Toolbox for exchanging constituent fatty acids in lecithins

Since the compositional variety of phospholipids in native lecithins is limited, and structurally diverse synthetic phospholipids are expensive, the aim of this work was to develop a lecithin modification toolbox capable of modifying the fatty acid composition of native lecithins at a convenient lab-scale of 10-100 g. Starting with the native phospholipids of soybean lecithin, two types of fatty acid modification were carried out using either phospholipase A2 from porcine pancreas or a lipase from Rhizopus oryzae. The former was immobilised onto celite and used to selectively hydrolyse the sn-2 positioned fatty acid and the latter, commercially available in an immobilised form, was used to transesterify novel fatty acids onto the sn-1 position. The degree of phospholipid hydrolysis could be controlled between 5 and 95% by varying the contact time with the biocatalyst. A key parameter was the water concentration. By avoiding the presence of a bulk phase of water, emulsion formation was prevented and so simple product recovery was possible. However, sufficient water was required in order to maintain the water activity above 0.2, and because phospholipids increased the polarity of the solvent (hexane), it was necessary to add water in proportion to the lecithin concentration. During transesterification with methyllaurate, up to 43% lauric acid could be incorporated and although the recovery of fully acylated phospholipids was only 28%, due to the formation of hydrolysis products, they were isolated using solvent partitioning in hexane/isopropanol/water. The temperature was important in determining the relative rates of hydrolysis and transesterification and a lower temperature (40 degreesC) was favourable as the rate of hydrolysis was lowered without affecting the rate of transesterification.