Detection Of Bacteria In Eggs Of Southern Hebei Province And Development Of Preservative Antibacterial Membrane

Eggs are nutritious animal food,but they are easy to rot and deteriorate,so the shelf life is very short.During storage,egg quality is affected by many factors,and bacterial contamination is one of the most common factors.Therefore,it is of great significance to detect bacterial contamination of eggs and develop corresponding preservation measures,with the aim of ensuring egg quality and prolonging shelf life.Under the condition of simulated room temperature(25℃,relative humidity 50～60%),the quality deterioration the egg produced by the farms A and B in Southern Hebei Province,the growth of egg bacteria and the change of lysozyme activity were detected.Compared to 0 day,the eggs of the farms A and B were as follows after 28days of storage:The weight loss rate increased to 6.89±0.94%and 6.63±0.88%,respectively;The relative density decreased to 1.003±0.003 g/m L and 1.002±0.004g/m L,respectively;The Haugh units decreased to 43.25±2.49 and 42.35±4.07,respectively;The egg yolk index decreased to 0.19±0.02 and 0.18±0.02,respectively,and the phenomenon of egg yolk rupture appeared.The eggs are graded as inferior eggs,suggesting that the preservation time of eggs was only about one month.The results showed that the increase of the total number of bacteria on the surface of eggshell,the decrease of lysozyme activity in egg white and the reproduction of bacteria in egg lead to the decomposition of egg substance,the decrease of concentrated proteins and the softening and rupture of yolk membrane,resulting in the deterioration of egg quality.A total of 41 strains of egg-derived bacteria were identified by bacterial culture,DNA extraction,PCR amplification of 16S r DNA,gene sequencing and BLAST sequence analysis,and these bacteria mainly belonged to Micrococcus luteus,Staphylococcus agnetis,Corynebacterium,Bacillus,Kocuria and some Uncultured bacteria.Most of the bacteria came from the surface of the eggshell,and some of them came from the egg white and yolk stored for 7 to 14 days(no bacteria were detected in egg white and yolk at 0 day),so these bacteria can accelerate egg deterioration and even cause disease risk.The phylogenetic trees of main bacterial groups were established by sequence similarity comparison with standard bacterial strains,which provided a novel basis for controlling bacterial contamination of eggs and improving food safety.The bacteriostatic circle test showed that lysozyme had obvious inhibitory effects on the above kinds of egg-derived bacteria,indicating that lysozyme may have the effect of egg preservation.Therefore,chitosan,acetic acid and lysozyme were used as the main raw materials to prepare the composite membrane.The moisture permeability of the membrane was taken as the main index to optimize the concentration of the three substances and determine the optimal ratios.In the single-factor experiments,the optimal concentrations of chitosan,acetic acid and lysozyme were 4.0%,2.0%and0.15%,respectively.On this basis,according to Box-Behnken principle,response surface methodology was designed,and the fitting equation was obtained:moisture permeability=465.28-19.39A-8.91B+2.53C-18.39AB-4.31AC-5.05BC+81.32A~2+29.70B~2+21.42C~2.The optimal ratios were obtained as follows:4.14%chitosan(A),2.10%acetic acid(B),and 0.15%lysozyme(C).Under the optimal condition,the chitosan-acetic acid-lysozyme antibacterial membrane was applied on the surface of eggs.Compared with the control group and the water-washing group,the sensory indexes of the control group and the water-washing group were significantly deteriorated at about 30 days,while the coating group still maintained a good sensory shape on the 80th day.The coating method significantly delayed the increase of the weight loss rate(P<0.05),and significantly delayed the decrease of relative density(P<0.05),Haugh unit(P<0.05)and yolk index(P<0.05),which also reflects that the bacterial contamination of eggs was controlled and ameliorated.It can be seen that the coating method has an obvious effect on egg preservation,extending the preservation time from about 30 days(control group and water-washing group)to 70～80 days.The main reasons are that chitosan can block water and oxygen,that lysozyme can inhibit the growth and reproduction of bacteria,and that acetic acid can adjust the conditions of film formation and optimize the physical and chemical characteristics of the composite membrane,so as to alleviate the internal water loss,enzyme activation,bacterial growth metabolism and nutrient decomposition.To sum up,this study analyzed the rules and the reasons of egg quality deterioration in Southern Hebei Province,recognized the quantity and species of egg-derived bacteria,and developed a novel antibacterial coating method of eggs by using chitosan,acetic acid and lysozyme as the main raw materials.These data and conclusions provide new ideas for controlling bacterial contamination of eggs,for delaying quality decline of eggs,and for prolonging the shelf life of eggs,which is conducive to promote egg production and consumption,to promote egg safety,and to improve the economic value of eggs in Southern Hebei Province.