Grains, legumes and oily seeds, roots, tubers and plantains: nutrients, processing and dishes

Cereals are the edible seeds of cultivated grasses. They are the world’s main staple foods. In Nigeria the main cereals are rice, maize (corn), millet, sorghum (guinea corn), wheat (mostly imported, grown in the north), and acha (fonio), a small grain grown on the Jos Plateau and nearby states.

Composition and nutritive value

• Mainly starch (about 70 to 80% of dry grain): energy.
• Protein about 7 to 14% depending on the grain, of low biological value (lysine is limiting); wheat proteins form gluten.
• B vitamins (thiamine, niacin, riboflavin), mostly in the germ and bran.
• Minerals: iron, phosphorus, magnesium, zinc (bound partly by phytate).
• Fat in the germ (corn oil comes from maize germ).
• Fibre in the bran.
• No vitamin C (except fresh green maize, which has a little), and little vitamin A except yellow maize, which contains carotene.

Effects of milling

Milling removes the husk, then bran and germ, to give white flour, white rice or degermed maize. This improves keeping quality (fat in the germ goes rancid) and gives a lighter colour and finer texture, but removes most of the fibre, B vitamins, iron and some protein. This is why polished rice diets caused beriberi, and why flour is often fortified. Parboiling rice (soaking and steaming paddy before milling, as in local ofada and much Nigerian rice) drives B vitamins into the endosperm and reduces losses.

Forms in which cereals are bought

• Whole grain: paddy rice, dried maize cobs or grains, millet heads, sorghum.
• Processed grain: polished or parboiled rice, pearled millet, broken rice, maize grits.
• Flours and meals: wheat flour of various extraction rates, maize flour, rice flour, millet flour, semolina.
• Starches: cornflour, custard powder, wet ogi starch.
• Ready-to-eat products: breakfast cereals, noodles, pasta, bread, biscuits, popcorn.
• Fermented and malted products: ogi, masa batter, malted sorghum, kunu, pito, burukutu, malt extract.

Extraction rate

The extraction rate is the percentage of the whole grain retained in the flour. Whole wheat (wholemeal) flour is 100% extraction; brown flour about 85 to 90%; white flour roughly 70 to 75%. The lower the extraction rate, the whiter the flour and the lower its fibre, iron and B vitamins. If 50 kg of wheat is milled at 72% extraction, the flour obtained is 50 × 0.72 = 36 kg, and 14 kg of bran and germ go mainly to animal feed.