Abstract
Cereals and legumes are staple foods in India and are limiting in lysine and sulphur amino acids, respectively. Available lysine loss, due to Maillard-type reactions that may occur during food preparation, exacerbates the problem of lysine deficiency particularly in cereals. Consequently, determining the contents of digestible essential amino acids, particularly lysine, is important. True ileal digestibilities of most amino acids (including total and reactive lysine) were determined for ten food ingredients and eleven foods commonly consumed in India. Semi-synthetic diets each containing either an ingredient or the prepared food as the sole protein source were formulated to contain 100 g kg 21 protein (75 g kg 21 for rice-based diets) and fed to growing rats. Titanium dioxide was included as an indigestible marker. Digesta were collected and the amino acid content (including reactive lysine) of diets and ileal digesta determined. Available (digestible reactive) lysine content ranged from 1•9-15•4 g kg 21 and 1•8 -12•7 g kg 21 across the ingredients and prepared foods respectively. True ileal amino acid digestibility varied widely both across ingredients and prepared foods for each amino acid (on average 60-92 %) and across amino acids within each ingredient and prepared food (overall digestibility 31 -96 %). Amino acid digestibility was low for many of the ingredients and prepared foods and consequently digestibility must be considered when assessing the protein quality of poorer quality foods. Given commonly encountered daily energy intakes for members of the Indian population, it is estimated that lysine is limiting for adults in many Indian diets. India, like many other developing countries has not as yet eliminated the problem of under-nourishment in its poorer communities particularly with respect to protein. In these communities protein intakes tend to be low, and to exacerbate the problem Indian diets are generally cereal and legume based, the proteins of which tend to be more poorly digested than North American protein-based foods (57 -75 % versus 88 -94 %), largely due to the presence of high levels of insoluble fibre and anti-nutritional factors (1) . Cereals tend to be limiting in lysine while legumes are limiting in sulphur containing amino acids. Ensuring food and nutritional security is a challenge for India, given its large population and high levels of poverty and malnutrition. National Nutrition Monitoring Bureau of India (NNMB) data have revealed a gradual decline in daily per capita intake of protein from 62•9 g in 1975-1979 to 48•8 g in 2004-2005. In countries like India, where dietary amino acid supply may potentially limit protein metabolism, it is imperative to accurately monitor the dietary supply of 'available amino acids' in relation to the dietary requirement (2) . Consequently, it is essential to have a fundamental understanding of the digestible amino acid content of Indian foods and the extent to which the digestible amino acids meet the requirements of people in India. Protein digestibility-corrected amino acid score (PDCAAS), scores proteins based on their ability to meet the deemed amino acid requirement of humans for the first limiting amino acid and in the case of cereal-based diets that is likely to be lysine. While the amino acid composition of many foods consumed in developing countries, including India, is known there is scant data about the digestibility of those amino acids and it is important that this gap in knowledge be addressed. Currently, PDCAAS uses faecal nitrogen digestibility values to correct amino acid scores to PDCAAS values. However, a single nitrogen digestibility value may not reflect the digestibility of all dietary amino acids (2) . Moreover, faecal amino acid digestibility values are often higher than ileal amino acid digestibility values, particularly for poorly digested protein sources (2, 3) . Consequently, PDCAAS values may be more accurate when derived using true ileal amino acid digestibility values as opposed to faecal nitrogen digestibility values (4, 5) . Lysine is of particular interest since it is often first limiting in cereal-based diets and is susceptible to chemical modification during processing or cooking to form nutritionally unavailable derivatives (4, 6) . Furthermore, lysine intakes have been shown to be marginal in low socio-economic group Indians (7, 8) , which is of even greater concern given that the daily requirement for lysine has been shown to be approximately 30 mg kg 21 day 21 for healthy Indian men (7) or higher (44 mg kg 21 day 21 ) where there is chronic undernourishment (8) . This value is more than double the requirement estimate laid out in 1985 by the WHO/FAO/UNU expert consultation group. Values for digestible lysine based on true ileal digestible total lysine are likely to overestimate the nutritional value of foods and food ingredients that have been processed or cooked. Instead true ileal digestible reactive lysine provides a more accurate measure of available lysine in such foods (4) . A method has been developed (9, 10) that allows the accurate determination of the available lysine (true ileal digestible reactive lysine) content of processed foods (Biolysinee). The objective of this study was to determine true ileal amino acid digestibility and available (digestible reactive) lysine contents for a range of typical cereal-and legume-based foods from India.
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