Interesterification of fats and oils by immobilized fungus at constant water concentration

The kinetics of enzymatic interesterification of oils and fats, using acetone-dried cells of Rhizopus chinensis immobilized on biomass support particles as a lipase catalyst, were investigated in batch operations at several constant water concentrations.Even under microaqueous (i.e., low-water-content) conditions, not only interesterification but also hydrolysis occured, and the water content in the reaction system decreased. The reaction rates of interesterification and hydrolysis at constant water concentrations were determined.For the reactions between olive oil and methyl stearate at several water concentrations, the parameters involved in the reaction model were determined by a trial-and-error method so as to make the calculated results correlate with the experimental data. The relationship between the parameters obtained and water concentration were examined.The rate constants involved in the reaction model of both interesterification and hydrolysis increased or decreased monotonically with the increasing water content, while the apparent activity of the lipase catalyst for interesterification had a maximum value at a water concentration of about 50 ppm. This suggests that when the water content is excessive the hydrolysis activity of lipase is accelerated more than its interesterification activity, and that when the water content is too little lipase activity can not be activated for either hydrolysis or interesterification.