Predominant processing adaptability of Staphylococcus xylosus strains isolated from Chinese traditional low-salt fermented whole fish

Metabolomics ravels flavor compound formation and metabolite transformation in rapid fermentation of salt-free fish sauce from catfish frames induced by mixed microbial cultures

This study demonstrates that the co-inoculation with Lactiplantibacillus plantarum, Pichia fermentans and Staphylococcus saprophyticus accelerates catfish frame fish sauce fermentation. Over a 3-day period, significant changes occurred in physicochemical properties, microbial profiles, flavor compounds, and metabolomic spectra. Notable increases in acidity coupled with decreases in glucose underscored the robust environmental adaptability of the employed microorganisms. A reduction in total amino acids, alongside a rise in umami amino acids, suggested flavor enhancement. GC-MS analysis identified 40 key volatile compounds, with esters and aldehydes crucial for aroma development. UPLC-QTOF-MS-based untargeted analysis identified 934 metabolites, with 377 differential metabolites being vital (VIP > 1.5, P < 0.05), including amino acids, peptides, organic acids, nucleic acids, and fatty acids. Metabolites linked to amino acid metabolism, particularly phenylalanine and arginine, were associated with fermentation duration. These findings offer a theoretical basis for optimizing flavor and quality in fish sauces from fish by-products through accelerated fermentation.

Technological and Safety Characterization of Coagulase-Negative Staphylococci Isolated from Sardinian Fermented Sausage Made by Ovine Meat

Ripened sheep sausages are widely consumed in Italy, particularly in Sardinia. Despite their driving role in flavor and color development, coagulase-negative staphylococci in these products have been rarely investigated. A total of 70 CoNS cultures isolated from Sardinian sheep sausages were characterized by rep-PCR and M13-RAPD typing and identified by 16S rDNA sequencing. S. xylosus and S. equorum accounted for more than 70% of the total isolates, whilst S. pasteuri (8.5%), S. succinus (2.8%), and S. haemolyticus (2.8%) were less represented. The genes encoding the synthesis of putrescine, tyramine, cadaverine, and histamine were evaluated by PCR. None of the strains hosted genes for decarboxylases, except one S. pasteuri strain that was potentially a tyramine-producer. Antibiotic resistance was evaluated, along with nitrate reductase, lipolytic, and proteolytic activity, in a pool of selected cultures. Resistance to the primary antibiotics was rather widespread. S. xylosus, S. equorum, and S. pasteuri strains were all resistant to amoxicillin and kanamycin. S. equorum strains were sensitive to all tested antibiotics. S. xylosus strains were all resistant to penicillin B. Conversely, all S. pasteuri strains were resistant to both ampicillin and penicillin B, and four out of five strains exhibited tetracycline resistance. The high variability in the production of sheep sausages makes the search for adjunct cultures of crucial relevance. According to this perspective, the characterization of the autochthonous CSN population represents the first step to approach a starter selection.

Metabolic cross-feeding enhances branched-chain aldehydes production in a synthetic community of fermented sausages

Microbial interactions play an important role in regulating the metabolic function of fermented food communities, especially the production of key flavor compounds. However, little is known about specific molecular mechanisms that regulate the production of key flavor compounds through microbial interactions. Here, we designed a synthetic consortium containing Debaryomyces hansenii D1, Staphylococcus xylosus S1, and Pediococcus pentosaceus PP1 to explore the mechanism of the microbial interactions underlying the branched-chain aldehydes production. In this consortium, firstly, D. hansenii secreted amino acids that promoted the growth of P. pentosaceus and S. xylosus. Specifically, D. hansenii D1 secreted alanine, aspartate, glutamate, glutamine, glycine, phenylalanine, serine, and threonine, which were the primary nutrients for bacterial growth. P. pentosaceus PP1 utilized all these eight amino acids through cross-feeding, whereas S. xylosus S1 did not utilize aspartate and serine. Furthermore, D. hansenii D1 promoted the production of branched-chain aldehydes from S. xylosus and P. pentosaceus through cross-feeding of α-keto acids (intermediate metabolites). Thus, the accumulation of 2-methyl-butanal was promoted in all co-culture. Overall, this work revealed the mechanism by which D. hansenii and bacteria cross-feed to produce branched-chain aldehydes in fermented sausages.

