Dynamics and diversity of microbial community succession during fermentation of Suan yu, a Chinese traditional fermented fish, determined by high throughput sequencing

Inhibitory effects of glutathione peroxidase on microbial spoilage of crayfish (Procambarus clarkii) during refrigerated storage

The variety of enzyme-based biological preservatives is limited. This study evaluated the effects of glutathione peroxidase (GSH-Px) on the quality of crayfish during refrigerated storage by measuring the pH, total volatile basic nitrogen, trimethylamine, and microbial contamination in crayfish muscle simulation system. The results revealed that 0.3% GSH-Px (CK3) not only suppressed the degradation of nitrogenous substances but also decreased the contamination levels of total viable, Enterobacteriaceae, and Pseudomonas counts (P < 0.05). Furthermore, the populations of Lactococcus, Aeromonas, and Massilia differed in the CK3 group compared to the other groups (P < 0.05) at the end of the storage (day 15). Moreover, the principal coordinate analysis showed that the colony composition of CK3 stored for 15 days was similar to that of the control group stored for 10 days. Therefore, GSH-Px exhibits antibacterial activity against Gram-negative bacteria and has good application potential in freshwater aquatic product preservation.

Insight into the autochthonous bacterial strains as starter cultures for improving the flavor profiles of dry-cured duck: Changes in microbial diversity and metabolic profiles

The purpose of this study was to reveal the effect of inoculating autochthonous bacterial strains (Lactobacillus and Staphylococcus simulans) on the flavor profiles, microbial community, and metabolites, and to elucidate the potential mechanism of flavor formation in dry-cured duck. The results indicated that the inoculation of bacterial strains could improve the amount of lactic acid bacteria and Staphylococcus and reduce the counts of Enterobacteria. There was a significant difference in flavor profiles between samples inoculated with different strains. Hexanal-D, acetone, 3-methyl-1-butanol-D, thiophene, hexanal-M, propanal, pentanal, (Z)-2-penten-1-ol and ethanol-D were the potential biomarkers. A total of 70 differential metabolites were screened and identified. Amino acid metabolism and lipid metabolism were the key pathways for the production of flavor and metabolites in dry-cured duck. The results of this study will improve our understanding of the mechanism of flavor formation regarding the inoculation of autochthonous starter cultures.

The Contribution of Microorganisms to the Quality and Flavor Formation of Chinese Traditional Fermented Meat and Fish Products

Guizhou sour meat and sour fish, Chaoshan fish sauce, Sichuan sausage and bacon, Cantonese sausage, Jinhua ham, and Xinjiang air-dried beef are eight representatives of Chinese traditional fermented meat and fish products (FMFPs), which are favored by Chinese consumers due to their high nutritional value and quality. The quality of the spontaneously fermented Chinese traditional FMFP is closely correlated with microorganisms. Moreover, the dominant microorganisms are significantly different due to regional differences. The effects of microorganisms on the texture, color, flavor, nutrition, functional properties, and safety of Chinese traditional FMFPs have not been not fully described. Additionally, metabolic pathways for flavor formation of Chinese traditional FMFPs have not well been summarized. This article describes the seven characteristic Chinese traditional FMFPs and correlated dominant microorganisms in different regions of China. The effects of microorganisms on the texture, color, and flavor of Chinese traditional FMFPs are discussed. Furthermore, the metabolic pathways of microbial regulation of flavor formation in Chinese traditional FMFPs are proposed. This work provides a theoretical basis for improvement of Chinese traditional FMFPs by inoculating functional microorganisms isolated from Chinese traditional fermented foods.

Physicochemical and microbial community dynamics of Kocho fermented from different enset varieties in South West Ethiopia

Enset (Ensete ventricosum (Welw.) Cheesman) is an indigenous multipurpose plant in Ethiopia. More than 20 % of people in Ethiopia rely on enset for their subsistence livelihood. Its fermentation produces a starchy food named Kocho, which is yet poorly studied. In this study, physicochemical and microbial community dynamics of Kocho fermented from different enset varieties (Maziya, Genna, and Arkiya) were collected at Dawro Zone (Southern Ethiopia). Samples were collected at various fermentation times (days 1-60) for physicochemical and microbial (culture-dependent and culture-independent) characterization. Results showed that increasing fermentation time has a significantly strong positive (R2 = 0.768, p = 0.004) correlation between titrable acidity, and a significantly strong negative association with pH (R2 = -0.715, p = 0.009), moisture (R2 = -0.982, p < 0.05), ash (R2 = -0.932, p < 0.05), fat (R2 = -0.861, p < 0.05), fiber (R2 = -0.981, p < 0.05) and carbohydrate (R2 = -0.994, p < 0.001) contents. An increasing or decreasing trend of physicochemical parameters observed during enset fermentation is significantly associated with microbial community dynamics. Shifts of microbial community observed during culture-dependent analysis were also confirmed by metagenomic results. During fermentation, Firmicutes (39-68 %) > Proteobacteria (7-53 %) > Cyanobacteria (7-24 %) were dominant phyla in the three enset varieties. Gamma (traditional starter culture) is dominated by Lactobacillus plantrum and Lactobacillus manihotivorans most probably the two species that play a significant role in initiating enset fermentation.

