The Effect of Nixtamalization Extrusion Process and Tortillas Making on the Stability of Anthocyanins from Blue Corn through the Kinetic and Thermodynamic Parameters

Abstract

The blue corn-based products are considered functional foods due to their high concentration of anthocyanins. The aim of this study was to estimate the kinetic and thermodynamic parameters of the thermal degradation of anthocyanins from extruded nixtamalized corn products. A comparative study of anthocyanins thermal stability in these matrices in a buffer solution (pH 2.5) was investigated at different temperatures (60, 75 or 90 °C). Results showed the mechanism of anthocyanins degradation followed first-order reaction kinetics. The values of the reaction rate constant (k) were found to be in a range of 0.027-0.037 h −1 at 60 °C, 0.107-0.113 h −1 at 75 °C and 0.340-0.354 h −1 at 90 °C. The higher the k value was, the shorter the half-life time and D-value. The activation energy (Ea) and z-values were in the range of 75.1-89.2 kJ/mol and 28.8-35.1 °C, respectively. The coefficient Q 10 indicated the reaction rate approximately doubles with every 10 °C temperature increase. ∆H, ∆S and ∆G indicated the degradation of anthocyanins was an endothermic and nonspontaneous reaction. Even the major susceptibility of the anthocyanins in extruded nixtamalized corn products at the time-temperature combination applied, there was not difference between flour and tortilla, this imply that most of the anthocyanins were degraded during the nixtamalization extrusion process and no significative further degradation occur in the cooking step. This study provides and advance in the knowledge on the effect of nixtamalization extrusion process and tortillas making on the stability of anthocyanins from blue corn. However, further studies are needed.

A Review of the Current Knowledge of Thermal Stability of Anthocyanins and Approaches to Their Stabilization to Heat

“…The degradation of anthocyanins in blue corn-based extruded nixtamalized products followed a first-order model at temperatures ranging from 60 • C to 90 • C at pH 2.5, with the determined thermodynamic parameters showing that the process was endothermic and non-spontaneous [79]. The authors of the paper showed that anthocyanin degradation kinetics of extruded corn flour and of prepared tortilla were similar, although tortilla making involved much higher temperatures (300 • C) than those applied in the extrusion process, probably in relation to the matrix protective effects, which caused a slower heat flow to the center of the tortilla due to some anatomical parts of the kernel.…”