| In China,meatballs are traditional prepared meat products that have been consumed for nearly a millennium.They have the transient shelf-life since their rich nutrients and are prone to polluted secondarily during the process of packaging,which had brought tremendous economic loss for the meat processing industry.Recent years,researches about meatballs had been mainly concentrated on the aspect of flavor improvement,while its studies on preservation technology were rare.Cold plasma has an advantage of keeping the original flavor and nutrition substances of meat products compared with the thermal sterilization technology,with highly effective property of sterilization and extensive bacteriostatic performance.These characteristics demonstrated that cold plasma technology owned optimistic application potential in the field of preservation of meatballs.However,the effects of cold plasma on the microbiological and physicochemical qualities of meatballs were still fuzzy.Meanwhile,cold plasma treated condition for prolonging the shelf-life of meatballs was not established as well.Therefore,in order to obtain the relatively long shelf-life of meatballs,lion head was been chosen as object of study,a typical representative of meatball products.Exploring the effects of secondary sterilization(121°C 15min)on the flavor and bacterial community of pork meatballs during storage so as to comprehensively elaborate the pros and cons of present preservation way on the pork meatballs.Besides,screening spoilage bacteria in pork meatballs and evaluating their spoilage potential according to the result of bacterial community.Eventually,we evaluated the potential advantages of Ar-based MAP combining with cold plasma technologies on the microbiological shelf-life and quality attributes in pork meatballs in order to acquire a novel preservation method.1.Analyzing the differences of quality attributes in the secondary sterilized and non-sterilized pork meatballs during storageIn order to provide deep understanding about secondary sterilization prepared meat products for consumers and meat processing industry,and this chapter analyzed the changes of sensory,physicochemical quality,and flavor in the thermal sterilized and non-sterilized pork meatballs during storage so as to deeply investigated the influence of secondary sterilization(121°C 15min)on the quality characteristics of pork meatballs.Results showed that the sensory scores of odour,texture,and overall acceptability were lower in the secondary sterilized group than those in the non-sterilized group.In addition,the significantly higher lipid oxidation,total volatile base nitrogen,and protein carbonyl content values were obtained in the secondary sterilized group compared with the non-sterilized group on day 0(P < 0.05).GC-MS showed that the initial flavor composition in pork meatballs was changed via secondary sterilization treatment(121°C 15min),and the more volatile organic compounds that associated with lipid and protein oxidation were detected in the process of thermal treatment,such as(E)-2-nonenal,(E)-2-octenal,(E,E)-2,4-decadienal,hexanal,and so on.In conclusion,the speed of the oxidation reaction was evidently increased during the process of secondary sterilization treatment(121°C15min),thereby the more flavor compounds that related with the lipid oxidation were generated in pork meatballs.These would decreased the sensory quality of pork meatballs after secondary sterilization technology.2.Evaluation of the spoilage potential of bacteria isolated from non-sterilized pork meatballsIn order to explore the effect of secondary sterilization treatment on the microbiological quality pork meatballs during storage and evaluate of the spoilage potential of bacteria isolated from non-sterilized pork meatballs.This chapter investigated the difference of bacterial community between the secondary sterilized and non-sterilized pork meatballs during storage via the high-thought sequencing technology.Then we screened underlying spoilage bacteria from pork meatballs and evaluated their spoilage potential according to the result of bacterial community.Ultimately,the dominant spoilage bacteria of pork meatballs was determined.Results showed that secondary sterilization treatment significantly decreased the initial total viable bacterial counts by approximately 2 log CFU/g(P < 0.05)and effectively inhibited the bacterial growth in pork meatballs during storage and prolonged the shelf-life of pork