Denitrifying halophilic archaea derived from salt dominate the degradation of nitrite in salted radish during pickling

Halobellus marinus sp. nov., Halobellus ordinarius sp. nov., Halobaculum rarum sp. nov., and Halorarum halobium sp. nov., halophilic archaea isolated from marine solar salt and a saline lake

Four halophilic archaeal strains were isolated from sea salt and a saline lake in China. Based on phylogenetic and phylogenomic analyses, the four strains are related to the genera of Halobellus, Halobaculum, and Halorarum within the family Haloferacaceae. The four strains possess genes responsible for carotenoid synthesis, maintenance of a high internal salt concentration, as well as diverse enzymes with biotechnological potential. The average nucleotide identity (ANI), average amino acid identity (AAI), and digital DNA-DNA hybridization (dDDH) values among these four strains and their related species were lower than the established thresholds proposed for species demarcation. Strains DFY28T, ZY16T, QDC11T, and XH14T were distinguished from related species based on a variety of phenotypic characteristics. The major polar lipids of these four strains were similar to those of respective relatives within the genera Halobellus, Halobaculum, and Halorarum. The phenotypic, phylogenetic, and genome-based analyses suggest that strains DFY28T (= CGMCC 1.17470T = JCM 34310T), ZY16T (= CGMCC 1.17476T = JCM 34311T), QDC11T (= MCCC 4K00127T = KCTC 4308T), and XH14T (= CGMCC 1.17028T = JCM 34145T) represent four novel species of the genera Halobellus, Halobaculum and Halorarum, for which the names Halobellus marinus sp. nov., Halobellus ordinarius sp. nov., Halobaculum rarum sp. nov., and Halorarum halobium sp. nov. are proposed.

Screening of Lactic Acid Bacteria Isolated from Fermented Cowpea and Optimization of Biomass Production Conditions

Considering the four characteristics of strains, including acid production, acid tolerance, salt tolerance, and nitrite degradation rate, Pediococcus pentosaceus NCU006063 was selected as the fermentation agent, and the medium composition of Pediococcus pentosaceus NCU006063 was optimized using Plackett-Burman and central composite rotational design. Three of the seven factors studied in the Plackett-Burman design significantly affected the viable counts. A central composite rotational design was used to optimize the significant factors and generate response surface plots. Using these response surface plots and point predictions, the optimal factors were soy peptone (38.75 g/L), FeSO4 (0.10 g/L), and VB7 (20 g/L). In addition, the optimized incubation conditions were a temperature of 39 °C, an initial pH value of 7, and an inoculation volume of 3%. The optimized biomass production parameters were a constant pH (6.5), neutralizing agent types (25% NH3·H2O), and gas types (N2). Under these optimal conditions, Pediococcus pentosaceus NCU006063 exhibited a great viable bacterial count of up to 2.65 × 1010 CFU/mL, which is 9.71 times higher than that of MRS broth (2.73 × 109 CFU/mL). These results demonstrated that the Pediococcus pentosaceus NCU006063 strain has excellent potential as a fermentation agent and can provide a theoretical base for the in-depth exploration and promotion of fermented cowpea use in human diets.

Analysis of Microbial Diversity Dominating Nitrite Enzymatic Degradation and Acidic Degradation in the Fermentation Broth of Northeast Sauerkraut

