Date of Award
Doctor of Philosophy
An objective method to predict the optimum cooking time of corn for tortilla production does not exist. Since nixtamalization (lime-heat treatment) is the most important step in the preparation of tortillas, the changes in the corn kernel during this period should be analyzed for the development of an optimal tortilla-making process. This study presents a mathematical model for quantitatively analyzing the kinetics of water diffusion and starch gelatinization during the nixtamalization process;Corn was cooked with and without calcium hydroxide, according to traditional processing steps. The temperature of the cooking solution, the amount of water absorbed by the corn, and the extent of starch gelatinization in the corn were monitored throughout the process. The data were quantitatively analyzed using the mathematical model that was developed based on the principles of diffusion and chemical reaction kinetics. The simplex pattern search scheme was used to locate the optimum rate parameters, which were used to calculate the extent of starch gelatinization. The calculated degree of gelatinization was then compared with that experimentally determined;The result shows that the developed mathematical model is useful for simulating the changes that take place during water-cooking and lime-cooking of corn. The calculated degree of starch gelatinization in corn, based on the quantitative analysis of water uptake data, was highly correlated with those data experimentally determined;Comparison among the responses of nine cultivars of corn to lime-heat treatment showed that the sensitivity of the diffusion process and of the gelatinization reaction to temperature change was the same for the nine corn samples studied. The results also show that the values of diffusivity, D[subscript]0, and the reaction rate constant, K[subscript]0, determine the differences in water uptake and starch gelatinization among samples;According to the stickiness values of masa, the range of degree of starch gelatinization for the preparation of suitable masa dough was between 14 and 20%. Twenty to 30 min cooking time for the sample studied was found to produce this degree of starch gelatinization.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Chang, Yung-Ho, "A kinetic study on the lime-heat treatment of corn for masa production " (1987). Retrospective Theses and Dissertations. 11671.