Limosilactobacillus fermentum CGMCC 1.7434 and Debaryomyces hansenii GDMCC 2.149 synergize with ultrasound treatment to efficiently degrade nitrite in air-dried ducks

Nitrites in meat products are important food additives with coloring, antibacterial and antioxidant effects, but excessive intake of nitrites can pose health risks, including an increased risk of cancer due to the formation of carcinogenic nitrosamines. In the present study, Limosilactobacillus fermentum CGMCC 1.7434 was screened and the effects of it and Debaryomyces hansenii GDMCC 2.149 and their combination on nitrite degradation were investigated. It was found that the co-culture of L. fermentum CGMCC 1.7434 and D. hansenii GDMCC 2.149 significantly enhanced nitrite degradation (99.58%). The findings on salt and ethanol tolerance suggest suitability for application in meat fermentation processes. Scanning electron microscopy and additional data indicate that D. hansenii GDMCC 2.149 facilitates the growth, acid production, adhesion, secretion of AI-2 signaling molecules, and biofilm formation of L. fermentum CGMCC 1.7434. Metabolomics analysis suggests that these microorganisms reduce nitrite levels by converting NH3 derived from nitrite into L-glutamine, which is further transformed into N-nitroso compounds and their downstream derivatives through the ABC transporter pathway, the TCA cycle, and the amino acid metabolism pathway. Microbial community analyses showed that L. fermentum CGMCC 1.7434 and D. hansenii GDMCC 2.149 were successfully inoculated into air-dried ducks, becoming dominant strains and effectively inhibiting the growth of pathogenic bacteria. Furthermore, during the processing of air-dried duck, the combination of ultrasonic cavitation (250 W, 4 min, 30°C, 40 kHz) with the co-fermentation of L. fermentum CGMCC 1.7434 and D. hansenii GDMCC 2.149 effectively reduced nitrite content (84.55%) and TVB-N levels in the meat, without compromising color or TBARS values. This is crucial for understanding the mechanism of nitrite degradation by LAB in synergy with yeast and for the advancement of low-nitrite air-dried duck products.

Fermented Vegetables: Health Benefits, Defects, and Current Technological Solutions

This review summarizes current studies on fermented vegetables, analyzing the changes in nutritional components during pickling, the health benefits of fermented vegetables, and their safety concerns. Additionally, the review provides an overview of the applications of emergent non-thermal technologies for addressing these safety concerns during the production and processing of fermented vegetables. It was found that vitamin C would commonly be lost, the soluble protein would degrade into free amino acids, new nutrient compositions would be produced, and the flavor correlated with the chemical changes. These changes would be influenced by the variety/location of raw materials, the original bacterial population, starter cultures, fermentation conditions, seasoning additions, and post-fermentation processing. Consuming fermented vegetables benefits human health, including antibacterial effects, regulating intestinal bacterial populations, and promoting health (anti-cancer effects, anti-diabetes effects, and immune regulation). However, fermented vegetables have chemical and biological safety concerns, such as biogenic amines and the formation of nitrites, as well as the existence of pathogenic microorganisms. To reduce hazardous components and control the quality of fermented vegetables, unique starter cultures, high pressure, ultrasound, cold plasma, photodynamic, and other technologies can be used to solve these problems.

The Mechanism of Oxidative Stress in Cells Isolation, Identification, and Genome-Wide Sequence Analysis of Nitrite Amylolytic Bacillus

To improve the quality of traditional fermented pickles and reduce the nitrite content in the production process of pickles, the target bacteria for efficient nitrite degradation were screened from traditional fermented pickles. Pickles (picked vegetables), a traditional dish favored by many Chinese, are mildly salted and lactic acid-fermented vegetables in China. However, the presence of nitrite in pickles is a bottleneck which limits further development of the pickle industry. More attention is drawn to the problem of the presence of nitrite in pickles. Having harmful effect in the acidic environment produced by gastric acid, nitrite is converted into carcinogenic nitrosamine. After screening several nitrite-degrading bacteria in the early stage, a Gram-positive round ended Bacillus amyloliquefaciens is named as Bacillus amyloliquefaciens JBA-CH9, which can degrade nitrite efficiently. Bacillus amyloliquefaciens is a common bacterium in the food fermentation industry. Then, the optimum conditions for nitrite degradation of the strain were explored according to the inoculation amount, temperature and salinity, and the whole genome of Bacillus amyloliquefaciens JBA-CH9 was sequenced. The results showed that the strain had the best degradation effect on nitrite under the conditions of inoculation amount of 9%, salinity of 5%, and 30°C, and the highest degradation rate of nitrite was 91.47%. The results of whole genome sequencing showed that the strain had a large number of functional genes related to amino acids, carbohydrates, and lipids and contained nitrite reductase genes related to nitrite metabolism. Therefore, Bacillus amyloliquefaciens JBA-CH9 is a functional strain that can degrade nitrite efficiently.

