Diversity of the Predominant Spoilage Bacteria in Water-Boiled Salted Duck during Storage

Dynamic changes of the bacterial communities in roast chicken stored under normal and modified atmosphere packaging

This study systematically investigated the dynamic changes in bacterial communities in roast chicken in normal and modified atmosphere packaging (MAP). The samples were stored under normal atmosphere and 40%/60% CO₂ /N₂ MAP conditions for 28 days at 4 °C. Changes in the number and type of microorganisms in roast chicken during storage were defined via cultural and 16S rDNA sequencing techniques. More Bacteroides, Chryseobacterium, Lactobacillus, and Acinetobacter than other bacteria were initially found in roast chicken. With normal packaging, Pseudomonas rapidly multiplied and became the main spoilage organism in roast chicken after 7 days, with a relative abundance of >90% of the entire bacterial flora. With MAP, due to the high salt content, Halomonas became the main spoilage organism in roast chicken by the middle of the storage period (14 days). Between days 21 and 28 of storage, Pseudomonas gradually became the main spoilage organism in roast chicken, but its relative abundance was much lower in MAP than in normal packaging, followed by Lachnospiraceae (NK4A136 group) and Altererythrobacter. Our research shows that the microbes in roast chicken mainly originated from the processing environment and operators. The combination of MAP with a low storage temperature could effectively improve the quality and safety of roast chicken meat. PRACTICAL APPLICATIONS: This research showed the dynamic changes in the bacterial community of roast chicken stored under normal and modified atmosphere packaging (MAP). Microorganisms in roast chicken are mainly obtained from the processing environment and operators. Combining MAP with storage at low temperatures can effectively improve the quality and safety of roast chicken.

Changes of Dominant Spoilage Bacteria and Biogenic Amines of Taihu White Prawn (Exopalaemon modestus) during Ice Storage

The microbiological and chemical changes in Taihu white prawn (Exopalaemon modestus) during ice storage were evaluated. For the microbiological changes, total viable counts were obtained. PCR coupled with denatured gradient gel electrophoresis was then performed to investigate the changes in microflora. For the chemical changes, total volatile basic nitrogen was determined and biogenic amines were detected. The initial total viable count was 6.2 log CFU/g, which increased to 7.1 log CFU/g after storage at 0°C for 10 days. Pseudomonas sp., Shewanella, Flavobacterium, and Staphylococcus were the dominant bacteria in fresh white prawn, whereas lactic acid bacteria, Pseudomonas sp., Shewanella, and Flavobacterium were dominant in the spoiled products. The initial total volatile basic nitrogen was 7.2 mg/100 g, a value that significantly increased to 30.5 mg/100 g at the end of storage. Putrescine was the dominant biogenic amine, and its content reached 95.5 mg/kg at the end of storage. PCR coupled with denatured gradient gel electrophoresis showed that Chryseobacterium sp., Acidovorax sp., Pelomonas sp., Kinneretia asaccharophila, and uncultured Curvibacter sp. were the dominant strains during storage, whereas Lactococcus garvieae became dominant at the end of storage. This study facilitated the development of preservation techniques that target these predominant spoilage bacteria.

Shelf-Life of Boiled Salted Duck Meat Stored Under Normal and Modified Atmosphere

The objective of this study was to investigate the physicochemical properties and changes in the microbial counts of boiled salted duck (BSD) meat packed under various conditions. BSD meat was stored under normal atmosphere (C) and two modified atmosphere packaging (MAP) conditions: M1 (N₂ , 100%) and M2 (CO₂ /N₂ , 30%/70%) at 4 °C. Microbiological quality, pH, redness, lipid oxidation, headspace gas composition, and water activity of BSD meat were measured. The results showed that the time to reach the maximum acceptable total viable counts (TVC, 4.9 log CFU/g) was 12, 18, and 21 d in C, M1, and M2 samples, respectively. Significant difference in the redness values was observed in all treatments during storage. The redness value of C group was significantly lower than that in M1 and M2 groups at the end of storage. The thiobarbituric acid-reactive substances (TBARS) values under MAP were 0.24 to 0.26 mg MDA/kg meat at the end of storage, lower (P < 0.05) than that in C group (0.78 mg MDA/kg meat). The water activity in M2 group was the lowest among all 3 groups. The CO₂ concentration in M2 decreased significantly during storage. Our study demonstrates that packaging with 30% CO₂ and 70% N₂ (M2) could extend the shelf-life of BSD meat to 21 d during storage at 4 °C, suggesting that MAP can be a practical approach to extend the shelf-life and maintain the quality of BSD products.

