A Preliminary Study on Enzymatic Properties of Rice Bran Lipase

Abstract

The lipase enzyme extracted from defatted Thai scented rice bran with calcium chloride solution which has been purified by ammonium sulfate precipitation, followed by dialysis had the specific activity of 2.04 units/mg protein and 1.32 times that of starting crude extract. The semi-purified lipase obtained showed the optimum pH at 7.6 with equilibrium rate constants, K₁ and K₂, and maximum enzyme reaction rate, (EA)_max of                  3.2x10^-7, 1.7 x 10^-9 M and 44.2 units/ml, respectively. Based upon the enzyme kinetics of the temperature effect, the lipase enzyme had the activation energy, E_a = 11.03 kcal/mol and the energy for the thermal inactivation, ΔH_d =30.8 kcal/mol. The absolute reaction rate function with the remained parameter constants estimated by non-linear regression analysis was EA = . As a result, the maximum enzyme activity of 42.7 units/ml was calculated with the mentioned equation at T_max equal to 35^oC. Moreover, the Thai scented rice bran lipase were stable over the pH range from 4 to 9 and the temperature range from 20 to 45^oC, but completely lost the activity by heating at 50^oC for 60 min. Finally, the model for lipase activity affected by pH and temperature was proposed and figuredly simulated to predict the enzyme activity under various pH and temperature conditions.