Lipase-catalyzed synthesis of sugar fatty acid esters. Study of the reaction conditions through a DoE approach

Sugar fatty acid esters (SFAEs), usually called sugar esters, are non-ionic surfactants which are characterized by excellent emulsifying, stabilizing and detergency properties. SFAEs are widely used in many market sectors (i.e. food, detergent, cosmetic and pharmaceutical industry); depending on carbon chain length and nature of the sugar head group, SFAEs cover a wide range of hydrophilic-lipophilic balance (HLB). SFAEs have many advantages over petrochemical-derived surfactants as they are neither harmful to the environment nor skin irritants, are fully biodegradable and non-toxic. More interestingly, they can be produced from renewable resources. [1] Chemical synthesis of SFAEs requires harsh reaction conditions which result, in most cases, in complex mixtures of monoesters, di- or triester isomers, and by-products. Enzyme-based synthesis is an alternative strategy that can overcome the above mentioned drawbacks: enzymatic reactions occur under milder conditions and do not generally require tedious protection/deprotection steps. Moreover, biotransformations provide more environmentally friendly synthetic routes. Sugar fatty acid esters can be prepared, indeed, through an esterification reaction between a sugar (Cn(H2O)n) and a fatty acid (RCO2H) catalyzed by a lipase. [2-4] In this work, SFAEs, including glucose monooleate (GluMO), monostearate (GluMS), monopalmitate (GluMP), monolaurate (GluML), and galactose monooleate (GaMO), monostearate (GaMS), monopalmitate (GaMP), monolaurate (GaML), were synthesized by enzymatic esterification of fatty acids and the corresponding sugar. Immobilized lipases were used to catalyze this reaction in organic solvent by using molecular sieves (4 Å) to scavenge the water by-product and thus shift the reaction towards sugar ester formation. Reaction yields and product characterization were assessed by 1H NMR. Rational design of enzymatic reactions was carried out by using the synthesis of GluMP as the model reaction. Sugar:fatty acid ratio, temperature, and reaction time were selected as variables (response: product yield). References [1] N.S. Neta, J.A. Texteira and L.R. Rodrigues, Crit. Rev. Food Sci. Nutr. 55 (2015) 595-610 [2] N. Sarmah, D. Revathi, G. Sheelu, K. Yamuna, Rani, S. Sridhar, V. Mehtab and C. Sumana, Biotechnol. Prog. 34 (2018) 5-28 [3] M. Enayati, Y. Gong, J.M. Goddard and A. Abbaspourrad, Food Chem. 266 (2018) 508–513 [4] K. Ren and B.P. Lamsal, Food Chem. 214 (2017) 556-563 and refs therein