| Branched-chain fatty acids(BCFAs)are a class of fatty acids with a or more methyl group on the carbon chain.BCFAs are in low content in the diet but naturally present in human breast milk.BCFAs can not only reduce the intestinal inflammation but also inhibit the formation of biofilms in intestinal pathogens,providing important protection for infantile intestines.Based on the synthesis of high-purity sn-1/3 and sn-2 monoacylglycerols(1/3-MAG and 2-MAG)of five branched-/straight-chain fatty acids,the effects of the branched structure and positional distribution of BCFAs on bacterial biofilm inhibition were studied.It provides a theoretical and technical basis for exploring the mechanism of breast milk BCFAs to protect infantile intestinal health and adding BCFAs to infant formula.The main research contents are as follows:Firstly,this paper selected BCFAs including anteiso-17:0 and iso-17:0 in breast milk and straight-chain fatty acids 17:0,16:0 and 16:1 of similar carbon numbers.The 1/3-MAGs were synthesized enzymatically with the reaction conditions optimized.The results showed that the optimal conditions for the synthesis of 1/3-16:0-MAG were:tert-butanol as the reaction solvent,the substrate molar ratio of palmitic acid to glycerol was 1:16,and Lipozyme 435was added in 4%(w/w),reacted at 40°C for 2 h.The conversion of 1/3-MAGs under optimized conditions was 84.95%~93.20%,the yield was 41.97%~54.28%,and the purity after purification was above 92%.Secondly,the 2-MAG was synthesized by two-step enzymatic method,and the reaction conditions were optimized.The results showed that the purity of the triacylglycerol(TAG)synthesized by esterification of five fatty acids(16:0,17:0,16:1,iso-17:0 and anteiso-17:0)was above 95%.Then the 2-MAG was enzymatically synthesized from the alcoholysis of TAG.The optimum conditions are:the weight ratio of absolute ethanol to TAG is 4:1,and the amount of Lipozyme 435 is 8%(w/w),reacted at 55°C for 1 h.The conversion of 2-MAGs was 68.03%~89.75%,and the yield was 20.77%~52.16%.The purity after purification was more than 92%.The structure of the synthesized compounds were confirmed by MS and ~1H NMR,and the thermal properties were determined by DSC.Finally,using C.violaceum as a biofilm inhibition model,the inhibitory effects of different branched-/straight-chain fatty acids and their MAGs on the biofilm of C.violaceum were studied.The results showed that anteiso-15:0,anteiso-17:0 and iso-17:0 had the greatest inhibitory effect on the biofilm of C.violaceum,which were 51.34%,47.20%and 23.60%,respectively.16:1 also showed some inhibitory effect,while the inhibition of 16:0 and 17:0was relatively weak.The inhibitory effects of iso-17:0,17:0 and its MAG isomers on the biofilm of C.violaceum were 2-MAGs,fatty acids and 1/3-MAGs,while the inhibitory effects of anteiso-17:0,16:1,16:0 and its MAGs on the biofilm was fatty acid,2-MAG and 1/3-MAG,respectively.The inhibitory effects on the biofilm of 2-MAGs was greater than 1/3-MAGs.The results indicated that the BCFAs and its positional distribution in the TAG carbon skeleton have effects on its antibacterial biofilm properties.The mechanism of inhibition of bacterial biofilm by the branched structure of BCFAs and its positional distribution needs further study. |
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