Characterization of the physicochemical Properties, bacterial community and non-volatile profiles of fermented Yu jiangsuan by Weissella cibaria and Lactobacillus plantarum

Yu jiangsuan (YJS) is a unique traditional fermented condiment in China. Physicochemical, bacterial communities, and non-volatile properties were examined in inoculation Autochthonous Weissella cibaria and Lactobacillus plantarum. The results indicated that inoculation samples did well in shortening fermentation time; amino acid nitrogen (AN) and TCA-soluble peptide contents of fermented YJS were 10.8% and 17.4% higher than those of naturally fermented YJS, respectively. However, its total volatile base nitrogen (TVB-N), thiobarbituric acid (TBARS), and nitrite were only 74.3%, 87.2% and 83.6% of those of naturally fermented YJS. In addition, the dominant bacterial genera were Lactobacillus, Weissella and Pectobacterium, whose contributions were 41.2%, 20.3% and 5.5%, respectively. Moreover, 26 significantly differential metabolites were identified, and involved in 10 metabolic pathways. The decomposition of substrates and the formation of differential metabolites in YJS were primarily centered on the TCA cycle and the metabolism of carbohydrates. Therefore, this study is conducive to discovering the bacterial community structure and metabolite composition of probiotic inoculated YJS fermentation, as well as the potential value of core functional bacteria genera in controlling YJS production in industry.

Spontaneously growing fungi on the surface and processing areas of matured sheep ham and volatile compounds produced

Raw ham is a dried and matured product traditionally made from pork leg, but other animals, such as sheep, can be used. The natural presence of bacteria and fungi in this product influences its characteristics throughout the process. This study analysed the fungal populations present during raw sheep hams' processing. Two types of products were developed: without and with the addition of seasonings. Mycological analyses were carried out from the ingredients, seasonings, facilities air, as well as on the surfaces of the hams and the air in the chamber throughout the maturation period (0, 45, 90, and 180 days) using 18 % dichloran glycerol agar and the data were submitted to Principal Component Analysis. Volatile compounds were evaluated at the end of the sheep ham manufacturing process through a gas chromatograph coupled to a mass spectrometer. At 45 days of aging, a more remarkable similarity was observed between the fungi present on the non-seasoned hams and those in the ripening chamber's air, while the seasoned hams showed a more evident relation with those fungi present in the spices. With time, the fungi in the air of the ripening chamber started to be influenced by Aspergillus ser. Aspergillus and Aspergillus ser. Rubri already installed in the seasoned hams at 45 days, and then it probably dispersed the non-seasoned ones due to the airborne spores, becoming the most prevalent in both treatments at 90 days. At the end of ripening, the mycobiota of both raw hams was composed mainly by xerophilic species of Aspergillus section Aspergillus. The total fungal count was 5.78 log CFU/cm2 for the non-seasoned and 7.19 log CFU/cm2 for the seasoned ones. A potentially ochratoxigenic Aspergillus ser. Circumdati was detected at the end of aging in raw, unseasoned hams. In conclusion, seasoning directly influences the species developing on the surface of seasoned hams throughout the ripening process, and indirectly affects the mycobiota of the non-seasoned hams when sharing the same ripening chamber. The presence of fungi in the matured sheep ham seems to contribute to the formation of volatile compounds, which are related to the sensory quality of these products.

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.

Diversifying the Flavor of Black Rice Wines through Three Different Regional Xiaoqus in China and Unraveling Their Core Functional Microorganisms

The flavor of black rice wine (BRW) can be diversified by the Xiaoqus, from different regions; however, the functional microbiota that contributes to its flavor remains unclear. Accordingly, this study selected three regional Xiaoqus from Sichuan Dazhu (Q1), Jiangxi Yingtan (Q2), and Hubei Fangxian (Q3) as starters to investigate flavor compounds and microbial communities during BRW brewing. Results indicated that altogether 61 flavor substances were identified, 16 of which were common characteristic flavor compounds (odor activity value > 0.1). Each BRW possessed unique characteristic flavor compounds. O2PLS and Spearman's correlation analysis determined that characteristic flavor compounds of BRW were mainly produced by Saccharomyces cerevisiae, non-Saccharomyces yeasts, and lactic acid bacteria, with the common core functional strains being Wickerhamomyces and Pediococcus, and with their unique core functional strain likely causing a unique characteristic flavor. This study could promote the high-quality development of the black rice wine industry.

