Studies On The Synthesis And Anti-microbial Activity Of Sorbic Acid Derivatives

Food preservatives are commonly used in food processing to inhibit microorganism growth, prevent food spoilage and prolong shelf life of product. It is always a hot subject in food research area to search broad spectra, high efficiency and safety preservatives. In this paper, based on the relationship between molecular structure and anti-microbial activity, the synthesis methods and anti-microbial activity of several sorbic acid derivatives were studied. This work may provide reference for the development of novel food preservatives. First, the synthesis method and anti-microbial activity of bromo-sorbic acid were studied. Following the addition-elimination reaction mechanism, Br₂ electrophilic added to sorbic acid in anhydrous acetic acid solution forming dibromo-sorbic acid. Then dibromo-sorbic acid changed to bromo-sorbic acid through double molecule elimination reaction. The rate of addition reaction yield was 89%. The rate of elimination reaction yield was 76%. Addition reaction of Br2 to sorbic acid was occurred at γ,δcarbon-carbon double bond. Only one product 4,5-dibromo-hex-2-enoic acid was formed. The elimination reaction product was γ-bromo-sorbic acid. The result of anti-microbial activity test showed that anti-microbial activity of dibromo-sorbic acid to Escherichia coli, Saccharomyces cerevisiae and Aspergillus niger was poorer than that of sorbic acid. This may indicated theγ,δcarbon-carbon double bond is necessary for the anti-microbial activity of sorbic acid. Compared with sorbic acid, the microorganism growth lag phase was shortened, biomass and colony forming unit were decrease under the action of bromo-sorbic acid. 0.06-0.07% of bromo-sorbic acid can inhibit the growth of Escherichia coli, and Saccharomyces cerevisiae. In the aspect of inhibition parameter of sorbic acid and bromo-sorbic acid to milk spoilage microorganism, the half-life of bromo-sorbic acid anti-microbial activity was 3.3 times longer than that of sorbic acid. It can be concluded the anti-microbial activity obviously increase when sorbic acid was bromo-substituted. Second, The synthesis method and anti-microbial activity of methyl sorbate, ethyl sorbate, propyl sorbate and butyl sorbate were studied. Two methods of direct estification and acyl chloride estification were employed. The reaction product was light yellow oily liquid. The melt point were 6℃,-22℃,-33℃,-65℃respectively. Direct estification was occurred at the temperature of alcohol bolting point and using catalyst. The catalyzing efficiency of H₂SO₄,HCl,BF₃ were studied. The mixture of HCl and BF₃ show the highest efficiency. When the sorbic acid was 0.1mol, the usage of HCl+BF₃.was 0.002 or 0.003 mol. The mole ratio of sorbic acid to alcohol was 1:6. The yield of sorbate ester is 70%. In acyl chloride estification, the temperature of reaction was 90℃, the mole ratio of sorbic acid to alcohol is 1:1.2 or 1:1.3, and the yield of sorbate ester is 61-65%. No catalyst is needed. The results of anti-microbial showed that under the action of sorbic acid, methyl sorbate, ethyl sorbate, propyl sorbate and butyl sorbate sorbate, the lag phase of Escherichia coli were 4, above 48, 24, above 48 and 36 hours respectively. The anti-microbial activity of sorbate ester was greater than that sorbic acid. The inhibition rate of sorbate ester toward Bacillus thuringiensis was higher than that toward Escherichia coli. This demonstrated the difference of sorbate ester anti-microbial activity toward G+ and G-bacteria. 600ppm propyl sorbate or butyl sorbate can inhibit the growth of Saccharomyces cerevisiae. The number of Aspergillus niger colony forming unit decreased dramatically under the action of sorbate ester. By comparison the anti-microbial activity parameters of sorbic acid and sorbate ester, It can be seen that sorbate ester possess higher inhibition rate and longer half-life. The half-life of sorbic acid, methyl sorbate, ethyl sorbate, propyl sorbate and butyl sorbate toward milk spoilage microorganism were 22.9, 43.2, 34.4, 61.6, and 60.6 hours respective...