Lipase-catalyzed incorporation of docosahexaenoic acid (DHA) into borage oil: optimization using response surface methodology

The ability of immobilized lipase Novozym 435, from Candida antarctica, to modify the fatty acid composition of borage oil (Borago officinalis L.) in hexane, by incorporation of docosahexaenoic acid (DHA), was studied. Response surface methodology (RSM) was used to evaluate the effects of variables, namely the amount of enzyme (100–200 U), reaction temperature (30–60 °C) and reaction time (18–30 h), on the yield (%) of DHA incorporation. Optimization of the acidolysis reaction was attempted in order to obtain a maximum yield of DHA incorporation while using the minimum amount of enzyme possible. Computer-generated contour plot interpretation revealed that an enzyme concentration of 165 units, after 25 h of reaction at 50 °C, gave optimum incorporation of DHA, up to 34.1%. Analysis of variance (ANOVA) showed that 94% (R2=0.94) of the observed variation was explained by the polynomial model. A low coefficient of variation (2.92) showed that the reproducibility of the model was satisfactory. Lack of fit analysis revealed a non-significant value for the model equation, indicating that the regression equation was adequate for predicting the degree of DHA incorporation under any combination of values of the variables. The positional distribution of DHA in modified borage oil, produced under optimum reaction conditions, was determined using pancreatic lipase hydrolysis. The results showed that DHA was fairly evenly distributed at the sn-2 and sn-1+sn-3 positions of the structured triacylglycerols.