Relationship between the Dynamics of Flavor Compounds and Microbial Succession in the Natural Fermentation of Zhalajiao, a Popular Traditional Chinese Fermented Chili Paste

Zhalajiao, a traditional Chinese fermented food, is popular due to its unique flavor. Traditional Zhalajiao fermentation is closely related to flavor compounds production. However, the mechanisms underlying the formation of these crucial flavor components in Zhalajiao remain unclear. Here, we explored the dynamic changes in physical and chemical properties, microbial diversity, and flavor components of Zhalajiao at various fermentation times. In total, 6 organic acids, 17 amino acids, and 21 key volatile compounds were determined as flavor components. In Zhalajiao, Lactobacillus and Cyanobacterium were the main bacteria that were involved in the formation of crucial flavor compounds. Candida showed a significant correlation with 14 key flavor compounds during fermentation (p < 0.05) and was the main fungal genus associated with flavor formation in Zhalajiao. This research offers a theoretical foundation for the flavor regulation and quality assurance of Zhalajiao.

Fermented fish and fermented fish-based products, an ever-growing source of microbial diversity: A literature review

Fermented fish and fermented fish-based products are part of the diet of many countries all over the world. Their popularity is not only due to the unique flavor, the distinct texture, and the good nutritional quality, but also to the easiness of the production process, that is commonly based on empirical traditional methods. Fish fermentation techniques ususally rely on the combination of some key steps, including salting, addition of spices or additives, and maintenance of anaerobic conditions, thus selecting for the multiplication of some pro-technological microorganisms. The objective of the present review was to provide an overview of the current knowledge of the microbial communities occurring in fermented fish and fish-based products. Specific information was collected from scientific publications published from 2000 to 2022 with the aim of generating a comprehensive database. The production of fermented fish and fish-based foods was mostly localized in West African countries, Northern European countries, and Southeast Asian countries. Based on the available literature, the microbial composition of fermented fish and fish-based products was delineated by using viable counting combined with identification of isolates, and culture-independent techniques. The data obtained from viable counting highlighted the occurrence of microbial groups usually associated with food fermentation, namely lactic acid bacteria, staphylococci, Bacillus spp., and yeasts. The identification of isolates combined with culture-independent methods showed that the fermentative process of fish-based products was generally guided by lactobacilli (Lactiplantibacillus plantarum, Latilactobacillus sakei, and Latilactobacillus curvatus) or Tetragenococcus spp. depending on the salt concentration. Among lactic acid bacteria populations, Lactococcus spp., Pediococcus spp., Leuconostoc spp., Weissella spp., Enterococcus spp., Streptococcus spp., and Vagococcus spp. were frequently identified. Staphylococcus spp. and Bacillus spp. confirmed a great adaptation to fermented fish-based products. Other noteworthy bacterial taxa included Micrococcus spp., Pseudomonas spp., Psychrobacter spp., Halanaerobium spp., and Halomonas spp. Among human pathogenic bacteria, the occurrence of Clostridium spp. and Vibrio spp. was documented. As for yeast populations, the predominance of Candida spp., Debaryomyces spp., and Saccharomyces spp. was evidenced. The present literature review could serve as comprehensive database for the scientific community, and as a reference for the food industry in order to formulate tailored starter or adjunctive cultures for product improvement.

Role of Microorganisms in the Development of Quality during the Fermentation of Salted White Herring (Ilisha elongata)

Salted white herring (Ilisha elongata) is a popular fish product in the coastal region of China. The complex endogenous enzymes and microbial action determine the quality of a traditionally salted herring. In order to investigate the role of microorganisms in the quality formation of salted herring, three groups for different salting processes were established: traditional salted (TS), non-starter salted (NS), and starter culture salted (SS). The predominant microorganism in each processing group was Staphylococcus spp., as inferred by next-generation sequencing data. Different physicochemical parameters were obtained in each of the three processing groups (TCA-soluble peptide (trichloroacetic acid-soluble peptide), TVB-N (Total volatile basic nitrogen), and TBA values (thiobarbituric acid-reactive substance)). The TS group had the maximum level of total biogenic amines, while the SS group had the lowest. A strong positive correlation was found between Staphylococcus and 14 aromatic compounds, of which 5 were odor-active compounds that created fishy, grassy, fatty, and fruity flavors. Shewanella may produce trimethylamine, which is responsible for the salted herrings’ fishy, salty, and deteriorating flavor. The findings demonstrated that autochthonous strains of Staphylococcus saprophyticus M90−61 were useful in improving product quality because they adapted quickly to the high osmotic environment.

