Viscoamylographic studies on Zea mays [Mexican White Tuxpeño maize] partial gelatinization with calcium hydroxide

Mexicans staple food is maize “tortilla”, prepared by thermal-alkaline processes. The sensory properties of “masa” and “tortilla” depend on the reactions occuring between lime and chemical compounds in maize. In the present study, the effect of different calcium hydroxide, Ca(OH)2, concentrations (0.0, 0.10, 0.30, 0.50 %, dry basis, d.b.) on the apparent viscosity and maximum gelatinization temperature of a cornstarch water slurry was assessed. This Mexican traditional thermal-alkaline gelatinization reaction (TAGR) was evaluated in a Brabender Viscoamylograph. This small well-mixed reactor was homogeneously heated, and apparent viscosity data from corn starch were recorded in Brabender Units BU). It was found that an increase in Ca(OH)2 concentrations considerably increases the apparent viscosity, thus reducing the time needed to reach the maximum gelatinization temperature. A mathematical model that represents the phenomena, that occur in the Viscoamylograph, was developed. In the model the Viscoamylograph was considered as a batch reactor and the apparent kinetic coefficients for the TAGR were obtained, including mass balances and thermal-alkaline gelatinization rates, considering a spherical cornstarch granule formed by a starchy matrix. Activation energy found for this reaction was 1241 kJ.