Content area
Full Text
Corn tortillas have been a staple food in Mexico and Central America for many centuries and its consumption has rapidly moved to other countries during the last decade (Almeida-Dominguez et al 1996).
In Mexico, the daily per capita consumption of tortilla is [approximate]325 g (Paredes-Lopez and Saharopulos-Paredes 1983). Tortillas also supply 70% of the calories and 50% of the protein consumed daily (Trejo-Gonzalez et al 1982). The deficiency of proteins with sufficient essential amino acids is a great problem in some rural areas of Mexico and Central America, principally where corn is the basic staple food. Corn proteins are considered to have low nutritional quality because zein, the main protein fraction in corn, has low concentration of the essential amino acids lysine and tryptophan (Wilson 1987). The nixtamalization process produces changes that improve the nutritional quality of tortillas. Many studies have been conducted on nutritional aspects of nixtamalized maize but very few works have studied the bioavailability of its carbohydrate constituents (Rendon-Villalobos et al 2002). Carbohydrates represent the main fraction of cereal grains, accounting for up to 50-70% of the dry matter, of which starch and nonstarch polysaccharides (dietary fiber) are the major constituents.
Dry legumes are a rich and inexpensive source of protein and calories for a large part of the world's population, mainly in developing countries. The dry common bean (Phaseolus vulgaris) has an important place among the legumes of major production and consumption in Africa, India, Latin America, and Mexico (Sathe et al 1982; Bourges 1987; Reyes-Moreno and Paredes-Lopez 1993). In Mexico, consumption of beans in a normal diet of rural zones represents 15%, and the protein level of this legume doubles that of maize (Paredes-Lopez et al 2000). Carbohydrates account for up to 55-65% of dry legumes. Of these fractions, starch, and nonstarch polysaccharides (dietary fiber) are the major constituents, with smaller but significant amounts of oligosaccharides (Bravo et al 1998).
Besides being a major plant metabolite, starch is also the dominating carbohydrate in the human diet (Bjorck et al 1994; Skrabanja et al 1999). Current knowledge on nutritional features of starch indicates that the bioavailability of the polysaccharide in foods may vary widely (Tovar 2001). Hence, a nutritional classification of dietary starch has been proposed that takes into account...