Nitrite hazard is an important food safety issue in the production process of Chinese Northeastern sauerkraut, but this nitrite can be eliminated through microbial enzymatic degradation and acidic degradation as fermentation progresses. Therefore, analyzing the microbial diversity that dominates nitrite degradation in Chinese Northeastern sauerkraut can provide a reference for its safe production. In this study, based on the dynamic monitoring of nitrite concentration, pH, and the abundance of nitrite reductase genes (nirK and nirS) and the application of high-throughput sequencing technology and various statistical analysis methods, the microbial groups associated with nitrite enzymatic degradation and acidic degradation in Northeast sauerkraut fermentation broth were analyzed. During the nitrite peak period of Northeast sauerkraut fermentation broth, the nitrite concentration reached 32.15 mg/kg, the pH was 4.7, and the abundances of the nitrite reductase genes nirK and nirS were 3.0 × 104 and 4.9 × 104 copies/μL, respectively. At this stage, nitrite degradation was likely dominated by enzymatic activities. Microbial phyla such as Bacteroidetes (38.8%), Proteobacteria (19.2%), and the archaeal phylum Euryarchaeota (1.1%) showed strong correlations with nitrite. Among the genera within these three phyla, Chryseobacterium, Elizabethkingia, and Aeromonas exhibited significant differences in abundance compared to the late fermentation stage and were identified as the primary microbial groups likely driving the enzymatic degradation. During the nitrite degradation period, the nitrite concentration decreased to 0.04 mg/kg, the pH dropped to 3.6, and the abundances of nirK and nirS genes were reduced to 1.0 × 103 copies/μL. At this stage, the nitrite degradation was primarily driven by acid activity. The bacterial phylum Firmicutes (99%) exhibited a strong correlation with pH. Within this phylum, the genus Lactobacillus, which showed significant differences in abundance compared to the early fermentation stage, was identified as the primary microbial group indirectly contributing to acidic degradation. This study provides guidance for the isolation of food-grade prokaryotic microbial strains capable of nitrite degradation. Additionally, the findings offer a methodological reference for conducting future research on nitrite-degrading microorganisms in fermented vegetable broths.

The role of water distribution, cell wall polysaccharides, and microstructure on radish (Raphanus sativus L.) textural properties during dry-salting process

Radish (Raphanus sativus L.) undergoes texture changes in their phy-chemical properties during the long-term dry-salting process. In our study, we found that during the 60-day salting period, the hardness and crispness of radish decreased significantly. In further investigation, we observed that the collaborative action of pectin methylesterase (PME) and polygalacturonase (PG) significantly decreased the total pectin, alkali-soluble pectin (ASP), and chelator-soluble pectin (CSP) content, while increasing the water-soluble pectin (WSP) content. Furthermore, the elevated activities of cellulase and hemicellulase directly led to the notable fragmentation of cellulose and hemicellulose. The above reactions jointly induced the depolymerization and degradation of cell wall polysaccharides, resulting in an enlargement of intercellular spaces and shrinkage of the cell wall, which ultimately led to a reduction in the hardness and crispness of the salted radish. This study provided key insights and guidance for better maintaining textural properties during the dry-salting process of radish.

Halophilic lactic acid bacteria - Play a vital role in the fermented food industry

Halophilic lactic acid bacteria have been widely found in various high-salt fermented foods. The distribution of these species in salt-fermented foods contributes significantly to the development of the product's flavor. Besides, these bacteria also have the ability to biosynthesize bioactive components which potentially apply to different areas. In this review, insights into the metabolic properties, salt stress responses, and potential applications of these bacteria have been have been elucidated. The purpose of this review highlights the important role of halophilic lactic acid bacteria in improving the quality and safety of salt-fermented products and explores the potential application of these bacteria.

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.

Potential role of cell wall pectin polysaccharides, water state, and cellular structure on twice "increase-decrease" texture changes during kohlrabi pickling process

Pickled kohlrabi is a traditional and favored vegetable product in China. During pickling, the hardness, springiness, and chewiness of kohlrabi all experienced a typical change with twice "increase-decrease" trend. However, little is known about its mechanism. In this study, in situ analysis including immunofluorescence, low field nuclear magnetic, and transmission electron microscopy were used to explore the effects of cell wall pectin, water state, and cellular structure on kohlrabi texture changes during pickling. Results revealed that at the early stage, due to the rapid loss of water after three times salting, the cells shrank and the interstitial space reduced, resulting in the first increase on kohlrabi texture. Subsequently, the dehydration-rehydration caused by the first brine processing resulted in the first decrease on kohlrabi texture. Then under the action of PME enzyme, more low-esterified pectin was produced, and chelate-soluble pectin with more branched structure was further formed, leading to another elevation of the sample texture. As the pickling continued, under the combined action of PG and PME, the molecular weight of pectin was decreased and the rigidity of the cell tissue was destroyed, caused kohlrabi texture continued to decline. These researches could provide important information and guidance for better maintaining the texture of pickled vegetables during processing.