meatballs from 14 d to 60 d.Besides,secondary sterilization treatment(121°C 15min)evidently decreased the diversity and changed the composition of initial bacterial community,and maintain their stability of bacterial community in pork meatballs during storage.At 0 days,the bacterial community was dominated by Streptococcus(29.80%),Acinetobacter(27.37%),and Pseudomonas(13.16%)in the secondary sterilized pork meatballs,whereas Caulobacteraceae-uncultured(44.86%),Bradyrhizobium(12.33%),Sphingomonas(4.26%),and Acinetobacter(4.42%)dominated the bacterial community of the non-sterilized group.At the end of storage,the bacterial community was dominated by Streptococcus(35.49%),Acinetobacter(11.60%),and Pseudomonas(14.27%)in the secondary sterilized pork meatballs,whereas Pseudomonas(43.76%),Pantoea(27.18%),and Serratia(16.94%)dominated the bacterial community of the non-sterilized group.In order to the shelf-life of non-sterilized pork meatballs was prolonged,the total of 109 strains bacteria were screened from the samples,including 11 strains Pseudomonas spp,11 strains Pantoea spp.,1 strains Aeromonas spp.,49 strains Serratia spp.,27 strains Enterobacter spp.,3 strains Carnobacterium spp.,3strains Raoultella spp.,and 4 strains other bacterial genus.Then the abilities of proteolysis and growth of identified bacteria from the non-sterilized pork meatballs.Results showed that Pseudomonas fragi 19 Y owned the strongest abilities of growth and proteolysis compared with the other strains,with its proteolysis circle and growth speed was28.31±3.51 mm and 0.262±0.042,respectively.These results may be explained the phenomenon that Pseudomonas became the absolutely dominant bacterial genus in bacterial community of non-sterilized pork meatballs at the end of storage.In conclusion,Pseudomonas fragi 19 Y 、 Serratia spp 13 W 、 Pantoea aglomerans 0W 、Enterobacter ludwigii 22 W 、 Raoultella ornithinolytica 18 W 、 Aeromonas spp 5Y 、Serratia liquefaciens 1Y、Serratia liquefaciens 10W、Carnobacterium TMW were the dominant spoilage bacteria of non-sterilized pork meatballs.3.Cold plasma combined with Ar-based MAP for pork meatballs: influence on microbiological shelf-life and quality attributesIn order to establish a preservation technology that was suitable for storing pork meatballs,the inhibited effect of the 100% Ar MAP+CP treatment on the dominant spoilage bacteria that was isolated from the previous chapter was investigated.Then,the effects of 100% Ar MAP+CP treatment on the storage characteristics and shelf-life of non-sterilized pork meatballs were explored as well,and different cold plasma treated times(0,3,6,and 9min)on the preservation effects of pork meatballs were optimized.Results showed that the 100% Ar MAP+CP treated for 6min could significantly decreased the number of all dominant spoilage bacteria from 4log to around 1log even to more less except for Carnobacterium TMW via the inhibited bacteria experiment in vitro(P < 0.05).However,the 100% Ar MAP+CP treated for 9min could significantly decreased the number of all dominant spoilage bacteria by below 1log of pork meatballs(P < 0.05).On this basis,100% Ar MAP+CP treated for 0,3,6,9min were been applied for non-sterilized pork meatballs.Results of microbiological experiment showed that 100% Ar MAP+CP treated for 6 and 9min significantly decreased the total viable counts approximately 1.5log in the non-sterilized pork meatballs compared with the control group.Meanwhile,treatments of CP for 6 min and 9 min could significantly decrease the relative abundance of unclassified-Enterobacteriaceae and Acinetobacter in the non-sterilized pork meatballs(P< 0.05),and they could prolong the pork meatballs’ shelf-life for 14 days according to the result of total viable count.Besides,cold plasma treatment did not significantly change the initial TVB-N compared with the Ar MAP group,although the lipid oxidation values were slightly higher in the CP treated groups.Results of GC-IMS analysis revealed that,unlike the Ar-3min and Ar-6min groups,the original odor of Ar-9min pork meatballs was significantly different from the fresh meatballs,which may be related to marked higher contents of decanal,E-2-nonenal,benzene acetaldehyde,benzaldehyde,and methyl isobutyrate in Ar-9min groups.Taken together,it is indicated that Ar-based MAP combining with cold plasma treated for 6min was more suitable to be applied for the preservation of pork meatballs. |
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