Production of structured phospholipids by lipase-catalyzed acidolysis: optimization using response surface methodology

Structured phospholipids were produced by lipase-catalyzed acidolysis between soybean phospholipids and free fatty acids. For this purpose three commercially available immobilized lipases were examined and Lipozyme TL IM was finally selected for further optimization. Incorporation of acyl donors, including caprylic acid, conjugated linoleic acid (CLA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), into phospholipids was examined.

Different apparent incorporation rates were observed for the individual fatty acids. The main reason was attributed to the purity of the starting acyl donor mixtures, for example the starting material for CLA contained only 77% CLA. The nature of the phospholipids also affected the incorporation rates of caprylic acid catalyzed by Lipozyme TL IM.

The following order of reactivity was observed phosphatidylcholine>phosphatidylethanolamine>phosphatidic acid>phosphatidylinositol. Lipozyme TL IM-catalyzed acidolysis in a solvent-free system was optimized using response surface methodology (RSM). A three-level five-factor fractional factorial design with star points was adopted.

The five major factors chosen were lipase dosage (Ld, wt.% based on substrates), water addition (Wc, wt.% based on lipase), reaction time (Ti, h), reaction temperature (Te, °C), and substrate ratio (Sr, caprylic acid/phospholipids, mol/mol). Acidolysis was influenced by these factors in the following order: Ti>Ld>Sr>Te, whereas water addition had no effect on the incorporation in the range of 2–4wt.%.

The best fitting quadratic model was determined by regression and backward elimination. Based on the fitted model, the optimal reaction conditions for the production of structured phospholipids by Lipozyme TL IM-catalyzed acidolysis between soybean phospholipids and caprylic acid were found to be Ti, 70h; Ld, 30wt.%; Te, 57°C, Sr, 5.5/1mol/mol, and no water addition.

At these experimental conditions, 39% incorporation of caprylic acid can be obtained.