High-throughput sequencing approach to reveal the bacterial diversity of traditional yak jerky from the Tibetan regions

Effects of temperature fluctuations on the quality and microbial diversity of beef meatballs during simulated cold chain distribution

BACKGROUND

Cold chain distribution with multiple links maintains low temperatures to ensure the quality of meat products, whereas temperature fluctuations during this are often disregarded by the industry. The present study simulated two distinct temperatures cold chain distribution processes. Quality indicators and high-throughput sequencing were employed to investigate the effects of temperature fluctuations on the quality and microbial diversity of beef meatballs during cold chain distribution.

RESULTS

Quality indicators revealed that temperature fluctuations during simulated cold chain distribution significantly (P < 0.05) exacerbated the quality deterioration of beef meatballs. High-throughput sequencing demonstrated that temperature fluctuations affected the diversity and structure of microbial community. Lower microbial species abundance and higher microbial species diversity were observed in the temperature fluctuations group. Proteobacteria and Pseudomonas were identified as the dominant phylum and genus in beef meatballs, respectively, exhibiting faster growth rates and greater relative abundance under temperature fluctuations.

CONCLUSION

The present study demonstrates that temperature fluctuations during simulated cold chain distribution can worsen spoilage and shorten the shelf life of beef meatballs. It also offers certain insights into the spoilage mechanism and preservation of meat products during cold chain distribution. © 2024 Society of Chemical Industry.

Effect of Yeast Inoculation on the Bacterial Community Structure in Reduced-Salt Harbin Dry Sausages: A Perspective of Fungi-Bacteria Interactions

Yeast strains are promising starters to compensate for the flavor deficiencies of reduced-salt dry sausages, but their influence on the bacterial community's structure has not yet been clarified. In this study, the effect of separately inoculating Pichia kudriavzevii MDJ1 (Pk) and Debaryomyces hansenii HRB3 (Dh) on the bacterial community structure in reduced-salt dry sausage was investigated. The results demonstrated that the inoculation of two yeast strains significantly reduced the pH, and enhanced the total acid content, lactic acid bacteria (LAB) counts, and total bacterial counts of reduced-salt sausages after a 12-day fermentation (p < 0.05). Furthermore, high-throughput sequencing results elucidated that the inoculation of yeast strains significantly affected the bacterial composition of the dry sausages. Especially, the relative abundance of bacteria at the firmicute level in the Pk and Dh treatments exhibited a significant increase of 83.22% and 82.19%, respectively, compared to the noninoculated reduced-salt dry sausage treatment (Cr). The relative abundance of Latilactobacillus, especially L. sakei (0.46%, 2.80%, 65.88%, and 33.41% for the traditional dry sausage (Ct), Cr, Pk, and Dh treatments, respectively), increased significantly in the reduced-salt sausages inoculated with two yeast strains. Our work demonstrates the dynamic changes in the bacterial composition of reduced-salt sausages inoculated with different yeast strains, which could provide the foundation for the in-depth study of fungi-bacteria interactions in fermented foods.

Flavour Profile of Traditional Dry Sausage Prepared with Partial Substitution of NaCl with KCl

The effects of partial substitution of NaCl with 0%, 20%, 30% and 40% KCl on the physical characteristics, bacterial community and flavour profile of traditional dry sausage were investigated in this study. With the increase in KCl substitution ratio, the moisture content, astringency, bitterness and umami increased significantly, and the saltiness gradually decreased (p < 0.05). The high-throughput sequencing results showed that the dry sausages with KCl substitution had relatively high abundances of Staphylococcus. For volatile compounds, increasing the KCl substitution ratio reduced the formation of aldehydes, ketones and some alcohols, but promoted the formation of acids and esters (p < 0.05). Sensory evaluation and partial least square regression analysis showed that the dry sausages with 20% and 30% KCl were similar in overall physical and microbial properties, flavour profiles and sensory attributes, and the sausages with 40% KCl were characterized by taste defects. Overall, partial substitution of NaCl with 30% KCl could ensure the acceptable flavour and sensory attributes of dry sausages.

