Effect of calcium content in the corn flour on RVA profiles

Corn flour was produced using the traditional nixtamalization process and different steeping times of 0, 1, 5, 6, 10, 13, and 24 h. The flour particle size distribution was then evaluated in terms of the particles retained by using a 40 US mesh screen. The lime content, the Rapid Visco Analyzer (RVA) profiles, maximum peak viscosity, breakdown and final viscosity (V) were measured as a function of the steeping time. It was found that the initial rate of increase in viscosity (dV/dt), maximum peak viscosity, breakdown and final viscosity of fractions depended on the amount of calcium incorporated in the corn kernels during the steeping time (T_s) of the nixtamalization process. The particles retained using a 40 mesh that were steeped for 0-5 h, do not have the characteristic points of an RVA profile, i.e., maximum peak viscosity and breakdown. However, the particles retained using a 40 mesh and steeped for 6-24 h developed peak viscosity, breakdown and final viscosity. The corn flours that are recommended for making tortillas are precisely the flours whose particle size distributions develop these three characteristic points in the RVA profile. Differences in RVA measurements of the size fractions can be explained on the basis of the calcium content of the course fractions of corn flours. It was concluded that RVA characteristics may be changed by the calcium content in the starch polymer structures created during the nixtamalization process. Consequently, the increased calcium content in starch particles should be reflected in RVA measurements as an increase in the peak viscosity, in the gelatinization rate and in the development of a noticeable breakdown.