Enzymatic Production of Sugar Fatty Acid Esters

Sugar fatty acid esters (SFAE) are well known as bio-surfactants. Their excellent biodegradability as well as the fact that they are tasteless, odorless, nontoxic, non-irritant and non-ionic explains their increasing importance in numerous areas. On the other hand, for a long time, large scale production of SFAE remained mainly in the realms of organic chemistry and chemical processing. Chemical methods are mainly performed at high temperatures in the presence of alkaline catalysts. High energy consumption, coloring of products and low selectivity are major disadvantages of these methods. Moreover, some chemically synthesized SFAE are toxic and not readily biodegradable, thus causing their limited application in cosmetics, food industry and pharmaceutics. Enzymatic synthesis offers an alternative way. In the present work, a novel and effective enzymatic method eliminating most difficulties was developed for the production of SFAE. Unprotected sugars and non-activated fatty acids were directly used as starting materials in order to decrease production cost. The selection of organic solvent is very crucial. It turned out that only ethyl methylketone (EMK) or a mixture of EMK and hexane are useful for the production of SFAE, because both organic solvents are not only easily eliminated and allowed for use in the manufacture of foods and/or food additives, but also can form an azeotrope with reaction water which is easily removed from the reaction medium by azeotropic distillation. For the application of the membrane pervaporation for the solvent regeneration, the selection of membrane material is quite important. It was found that Pervap 2200 membrane is suitable to remove water from EMK. In order to get high conversion, some important parameters such as reaction time (Tr), substrate ratio (Sr, acyl donor to glucose), reaction temperature (Rt), solvent EMK or mixture of EMK and hexane amount (Sa, based on excess of substrates) and enzyme load (El, based on substrates) were investigated by response surface methodology in this work. In case of EMK, due to the various parameters to be considered, response surface methodology was used to identify best process conditions and up to 93 % yield of glucose stearate were achieved under optimized conditions (Tr = 58 h; Sr = 2.7; El = 8.9 % [w/w]; Rt = 78 °C; Sa = 1.9). In the case of a solvent mixture of EMK and hexane, 93% yield were also achieved at 59°C after 48 h using an equimolar ratio of glucose and stearic acid. Since the price of the biocatalyst largely contributes to the overall process costs, the factors affecting its long-term stability have been investigated in detail. Systematic analyses using supports of different aquaphilicity were used to find an optimum in enzyme stabilization. For