Denitrifying Woodchip Bioreactors: A Microbial Solution for Nitrate in Agricultural Wastewater-A Review

Nitrate (NO3-) is highly water-soluble and considered to be the main nitrogen pollutants leached from agricultural soils. Its presence in aquatic ecosystems is reported to cause various environmental and public health problems. Bioreactors containing microbes capable of transforming NO3- have been proposed as a means to remediate contaminated waters. Woodchip bioreactors (WBRs) are continuous flow, reactor systems located below or above ground. Below ground systems are comprised of a trench filled with woodchips, or other support matrices. The nitrate present in agricultural drainage wastewater passing through the bioreactor is converted to harmless dinitrogen gas (N2) via the action of several bacteria species. The WBR has been suggested as one of the most cost-effective NO3--removing strategy among several edge-of-field practices, and has been shown to successfully remove NO3- in several field studies. NO3- removal in the WBR primarily occurs via the activity of denitrifying microorganisms via enzymatic reactions sequentially reducing NO3- to N2. While previous woodchip bioreactor studies have focused extensively on its engineering and hydrological aspects, relatively fewer studies have dealt with the microorganisms playing key roles in the technology. This review discusses NO3- pollution cases originating from intensive farming practices and N-cycling microbial metabolisms which is one biological solution to remove NO3- from agricultural wastewater. Moreover, here we review the current knowledge on the physicochemical and operational factors affecting microbial metabolisms resulting in removal of NO3- in WBR, and perspectives to enhance WBR performance in the future.

Cold Plasma Controls Nitrite Hazards by Modulating Microbial Communities in Pickled Radish

The hazard of nitrite caused by microorganisms is the main food safety problem in the pickle production. To seek a method to control the nitrite hazards of pickles by regulating microbial community without additional substances, we focused on cold plasma because Gram-negative and Gram-positive bacteria have different degrees of sensitivity to the sterilization of cold plasma. Using radish pickles as the experimental object, based on colony counting, dynamic monitoring of pH and nitrite, qPCR and high-throughput sequencing, it was found that when the raw material was treated with dielectric barrier discharge (DBD) cold plasma at 40 kV for 60 s, Gram-negative bacteria with the potential to produce nitrite were preferentially sterilized. Meanwhile, Gram-positive bacteria dominated by the lactic acid bacteria were retained to accelerate the acid production rate, initiate the self-degradation of nitrite in advance and significantly reduce the peak value and accumulation of nitrite during the fermentation process of pickled radish. This study preliminarily verified that DBD cold plasma can inhibit the nitrite generation and accelerate the self-degradation of nitrite by regulating the structure and abundance of microbial community in radish pickles, which provides an important reference for the control of nitrite hazards in the fermentation process of pickles without additives.

Bioactive molecules from haloarchaea: Scope and prospects for industrial and therapeutic applications

