| With the development of lfood industry, higher requirements are presented for food preservatives, which are not only safe, non-toxicand efficient, but also possess, nutritional and functional festures. Fatty acids and their derivatives have become the target group to screen natural food preservatives and pharmaceuticals, veterinary drugs and pesticides for theirefficient, safe and functional diversification. However, previous reports and experiences of researchers are mainly accumulated on abundant experiments, which would inevitably be blindness or random, therefor, it is urgent to understand the relationships between molecular structure of fatty acids and their derivatives and their antibacterial activities. Our group has reported the antibacterial quantitative structure-activity relationship (QSAR) model of fatty acid and their derivatives against Gram-positive Staphylococcus aureus and Bacillus cereus. In order to get a more comprehensive understanding of the antimicrobial quantitative structure-activity relationship of fatty acids and their derivatives,35kinds of fatty acids and their derivatives were chosen to test their IC50against Gram-negative Escherichia coli O157:H7and the typical Eufloria Candida albicans and3statistically reliable QSAR models were establish.By analyzing the obtained models, it was found that steric and electronic properties are the most related factors with antimicrobial activity, and the molecules of fatty acid derivative which possessed denser atomic distribution, space volume in certain range, no steric effect in some regions, more electronic negativity of carboxyl terminal of fatty acid chains, special electron cloud distribution and particular sensitivity to out electric fieldwere tend to display more potent antimicrobial activity. This study also confirmed that medium chain fatty acid derivatives have the strongest antimicrobial activities, especially glycerol monolaurate (GML). However, GML is deficient in water solubility and taste when applied to actual food system, which may restrict its application and development in food industry. In view of this, we use sugar instead of glycerol to sythensis sugar medium chain fatty acid monoester with medium chain fatty acid, aimed to obtain new antibacterial fatty acid derivatives with good water-solublility, taste, physical and chemicalproperties as well.In order to comprehensively analyze and compare the antimicrobial activity and physico-chemical properties of sugar medium chain fatty acid monoesters, firstly, the synthesis of monolauroyl sucrose in2-methyl-2-butanol and dimethylsulfoxide (DMSO) solution by Lipozyme TL IM, and the separation and purification of monoester have been studied. On the basis of single factor experiments, response surface methodology was used to optimize the synthesis system of sucrose laurate, the obtained conditions are: sucrose (0.04mol/L),2-methyl-2-butanol:DMSO=4:1(v/v), plus the amount of Lipozyme TL IM100mg/mL, molecular sieve amount of100mg/mL, after oscillating30min at50?, lauric acid vinyl ester (0.4mol/L) was added tothe system, and the reaction time was4h. Then,the other18kinds of different monoesters were synthesized under the similiar conditions. Finally,19different sugar monoesters involved6monosaccharide monoesters,10kinds of disaccharide monoesters and3types of trisaccharide monoesters were synthesized and purified.Afterwards, the antimicrobial activities and surface-active properties including surface tension, critical micelle concentration (CMC), foamability, foaming stability, oil-water emulsifying ability and emulsion stability of sugar fatty acid monoesters were tested and analyzed. It was found that most monoesters showed the strongest antimicrobial activity against S. aureus. However, inhibition rate against E. coli O157:H7and C. albicans were relatively lower. Among the tested monoesters, MGL showed the best antimicrobial activity against the three tested microbes, and the minimum inhibitory concentrations (MICs) for them were all188?g/mL, and the raffinose monoesters exhibited no antimicrobial activity against the three tested cultures. The antimicrobial activities of diester and triesters were lower than monoesters. The length of fatty acid chain (hydrophobic group) and sugar groups (hydrophilic group) for sugar medium chain fatty acid monoesters both affected the surface properties and antimicrobial activities. According to the results, the MGL possessed the best antimicrobial activity; while disaccharide monoester showed better surface properties, water solubility, taste than GML, and has great potential developing and applying value. |
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