Study On Antibacterial Mechanism And Application Of Clove Oil Combined With Lauric Acid Against Staphylococcus Aureus

Staphylococcus aureus(S.aureus)is a common foodborne pathogen that widely exists in the natural environment.Accidentally eating food that contaminated by S.aureus may cause food poisoning.Therefore,it is very important to control S.aureus and inhibit its growth and reproduction in food.In this paper,clove oil,thyme oil,peppermint oil and medium chain fatty acid lauric acid were used to inhibit S.aureus.The combination of clove oil and lauric acid with synergistic inhibitory effect was selected,and the inhibitory effect of this combination on S.aureus was studied.Combined with RNA transcriptome sequencing technique,the inhibitory mechanism of this combination on S.aureus were revealed.The antibacterial and fresh-keeping solution which made by clove oil and lauric acid was applied to fresh rice noodles to explore its fresh-keeping effect on fresh rice noodles.In this study,the minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)of clove oil,peppermint oil,thyme oil and medium chain fatty acid lauric acid against S.aureus were determined.Clove oil had the best inhibitory effect,MIC and MBC of clove oil were 2.00 μg/m L and 4.00 μg/m L,respectively;and MIC and MBC of lauric acid were 9.00 μg/m L and 18.00 μg/m L,respectively.Then the antibacterial effect of the combination of clove oil,thyme oil,peppermint oil with lauric acid was determined by chessboard method.The combination with synergistic effect was obtained: clove oil and lauric acid,and the best ratio was 1/4MIC clove oil+1/4MIC lauric acid,with a FICI value of 0.50.Compared with clove oil or lauric acid alone,the combination of clove oil and lauric acid had obvious inhibitory effect on the growth of S.aureus,destroyed the cell membrane and resulting in the leakage of nucleic acid,protein,various ion and inorganic salts in cells.Fluorescence microscope showed that bacteria died in different degrees.In addition,the crystal violet staining experiment showed that the synergistic treatment of clove oil and lauric acid could not only inhibit the biofilm formation of S.aureus,but also had a significant scavenging effect on mature biofilm.The bacteriostatic mechanism of clove oil and lauric acid on S.aureus was analyzed by RNA transcriptome sequencing technique.273 DEGs were identified to be mainly concentrated in metabolism,genetic information processing,environmental information processing,cell process and so on.After co-treatment with clove oil and lauric acid,genes mur G,upp S and dgk A,which involved in peptidoglycan biosynthesis,genes crt I,crt M and crt O,which involved in staphyloxanthin biosynthesis,gene sdh C which involved in tricarboxylic acid cycle,gene rpi A which involved in pentose phosphate pathway,genes aro D、opp B and B4602＿RS01475 which involved in amino acid biosynthesis and transport,and potassium transport gene ktr B were all up-regulated.While genes gcd H,fad D and fad N which involved in lipid metabolism,genes alr,hut H and pru A which involved in amino acid metabolism,gene lac C which involved in lactose metabolism,and potassium transport gene kdp A were all down-regulated.The synergistic treatment of clove oil and lauric acid inhibit the growth and reproduction of Staphylococcus aureus and lead to bacterial death by destroying cell wall,affecting cell membrane fluidity,disturbing energy metabolism,and interfering with cell osmotic pressure balance.The antibacterial solution made by clove oil and lauric acid were applied to fresh rice noodles.After the treatment of antibacterial solution,the initial colony number of fresh rice noodles was at least1.5 log CFU/g lower than that of the control group,and the time to exceed the safety limit(6 log CFU/g)was prolonged from 24 h to 72 h.The fresh-keeping solution treatment had little effect on the water content of fresh rice noodles during storage.At 72 h,the acid value of the control group was at least0.8 °T higher than that of the treatment group.The antibacterial solution treatment can improve the cooking quality of fresh rice noodles,reduce the cooking loss rate,increase cooking water absorption,reduce the rate of cooked strips and reduce the absorbance of paste soup.The treatment of bacteriostatic and antibacterial solution has a positive effect on the sensory quality,which can stabilize the color,smell,texture,tasty and appearance of fresh rice noodles,and maintain the quality of fresh rice noodles.To sum up,this study verified that clove oil and lauric acid have synergistic inhibitory effect on S.aureus,which provides a new idea for inhibiting the growth of S.aureus in food.