Composting temperature directly affects the removal of antibiotic resistance genes and mobile genetic elements in livestock manure

The high antibiotic resistance gene (ARGs) contents in livestock manure pose a potential risk to environment and human health. The heap composting with an ambient temperature and thermophilic composting are two methods for converting livestock manure into fertilizer. This study investigated the variations in ARGs and mobile genetic elements (MGEs) and revealed potential mechanisms for ARGs removal using the two composting methods. The ARGs abundance were enriched by 44-fold in heap composting, among them, the macrolide-resistance genes increased significantly. On the contrary, the ARGs were removed by 92% in thermophilic composting, among them, tetracycline-resistance genes decreased by 97%. The bacterial hosts of ARGs were associated with the variations of ARGs and MGEs. The tetO was correlated with the most diverse bacteria in heap composting, and Bacteroidetes was the major host bacteria. While tetT was correlated with the most diverse bacteria in thermophilic composting, and Proteobacteria was the major host bacteria. Structural equation models showed that the enrichment of ARGs in heap composting was mainly correlated with bacterial communities, whereas, the removal of ARGs in thermophilic composting was directly affect by MGEs. Composting temperature directly affected the variations in ARGs. Higher and lower temperatures significantly decreased and increased, respectively, ARGs and MGEs abundance levels.

Flavour Compensation Role of Yeast Strains in Reduced-Salt Dry Sausages: Taste and Odour Profiles

The effects of different yeast strains including Pichia kudriavzevii, Torulaspora delbrueckii, and Debaryomyces hansenii on the taste and odour profiles of reduced-salt dry sausages were explored. Inoculation of P. kudriavzevii and D. hansenii compensated for the lack of saltiness and umami tastes of reduced-salt sausages. Furthermore, inoculation of P. kudriavzevii and T. delbrueckii resulted in an odour profile in the reduced-salt dry sausages that was similar to traditional dry sausages. According to the volatile analysis, the contents of certain alcohols, acids, esters and terpenes were higher in the inoculated sausages. Finally, the sensory evaluation indicated that the inoculation of P. kudriavzevii and D. hansenii contributed positively to the aroma and saltiness of reduced-salt dry sausages. In conclusion, P. kudriavzevii and D. hansenii can be employed as effective starter cultures to compensate for the flavour deficiencies of reduced-salt dry sausages.

Fungal communities in Nelumbinis semen characterized by high-throughput sequencing

For a long period, Nelumbinis semen has been widely used as a medicinal and edible product. However, it is susceptible to contamination with toxigenic fungi and aflatoxins during the growth, collection, transportation, and storage processes, causing serious health threats to humans and huge economic losses. Effectively monitoring the fungal communities is of great importance to avoid aflatoxins contamination in Nelumbinis semen. High-throughput sequencing (HTS) is a new technology to evaluate fungal communities so as to overcome the limitations of the traditional cultural ways. In this study, the ITS2 based Illumina-MiSeq platform was developed to evaluate the fungal communities in normal and moldy Nelumbinis semen by using the HTS technology. Two different primer pairs were introduced to compare their performance in amplifying the target gene. The primer pair that produced more reads was selected to analyze the results. In all the nine tested Nelumbinis semen samples, 2 phyla, 5 classes, 6 orders, 8 families, 9 genera and 4 species were detected. A total of 9 genera were spotted, of which, Aspergillus (0.04%-72.93%) and Rhizopus (0.002%-48.12%) were the most dominant. ANOISM analysis showed no significant differences in the normal and moldy groups. The use of HTS technology can detect the fungal communities in complex Nelumbinis semen samples, providing an early warning for toxigenic fungi and aflatoxins contamination to warrant their quality and safety.

Characterisation of flavour profile of beef jerky inoculated with different autochthonous lactic acid bacteria using electronic nose and gas chromatography-ion mobility spectrometry

The flavour profiles of beef jerky separately inoculated with different autochthonous lactic acid bacteria (LAB) strains (Lactobacillus sakei BL6, Pediococcus acidilactici BP2, and Lactobacillus fermentum BL11) and a non-inoculated control were analysed using electronic nose (E-nose) and gas chromatography-ion mobility spectrometry (GC-IMS). GC-IMS results revealed a total of 42 volatile compounds in beef jerky. Inoculation of the three LAB strains decreased the levels of lipid autoxidation-derived aldehydes (e.g., hexanal, heptanal, octanal, and nonanal). In addition, inoculation of P. acidilactici BP2 increased the levels of esters. Principal component analysis of the E-nose and GC-IMS results could effectively differentiate non-inoculated beef jerky and beef jerky separately inoculated with different LAB strains. Furthermore, there was a high correlation between the E-nose and GC-IMS results, providing a theoretical basis for the identification of different beef jerky formulations and selection of autochthonous starter cultures for beef jerky fermentation.