Comparative nutritive value of various staple foods*

Abstract

A population successful in an ecological niche must have a dietary pattern that provides the minimum requirements of all 40–45 essential nutrients, in addition to the energy sources—carbohydrates, fat, and protein. Cereal production and its contribution to diets in developing countries exceed that of legumes and roots, tubers, plantains and bananas. Legumes are highest in protein and is rich in lysine but deficient in cystine and methionine. Cereals are intermediate in protein content; their protein is rich in cystine and methionine but deficient in lysine. Thus cereal‐legume diets have a better amino acid balance than either diet alone, as shown by the high protein quality of most composite diets. Storage proteins are prolamin and glutelin in cereal endosperm, but globulin in legume cotyledon, occurring as prolamin protein body (PB) in cereals and globulin PB in legumes. Glutelin PB occurs in rice endosperm. Roots, tubers, plantains and bananas are high in moisture, hence, poor in protein content and other nutrients and have a poor postharvest shelf life. Potato protein has a balanced amino acid composition. Antinutrition factors for protein include protease (trypsin) inhibitor, tannins, and phytate. Digestible energy correlates with true protein digestibility and increases with processing. Starch occurs as partially crystalline storage granules. The amylose content of starch correlates negatively with gly‐cemic index and positively with resistant starch, a component of soluble dietary fiber. In some cases, starch gelatinization temperature correlates negatively with glycémie index and positively with resistant starch. Antinutrition factors for starch include amylase inhibitor, tannins, and phytate. Flatulence factors include galactose‐containing oligosaccha‐rides, which are particularly high in legumes. Soluble cc‐glucans of oat and barley have hypocholesterolemic activity. Legumes are generally energy‐dense due to their high fat content, particularly peanut and soybean. The unsaponifiable matter of rice oil has hypocholesterolemic activity. Some varieties of root crops have cy‐anogenic glycosides that release HCN on hydrolysis, causing death to consumers. Others have saponins and tannins that contribute to a bitter taste. Staple foods are a major source of vitamins and minerals due to the large amount consumed. Breeding efforts in the 1960s and 1970s attempted to improve the protein content and limiting amino acid (lysine content in cereals and cystine and methionine in legumes) in staple foods, both of which require more energy to produce. CGIAR recently launched a project to increase the micronutrient density of selected crops, particularly vitamin A, iron, and zinc, although mineral absorption from a vegetable source is poor. The low phytate mutant of cereals may improve protein digestibility, glycémie index, and mineral absorption. Rice mutant lacking li‐poxygenase 3 and a lower polyunsaturated fatty acid content may reduce fat rancidity and maintain the essential fatty acid level of food during storage, as in soybean. The adoption of GATT‐WTO in most countries, the accompanying emphasis on value‐added food products, and the popularization of functional foods and nutraceuticals in developed countries will have an impact on the properties and nutritive value of food products in developing countries in the 2000s.