15种植物精油添加剂热稳定性和体外抑菌作用研究

The thermal stability and antibacterial effect of 15 plant essential oil additives

肉桂醛、香芹酚、丁香酚、百里香酚等植物精油活性物质具有广谱抑菌作用,在兽用抗菌药物减量化使用试点行动推动下,以植物精油为核心的添加剂产品越来越多。本研究旨在比较市售的15种猪、禽用植物精油添加剂的热稳定性,并探究它们对畜禽生产中常见病原菌的体外抑菌作用,以期为植物精油添加剂的合理使用提供参考。分别以多重耐药的猪源沙门菌、大肠杆菌和链球菌以及禽源沙门菌和大肠杆菌为研究对象,以大肠杆菌ATCC25922为质控菌,采用微量肉汤法体外测定肉桂醛、香芹酚、丁香酚、百里香酚和各精油添加剂的最小抑菌浓度(MIC)。通过棋盘稀释法比较肉桂醛、香芹酚、丁香酚和百里香酚不同复配组合对猪源大肠杆菌的抑菌效果。将每种添加剂等量分为对照组和热处理组,分别经乙醚抽提和气相色谱仪分析后,对每种添加剂中肉桂醛、香芹酚、丁香酚和百里香酚及其总量进行测定比较。结果显示:6株供试菌株对肉桂醛、香芹酚、丁香酚和百里香酚均表现出高度敏感性(MIC值0.25～2 mg/mL);当香芹酚:百里香酚和丁香酚?百里香酚复配比例为2∶1时表现出协同作用(FICI=0.5);植物精油添加剂EG2对6株供试菌无明显抑菌作用,其余14种产品的MIC值为1～32 mg/mL。此外,15种添加剂含肉桂醛、香芹酚、丁香酚和百里香酚的总量范围在2.64～691.40 mg/g;15种产品热处理前后精油总量变化范围在0.2%～14.11%。综上所述,受试精油添加剂产品普遍热稳定性较好,并具有一定的抑菌作用,且抑菌效果与产品肉桂醛、香芹酚、丁香酚、百里香酚和精油总量存在一定的正相关;EG7、EG3、ES2、ES1、EAP2和EP1这6种产品的体外抑菌效果明显,有潜力用于预防和治疗多重耐药菌引起的猪禽疾病。

The active chemical components of plant essential oil such as cinnamaldehyde,carvacrol,eugenol and thymol have been proved to have a broad-spectrum antibacterial effect.Under the pressure of reducing the use of veterinary antimicrobial,additive products based on the plant essential oil are becoming popular at the market.The aim of this study was to compare the thermal stability of 15 commercially available essential oil products and their antibacterial effect in vitro on the common pathogens in swine and poultry.The results of the current study might provide a reference for rational use of plant essential oil additives.Firstly,the micro-broth dilution assay was adopted to determine the minimal inhibitory concentrations(MIC) of 15 essential oil additives and their chemical components(cinnamaldehyde,carvacrol,eugenol and thymol) against multiple resistant isolates(pig-derived Salmonella,Escherichia coli,Streptococcosis suis;poultry-derived Salmonella,E.coli and sensitive E.coli ATCC25922).The combined effects of cinnamaldehyde,carvacrol,eugenol and thymol were also evaluated by the chequerboard method.Secondly,each of the 15 essential oil products was equally divided into two groups(the control group and the heat treatment group),after diethyl ether was extracted;and the concentrations of cinnamaldehyde,carvacrol,eugenol and thymol were detected by gas chromatography(GC).The results showed that the tested strains of bacteria exhibited high sensitivity(MIC values ranging from 0.25 mg/mL to 2 mg/mL) to these active chemical components.The compound ratios of carvacrol/thymol(2:1) and eugenol/thymol(2:1) showed synergistic effects according to the indices of fraction inhibitory concentration(FICI=0.5).Among the 15 essential oil additives,only EG2 had no antibacterial activity for the 6 selected bacterial strains,but the other 14 products had a good antibacterial capacity with the MIC value ranging from 1 to 32 mg/mL.The total levels of cinnamaldehyde,carvacrol,eugenol and thymol in 15 additives ranged from 2.64 to 691.40 mg/g.In addition,there was a 0.2% to 14.11% essential oil difference before and after heat treatment.In conclusion,the tested plant essential oil additives generally had good thermostability and in vitro antibacterial capability which was positively correlated with the levels of cinnamaldehyde,carvacrol,eugenol,thymol and the content of total essential oil.Six of the additives with high antibacterial capability were EG7,EG3,ES2,ES1,EAP2 and EP1.These additives had a potential to be applied to prevention and treatment of swine and poultry diseases caused by multiple resistant bacteria.