Tortilla traditional preparation

Another example of a protein-containing material that is processed with alkali is corn, which traditionally has been treated with aqueous lime, ashes or caustic soda (11,12). Tortillas, a primary source of protein for a large portion of the Mexican population, are prepared by simmering corn in a 1% lime solution. The pH reached during this process is about 12.4, and 175 C temperature is used during the final stage of cooking. Limited racemization of protein in tortillas has been reported (13). 

Zein, which is the major protein in corn, was chosen because it contains no lysine. This precluded the formation of LAL during alkali treatment. Therefore, any changes in digestibility or uptake could be attributed to racemization effects alone. Additionally, we were interested in comparing the effects of sodium hydroxide treatment with the effects of calcium hydroxide treatment because lime is used in the preparation of corn meal for use in tortillas. If the traditional lime treatment of com meal is unnecessarily harsh, it could have important nutritional consequences because a large segment of the Mexican population obtains much of their dietary protein in the form of tortillas (22). 

Treatment of cereals with alkali (for example soaking overnight in calcium hydroxide solution, as is the traditional method for the preparation of tortillas in Mexico) releases much of the nicotinic acid. This may explain why pellagra has always been rare in Mexico, despite the fact that maize is the dietary staple. Up to 10% of the niacin in niacytin may be biologically available as a result of hydrolysis by gastric acid. 

Niacin may be present in foods in a bound form (i.e., nia-cytin in corn) which is not absorbable. This is particularly true of corn, wheat, oats, rice, and rye. Yet, pellagra occurs less frequently than one might expect in Mexico, where corn consumption is high. Born of centuries of experience, it is the custom in Mexico to treat corn with limewater before making tortillas, thereby liberating the nicotinic acid. Likewise, the Hopi Indians of Arizona roast sweet-corn in hot ashes, another traditional practice that liberates the nicotinic acid. But the ways of food preparation in Africa do not have this effect. 

FIGURE 16.8 The traditional processes used to prepare atole and tortillas in Mexico and Central America. 

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