The Antibacterial Mechanism Of Moringa Oil Against Listeria Monocytogenes And Its Application On Cheese Preservations

Listeria monocytogenes is a typical foodborne pathogen.After eating the contaminated food,it will lead to sepsis,meningitis and even abortion,with the mortality rate of up to 30%.In this study,we used moringa oil(MO)as the antibacterial agent,and explored the antibacterial mechanism of MO against L.monocytogenes and the application of MO on cheese preservation.The antibacterial mechanism was studied based on the antibacterial activities of MO.The effects of MO on the cell structure,physiological metabolism and genes of L.monocytogenes were also investigated.The application of MO on cheese preservation is evaluated from four aspects: antibacterial preservation application,color evaluation,texture analysis and sensory evaluation.The main research results are as follows:(1)The main component of MO is palmitic acid(38.67%)by GC-MS analysis.The MIC and MBC of MO against L.monocytogenes were both 10.0 mg/mL.The results of TEM showed that the membrane integrity of L.monocytogenes was destroyed after the addition of MO.The cell membrane permeability,electrical conductivity and surface zeta potential were significantly increased,indicating that the cell membrane was severely damaged,thus leading to a large amount of leakage of intracellular proteins and soluble proteins.(2)The activity of key intracellular enzymes(alkaline phosphatase and ?-galactosidase)were decreased significantly after the addition of MO.At the same time,the energy metabolism of L.monocytogenes was significantly inhibited,which was reflected in the decrease of ATP content and ATPase activity.The metabolic activity of the bacteria was determined by the resazurin method.And the results inhibited that the metabolic activity of L.monocytogenes decreased by 72% after MO treatment.The pathway of respiratory metabolism inhibited by MO is the Embden-Meyerhof-Parnas pathway(EMP).And the activity hexokinase(HK),phosphofructokinase(PFK)and pyruvate kinase(PK)of EMP pathway were also inhibited by MO.(3)The loss of intracellular DNA of L.monocytogenes was serious after the treatment of MO,which was consistent with the observation of LSCM.The results of agarose gel electrophoresis displayed that MO inhibited the activity of topoisomerase I/II.Through the ultraviolet absorption spectroscopy experiment,the interaction between MO and DNA is embedded binding.Real-time PCR showed that MO had different degrees of inhibition activities on LPI-1 virulence islands(prfA,plcA,hly,actA,plcB)and LPI-2 virulence islands(inlA,inlB).MO had no inhibitory effect on mpl of LPI-1 virulence island,the possible reason is that MO does not regulate the expression of mpl.(4)MO could inhibit the growth of L.monocytogenes effectively and extend the shelf life of cheese.After 14-days storage period at 4 °C,the population of L.monocytogenes in control group increased sharply and reached 4.79 log CFU/g;however,the population of four kinds of cheese treated with MO increased slowly.The population of L.monocytogenes in mozzarella cheese,cheddar cheese,parmesan cheese and camembert cheese only increased by 1.48 log CFU/g,1.51 log CFU/g,1.42 log CFU/g and 1.35 log CFU/g,respectively.After 7-days storage period at 12 °C,the population of L.monocytogenes in control group increased by 4.82 log CFU/g.The population of L.monocytogenes in mozzarella cheese,cheddar cheese,parmesan cheese and camembert cheese only increased by 2.09 log CFU/g,2.18 log CFU/g,2.14 log CFU/g and 2.11 log CFU/g,respectively.During the storage period,the colorimetric analysis,texture evaluation and sensory evaluation showed that MO do not have adverse effects on cheese,and it can effectively maintain their quality.Therefore,MO,as a natural antibacterial agent,has a broad prospect in the field of food storage and preservation.