Effect and mechanism of thyme microcapsules on histamine production by Morganella morganii MN483274 during the processing of smoked horse meat sausage

Characterization of ornithine decarboxylase with histidine decarboxylase activity in natural histidine decarboxylase gene deletion Enterobacter hormaechei RH3

Histamine is predominantly produced in sausages via the decarboxylation of histidine by bacteria. Furthermore, histamine-producing bacteria usually possess the enzyme histidine decarboxylase (hdc). Enterobacter hormaechei RH3 isolated from sausages exhibited significant levels of histamine production despite the absence of hdc. In this study, we elucidated the previously unidentified mechanism underlying histamine production by RH3. We identified an enzyme, NehdX-772, exhibiting the hdc activity from the cell lysate supernatant of RH3, which was annotated as ornithine decarboxylase. The optimal activity of NehdX-772 was recorded at 35 °C and pH 6.0, and it could tolerate a salt concentration of 2.5% (w/v) NaCl. Moreover, artificial inoculation revealed that NehdX-772 was synthesized at significant levels in sausages, leading to an increase in histamine levels. The discovery of NehdX-772 explains the underlying mechanism of histamine production by RH3 and can be applied to decrease histamine production in sausages.

Elucidating the potential of chlorogenic acid for controlling Morganella psychrotolerans growth and histamine formation

AIM

To investigate the inhibitory impact of chlorogenic acid (CGA) on the growth of Morganella psychrotolerans and its ability to form histamine.

METHODS AND RESULTS

The antimicrobial effect of CGA on M. psychrotolerans was evaluated using the minimum inhibitory concentration (MIC) method, revealing an MIC value of 10 mg ml-1. The alkaline phosphatase (AKP) activity, cell membrane potential, and scanning electron microscopy images revealed that CGA treatment disrupted cell structure and cell membrane. Moreover, CGA treatment led to a dose-dependent decrease in crude histidine decarboxylase (HDC) activity and gene expression of histidine decarboxylase (hdc). Molecular docking analysis demonstrated that CGA interacted with HDC through hydrogen bonds. Furthermore, in situ investigation confirmed the efficacy of CGA in controlling the growth of M. psychrotolerans and significantly reducing histamine formation in raw tuna.

CONCLUSION

CGA had good activity in controlling the growth of M. psychrotolerans and histamine formation.

Bacterial community succession and volatile compound changes in Xinjiang smoked horsemeat sausage during fermentation

This study examined the bacterial community dynamics and their relationship with volatile compounds in Xinjiang smoked horsemeat sausage during fermentation. We employed single-molecule real-time sequencing (SMRT) to identify the bacterial composition, while headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) was utilized to detect volatile compounds in the sausage. The findings indicated that Staphylococcus xylosus, Lactococcus garvieae, Latilactobacillus sakei, Lactococcus lactis, and Weissella hellenica were the predominant species during the fermentation. Moreover, we identified 56 volatile substances in the smoked horsemeat sausages, including alcohols, esters, ketones, acids, aldehydes, terpenes, and phenols. Notably, the correlation analysis demonstrated positive associations between the major bacteria and the primary volatile compounds, with notable connections observed for Staphylococcus xylosus, Lactococcus garvieae and Weissella hellenica. These research findings provide a foundation for future endeavors aimed at enhancing the flavor quality of smoked horsemeat sausage.

Bacterial community diversity and its potential contributions to the flavor components of traditional smoked horsemeat sausage in Xinjiang, China

Smoked horsemeat sausage is a famous fermented traditional food in Xinjiang, China. However, the microbial diversity and its potential contributions to the flavor components of smoked horsemeat sausage are unclear. In this study, the microbial community and flavor components of smoked horsemeat sausage from six regions of Xinjiang were measured by using amplicon sequencing and headspace solid-phase microextraction combined with gas chromatography–mass spectrometry (HS-SPME-GC–MS) technology, respectively. Relations among microbial communities, flavor components and environmental factors were subsequently predicted based on redundancy analysis (RDA) and Monte Carlo permutation tests. Although smoked horsemeat sausage samples from different regions possessed distinct microbial communities, lactic acid bacteria (LAB) were identified as the dominant consortium in smoked horsemeat sausage. Lactobacillus, Vagococcus, Lactococcus, and Carnobacterium were detected at high abundance in different sausages. The moisture content, nitrite content, and pH of the sausage might be important factors influencing the dominant bacterial community, according to the RDA. Among the dominant consortia, the eight core bacterial genera showed considerable correlations with the formation of sixteen volatile compounds in smoked horsemeat sausage based on multivariate statistical analysis. For example, the levels of Leuconostoc and Lactobacillus were positively correlated with those of 1-hexadecanol, hexyl acetate, 2-methyl-phenol, 1-pentanol, d-limonene, and 2-heptanone, and the levels of Leuconostoc, Lactobacillus, and Weissella were negatively correlated with those of 1-octanol, acetic acid, octanal, heptanal, and 1-hexanol. This study will provide a theoretical basis for understanding the microbial metabolic modes of Xinjiang smoked horsemeat sausages.

Origanum majorana L. Essential Oil-Coated Paper Acts as an Antimicrobial and Antioxidant Agent against Meat Spoilage

This study first-ever tested the impact of active packaging paper coated with cationic starch containing Origanum majorana L. essential oil with 69.26% carvacrol polyphenol on the physical, chemical, and microbiological quality of minced beef stored at +4 °C for 0, 6, and 12 days. An analysis of electron scanning microscopy and infrared spectroscopy showed origanum oil entrapment on paper. Meat samples packaged without origanum oil at 6th and 12th days of storage were unfit for consumption. In contrary, origanum oil significantly reduced microbial counts by 2.5 log 10 CFU/g, the peroxide value by 22%, lipid oxidation by 22, the pH-dependent meat spoilage value by 27%, dry matter losses by 7%, and antioxidant activity losses by 40% and restored color and odor reductions. Origanum oil extended the shelf-life of minced beef up to the 6th day of cold storage with no negative effect on meat color and odor.

Structural characteristics of polysaccharide microcapsules fromNostoc commune, and their applications in skin wound healing and pathological repair

In this study, the extraction conditions of Nostoc commune Vauch polysaccharide (NCVP) were optimized by single factor and orthogonal experiments. Then, the microcapsules (NCVPM) was prepared. After analyzing the microcapsule structural, thermal characteristics, the skin wound healing ability was studied by establishing back trauma rat models. Results showed that, the NCVP yield was 10.37% under the following optimum conditions: 210 minute extraction time, solid-liquid ratio of 1:50 and extraction temperature of 90°C. The overall performance of the microcapsule was the best when the concentration of sodium alginate, calcium chloride and chitosan was 2%, 3% and 0.3%, respectively. NCVPM had spherical morphology, typical microcapsule structural characteristics and good thermal stability, and NCVP was dispersed in the microcapsules. NCVPM showed good biocompatibility and biodegradability, which met the requirements for slow-release polymer materials. After 14 days treatment, the wound healing rate was 92.4%, the cells were arranged neatly and regularly, the cell nucleus became large and elliptical, and the cell has a tendency to divide, the fibers and microvessel were significantly more. By evaluating mechanism, NVCPM could increase the contents of hydroxyproline (HYP) and glutathione (GSH-Px) to protect cells from oxidative damage, leading in turn to accelerate wound healing and shorted wound healing times. And could accelerate cell division, collagen and microvascular production by increasing transcription levels of Vascular endothelial growth factor (VEGF) mRNA and miRNA-21.