Study On The Bacterial Effect And Mechannism Of High Pressure CO₂ On Whole Egg Liquid

Heat treatment is often used in the production of liquid eggs to sterilize them.This topic in order to solve this problem,High pressure CO₂ sterilization technology is applied to sterilize pathogenic bacteria and spoilage bacteria in liquid eggs and to ensure the functional characteristics of liquid eggs,providing a basis for the application of high pressure CO₂ sterilization technology in egg products.The main research contents are as follows:1.Study on the lethal effect of high pressure CO₂ on Salmonella in whole egg liquid.High pressure CO₂ sterilization conditions were optimized by single factor experiment and response surface experiment.Concluded that pressure,temperature,time,stirring rate,mortality rate of Salmonella have a significant impact,and the interaction between pressure and temperature on the degree of deadly Salmonella is not obvious,Optimum sterilization condition for 30 MPa,40℃,60 min and 125 r/min,to whole egg liquid in3×10⁶³×10⁷ CFU/mL to completely kill Salmonella.After dealing with the high pressure CO₂ and pasteurized whole egg liquid at 4℃storage long phenomenon exists in both microbial regeneration.Compared with the shelf life of the original egg liquid,the shelf life of the whole egg liquid after pasteurization and high pressure CO₂ was extended by 9 d and 39 d respectively.Therefore,compared with pasteurization,high pressure CO₂sterilization can prolong the shelf life of whole egg liquid.2.Changes in the functional characteristics of the whole egg liquid with high pressure CO₂.The effect of whole egg liquid was studied by studying the function and physicochemical properties of the whole egg solution at different time.Results showed that under 30 MPa,125 r/min,40℃,when high pressure CO₂ treatment 60 min,compared with untreated liquid whole egg,foaming ability and stability is improved by26.68%and 26.68%respectively;When the processing time was greater than 30⁶0min,the emulsion particle size gradually decreased,the emulsion potential increased,the emulsion droplet dispersed uniformly under the microscope,the volume of droplet decreased,and the emulsifying ability and stability of the emulsion increased.The gel strength decreased significantly at different times（p<0.05）.Through low field nuclear magnetic analysis,the T₂₂2 of high pressure CO₂ was gradually reduced,but T₂₂2 at different time was higher than that of untreated group and pasteurization group.And the peak of the whole egg liquid was transferred from 20¹00ms to 60¹000ms at the peak of T₂₂.Show that after high pressure CO₂ treatment,moisture by force binding of whole egg liquid is reduced,the water become more freedom,more loose contact with the water molecules,protein causes the whole egg liquid moisture ability than untreated,pasteurized whole egg liquid decreased significantly（p<0.05）.Rheological data show that high pressure CO₂ reduces the viscosity,elastic modulus and viscous modulus of whole egg solution.Then from the physical and chemical properties and structure analysis of the functional properties of protein change mechanism,it is concluded that in 15⁶0min,high pressure CO₂ cause protein solubility increased free sulfhydryl content gradually increased,surface hydrophobicity increase,lead to the spatial structure of protein,protein molecules in the air and water interface,along with the high pressure processing time protein to solubility decreased,after more than 60 min free sulfhydryl content and a decrease in surface hydrophobicity.SDS-PAGE showed that high pressure CO₂ did not change the composition of protein.3.Under 4℃storage of liquid whole egg and egg white liquid separation and identification.The whole egg liquid and egg white liquid reached putrid metamorphism at9 d and 35 d respectively.Through high-throughput sequencing technology and 16r sDNA sequencing,it was identified that the putrefied bacteria in the whole egg liquid were Bacillus cereus,Serratia liquefaciens and Enterococcus faecalis.The putrefied bacteria isolated from egg white were Serratia liquefaciens,Enterococcus faecalis,Methyl nutritional bacillus,Fluorescent pseudomonas,and Enterobacter cloacae.The largest number of strains isolated by Serratia liquefacienswe re 33.96%.The hydrolysis protein capacity of 6 strains was:Enterococcus faecalis>Enterobacter cloacae>Serratia liquefaciens>Fluorescent pseudomonas>Bacillus cereus>Methyl nutritional bacillus.4.Investigate the lethal effect of high pressure CO₂ sterilization technology on 6kinds of spoilage bacteria.The inactivation curves of 6 types of spoilage bacteria were fitted with the logistics model.Results show that in the 30MPa,40℃,under the condition of 125 r/min for Serratia liquefaciens in the treatment of 25 min to completely kill,Enterobacter cloacae and Pseudomonas,Methyl nutritional bacillus in 15,20,20 min was suppressed,and the sample for the Bacillus cereus and Enterococcus faecalis are reached in 75 min completely kill.Finally simulation in 6 strains of hybrid system,0.6μL/mL of oregano essential oil mixed with high pressure CO₂ synergy 20 min completely kill bacteria,PI transparent rate and fatality rate change is consistent,and high pressure CO₂ in 70 to 4.26 min.Under 25℃storage found that compared with the original whole egg liquid,high pressure liquid CO₂ with oregano essential oil make egg shelf life extension of 20 d,high pressure CO₂ extended to 10 d.5.Taking Enterococcus faecalis and Salmonella as indicator bacteria,the death mechanism of bacteria under different pressure of high CO₂ was explained by changes in cell membrane morphology and membrane protein,enzyme activity and DNA.The OD₆₀₀value indicated that Enterococcus faecalis was completely killed when the pressure was18MPa and 30MPa.The survival rate for salmonella was 0 at 30MPa.Further analysis by scanning electron microscopy revealed that under 18MPa,the surface of Enterococcus faecalis cells had aggregation and adhesion,and the cell morphology was completely changed when intracellular solutes leaked out.Changes in the morphology of Salmonella cells become more severe with increased stress.Flow cytometry instrument results show that under 18 MPa there are 92.7%of the bacteria in Enterococcus faecalis sublethal state,when the pressure is greater than 18MPa,the number of deaths in Enterococcus faecalis reached 43.8%,Salmonella under 30 MPa deaths at 79.3%;The results of laser confocal analysis showed that high pressure CO₂ caused cell membranes of Enterococcus faecalis and Salmonella to be damaged and lipoenzyme activity decreased.SDS-PAGE results showed that high pressure CO₂ could induce the degradation of proteins on cell membranes of Enterococcus faecalis and Salmonella.Both bacteria have DNA degradation,but Enterococcus faecalis is less degraded than Salmonella.