| As a popular food, chilled beef is recognized as one of the most perishable foods forits high water content and abundance of essential nutrients. Microbial contamination hasbeen considered as a major reason for meat spoilage during storage. Microbial growth andreproduction will induce toxic metabolites and color distortion so that meat becomesunappealing and unsuitable for human consumption. With the improvement of livingstandards, people are increasingly focusing on meat quality. At present, sensory analysis,physicochemical analysis and the microbiological analysis are generally used for qualityevaluation, but some drawbacks exists and inconsistent results may be obtained.The microbial diversity and dynamic changes of predominant bacteria in beef storedunder low temperature with modified atmosphere packaging (MAP) were respectivelyanalyzed. The changes of pH, total bacteria, TVB-N and biogenic amines were detectedduring storage and correlation analysis were made. The process of storage were studied intwo ways:spoilageorganismsand corruption, in addition, the influence of MAP and storagetemperature were investigated. This study will be meaningful for improving storageconditions and extending shelf life, and it can also establish the foundation for qualityevaluation of meat.1. The microbial diversity and dynamic changes of predominant bacteria in beefstored under low temperature (-2℃，0℃，5℃and10℃) with modified atmospherepackaging (MAP1:65%O2and35%CO2, MAP2:80%O2and20%CO2and airpackaging) were respectively analyzed by denaturing gradient gel electrophoresis(PCR-DGGE).The Shannon-Winer index of diversity(H), richness(S), evenness(EH) andsimilarity indices were used to represent dynamic changes of microbial community duringstorage. The results indicated that the types and intensity of bands in the DGGE profileschanged obviously. Overall, richness of air packaging samples were higher than those with MAP. The EHand H were in the range of1.87-3.04and0.73-0.97, respectively. The resultsof clustering analysis showed that the microorganisms were greatly influenced by MAPunder the condition of-2℃,0℃and5℃, while little effect occurred in the10℃storage.The DGGE fragments were sequenced and phylogenetic tree was constructed. Thirteenkinds of spoilage bacteria were found by cloning and sequencing: Bacillus, Lactococcus,Carnobacterium, Acinetobacter, Brochothrix, Enterobacter, Psychrobacter, Staphylococcus,Pseudomoas, Arthrobacter, Lactobacillus, Aeromonas and Micrococcus.Bacillus andCarnobacterium were the initial spoilage organisms and they play an important role duringthe storage of-2℃-5℃. Under the condition of10℃, less species of spoilage bacteriawere detected and Lactococcus and Lactobacillus turned into predominant bacteriagradually.2. The changes of pH, total bacteria and TVB-N were detected during storage andcorrelation analysis were made in this article. The initial pH of chilled beef is5.78. Underthe condition of-2℃and0℃, pH changed little and the effect of MAP was little. Underthe conditions of5℃and10℃, pH decreased firstly and then increased. After2-4days ofstorage under10℃, pH decreased to a minimum, and the reduction was shortenedsignificantly. On the other hand, the impact of MAP was obvious at earlier storage of10℃.During the storage of-2℃and0℃, total bacteria increased gradually and reached to106after20and16days of storage, respectively, which indicated extended shelf-life.Under the conditions of5℃and10℃, the number of microorganisms grew rapidly. TheMAP had some inhibitory effect on the growth of microorganisms during storage.Especially, MAP1had the strongest inhibitory effect under the condition of10℃.Under the condition of-2℃and0℃, TVB-N reached to15mg/100g at8-12days andthe effect of MAP was not significant. During the storage of5℃and10℃, TVB-Nincreased rapidly, especially under the storage conditions of10℃. However, under thecondition of5℃, TVB-N reached to15mg/100g at6-9days. MAP had a certain influenceon the increase of TVB-N and the influence is greater under the conditionof10℃.Pearson correlation coefficient between pH, total bacteria and TVB-N were analysisedand the results showed that total bacteria and TVB-N correlated significantly at0.01levelunder different storage temperature and MAP, and the Pearson correlation coefficient of pHand total bacteria and pH and TVB-N was low.3. A high-performance liquid chromatographic hyphenated with mass spectrometry detection method was developed for determination of six kinds of biogenicamines(cadaverine, tyramine, tryptamine, putrescine, histamine and phenethylamine) inchilled beef. Linear correlation coefficients were greater than0.994in the range of0-1.0mg/L. The detection limit was1-10μg/kg. The average recoveries and standarddeviations were in the range of82.4%-116.7%and5.3%-8.7%, respectively. The methodwas convenient, rapid, sensitive and reliable,it can also meet the demand of measurementand shorten the measurement time significantly.Changes of biogenic amines were monitored by the established method. Under thecondition of-2℃and0℃, neither of the six biogenic amines were detected, whichindicated the great influence of storage temperature for producing of biogenic amines.Under the condition of5℃and10℃, three kinds of biogenic amines were detected in beef(tyramine, putrescine and cadaverine) and the content of tyramine was highest. Duringstorage, contents of biogenic amines increased gradually. The influence of MAP on thegeneration of biogenic amines was obvious during the storage of10℃, while it was lessunder the condition of5℃.Under the condition of5℃and10℃, the Pearson correlation coefficient of tyramineand total bacteria and tyramine and TVB-N was correlated significantly at0.01level. ThePearson correlation coefficient of cadaverine and TVB-N, cadaverine and total bacteria,putrescine and TVB-N and putrescine total bacteria correlated significantly at0.05level,which illustrated that tyramine, cadaverine and putrescine had a close relationship withtotal bacteria and TVB-N, and tyramine was the most suitable index for evaluating thequality of beef. |
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