Production of structured triacylglycerols rich in palmitic acid at sn-2 position and oleic acid at sn-1,3 positions as human milk fat substitutes by enzymatic acidolysis

This paper studies the synthesis of structured triacylglycerols (STAGs) of type oleic acid–palmitic acid–oleic acid (OA–PA–OA or OPO) by acidolysis of PA enriched triacylglycerols (TAGs) (79.2% PA, 74.5% PA at sn-2 position) and several OA-rich free fatty acid (FFA) fractions. The PA located at sn-1,3 positions was replaced by OA, maintaining the PA at sn-2 position; for this purpose several sn-1,3 specific lipases (lipase DF from Rhizopus oryzae, Palatase 20000L from Mucor miehei, Lipozyme RM IM from Rhizomucor miehei, Lipozyme TL IM from Thermomyces lanuginosus and lipase QLC from Alcaligenes sp.) were tested in experiments carried out in presence of solvent at 37 °C. Lipase DF immobilized on Accurel MP1000 was selected because this lipase gave a high incorporation of OA at the extreme positions of TAGs (50.4%) in short reaction times (1 h) or IOT (intensity of treatment, lipase amount × reaction time/TAG amount) of only 0.4 g lipase × h/g TAG, maintaining a high content of PA at sn-2 position (68.6%). Using this lipase, the influence of FFA/TAG molar ratio and purity of OA-rich FFAs were studied. With a 6:1 FFA/TAG molar ratio and 90% OA it was possible to obtain STAGs with 67.2% OA at sn-1,3 positions and 67.8% PA at sn-2 position (57.2% of total PA was located at sn-2 position). Next, the synthesis of OPO STAGs was studied in solvent-free media at 50 °C. The best results were also attained with a 6:1 FFA/TAG molar ratio, 90% OA and using an IOT of 1.9 g lipase × h/g TAG. In these conditions it was possible to obtain STAGs with identical composition to the previously obtained with solvent. These STAGs were purified by two procedures which differed in that solvent was or was not used to separate STAGs and FFAs. Both with and without hexane, STAGs were obtained with approximately 99% purity and over 96% recovery yields.

Research highlights
► Structured triacylglycerols (STAGs) of structure oleic acid-palmitic acid-oleic acid (OPO) were obtained by a process with two lipase-catalyzed reactions.
► In presence and absence of solvent STAGs were obtained with 67% OA at sn-1,3 positions and 57-68% PA at sn-2 position.
► These STAGs were purified by two procedures differing in whether or not solvent was used and STAGs of approximately 99% purity and recovery yields of over 96% were obtained.
► The STAGs synthesized may be useful for preparing human milk fat substitutes (HMFS) because present PA contents at sn-2 position and OA at sn-1,3 positions higher than human milk TAGs.