Heat-moisture treatments of cowpea flour and their effects on phytase inactivation

Samples of finely ground cowpea flour with moisture content adjusted to 10%, 25%, 35% (dry basis) were heated in sealed retort pouches at 70 to 95°C for periods of 2 to 32 min. Phytase showed a high thermal resistance with residual activity ranging between 50% and 95%. Thermal inactivation of cowpea phytase was adequately described by a fractional conversion model based on a 1st-order rate equation. Overall, increasing temperature and initial moisture content resulted in increased enzyme inactivation. Estimated activation energies between 70 and 95°C were 33.3, 37.9, and 43.4 kJ/mol at 10%, 25%, and 35% moisture, respectively. The kinetic models generated were successfully used to predict phytase activity in cowpea flour.