PRACTICAL APPLICATION

This study evaluated the application of MAP for a cooked duck product. Our results showed that MAP can be utilized to extend the shelf-life. This technology may be used for preservation of other cooked meat products.

Microbiological changes, shelf life and identification of initial and spoilage microbiota of sea bream fillets stored under various conditions using 16S rRNA gene analysis

BACKGROUND

Sea bream fillets are one of the most important value-added products of the seafood market. Fresh seafood spoils mainly owing to bacterial action. In this study an exploration of initial and spoilage microbiota of sea bream fillets stored under air and commercial modified atmosphere packaging (MAP) at 0 and 5 °C was conducted by 16S rRNA gene sequence analysis of isolates grown on plates. Sensory evaluation and enumeration of total viable counts and spoilage microorganisms were also conducted to determine shelf life and bacterial growth respectively.

RESULTS

Different temperatures and atmospheres affected growth and synthesis of spoilage microbiota as well as shelf life. Shelf life under air at 0 and 5 °C was 14 and 5 days respectively, while under MAP it was 20 and 8 days respectively. Initial microbiota were dominated by Pseudomonas fluorescens, Psychrobacter and Macrococcus caseolyticus. Different temperatures and atmospheres affected the synthesis of spoilage microbiota. At the end of shelf life, different phylotypes of Pseudomonas closely related to Pseudomonas fragi were found to dominate in most cases, while Pseudomonas veronii dominated in fillets under MAP at 0 °C. Furthermore, in fillets under MAP at 5 °C, new dominant species such as Carnobacterium maltaromaticum, Carnobacterium divergens and Vagococcus fluvialis were revealed.

CONCLUSION

Different temperature and atmospheric conditions affected bacterial growth, shelf life and the synthesis of spoilage microbiota. Molecular identification revealed species and strains of microorganisms that have not been reported before for sea bream fillets stored under various conditions, thus providing valuable information regarding microbiological spoilage.

Effects of storage temperature on tyramine production by Enterococcus faecalis R612Z1 in water-boiled salted ducks

Tyramine production by Enterococcus faecalis R612Z1 in water-boiled salted ducks was evaluated during storage at different temperatures. The results showed that E. faecalis R612Z1 could produce tyramine in meat samples when the storage temperature was no less than 4°C. The E. faecalis R612Z1 counts of the meat samples reached 10(8) CFU/g on day 7 at 4°C and on day 4 at 10°C. However, the tyramine content of the meat samples stored at 10°C increased to 23.73 μg/g (on day 10), which was greater than the level in the samples stored at 4°C (7.56 μg/g). Reverse transcription quantitative PCR detection of the expression level of the tyrDC gene in E. faecalis R612Z1 in the meat samples revealed no significant changes at different storage temperatures. Thus, the changes in tyramine production of E. faecalis R612Z1 may be due to the different enzymatic activities at different storage temperatures.

Impact of high hydrostatic pressure treatment on microbial communities in chinese water-boiled salted duck

The objective of this study was to determine the impact of high hydrostatic pressure (HHP) treatment on microbial communities in Chinese water-boiled salted duck (CWBSD) and the synergistic effect of HHP and mild heat treatment. In this work, the bacterial diversity was evaluated by using both a culture-dependent method and denaturing gradient gel electrophoresis. The total aerobic bacterial counts in pressure-treated samples were significantly lower than those in controls, which indicated that HHP could extend the shelf life of CWBSD. Weissella hellenica and Enterobacteriaceae, the predominant bacteria found in CWBSD, were not detected after HHP treatment. On the other hand, Staphylococcus spp. and Bacillus spp. became the predominant bacteria in HHP-treated samples. Moreover, the inhibitory effect was greater at 400 MPa than at 200 MPa combined with mild heat at 40°C. This study investigated the diversity of bacteria in HHP-treated CWBSD, and the information derived from this research may help to understand the bacterial ecology and develop effective HHP treatments to extend the shelf life of CWBSD.

