Enzymatic Synthesis Of Lauroyl Mannoses And The Study Of Their Properties

Carbohydrate fatty acid esters can be synthesized from renewable sources. The main properties of these compounds are their biodegradability and nontoxicity. They have hydrophilic-lipophilic structure and play an important role in non-ionic surfactants because they are environmental protective. Now they have been widely used in food, pharmaceutical industries and cosmetic. In this paper lauroyl mannose was synthesized by lauric acid and mannose.The methods of detection and separation were firstly studied. The analysis condition for the TLC was confirmed, n-hexane: ethyl acetate(1:1, v/v)and methanol were used as mobile phase. The monoester, diesterⅠ, diesterⅡand diesterⅢcould be separated effectively. The retention factor(Rf)were 0.13,0.26,0.43and 0.59 respectively.Then the condition of TLC was applied to silica gel column chromatography for separating and purifying the lauroyl mannose: 1000 mL ethyl acetate/n-hexane(1:1, v/v),1000 mL ethyl acetate/n-hexane(6:4, v/v),1000 mL ethyl acetate/n-hexane/methanol(7:2:1, v/v/v),500 mL ethyl acetate/n-hexane/methanol(4:2:4, v/v/v)and 500 mL methanol were used as mobile phase. The separated products were identified by HPLC, HPLC-MS and NMR. It was certain that the product consisted of 6-O-lauryl mannose mannose, 1,6-di-O-lauryl mannose, 4,6-di-O-lauryl mannose, and 3,6-di-O-lauryl mannose.In order to synthesize diesters selectively, simultaneous reaction and solvent extraction system(SRE)was designed. The optimal condition for biphasic system was as follows: Diester productivity of 51.2% and monoester productivity of 25.3% were obtained under such conditions as the amount of mannose 0.05 mol/L, lipase 15 mg/mL, the phase ratio n-hexane:acetonitrile 7.5:7.5(v/v), the molar ratio of lauric acid to mannose 4:1, the amount of molecular sieve 60 mg/mL, the temperature 50℃, the shaking speed of the water bath 150 r/min, and the reaction time 72 h. The fractional conversion of lauroyl mannose was much higher than that in acetone system.The surfactant properties of monoester and diesters were also studied. The solubility, HLB, critical micelle concentration, foaming ability, foam stability, emulsifying ability, emulsion stability and also the Maillard reaction. The result showed that lauroyl mannoses had good surface activity. The HLB of diesters were all about 8~9, which could be used as wetting agent, while the HLB of monoester was 11.22 which could be used as O/W emulsifier. The foaming ability, foam stability, emulsifying ability and emulsion stability of monoester were better than diesters'but not so good in foam stability. The foaming property and emulsifying property became better while mixing diester and monoester together. It showed 1,6-di-O-lauryl mannose retarded Maillard reaction. The structures of diesters were identified further.