Tortilla lysine

Tortillas prepared from mixtures of com with wheat, broadbean, rice, chickpea, and/or potato were studied. These mixes resulted in tortillas of very similar mechanical and sensory properties as those prepared from corn alone. However, the contents of protein and available lysine were in many cases higher (see Table XIII). Such mixtures provide an efficient way to improve the quantity and quality of protein in tortillas. 

Table XIII. Protein and Available Lysine in Tortillas Prepared from Different Mixtures of Corn, Other Grains, and Potatoes0...

Humans can synthesize only 10 of the 20 amino acids needed for protein synthesis. The remaining 10, called essential amino acids, must be obtained from the diet and consumed on a regular, almost daily basis. Diets that include animal products readily supply all the needed amino acids. Because no one plant source has sufficient amounts of all the essential amino acids, vegetarian diets must be carefully balanced. Grains—wheat, rice, and corn—are low in lysine, and legumes— beans, peas, and peanuts— are low in methionine, but a combination of these foods provides all the needed amino acids. Thus, a diet of corn tortillas and beans, or rice and tofu, provides all essential amino acids. A peanut butter sandwich on wheat bread does, too. 

Because grains such as rice and corn are usually poor in lysine, and because beans are usually poor in methionine, vegetarians are at risk for malnutrition unless they eat grains and beans together. This leads to the concept of complementary proteins, mixtures that provide all the essential amino acids—for example, corn and beans in succotash, or a bean burrito made with a corn tortilla. The specific recommended dietary allowances for adult males follow. Adult females who are neither pregnant nor lactat-ing need 20% less than the amounts indicated for adult males. 

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). 

Wheat flour tortillas have a high rate of protein digestibility (85%) but relatively low protein quality because gliadins and glutelins have insufficient levels of lysine and threonine (Gonzalez-Agramon and Sema-Saldivar 1988). Lysine is present in about half the amount required for optimum child growth. The protein quality of flour tortillas is improved when nonfat dry milk or related products are used in the formulation. Whole wheat flour tortillas contain 6.9% dietary fiber (3.2% insoluble and 3.7% soluble) instead of 1.8% (0.7% soluble and 1.1% insoluble) of counterparts produced from refined flour (Friend et al. 1992). 

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