Production of tyramine by Enterococcus faecalis strains in water-boiled salted duck

The potential to produce biogenic amines was investigated with 15 Lactococcus lactis and 15 Enterococcus faecalis strains isolated from water-boiled salted duck. The production of biogenic amines from the isolated strains grown in de Man Rogosa Sharpe broth containing precursor amino acids was determined by thin-layer chromatography and high-performance liquid chromatography. None of the L. lactis strains produced any biogenic amines, whereas 12 strains of E. faecalis produced tyramine and b -phenylethylamine. PCR assays were used to detect the presence of tyrosine decarboxylase genes in all of the isolated strains. Only the 12 biogenic amine-producing Enterococcus strains had a 924-bp fragment characteristic for the tyrosine decarboxylase gene. The comparison of the amplified partial tyrDC gene sequences of the 12 positive Enterococcus strains revealed 99% similarity within the same species. The tyramine production of the sterilized water-boiled salted duck inoculated with E. faecalis R612Z1 increased significantly during storage. This study reveals that the isolated E. faecalis strains can produce tyramine and β-phenylethylamine in the medium; however, they can only produce tyramine in water-boiled salted duck.

Characterization of microflora in Latin-style cheeses by next-generation sequencing technology

BACKGROUND

Cheese contamination can occur at numerous stages in the manufacturing process including the use of improperly pasteurized or raw milk. Of concern is the potential contamination by Listeria monocytogenes and other pathogenic bacteria that find the high moisture levels and moderate pH of popular Latin-style cheeses like queso fresco a hospitable environment. In the investigation of a foodborne outbreak, samples typically undergo enrichment in broth for 24 hours followed by selective agar plating to isolate bacterial colonies for confirmatory testing. The broth enrichment step may also enable background microflora to proliferate, which can confound subsequent analysis if not inhibited by effective broth or agar additives. We used 16S rRNA gene sequencing to provide a preliminary survey of bacterial species associated with three brands of Latin-style cheeses after 24-hour broth enrichment.

RESULTS

Brand A showed a greater diversity than the other two cheese brands (Brands B and C) at nearly every taxonomic level except phylum. Brand B showed the least diversity and was dominated by a single bacterial taxon, Exiguobacterium, not previously reported in cheese. This genus was also found in Brand C, although Lactococcus was prominent, an expected finding since this bacteria belongs to the group of lactic acid bacteria (LAB) commonly found in fermented foods.

CONCLUSIONS

The contrasting diversity observed in Latin-style cheese was surprising, demonstrating that despite similarity of cheese type, raw materials and cheese making conditions appear to play a critical role in the microflora composition of the final product. The high bacterial diversity associated with Brand A suggests it may have been prepared with raw materials of high bacterial diversity or influenced by the ecology of the processing environment. Additionally, the presence of Exiguobacterium in high proportions (96%) in Brand B and, to a lesser extent, Brand C (46%), may have been influenced by the enrichment process. This study is the first to define Latin-style cheese microflora using Next-Generation Sequencing. These valuable preliminary data will direct selective tailoring of agar formulations to improve culture-based detection of pathogens in Latin-style cheese.

Culture-based and denaturing gradient gel electrophoresis analysis of the bacterial community from Chungkookjang, a traditional Korean fermented soybean food

The bacterial community of Chungkookjang and raw rice-straw collected from various areas in South Korea was investigated using both culture-dependent and culture-independent methods. Pure cultures were isolated from Chungkookjang and raw rice-straw on tryptic soy agar plates with 72 to 121 colonies and identified by 16S rDNA gene sequence analysis, respectively. The traditional culture-based method and denaturing gradient gel electrophoresis analysis of PCR-amplified 16S rDNA confirmed that Pantoea agglomerans and B. subtilis were identified as predominant in the raw rice-straw and Chungkookjang, respectively, from Iljuk district of Gyeonggi province, P. ananatis and B. licheniformis were identified as predominant in the raw rice-straw and Chungkookjang from Wonju district of Gangwon province, and Microbacterium sp. and B. licheniformis were identified as predominant in the raw rice-straw and Chungkookjang from Sunchang district of Jeolla province. Other strains, such as Bacillus, Enterococcus, Pseudomonas, Rhodococcus, and uncultured bacteria were also present in raw rice-straw and Chungkookjang.

PRACTICAL APPLICATION

A comprehensive analysis of these microorganisms would provide a more detailed understanding of the biologically active components of Chungkookjang and help improve its quality. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis can be successfully applied to a fermented food to detect unculturable or more species than the culture-dependent method. This technique is an effective and convenient culture-independent method for studying the bacterial community in Chungkookjang. In this study, the bacterial community of Chungkookjang collected from various areas in South Korea was investigated using both culture-dependent and culture-independent methods.