand, has a higher proportion of amylopectin, which is a branched polymer with α-1,4 glycosidic linkages in the chains and α-1,6 glycosidic linkages at the branch points, giving it a more gelatinous and sticky texture.
Additionally, normal rice tends to become less sticky upon cooking because the amylose leaches out into the water, whereas the amylopectin in sticky rice creates a more viscous paste that holds the grains together. This structural difference between amylose and amylopectin determines the textural properties of the cooked rice, influencing its culinary uses. Unlike cellulose, which has β-1,4 glycosidic linkages and is indigestible by humans, both types of starches in rice can be broken down by enzymes such as amylase.