The Determination Of Phenyllactic Acid In Fermented Foods And Its Application In Fermented Vegetables Preservative

Fermented foods show long shelf life due to the natural antibacterial substances(i.e.,lactic acid,acetic acid,propionic acid)produced by microorganism fermentation.Phenyllactic acid(PLA)was a novel natural antimicrobial compound found in sourdough and pickles in recent years.However,whether PLA existed widely in fermented foods and how was the preservative effect of PLA in fermented vegetables remained unknown.Therefore,the method of ultra high performance liquid chromatography-tandem mass spectrometry(UPLC-MS)was firstly established to determine PLA in fermented foods in this investigation;Then the concentration of PLA in fermented dairy products,fermented condiments,fermented soybean products was determined by this method;Finally,the application of PLA in fermented vegetable preservative was preliminarily explored.The specific content was as follows:The method of ultra high performance liquid chromatography-tandem mass spectrometry(UPLC-MS)was established to determine PLA in fermented foods.Samples were pretreated with methanol,and then separated by Shim-pack XR-ODS C18.AB SCIEX QTRAP 6500 liquid chromatography-mass spectrometry was used for qualitative and quantitative analysis using the multiple reaction monitoring(MRM)mode.The mass-to-charge ratio(m/z)of quantitative and qualitative ion for PLA were 146.9 and118.8,respectively.The gradient elution was performed by a mobile phase consisting of0.3%formic acid-acetonitrile and 0.3%formic acid-aqueous.PLA showed a good linearity with the concentration ranged from 1 to 500 ng/m L(R~2=0.999 9).The limits of detection(LOD,S/N=3)and quantitation(LOQ,S/N=10)were 0.3 ng/m L and 1 ng/m L,respectively.The concentration of PLA in fermented foods such as fermented dairy products,fermented condiments,fermented soybean products was determined by UPLC-MS/MS.The results showed that PLA was detectable in all tested samples.We first determined the PLA content in vinegar and rice wine.75%of the tested fermented dairy product samples showed the concentration of PLA lower than 4 mg/kg.59 kinds of brewing vinegars were collected,the average concentration of PLA in all tested brewing vinegars was208.88±128.45 mg/L,and the highest level of PLA was 433.90±21.70 mg/L.The concentration of PLA in 11 kinds of rice wine samples over 20 mg/kg was 72.7%.The main spoiled microorganism in fermented vegetables was screened by using YPD and NA media,and the antimicrobial effect of PLA against the isolated spoiled microorganism was investigated in the fermented vegetable system.The result suggested that the addition of PLA at 5 mg/m L could lead to 2.1 log reduction of Trichosporon asahii after 4 hours,and made Trichosporon asahii remained at the concentration of 7×10~3CFU/m L after 12 h;While,10 mg/m L of PLA could result in 4.4 log reduction of Trichosporon asahii after 4 hours,and even killed all of Trichosporon asahii after 60hours.In addition,the antimicrobial effect of PLA in the fermented vegetables matrix was significantly higher than that in the culture medium.