| Salted duck is a pot-stewed meat product with local characteristics in Nanjing,which can be divided into two categories:high temperature and low temperature.Low temperature salted duck products are usually transported and sold in bulk,which has the problem of short shelf life.Antibacterial packaging can effectively inhibit the growth of microorganisms in meat products,maintain product quality and prolong product shelf life,which has become a hot spot in the field of anti-corrosion and preservation of low-temperature meat products.Nisin is a natural food antibacterial agent with strong inhibitory effect on gram-positive bacteria,which is widely used in the field of meat products,but its antibacterial activity and stability may be reduced by the influence of food matrix.Loading nisin into packaging materials can achieve the purpose of slow-release and stable antibacterial activity.In this paper,the vacuum-packaged salted duck leg was taken as the research object;firstly,the changes of quality and flora of salted duck legs during cold storage were determined to explore the law of corruption under cold storage conditions;secondly,gelatin/zein/nisin(GA/ZN/nisin)antibacterial fibrous films were prepared by electrospinning technology,and their structures and antibacterial properties were characterized;finally,the nanofibrous film with the strongest antibacterial properties was applied to salted duck legs to evaluate its storage and preservation effect.The research results can provide some theoretical guidance for the development and utilization of electrospun nisin antibacterial nanofibrous films,and provide technical support for the storage and preservation of vacuum-packaged meat products such as salted duck legs.The main research contents and results are as follows:1.Analysis of quality changes and bacterial diversity of vacuum-packed salted duck legs during cold storage.The salted duck legs were sampled after 0,2,4,6,8,10 and 12 days of refrigeration to determine their sensory qualities,physicochemical properties and total plate count;Illumina Novaseq 6000 sequencing technique was used to determine the changes of microflora in raw duck legs(R),pickled duck legs(P)and salted duck legs on day 0(S0),day 6(S6)and day 10(S10)after cold storage,and spoilage bacteria were isolated and identified at the end of shelf life.The results showed that with the extension of cold storage time,the total plate count,total volatile base nitrogen(TVB-N)and thiobarbituric acid(TBARS)increased,the overall acceptability of sensory qualities decreases,and the pH value decreased at first and then increased.On the 10th day of cold storage,the total plate count of the salted duck legs exceeded the national standard limit and reached 5.06 lg CFU/g,which was determined as the end of the shelf life.A total of 4687 OTUs were detected from different duck leg samples.Alpha diversity analysis showed that the bacterial community richness of the five groups of samples was not significantly different(P>0.05),while the bacterial community diversity of the samples showed an overall downward trend and it was significantly lower than that of other groups on the end of shelf life(P<0.05).The dominant bacterial genera of the five groups samples(R,P.S0,S6,S10)were Streptococcus,Acinetobacter,Ralstonia,Ralstonia,Macrococcus,respectively.At the end of the shelf life,3 strains of Bacillus,1 strain of Listeria monocytogenes,1 strain of Weissella viridescens and 1 strain of Macrococcus caseolyticus were isolated.Based on the analysis of bacterial diversity and the identification of spoilage bacteria,it was confirmed that Macrococcus caseolyticus was the dominant spoilage bacteria in salted duck legs.2.Preparation of electrospun antibacterial nanofibrous films and evaluation of their antibacterial activity against Macrococcus caseolyticus.By electrospinning technology,gelatin,zein and nisin were used as raw materials,and different GA/ZN ratios(1:5,1:2,1:1,2:1,5:1)were used to prepare antibacterial fibrous films.The micro-morphology,fiber diameter distribution,thickness,thermodynamic properties,mechanical properties,chemical structures,hydrophilicity and antibacterial abilities of the five groups of fibrous films were characterized.The results show that all the fibrous films were nano-sized with a smooth appearance.When the ratio of GA to ZN was 1:1,the average fiber diameter was 160.15 nm,the average thickness of the nanofibrous films was the largest(195.48 ?m),and it had the strongest thermal stability and hydrophobicity,good mechanical properties,and there was no chemical reaction between the raw materials that make up the nanofibrous films.In addition,the nanofibrous film(1:1)was put into the medium inoculated with Macrococcus caseolyticus,after 24 hours of culture,the colony number in this group was 1.99 lg CFU/g lower than that of the blank control group.The results showed that the electrospun antibacterial nanofibrous film prepared with the ratio of GA to ZN at the ratio of 1:1 had good comprehensive properties and strong antibacterial activity against Macrococcus caseolyticus.3.Application of gelatin/zein/nisin antibacterial nanofibrous film in storage and preservation of salted duck legs.The salted duck legs were divided into vacuum-packaging(NC),blank GA/ZN nanofibrous film combined with vacuum-packaging(GZ11)and GA/ZN/nisin antibacterial nanofibrous film combined with vacuum-packaging(GZ11-10N).The effects of three different packages on the overall acceptability score of sensory qualities,pH value,TVB-N value,TBARS value,color and total plate count of salted duck legs during cold storage were determined.The results showed that the physicochemical properties and sensory qualities of salted duck legs packaged with GZ11-10N were significantly better than that of other treatments(P<0.05).On the 15th day of cold storage,the total plate count in the GZ11-10N group was 4.35 lg CFU/g,which did not reach the national standard limit,and only increased by 1.86 lg CFU/g compared with the initial total plate count,and the added value was significantly lower than that in the control group(P<0.05).It was predicted by data fitting that the shelf life of GZ11-l0N group was 21 days,which was 10 days longer than that of the control group.The results showed that the nanofibrous film played a significant bacteriostatic effect in salted duck legs.In summary,the GA/ZN/nisin nanofibrous film prepared in this study has good antibacterial and fresh-keeping effect on salted duck legs,and has a good application prospect in the field of meat storage and preservation. |
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