Study On The Spoilage Deterioration Of Refrigerated Liquid Whole Egg And Its Quality Control

Liquid egg products are popular in the field of food processing because of their advantages of good nutrition and functional preservation,high hygiene and safety,simple operation,convenient storage and transportation,etc.,and have become indispensable food materials in the processing of baked goods,meat products,and minced fish products.However,the short shelf-life of liquid egg products is a technical problem that the industry needs to break through for a long time.In addition,more green and safer processing technology is also the development trend of the food industry.In this paper,the quality change of liquid whole egg during cold storage was investigated,and the spoilage potential of typical spoilage bacteria in liquid egg was studied.On this basis,Lactobacillus plantarum 90(L.Plantarum 90)was used to inhibit the typical spoilage bacteria in liquid egg.Finally,the effects of fermentation of L.plantarum 90 on the functional properties of liquid egg were studied.This research laid a theoretical foundation for the application of L.Plantarum 90 and its cell-free supernatant(CFS)in the field of liquid egg products processing and preservation.The main research contents and conclusions are as follows:1.Study on quality change of liquid whole egg during cold storage.The p H value of liquid whole egg decreased gradually,and the total volatile base nitrogen showed a curve increase.When the cold storage time reached one week,the microorganisms in the liquid whole egg entered the exponential growth stage,and the particle size of liquid egg gradually increased,along with the gelling,emulsifying and foaming properties decreased significantly(P<0.05).Psychrophilic bacteria represented by pseudomonas were the main microorganisms of liquid whole egg during cold storage.In addition,a total of 104 colonies were isolated and purified from liquid whole egg,and 34 strains were identified.The identified microorganisms mainly include: Pseudomonas sp.,Microbacterium sp.,Bacillus sp.,Enterococcus sp.,Streptococcus sp.,Stenotrophomonas sp.,Acinetobacter sp.,Rhodococcus sp.,Leclercia sp.,Moraxella sp.and Proteus sp.;Among them,the abundance of Pseudomonas sp.and Microbacterium sp.was higher.2.Inhibitory effect of cell-free supernatant of Lactic acid bacteria on typical spoilage bacteria in liquid egg.The microorganisms of Pseudomonas sp.and Microbacterium sp.had strong growth ability at low temperature,and showed high enzyme activity and the ability to cause the spoilage of whole egg under cold storage,which were the key microorganisms leading to the spoilage of liquid whole egg.While the CFS of L.plantarum 90,Lactobacillus rhamnosus 05 and Pediococcus pentosaceus L28-8 could inhibit the four typical spoilage bacteria(Pseudomonas putida strain I3,Pseudomonas fluorescens B16-140,Microbacterium sp.Cug5 and Microbacterium sp.ALBL＿062)in liquid egg.And the CFS of L.plantarum 90(LCFS)had the best bacteriostatic effect.When LCFS was applied to liquid whole egg,it was found that the inhibition of LCFS to the four typical spoilage bacteria in liquid whole egg was dose-dependent.3.Study on the antibacterial properties of the cell-free supernatant of L.Plantarum 90.L.Plantarum 90 began to exhibit bacteriostasis in the middle of its logarithmic growth phase and reached its peak in the stationary phase.The minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)of LCFS to the four indicators(Pseudomonas putida strain I3,Microbacterium sp.ALBL＿062,Salmonella CICC 21513 and Staphylococcus aureus ATCC 6538)were all 8 mg/m L and 16 mg/m L,and the results of bacteriostatic and bactericidal curves showed that Salmonella CICC 21513 was more sensitive to LCFS.The bacteriostatic effect of LCFS was the result of the interaction of organic acids and protein bacteriostatic substances,of which organic acids play a major role.After detection,the contents of lactic acid,citric acid,butyric acid and tartaric acid in LCFS were as follows:16.336 mg/m L,10.119 mg/m L,5.245 mg/m L,0.621 mg/m L.In addition,LCFS mainly achieves the bacteriostatic effect by increasing the permeability of the cell membrane of target microorganism,forming pores on the surface of the cell membrane and leading to the leakage of cell contents.The decolorization effect of LCFS can be achieved by using 100 mesh activated carbon,adding 3% activated carbon and 30℃ for 40 min,and the decolorization does not affect the bacteriostasis.After concentration,the bacteriostatic activity of LCFS was improved.Adding decolorized and concentrated LCFS into the liquid whole egg contaminated by indicator bacteria could significantly inhibit the growth of indicator bacteria.4.Effects of L.Plantarum 90 fermentation on the functional properties of liquid whole egg.After fermentation with L.Plantarum 90,the p H of liquid whole egg decreased,and the solubility showed a trend of first increasing and then decreasing.Moreover,L.Plantarum 90 fermentation made β-sheet and β-turn change to α-helix and irregular curl in the protein secondary structure of liquid whole egg,and the protein secondary structure became looser.Fermentation had little effect on the emulsifying and foaming properties of liquid whole egg,while moderate fermentation could promote the formation of more delicate gel of whole egg.After fermentation,the pores on the surface of the whole egg gel disappeared and the color became brighter.At the later stage of fermentation,the secondary structure of proteins in the whole egg gel changed from α-helix,β-turn and random curl to β-sheet,forming a more orderly and stable structure.In addition,the springiness and water retention of whole egg gel were improved after fermentation.5.Effects of L.Plantarum 90 fermentation on the functional properties of egg white and egg yolk.After fermentation by L.Plantarum 90,the p H of egg white decreased steadily,and the surface hydrophobicity of egg white protein increased,while the thermal stability of egg white protein decreased,and the β-sheet decreased with the increase of random curl,α-helix and β-turn,indicated that the protein structure of egg white protein expanded more loosely.As for egg yolk,after fermentation the p H value of the egg yolk decreased significantly(P<0.05)and then gradually stabilized,egg yolk protein surface hydrophobicity was on the decline,after fermentation the intramolecular β-sheet decreased,while the intermolecular β-sheet increased,which indicated that the yolk protein had undergone de-folding and then aggregation to a certain extent.L.Plantarum 90 fermentation reduced the hardness,springiness and water retention of egg white gel,while improved the gel brightness to a certain extent,and the gel microstructure became looser.On the contrary,the hardness,springiness and water retention of egg yolk gel increased after fermentation,the yolk gel color became more yellow,and the microstructure of the yolk gel became more compact.Based on the effect of fermentation on the gelling property of whole egg,it was concluded that the decrease in the hardness of the whole egg gel after fermentation was due to the unfolding and partial degradation of the protein in egg white;while the improved gel springiness and water retention were attributed to the more dense and compact three-dimensional network structure formed by the re-aggregation of egg yolk proteins after unfolding.