Marine environments and salty inland ecosystems encompass various environmental conditions, such as extremes of temperature, salinity, pH, pressure, altitude, dry conditions, and nutrient scarcity. The extremely halophilic archaea (also called haloarchaea) are a group of microorganisms requiring high salt concentrations (2-6 M NaCl) for optimal growth. Haloarchaea have different metabolic adaptations to withstand these extreme conditions. Among the adaptations, several vesicles, granules, primary and secondary metabolites are produced that are highly significant in biotechnology, such as carotenoids, halocins, enzymes, and granules of polyhydroxyalkanoates (PHAs). Among halophilic enzymes, reductases play a significant role in the textile industry and the degradation of hydrocarbon compounds. Enzymes like dehydrogenases, glycosyl hydrolases, lipases, esterases, and proteases can also be used in several industrial procedures. More recently, several studies stated that carotenoids, gas vacuoles, and liposomes produced by haloarchaea have specific applications in medicine and pharmacy. Additionally, the production of biodegradable and biocompatible polymers by haloarchaea to store carbon makes them potent candidates to be used as cell factories in the industrial production of bioplastics. Furthermore, some haloarchaeal species can synthesize nanoparticles during heavy metal detoxification, thus shedding light on a new approach to producing nanoparticles on a large scale. Recent studies also highlight that exopolysaccharides from haloarchaea can bind the SARS-CoV-2 spike protein. This review explores the potential of haloarchaea in the industry and biotechnology as cellular factories to upscale the production of diverse bioactive compounds.

Efficient thermal treatment of radish (Raphanus sativus) for enhancing its bioactive compounds

Old preserved radish (OPR), a traditional pickled-food of Asia, contains the healthy bioactive compounds, such as phenols and flavonoids. To preserve the phenols levels in radish by thermal treatment, which are decreased due to the polyphenol oxidase activity during long storage. Range of thermal processing evaluated to retain the maximum phenols level in the radish while processed at temperatures of 70 °C, 80 °C and 90 °C for 30 days. In this study, the bioactive compounds and antioxidant activity of thermal processing radish (TPR) were evaluated and compared with commercial products of OPR. Results showed the best condition of thermal processing, 80°C for 30 days, could increase the values of phenols, flavonoids and antioxidant activity that were 2.27, 2.74 and 2.89 times, respectively. When comparing the thermally processed radish or TPR with OPR, TPR has a higher content of phenols and flavonoids, indicating that the thermal processing was effective to increase the content of functional compounds in radish and significantly improved its nutritional values.

Improvement of physicochemical characteristics, flavor profiles and functional properties in Chinese radishes via spontaneous fermentation after drying

Spontaneously dried-fermented radishes have been consumed in China for hundreds of years and are usually fermented for a long time to acquire high quality. In this study, the spontaneously dried-fermented radishes with short-term manufacturing periods were made from five different varieties of radishes that grew in the same environment. In addition, the physicochemical characteristics (i.e., moisture content, soluble solid, and pH value), flavor profiles (i.e., free amino acids, organic acids, and volatile compounds), and functional properties (i.e., total phenolics content, total flavonoids content, sulforaphane content, and γ-aminobutyric acid [GABA] content) of these five raw radishes and spontaneously dried-fermented radishes were analyzed and compared. In detail, the content of volatile and nonvolatile compounds increased, especially in oxalic acid, succinic acid, and umami free amino acids. Furthermore, functional components, such as sulforaphane and GABA, were also enriched via spontaneous fermentation after drying. In addition, the results of principal component analysis, hierarchical clustering analysis, and redundancy analysis showed that there were significant discrepancies appeared when raw radishes were processed via spontaneous fermentation or not. These results suggested that the process of spontaneous fermentation after drying may contribute to improving the quality of fresh radishes. Notably, radishes with red skin and flesh were regarded as exceptional varieties for processing, because of the preferable flavor profiles and affluent functional substances via spontaneous fermentation after drying. Therefore, these findings could deliver a systematical insight into developing processed radishes with high quality. PRACTICAL APPLICATION: The spontaneously dried-fermented radishes were manufactured through the process of spontaneous fermentation after drying, which acquired tasty and healthy characteristics by accumulating the volatile and nonvolatile compounds as well as the functional components, like total phenolics, total flavonoids, sulforaphane, and γ-aminobutyric acid. Importantly, because of the excellent processing properties, the radishes with red skin and flesh could be more appropriate to produce spontaneously dried-fermented radishes. Our findings may provide a practical strategy for developing vegetable relishes with superb flavor profiles and good functional properties in pickled vegetables.