Lipase-catalyzed preparation of diacylglycerol-enriched oil from high-acid rice bran oil in solvent-free system.

The ability of immobilized lipase from Rhizomucor miehei (Lipozyme RM IM) to catalyze the reaction of high-acid rice bran oil (RBO) and monoglyceride (MG) for diacylglycerol-enriched rice bran oil (RBO-DG) preparation was investigated. The effects of substrate ratio, reaction temperature, time, and enzyme load on the respective content of free fatty acid (FFA) and DG in the final RBO-DG products was investigated. Enzyme screening on the reaction was also investigated. Response surface methodology (RSM) was used to optimize the effects of the reaction temperature (50-70 °C), the enzyme load (2-6 %; relative to the weight of total substrates), and the reaction time (4-8 h) on the respective content of FFA and DG. Validation of the RSM model was verified by the good agreement between the experimental and the predicted values. The optimum preparation conditions were as follows: MG/RBO, 0.25; temperature, 56 °C; enzyme load, 4.77 %; and reaction time, 5.75 h. Under the suggested conditions, the respective content of FFA and DG was 0.28 and 27.98 %, respectively. Repeated reaction tests indicated that Lipozyme RM IM could be used nine times under the optimum conditions with 90 % of its original catalytic activity still retained.