Technological and Safety Characterization of Kocuria rhizophila Isolates From Traditional Ethnic Dry-Cured Ham of Nuodeng, Southwest China

Nuodeng ham is known for its unique processing techniques and flavor. In the present study, proteolytic microorganisms from cured artisanal Nuodeng ham were investigated in order to identify and select potential starter cultures for its faster and safer fermentation. Eight isolates, accounting for 57% of proteolytic microorganisms, were found to be related to Kocuria rhizophila. Relevant properties of K. rhizophila as potential starter culture were evaluated in vitro for the first time. Intra-species diversities were found in phylogenetic and physiological properties of K. rhizophila isolates. Nevertheless, desirable attributes, such as halo-tolerance, nitrate reductase and protease activity, as well as the absence of antimicrobial resistance and amino acid decarboxylase activity, were observed in selected isolates. Moreover, genome analysis of isolates K24 and K45 confirmed their lack of typical genes for virulence, antimicrobial resistance and amino acid decarboxylase. K. rhizophila may thus represent a novel starter candidate of coagulase-negative cocci group and contribute to color and flavor development of fermented meats.

Changes in the microbiological, physicochemical properties of Chinese traditional fermented Suan rou at ripening fermentation

This study characterized the changes in the microbiological, physicochemical properties of Suan rou during fermentation via three different techniques (Technique A is a traditional production process. Based on technique A, technique B adds a total of 200 g of sucrose to the thinly sliced meat, and technique C changes the amount of salt in the thinly sliced meat to 200 grams.). Compared to batch A, the samples from batches B and C featured more rapid reduction in pH and generated more TA. Myofibrillar proteins in batches B and C showed higher degradation rate, and several low-molecular-weight metabolites were determined on the basis of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) gel lanes. The contents of thiobarbituric acid (TBARS) and total volatile base nitrogen (TVB-N) and the growth of spoilage bacteria and pathogens were suppressed in the three batches. A relatively compatible acid-salinity proportion was presented in the Suan rou of batches A and B compared with that of batch C. The results show that the Suan rou made by B technology was more palatable acid flavor and abundant nutrition.

The relationship between flavor formation, lipid metabolism, and microorganisms in fermented fish products

Traditional fermented fish products are favored due to their unique flavors. The fermentation process of fish is accompanied by the formation of flavor substances through a complex metabolic reaction of microorganisms, especially lipolysis and lipid oxidation. However, it is difficult to precisely control the reaction of microorganisms during the fermentation process in modern industrial production, and fermented fish products have lost their traditional characteristic flavors. The purpose of this review is to summarize the different kinds of fermented fish, core microorganisms in it, and flavor formation mechanisms, providing guidance for industrial cultural starters. Future research on the flavor formation mechanism is necessary to confirm the relationship between flavor formation, lipid metabolism, and microorganisms to ensure stable flavor and safety, and to elucidate the mechanism directly toward industrial application.

Effect of red koji as a Starter Culture in "Wanergao": A Traditional Fermented Food in China

The objective of this study was to explore the effect of red kojis on essential indices of Wanergao. The results showed that red koji-inoculated Wanergao showed higher pH values (4.38 ± 0.06 and 4.39 ± 0.06) and lower TA values (1.61 ± 0.05 and 1.63 ± 0.05) compared to the control group. LAB and yeast in the starter culture group gradually increased to 7.57 ± 0.12, 7.64 ± 0.15 log cfu.g-1 and 8.59 ± 0.21, 8.64 ± 0.23 log cfu.g-1, respectively. During fermentation, the dominant microorganism was Lactobacillus plantarum and Saccharomyces cerevisiae. Compared to the Wanergao made using traditional backslopping, the red koji-inoculated Wanergao contained more amylases, EAA and DAA contents compared to the control sample. The red kojis and control samples presented different hardness, chewiness, and cohesiveness, as well as similar values in springiness, gumminess, and adhesiveness. Sensory analysis also showed higher chewiness aroma and resilience of Wanergao in the starter culture group than in the control group.

Correlation between autochthonous microbial communities and key odorants during the fermentation of red pepper (Capsicum annuum L.)

High-throughput sequencing and gas chromatography-mass spectrometry (GC-MS) were used to investigate changes in bacterial and fungal communities and volatile flavor compounds during a 32-day fermentation process of red pepper (Capsicum annuum L.). Key odorants were identified by olfactometry combined with GC-MS. Sixteen volatile compounds differed significantly after fermentation, including seven odorants. After fermentation, 1-butanol, 3-methyl-, acetate, phenol, 4-ethyl-2-methoxy-, octanoic acid, ethyl ester, styrene and 2-methoxy-4-vinylphenol were the key odorants, producing a flavor described as peppery, fruity, sour, and spicy. The correlation between microorganisms and odorants in the fermentation was studied and 18 odorants significantly correlated with the core microbial communities in the fermented samples. For further analysis, strains of seven genera were isolated and correlation analysis by O2PLS indicated that Aspergillus, Bacillus, Brachybacterium, Microbacterium and Staphylococcus were highly correlated with the flavor formation. These findings would help to understand the fermentation mechanism of fermented red pepper flavor formation.

