Preparation Of Antibacterial Nanofiber Film Loaded With Perillaldehyde And Its Application In Chilled Chicken Preservation

In recent years,the trading mode of broilers has been changed from traditional fresh chicken to chilled chicken as the transformation and upgrading of broiler industry.Chilled chicken has superior taste,quality,and flavor compared to fresh chicken.However,the high nutritional content,sufficient moisture,and low-fat content of chicken make it vulnerable to microbial contamination even when stored under cold conditions.Therefore,it is increasingly crucial for research aimed at reducing bacterial contamination levels,delaying spoilage and extending the shelf life of chilled chicken in the field of food preservation.In this paper,the in vitro proteolytic activity and in situ spoilage potential of spoilage microorganisms isolated from chilled chicken were evaluated to find out the dominant spoilage bacteria in chilled chicken.Then,gelatin-chitosan/gelatin-perillaldehyde/gelatin-chitosan（GC/GP/GC）antibacterial nanofiber films were fabricated by electrospinning technology,and their structures as well as antibacterial properties were characterized.Finally,the antibacterial nanofiber films were applied to the antibacterial preservation of chilled chicken for evaluating their actual preservation capacity.The research contents and results of this paper are as follows:1.Evaluation of spoilage potential of spoilage bacteria in chilled chickenSpoilage bacteria play a remarkable role in the spoilage of chilled chicken.In this part,a total of 42 bacterial strains isolated from chilled chicken were studied.Firstly,the in vitro proteolytic activities of spoilage bacteria isolated from chilled chicken were evaluated using skim milk agar medium.It was found that the proteolytic abilities of different spoilage bacteria were different,wherein Pseudomonas lundensis J8 exhibited the strongest in vitro proteolytic activity.In order to further study the in situ spoilage potential of spoilage bacteria in chicken,six spoilage bacteria with significant difference in proteolytic activity,namely P.lundensis J7 and J8,Aeromonas hydrophila Q20,Aeromonas media Q23,Brochothrix thermosphacta R1 and R9,were further characterized to evaluate their spoilage potential in chicken.The results showed that P.lundensis J8 displayed the strongest in situ spoilage potential,which was characterized by rapid growth of bacterial content,p H,total volatile basic nitrogen（TVB-N）and peptides on chicken.After only one day of storage,the total number of colonies of P.lundensis J8 reached 6.49 log₁₀ CFU/g,which exceeded the upper limit allowed by national standard.At the end of storage,the total number of colonies(9.71±0.04 log₁₀ CFU/g),p H（6.50±0.02）,TVB-N（51.42±0.94 mg/100 g）and polypeptide content（16.57±0.18 mg/g）of P.lundensis J8 were significantly higher than those of other spoilage bacteria.In addition,all spoilage bacteria produced a variety of volatile odor components,including sulfide,aromatic compounds,organic sulfide and hydride during the storage at 10℃.Combined with the evaluation results of in vitro and in situ spoilage potential,it was found that P.lundensis J8exhibited the strongest spoilage ability among the 6 spoilage bacteria.2.Preparation,characterization and antibacterial performance evaluation of GC/GP/GC antibacterial nanofiber filmsGC/GP/GC antibacterial nanofiber films were prepared using electrospinning technology.Gelatin and chitosan were used as the carrier matrix,while perillaldehyde was used as the antibacterial agent.The outer layer was gelatin chitosan（GC）nanofiber film and the middle layer was gelatin（GP）nanofiber film loaded with perillaldehyde.Then,the micromorphology,chemical structure,thermal stability and other properities of GP,GC and GC/GP/GC antibacterial nanofiber films were characterized.The results of micromorphology indicated that the nanofibers of all GP nanofiber films were smooth.The diameter of nanofibers increased with the increase of perillaldehyde concentration.The average fiber diameter was 105.50±3.15 nm,122.06±3.11 nm and 141.98±3.37 nm when perillaldehyde was added at 1%,2%（w/v）and 3%,respectively.According to the infrared spectrum results,it was found the characteristic peaks of perillaldehyde appeared in GP nanofibers loaded with perillaldehyde at 2935 cm^-1,2855 cm^-1 and 1442 cm^-1,indicating that perillaldehyde was successfully embedded into gelatin nanofibers,but no new chemical structure was formed.However,the results of thermal stability showed that the addition of perillaldehyde reduced the thermal stability of GP nanofiber films.According to the results of the previous chapter,P.lundensis J8,A.hydrophila Q20 and B.thermosphacta R9 were selected to evaluate the antibacterial activities of antibacterial nanofiber films,and it was found that the GP₂antibacterial nanofiber film showed good antibacterial property.In order to further improve the antibacterial activity,GC antibacterial nanofiber film was selected as the outer layer to prepare GC/GP₂/GC antibacterial nanofiber film.The results showed that GC/GP₂/GC antibacterial nanofibers had obvious inhibition zone on P.lundensis J8,A.hydrophila Q20 and B.thermosphacta R9,and the inhibition zone diameter were 15.93±0.32 mm,17.51±0.23 mm and17.63±0.21 mm,respectively.In addition,the outer GC nanofiber film of GC/GP₂/GC nanofiber film can improve its antibacterial activity as well.3.Evaluation of the preservation of GC/GP/GC antibacterial nanofiber films in chilled chicken storageIn order to determine the actual preservation capacity of electrospinning antibacterial nanofiber films,the chicken breasts were packaged by pallet（blank control）,GC/GP₀/GC and GC/GP₂/GC respectively,and stored at 4℃.The results indicated that compared with blank control and GC/GP₀/GC,GC/GP₂/GC packaging could significantly delay the deterioration of chicken quality during storage.On the 6th day of storage,the total viable count（TVC）of blank control group was 6.13 log₁₀ CFU/g,which exceeded the national standard.On the 10th day of storage,the TVC of GC/GP₂/GC group was 5.76 log₁₀ CFU/g,which was still lower than the national standard.In addition,the changes of p H,TVB-N and peptides content of GC/GP₂/GC group during storage were significantly lower than those in blank control group.Therefore,GC/GP₂/GC antibacterial nanofiber film exhibited the significant antibacterial activity in the preservation of chilled chicken.In summary,the GC/GP/GC antibacterial nanofiber film prepared in this study has a good antibacterial and fresh-keeping effect on chilled chicken,and a good application prospect in the field of food package.