In the present work, direct enzyme-catalysed esterification of medium chain fatty acids (MCFA) from three different sources (Medium chain triacylglycerols, MCT; saponified MCT and a mixture of free MCFA) was evaluated to obtain structured mono- and diacylglycerols. The esterifications were carried out mixing the different sources of MCFA with glycerol at two weight ratios (1:1 and 4:1, w/w), using three immobilized lipases: Novozym 435, Lipozyme RM IM and Lipozyme TL IM; different reaction times (t = 0, 15, 30, 60, 120 min); enzyme loadings (5, 10 or 15% with respect to the total weight of substrates). The extent of esterification was determined by gas chromatography (GC) analysis of the acylglycerols produced. The highest incorporation of free MCFA into glycerol was obtained for a 1:1 (w/w) glycerol to free MCFA ratio, 5% of Novozym 435, at 50°C, 300 rpm, 10% of molecular sieves and a commercial MCFA mixture as starting material. Under these conditions, incorporation of at least 90% of MCFA into glycerol was achieved after 30 min of reaction.

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INTRODUCTION Medium chain fatty acids MCFAs are recognized for their health benefits. They are used in enteral and parenteral nutrition for a series of medical conditions of patients suffering low absorption of fats, poor digestion, and metabolic difficulties related to cystic fibrosis, Crohn s disease, colitis and enteritis 1, 2. MCFAs with 6 to 14 carbons are of high interest for green chemistry due to their lathering and low-viscosity properties. They are widely used in detergents and lubricants. After esterification with alcohol, they can also be used as emulsifiers for foods and cosmetics, solvents for flavours, surface treatment of food products and as well as readily digestible fat in high-energy diets 3. In lipid research, thin layer chromatography TLC is commonly used for a rapid lipid fractionation and fatty acids profile characterizations. Nowadays, TLC constitutes a basic tool for modern analytical chemistry because of its