Thursday, January 6, 2022

Carbohydrates in rice

Rice is a major cereal crop consumed as a staple food by over half of the world’s population. Consumption of rice is very high in developing countries. In general, cereals consist of carbohydrates, proteins, vitamins, minerals, antioxidants and phytochemicals.

Vitamins and minerals are largely confined to the bran and germ. The endosperm of rice is rich in carbohydrate.
Brown rice: 76.5 gm/100 gm
White rice: 80.2 gm/100 gm
Parboiled rice: 81.1 gm/100 gm

The major carbohydrate present in the brown rice is starch, which is a homopolymer of glucose forming an alpha-glucosidic chain, called glucosan or glucan.

Available carbohydrates, mainly starch, are higher in milled rice than in brown rice. The two main constituents of starch are amylose and amylopectin.

Amylose is one of the components of starch. Amylose has a slightly branched structure while amylopectin, the other starch component, has a highly branched structure. Amylose is less available for degradation by digestive enzymes because of the reduced surface area per molecule than amylopectin, thus inducing a lower impact on glycemic response.

Beyond amylose content, amylopectin content plays a role in starch digestion rate. For its highly branched structure, amylopectin is more available for degradation than amylose.

Dietary fiber is highest in the bran layer (and the hull) and lowest in milled rice. Density and bulk density are lowest in the hull, followed by the bran, and highest in milled rice because of the low oil content.

The presence of fiber in the diet increases the bulk of feces, which has a laxative effect in the gut. The dietary fibers also have potentials to reduce serum cholesterol, low density lipoprotein and blood pressure, and to improve glycaemia and insulin sensitivity. The fiber content is 0.5–1.0% for well-milled rice. Arabinoxylans, along with β-d-glucan, are the major component of soluble dietary fiber in rice.
Carbohydrates in rice

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