Research On Freshness Preservation Technology And Spoilage Mechanism Of Mutton In Low-Temperature Air Conditioning Packaging

Mutton is the 4^thlargest amount consumed meat in China.Mutton,as an important supplement to pork consumption in China,has a high nutritional level.Jintang black goat is an important local breed in the southwest and famous for its fast growth rate,high nutritional value,high reproduction rate and other characteristics.At present,more than 90%of mutton on the market is sold as fresh mutton,and frozen carcass,where mutton is not easy to preserve due to the not standardized slaughtering environment and logistics are,storage equipment Especially,the storage and preservation technology is immature compared to the art of state,which causes a big possibility for contamination and deterioration during transportation and sale.However,the mutton preservation is still a key issue in the mutton industry.These problems have restricted the further development of mutton industry.Modified atmospheres packaging（MAP）technology in Europe and the United States is applied for beef preservation,In China,most researcher has focus on the application of MAP for pork preservation,while the research on MAP technology in the preservation of mutton is relatively weak,MAP and low-temperature preservation is a good combination of fresh meat preservation.This paper compares three kinds of MAP,70%N₂+30%CO₂（CO₂group）,70%O₂+30%CO₂（O₂group）and 0.4%CO+69.6%N₂+30%CO₂（CO group）,group to the vacuum packing,the commonly used packing way as the control group,under 4°C refrigeration conditions in terms of meat quality,physicochemical characteristics,microbial diversity and flavor substances of,using the longissimus dorsi of Jintang black goat.This study will provide theoretical and technical support for the development of Sichuan mutton industry.（1）Optimal exploration of each gas component for mutton gas preservation:By measuring and comparing the total number of colonies,p H,a*value,TVB-N value and TBARS value of 90%O₂+10%N₂group,70%O₂+30%N₂group,50%O₂+50%N₂group,10%CO₂+90%N₂group,30%CO₂+70%N₂group,50%CO₂+50%N₂group,0.2%CO+69.8%N₂+30%CO₂group and 0.4%CO+69.6%N₂+30%CO₂group to analyze the effects of different MAP methods on the physicochemical characteristics of fresh mutton,and to screen out the suitable gas ratio for mutton preservation.The results showed that the total number of colonies,p H and TVB-N values of 70%O₂+30%N₂group were always significantly lower than those of 50%O₂+50%N₂and 90%O₂+10%N₂groups（P<0.05）,and could effectively improve meat color,and the70%O₂concentration level was more suitable for mutton preservation.The p H value of the 30%CO₂+70%N₂group was in the secondary fresh meat range and had a better color protection,and its TVB-N and TBARS values were always significantly lower than those of the 10%CO₂+90%N₂and 50%CO₂+50%N₂groups（P<0.05）,and the 30%CO₂concentration of was more suitable for mutton preservation.The total number of colonies in the 0.4%CO+69.6%N₂+30%CO₂group was always in the range of secondary fresh meat and significantly lower than the other two groups（P<0.05）,which shown a better bacterial inhibition effect.Furthermore,CO MAP had better color protection and also played a significant role in delaying oxidative rancidity of mutton（P<0.05）,and the CO concentration at 0.4%was more suitable for preserving mutton.（2）Optimization of mutton gas preservation process:Based on the optimization of gas conditioning ratios in Chapter 2,three more suitable gas conditioning ratios of 30%CO₂+70%N₂,70%O₂+30%N₂,and 0.4%CO+69.6%N₂+30%CO₂for mutton preservation were initially screened.The total number of colonies,lactobacillus,pseudomonas,p H,meat color,TVB-N value and TBARS value and shear force of mutton were measured on Day0,Day7,Day14,Day21 and Day28,respectively.In order to determine the best solution for mutton gas preservation,and to provide a theoretical basis for the study of volatile flavor substances of mutton under different gas packaging methods.The results showed that:At Day14,the total number of colonies in the Vac group is 6.12 lg（CFU/g）and had exceeded the standard for secondary fresh meat,while the total number of colonies in the CO group 4.12lg（CFU/g）significantly lower than the other three groups（P<0.05）,and alkaline anaerobic bacteria such as lactobacillus grew faster in the CO₂group,and by Day14,all groups were in the range of safe fresh meat（lg（CFU/g）<6）.Pseudomonas grew more rapidly in the O₂group.The CO₂group could not play a good role in color protection,and the high concentration of O₂,in the O₂group would accelerate fat oxidation.In contrast,the CO group reduced the oxidation rate of protein and fat in mutton,and had a significant bacterial inhibition effect,which made sure the muscle have a better water holding capacity;meanwhile,the carboxy-myoglobin formed by CO and myoglobin made the mutton have a bright meat color.In summary,the CO group showing better preservation effect,had a longer shelf life,and CO group was more suitable as a preservation solution for mutton in scenarios such as cold logistics and supermarket vending.（3）A total of 24 volatile flavor substances,including 9 alcohols,3 aldehydes,4 esters,5ketones,2 acids and 1 alkane,were identified at different storage times of mutton in different packaging methods using HS-SPME/GC-MS technique.The Vac group had the least variety of volatile flavor substances,the O₂group had the most variety of volatile flavor substances,and the O₂group was richer in flavor substances and its flavor was more attractive.A total of14 key volatile flavor substances were identified using the odor activity value（OAV）method,with the highest alcohol content in the CO₂group and the lowest alcohol content in the Vac group,where 1-octen-3-ol,isoamyl alcohol,2-methylbutanol,and hexanol were the most abundant alcohols in the CO₂group.The highest content of aldehydes was found in the O₂group,and the lowest content of aldehydes was found in the CO group,where heptanal,hexanal and nonanal were straight-chain saturated aldehydes,which interacted with microorganisms in the storage process and produced a foul odor.The highest ester content was found in the CO₂group,and the lowest ester content was found in the Vac group,which had a higher ester odor threshold and played a supportive role in the flavor formation of mutton.The ketone content in the CO group was higher than the other three groups,and the lowest ketone content was found in the Vac group.（4）Effect of mutton gas preservation process on changes in microbial colony populations:Proteobacteria,Firmicutes were the dominant bacteria at the phylum level.the dominant bacteria at the genus level were mainly Pseudomonas,Shewanella,Serratia and Lactococcus,occupying more than 60%of the mutton microbial species abundance.（5）The correlation between microbial genera and subject volatile flavor substances using Spearman’s correlation.Brochothrix promoted the formation of flavors of ethyl3-methylbutyrate,ethyl 2-methylbutyrate,and 2-nonanone,and Shewanella promoted the formation of flavors of ethyl 3-methylbutyrate,etc.Bacillus promoted the formation of heptanal,Bacillus promoted the formation of hexanal,and Serratia promoted the formation of1-octen-3-ol.The relative abundance of Shewanella was higher in the CO₂group.Brochothrix had a higher relative abundance content in the O₂group.The genus Brochothrix had a strong ability to break down proteins and fats,causing the mutton to form a green liquid and produce a foul odor.