| Salmonella is a Gram-negative bacterium,belonging to the Enterobacteriaceae family,which mainly contaminates the host through the fecal-oral route.A large number of foodborne infections worldwide have been shown to be caused by Salmonella,and the various symptoms of illness they produce are collectively referred to as salmonellosis.Salmonella has become a major pathogen of foodborne illness worldwide and poses a serious threat to public health.Therefore,we construct an ultrasound combined with Litsea cubeba essential oil nanoemulsion(LEON+US)sterilization technique to reduce the risk of Salmonella contamination of food products.In this study,we first investigated the optimal conditions for inactivation of Salmonella by LEON+US treatment.At the same time,the bactericidal mechanism of LEON+US was investigated.Finally,in order to investigate the application of LEON+US sterilization technology in fruits and vegetables,two models of artificially contaminated fruits and vegetables were constructed in this study,and the study was carried out in terms of both surface cleaning and internal sterilization of fruit juice.Firstly,a model of artificially contaminated cherry tomato was constructed to investigate the effect of LEON+US treatment on the inactivation of Salmonella on the surface of cherry tomato and the effect on the sensory quality of it.Secondly,a model of artificially contaminated kiwifruit juice was constructed to investigate the sterilization effect of LEON+US treatment on kiwi juice and the effects on the nutrient composition,antioxidant capacity and sensory quality of the juice during storage.Specific research contents are as follows:(1)Sterilization characteristics of Salmonella by US combined with LEONThe ultrasound intensity was adjusted to 115,230,345 W/cm~2 for 3,6,and 9 min,respectively,and the concentration of LEON was 0.08μL/m L.The experimental groups were set up:untreated group,US group(115,230,345 W/cm~2),LEON group(0.08μL/m L),and US combined with LEON treatment group.The results showed that the effect of synergistic sterilization was greater than that of individual sterilization,and the sterilization amount of synergistic treatment was greater than the sum of the two individual treatments.After 9 min of combined treatment,the number of Salmonella was reduced by 8.69 log CFU/m L,which was 4.79 log CFU/m L more than the sum of the two individual treatments.(2)The mechanism of US combined with LEON against SalmonellaThe effects of LEON+US treatment on the intracellular reactive oxygen species level(ROS)and malondialdehyde(MDA)content of Salmonella were investigated by using fluorescent probes,observing of nucleic acid leakage.The effects of LEON+US treatment on the cell membrane integrity and cell morphology of Salmonella were observed by flow cytometry,field emission scanning electron microscopy and transmission electron microscopy.The results showed that LEON(0.08μL/m L)+US(345 W/cm~2)for 6 min was able to induce intracellular ROS level and increase extracellular MDA content of bacteria,nucleic acid leakage.The results of field emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM)and flow cytometry showed that LEON+US treatment was able to alter cell morphology,leading to leakage of contents and disruption of cell membrane integrity.The results suggest that LEON+US treatment may exert a bactericidal effect by disrupting cell membrane integrity.(3)Effects of US combined with LEON on the inactivation characteristics and quality of cherry tomato model artificially contaminated with SalmonellaThe cherry tomato was treated with LEON at concentrations of 0.04,0.06,and 0.08μL/m L in combination with US(115,230,and 345 W/cm~2)for 3,6,and 9 min.The experimental groups were set:untreated group,ultrasound group(115,230,and 345 W/cm~2),LEON group(0.04,0.06,and 0.08μL/m L),and US combined with LEON treatment group.The results showed that the combined inactivation effect increased with increasing LEON concentration(0.06μL/m L)and ultrasound intensity(115,230 and 345 W/cm~2),and the amount of bacteria decreased by 1.55±0.27,2.40±0.23 and 3.38±0.27 log CFU/m L,respectively.Also,the LEON+US treatment did not affect the color,soluble solids content,acidity and hardness of cherry tomato during storage.The results of the study can provide a theoretical basis for the application of LEON+US sterilization technology in the cleaning of fresh agricultural products.(4)Effect of US combined with LEON on the inhibition of Salmonella in kiwi juice and the effect on sensory qualityThe effect of LEON+US treatment on the inhibition of Salmonella in kiwi juice during storage was investigated,as well as the effect on juice color,soluble solids,ascorbic acid,flavonoids and total phenol content,and the effect of this inhibition technique on the antioxidant properties of the juice.A sensory evaluation panel was set up to evaluate all aspects of kiwi juice during storage using a fuzzy mathematical-sensory evaluation method.The results showed that the LEON+US treatment had a slow increase in bacterial load during storage compared to the control,with less effect on the color of kiwifruit juice,no significant change in soluble solids content,and a significant increase in ascorbic acid,flavonoids and total phenols.Meanwhile,LEON+US treatment improved the antioxidant properties of the juice.The results indicate that the combination of LEON+US treatment can inhibit Salmonella in kiwi juice.The nutritional quality of kiwi juice was also improved after the combination treatment. |
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