| Glycerol mono-medium chain fatty acid esters are traditional food additives with both emulsifying and antibacterial properties.Currently,the glycerol mono-medium chain fatty acid esters,including lauric acid monoglyceride,have poor water solubility and affect the flavor of food,which limits their application in food.Polyglycerol medium-chain fatty acid esters have adjustable polarity and broad antibacterial spectrum without unpleasant smell,which becomes a development direction.However,the synthesis route of polyglycerol medium-chain fatty acid esters is long,and the processes of separation and purification are difficult.At present,many researches and applications are carried out using a mixture of complex ingredients,the studies of antibacterial activities and systematic action mechanisms of high-purity monomers are few.Therefore,triglycerol monolaurate(TGML)high-purity monomer was prepared in this paper,its broad-spectrum antibacterial activities and multiple action mechanisms were in-depth studied,and the application research was carried out in reconstituted milk.The specific experimental results were shown as follows:(1)The enzymatic synthesis,separation and purification and structural characterization of TGML.Lipase Lipozyme 435 was used to catalyze the synthesis of TGML from triglycerol and lauric acid.The optimized reaction conditions were shown as follows: triglycerol: lauric acid was 1.08: 1(mol: mol),the reaction temperature was 84.93 ?,the reaction time was 6 h,the enzyme dosage was 1.32%,and the content of TGML in the product was 49.76%.The crude product was purified by two stages molecular distillation combined with ethyl acetate and water extraction to obtain triglycerol monoester with a purity of 98.3%.By the characterizations by fourier transform infrared spectrum,electrospray ionization mass spectrometry and nuclear magnetic resonance carbon spectroscopy,the pure product was indeed TGML with a linear configuration.(2)The physicochemical properties and surface activities of TGML.TGML was a colorless and odorless high-purity monomer.Compared to glycerol monostearate,the acid value,saponification value and melting point of TGML were significantly lower,but its iodine value was slightly higher.The hydrophile lipophilic balance value of TGML was 9.89,indicating that it can be used as an oil in water emulsifier.The surface activity comparison showed that the interface properties of TGML were significantly better than glycerol monostearate.(3)Study on the inhibitory effects and action mechanisms of TGML on pathogenic bacteria and yeasts.The minimum inhibitory concentrations and minimum bactericidal concentrations of TGML against Escherichia coli,Salmonella typhimurium,Staphylococcus aureus,Listeria monocytogenes,Candida albicans and Cryptococcus neoformans were lower than that of sodium benzoate and potassium sorbate.PH did not affect the antibacterial effects of TGML.Its inhibitory times against pathogens were also better than sodium benzoate and potassium sorbate.The antibacterial mechanism experiments revealed that TGML would increase cell membrane permeabilities of bacteria and yeasts,destroy cell integrity,result in depressions and holes appeared on the cell surface,and simultaneously cause cell cycle stagnation and biosynthesis inhibition of macromolecules.(4)Study on the inhibitory effects and action mechanisms of TGML on foodborne molds.TGML had stronger inhibitory effects on the growths of mold colonies and mycelia than sodium benzoate and potassium sorbate.The half inhibitory concentrations of TGML on Aspergillus flavus,Fusarium moniliforme and Penicillium viridicatum were 79.00,44.86 and 10.59 ?g/m L.In different pH conditions,the antifungal activities of TGML remained stable.TGML also showed a significant inhibitory effects on the germinations of mold spores.The antifungal mechanism studies showed that TGML would reduce the ergosterol content of mold,increase intracellular material leakage and inhibit respiratory enzyme activity,but did not affect lipid peroxidation.(5)Study on the application of TGML.TGML showed a significant inhibitory effect on Cronobacter sakazakii in reconstituted milk.Above or below room temperature enhanced the antibacterial activity of TGML.Decreasing the pH also increased the antibacterial effect of TGML.However,the effect of ionic strength on its activity was not obvious.The gastric juice weakened the antibacterial effect of TGML in reconstituted milk.TGML and environmental factors(temperature,pH,and ionic strength)did not change the color and aroma of milk.In summary,this paper uses enzymatic synthesis,molecular distillation combined with ethyl acetate and water extraction to obtain TGML high purity monomer with a purity of 98.3%.TGML has a broad spectrum antibacterial activities on foodborne bacteria,yeasts and molds,and clarified the synergistic inhibitory mechanisms of multiple interferences in the cell membrane and intracellular.Therefore,this study will provide a multifunctional additive with emulsifying and antiseptic properties for the food,pharmaceutical and daily chemical industries,which has great application value.And the systematic studies of antimicrobial mechanisms also provide a reference for the development and theoretical research of antibacterial agent. |
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