Discovering microbiota and volatile compounds of surströmming, the traditional Swedish sour herring

In this study, the microbiota of ready-to-eat surströmming from three Swedish producers were studied using a combined approach. The pH values of the samples ranged between 6.67 ± 0.01 and 6.98 ± 0.01, whereas their a_w values were between 0.911 ± 0.001 and 0.940 ± 0.001. The acetic acid concentration was between 0.289 ± 0.009 g/100 g and 0.556 ± 0.036 g/100 g. Very low concentrations of lactic acid were measured. Viable counting revealed the presence of mesophilic aerobes, mesophilic lactobacilli and lactococci as well as halophilic lactobacilli and lactococci, coagulase-negative staphylococci, halophilic aerobes and anaerobes. Negligible counts for Enterobacteriaceae, Pseudomonadaceae and total eumycetes were observed, whereas no sulfite-reducing anaerobes were detected. Listeria monocytogenes and Salmonella spp. were absent in all samples. Multiplex real-time PCR revealed the absence of the bont/A, bont/B, bont/E, bont/F, and 4gyrB (CP) genes, which encode botulinic toxins, in all the samples analyzed. Metagenomic sequencing revealed the presence of a core microbiota dominated by Halanaerobium praevalens, Alkalibacterium gilvum, Carnobacterium spp., Tetragenococcus halophilus, Clostridiisalibacter spp. and Porphyromonadaceae. Psychrobacter celer, Ruminococcaceae, Marinilactibacillus psychrotolerans, Streptococcus infantis and Salinivibrio costicola were detected as minor OTUs. GC-MS analysis of volatile components revealed the massive presence of trimethylamine and sulphur compounds. Moreover, 1,2,4-trithiolane, phenols, ketones, aldehydes, alcohols, esters and long chain aliphatic hydrocarbons were also detected. The data obtained allowed pro-technological bacteria, which are well-adapted to saline environments, to be discovered for the first time. Further analyses are needed to better clarify the extent of the contribution of either the microbiota or autolytic enzymes of the fish flesh in the aroma definition.

Isolation and Screening of Staphylococcus Xylosus P2 from Chinese Bacon: A Novel Starter Culture in Fermented Meat Products

A novel coagulase negative staphylococci strain as flavor agent for the processing of fermented meat products, Staphylococcus xylosus P2, was screened from Chinese bacon. It was identified on the basis of morphology and 16S rDNA sequence analysis. Its proteolytic, lipolytic and nitrate reductive activities were evaluated. And its growth ability at different temperatures, pH, sodium chloride, sodium nitrite concentrations, biogenic amine and pigment were investigated or detected. Furthermore, the fermentation evaluation with S. xylosus P2 as starter culture was carried out. The result showed that the fermented beef jerky was more attractive on the color, odor, texture, tasty and overall acceptability. It indicated that S. xylosus P2 would be a good starter culture for fermented meat products (jerky).

Analyses of microbial community of naturally homemade soybean pastes in Liaoning Province of China by Illumina Miseq Sequencing

Traditional Chinese soybean pastes are homemade using natural fermentation and are quite common and popular in Liaoning Province. In this study, we investigated microbial diversity by collecting 23 samples from 10 cities and sequenced them using 2 × 300 bp Illumina Miseq Sequencing. 16S and ITS primers were used to amplify the V3-V4 region of the bacterial 16S rRNA gene and the ITS1 region of the fungal ITS rDNA gene, respectively. In total, 687,888 filtered bacterial sequences were obtained from nineteen samples and 1,091,649 filtered fungal sequences were obtained from twenty samples. Among the bacterial sequences, Firmicutes (74.77%), Proteobacteria (22.61%), and Actinobacteria (2.55%) were the predominant phyla, with Staphylococcus making up most of the Firmicutes. Among the fungal sequences, Ascomycota, Basidiomycota and Zygomycota accounted for 94.88%, 3.29% and 1.77%, respectively, while Glomeromycota and Chytridiomycota accounted for the remaining 0.06%. Most of the species from Ascomycota were unclassified Trichocomaceae and Debaryomyces, including 404578 and 187827 sequences, respectively. The microbial community in each sample was unique, most likely due to the geographical differences and external factors including the environment and manufacturing process during the fermentation. Soybean paste is the result of fermentation involving a great diversity of microorganisms, which include not only bacteria but also fungi.