Metagenomic insights into Chinese northeast suancai: Predominance and diversity of genes associated with nitrogen metabolism in traditional household suancai fermentation

Chinese northeast suancai represents a typical and valuable food product that has been handed down by traditional household procedures over centuries. Nitrite is formed and accumulated during the suancai fermentation process and commonly causes food safety problems. The biogeochemical cycle of nitrite may provide a reference and guidance for the enzymatic degradation of nitrite in fermented food. The potential nitrogen metabolic pathways in the microbially driven suancai fermentation were reasonably inferred through monitoring nitrogen conversions and detecting the genes of different functional enzymes. Complex microbial metabolism is responsible for the unique nitrogen conversions during suancai fermentation. The metagenomic results showed that Pseudomonas with nitrate reductase genes (narG, narH, narI) and nitrite reductase genes (nirB, nirD) contributed the most to both nitrite reduction and nitrate reduction. The majority of the sequences of nitrate reductase and nitrite reductase were derived from the families of Pseudomonadaceae, Erwiniaceae and Yersiniaceae. According to the physicochemical analysis, the nitrite concentration of the fermentation broth reached the peak value (0.48 mM) and gradually decreased to the minimum (0.02 mM). The downward trend of the pH and nitrite concentration were closely associated with the nitrite enzymatic degradation period before the acid degradation period. Our results indicated that nitrite removal in suancai fermentation involved the reduction of nitrite to ammonia and denitrification, which were mainly contributed by the reduction of nitrite to ammonia mediated by the nirB/nirD enzyme (Indentified ECs: 1.7.1.15). This research offers new insights into the metagenome-based bioinformatic roles of the previously unstudied microorganisms in spontaneous suancai fermentation for the enzymatic degradation of nitrite. It provides helpful basis for the detection and even elimination of nitrite in suancai and for improving the safety level of suancai.

Selection of nitrite-degrading and biogenic amine-degrading strains and its involved genes

Objectives

Accumulation of nitrite and biogenic amines (BAs) in fermented meat products is a matter of public health concern. The study aimed to screen nitrite-degrading and BA-degrading strains from sour porridges and sausages and bacon products in China.

Materials and Methods

After screening out 12 strains, the degradation of nitrite, the degradation of BAs, the activities of nitrite-reducing enzymes, and the detection of genes involved in the BAs were assessed by spectrophotometry method with hydrochloric acid naphthalene ethylenediamine, high-performance liquid chromatography, GENMED kit, and polymerase chain reaction, respectively.

Results

Pediococcus pentosaceus labelled M SZ1 2 and M GC 2, Lactobacillus plantarum labelled M SZ2 2, and Staphylococcus xylosus labelled Y CC 3 were selected. The activity of nitrite-reducing enzyme in M SZ2 2 was 2.663 units/mg. The degradation rate of total BAs of M SZ2 2 was 93.24%. The degradation rates of nitrite and BAs of M SZ1 2 were 86.49% and 37.87%, respectively. The activity of nitrite-reducing enzyme in M SZ1 2 was up to 1.962 units/mg. M GC 2 showed higher degradation rates of nitrite (89.19%) and Y CC 3 showed higher degradation rates of BAs (36.16%). The genes encoding the multicopper oxidases (suf I/D2EK17) were detected in the four strains, which also did not contain BAs (histidine decarboxylase (hdc), tyrosine decarboxylase (tdc), ornithine decarboxylase (odc), lysine decarboxylase (ldc)) formation encoding genes.

Conclusion

These four strains (M SZ1 2, M GC 2, M SZ2 2, and Y CC 3) are promising candidates to use as starter cultures for nitrite and BAs in fermented sausages.

Isolation, expression, and biochemical characterization: nitrite reductase from Bacillus cereus LJ01

Biological remediation of toxic oxygen-containing anions such as nitrate that are common in the environment is of great significance. Therefore, it is necessary to understand the specific role of nitrate and nitrite reductase in the bioremediation process. Bacillus cereus LJ01, which was isolated from traditional Chinese soybean paste, effectively degraded nitrite (such as NaNO₂) at 0–15 mmol L⁻¹ in LB medium. Moreover, the nitrite-degrading active substance (ASDN) was isolated and purified from B. cereus LJ01. The nitrite-degrading activity of nitrite reductase (named LJ01-NiR) was 4004.89 U mg⁻¹. The gene encoding the assimilation of nitrite reductase in B. cereus LJ01 was cloned and overexpressed in E. coli. The purified recombinant LJ01-NiR has a wide range of activities under temperature (20–60 °C), pH (6.5–8.0) and metal ions (Fe³⁺, Fe²⁺, Cu²⁺, Mn²⁺, and Al³⁺). Kinetic parameters of LJ01-NiR, including the values of K_m and V_max were 1.38 mM and 2.00 μmol g⁻¹ min⁻¹, respectively. The results showed that LJ01-NiR could degrade nitrite with or without an electron donor. In addition, sequence analysis revealed that LJ01-NiR was a ferredoxin-dependent nitrite reductase given the presence of conserved [Fe4–S4] cluster and heme-binding domain. The nitrite ion binds to the LJ01-NiR active site by forming three hydrogen bonds with the residues ASN72, ALA133 and ASN140. Due to its high nitrite-degrading activity, LJ01-NiR could potentially be used for environmental pollution treatment.

Biological remediation of toxic oxygen-containing anions such as nitrite in the environment is of great significance. Bacillus cereus LJ01 showed the activity of degradation for nitrite. the enzyme NiR from LJ01 can degrade the nitrite in vitro.