Rice

RICE
• Wild varieties have existed for centuries in both Asia (Oryza sativa) and Africa (Oryza glaberina).
• The outer layers and the germ together contain nearly 80 percent of the thiamine in the rice grain.
• The endosperm, though constituting 90 percent of the weight of the grain, contains less than 10 percent of the thiamine.
• Lysine and threonine are the limiting amino acids in rice.
• consisting mainly of starch: Amylosa vs. Amylopectin
• Waxy varieties (Beras Ketan) : >> Amylopectin.


RICE PROCESSING
• The traditional home method of pounding rice in a wooden mortar and winnowing it in a shallow tray:
– usually results in the loss of about half of the outer layers and germ, leaving a product containing about 0.25 mg thiamine per 100 g.

• The procedure of milling and subsequently polishing rice, removes nearly all the outer layers and germ, a product:
– containing only about 0.06 mg thiamine per 100 g
– grossly deficient

• In Asia, a person eating 500 g rice per day:
– if use highly milled polished rice would get only 0.3 mg thiamine
– if home-pounded or lightly milled rice would provide approximately 1.25 mg thiamine (normal requirement.


IMPORTANT:
• The solubility of the B vitamins has its disadvantages
• Parboiling is the way of providing highly milled rice that is reasonably white and yet contains adequate quantities of B vitamins:
– The paddy, is usually steamed, so that water is absorbed by the whole grain, including the endosperm.
– The B vitamins, which are water soluble, become evenly distributed throughout the whole grain
– The paddy is dried and it is then ready for milling in the ordinary way.
– Even if it is highly milled and polished, the parboiled grain still retains the major part of its thiamine and other B vitamins.
• Rice that is washed too thoroughly in water loses some of the B vitamins.
• If rice is boiled in excess water, a considerable proportion of the B vitamins is likely to be discarded with the water after cooking.