Regioselective synthesis of 6''-O-lauroyl-1-kestose and 6'''-O-lauroylnystose by sequential enzymatic reactions of transfructosylation and acylation

Fructan fatty acid esters are amphiphilic compounds with potential applications in the food industry due to their surface-active properties on the air/water interface. In this work, the regioselective synthesis of fatty acid esters of short-chain inulin-type fructooligosaccharides (FOS) was carried out in a two-step process comprising sequential enzymatic reactions of transfructosylation and acylation. In the first step, Schedonorus arundinaceus sucrose:sucrose 1-fructosyltransferase (1-SST, EC 2.4.1.99) converted sucrose (600 g/L) into the trisaccharide 1-kestose and the tetrasaccharide nystose in a ratio 9:1 with their sum accounting for 53% (w/w) of total carbohydrates. In the second step, the FOS mixture was transesterified with vinyl laurate in 2-methyl-2-butanol by immobilized Candida antarctica lipase B (CALB) (EC.3.1.1.3). NMR analysis of the synthesized monolaurate FOS esters revealed a regioselective acylation of the 6-OH of the terminal fructosyl moiety of both 1-kestose and nystose. The hydrophilic-lipophilic balance (HLB) values of 6''-O-lauroyl-1-kestose and 6'''-O-lauroylnystose were 14.7 and 15.7, respectively; which suggests their use as oil in water (O/W) emulsifiers. The main compound 6''-O-lauroyl-1-kestose with critical micelle concentration (CMC) of 0.6 mM and surface tension of 45.8 mN/m proved to be a more efficient surfactant than 6'''-O-lauroylnystose (CMC 5.38 mM) and surface tension 36.26 mN/m). We report a regioselective method for the synthesis of lauryl-FOS using the abundant and renewable resource sucrose as the starting substrate.