A Reliable Solvent-Free Transesterification Synthesis of Carbohydrate Fatty Acid esters: Optimization, Structure -Surface Activity Relationships And Antimicrobial Efficacy

A simple straight forward efficient method for the synthesis of sugar esters involving the transesterification of a sugar and fatty acid methyl ester is presented through a solvent -free alkali catalyzed procedure.

The influence of reaction temperature, reaction time, catalyst and molar ratio of the reactants were first screened to ensure the optimum conditions. After realizing the most suitable reaction media which achieve maximum conversion and yields, maltose, sucrose, and glucose fatty acid esters with acyl chains having 12 to 18 carbon atoms were chemically synthesized by following the base-catalyzed solvent- free transesterification of the sugar component and the methyl ester of the different fatty acids. In this study, the reaction afforded a total sugar ester (SE) yield over 88% with methyl fatty acid ester conversion of about 90% in most cases, by using K2CO3 catalyst under nearly ambient temperatures (40-50 oC) after a relatively short time (3 - 3.5 hrs.). The products were characterized by nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy. All the synthesized esters showed good solubility and distinct surface-active properties which depend on the balance between the length of the acyl chain and the hydrophilic head group (sugar the hydrophile-lipophile balance, HLB). The physicochemical characteristics were evaluated: surface tension values ranged from 38 to 44 mN/m, compared with 38.8 mN/m for sodium dodecyl sulfate (SDS). The critical micelle concentration (CMC) values were in the range 2.8x10-4 to 5.0 x 10-6 M/L. The longest the fatty acyl chain displayed the lowest CMC value. The variation of the molecular structure of the title compounds is reflected on certain of their important unique performance characteristics such as foamability, emulsifying and wetting potentialities, Moreover, the detergency capabilities were assessed in terms of their tendency of grease removal from wool substrates. Additionally, these esters also clearly display antimicrobial function against Gram-positive and Gram-negative bacteria as well as some fungi. Together, these findings imply that the synthesized esters from this work may be useful as foamers and emulsifiers as well as preservatives in dietary and other foods in the food and cosmetic industries