Degradation kinetic modeling of bioactive compounds and enzyme activity in wheat germ during stabilization

The stability of α-tocopherol (α-toco), total phenolic content (TPC), antioxidant capacity (DPPH and ABTS•+ radical scavenging capacity assays), activity of lipase (LA) and lipoxygenase (LOX) were investigated during stabilization of raw wheat germ with an industrial convection oven at different temperatures (120, 130, 140, 150 and 160 °C) and times (0, 5, 10, 15, and 20 min). Degradation kinetics were best fitted by first-order reaction models for all measured parameters with high R2 and low root mean square (RMSE) values, except ABTSassay which was modeled accurately with the second-order model. The temperature dependence of rate constants for all degradation kinetic parameters were calculated according to the Arrhenius, Eyring-Polanyi, and Ball models. Following the Arrhenius and Eyring models, activation energy (Ea) ranged from 20.69 to 55.04 kJ mol−1, activation enthalpy (ΔH*) ranged from 20.44 to 51.61 kJ mol−1 whereas the activation entropy (ΔS*) varied between −179.313 and −213.447 J mol−1K−1 for the stabilized germ, respectively. It can be concluded that heat treatment at 120 °C for 20 min was the best processing conditions to stabilize the raw germ to preserve its valuable bioactive compounds, antioxidant activity and the models can be useful to design different heat treatment conditions.