Transforming the fermented fish landscape: Microbiota enable novel, safe, flavorful, and healthy products for modern consumers

Regular consumption of fish promotes sustainable health while reducing negative environmental impacts. Fermentation has long been used for preserving perishable foods, including fish. Fermented fish products are popular consumer foods of historical and cultural significance owing to their abundant essential nutrients and distinct flavor. This review discusses the recent scientific progress on fermented fish, especially the involved flavor formation processes, microbial metabolic activities, and interconnected biochemical pathways (e.g., enzymatic/non-enzymatic reactions associated with lipids, proteins, and their interactions). The multiple roles of fermentation in preservation of fish, development of desirable flavors, and production of health-promoting nutrients and bioactive substances are also discussed. Finally, prospects for further studies on fermented fish are proposed, including the need of monitoring microorganisms, along with the precise control of a fermentation process to transform the traditional fermented fish to novel, flavorful, healthy, and affordable products for modern consumers. Microbial-enabled innovative fermented fish products that consider both flavor and health benefits are expected to become a significant segment in global food markets. The integration of multi-omics technologies, biotechnology-based approaches (including synthetic biology and metabolic engineering) and sensory and consumer sciences, is crucial for technological innovations related to fermented fish. The findings of this review will provide guidance on future development of new or improved fermented fish products through regulating microbial metabolic processes and enzymatic activities.

Three New Species of Fusicolla (Hypocreales) from China

To explore the species diversity of the genus Fusicolla, specimens from Henan, Hubei and Jiangsu Provinces in China are examined, and three undescribed taxa are encountered. The morphological characteristics and DNA sequence analyses of the combined acl1, ITS, LSU, rpb2 and tub2 regions support their placement in Fusicolla and their recognition as new species. Fusicolla aeria sp. nov. is distinguished by the formation of abundant aerial mycelia on PDA, falcate, (1-)3-septate macroconidia 16-35 × 1.5-2.8 μm and subcylindrical, aseptate microconidia 7.5-13 × 0.8-1.1 μm. Fusicolla coralloidea sp. nov. has a coralloid colony on PDA, falcate, 2-5-septate macroconidia 38-70 × 2-4.5 μm and rod-shaped to ellipisoidal, aseptate microconidia 2-7 × 1-1.9 μm. Fusicolla filiformis sp. nov. is characterized by filiform, 2-6-septate macroconidia 28-58 × 1.5-2.3 μm and lacking microconidia. Morphological differences between these novel species and their close relatives are compared in detail. The previously recorded species of the genus in China are listed and a key to these taxa is provided.

Correlation Study between Quality and Sensory Characteristics of Kelp Paste by Aspergillus oryzae and Aspergillus niger during Fermentation

In order to clarify the relationship between quality and sensory characteristics of kelp paste during fermentation, this study analyzed the quality and sensory characteristics of kelp paste through physicochemical indexes, nutritional components, electronic nose and electronic tongue. The results showed that with the extension of fermentation time, the contents of amino nitrogen, total acid, ammonium salt and ash increased gradually, while the pH value, moisture, fat, protein and carbohydrate decreased gradually. Short-chain alkanes such as nitrogen oxides and methane were the main causes of odor. Freshness, salinity and richness were the main indexes of kelp paste taste. Many quality indexes, such as amino nitrogen and protein, were significantly related to the odor sensor, which can better reflect the odor produced in the fermentation process of kelp paste. There was a significant correlation between quality indicators and important taste indicators such as umami, richness and salty taste, which can better reflect the taste of kelp paste during fermentation. To sum up, there was a significant correlation between the quality characteristics and sensory quality of kelp paste, so the relationship between quality characteristics and sensory characteristics in kelp paste can be clarified.

Application and Effect of Pediococcus pentosaceus and Lactiplantibacillus plantarum as Starter Cultures on Bacterial Communities and Volatile Flavor Compounds of Zhayu, a Chinese Traditional Fermented Fish Product

Zhayu is a type of traditional fermented fish product in China that is made through the fermentation of salted fish with a mixture of cereals and spices. Inoculation fermentation was performed using Pediococcus pentosaceus P1, Lactiplantibacillus plantarum L1, and a mixture of two strains, which were isolated from cured fish in Hunan Province. Compared with the natural fermentation, inoculation with lactic acid bacteria (LAB) accelerated the degradation of myosin and actin in Zhayu, increased the trichloroacetic acid (TCA)-soluble peptide content by about 1.3-fold, reduced the colony counts of Enterobacteriaceae and Staphylococcus aureus by about 40%, and inhibited their lipid oxidation. In the texture profile analysis performed, higher levels of hardness and chewiness were observed in the inoculation groups. In this study, the bacterial community and volatile flavor compounds were detected through 16S high-throughput sequencing and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Inoculation with L. plantarum L1 reduced around 75% abundance of Klebsiella compared with the natural fermentation group, which was positively correlated with 2,3-Butanediol, resulting in a less pungent alcohol odor in Zhayu products. The abundances of 2-pentylfuran and 2-butyl-3-methylpyrazine were increased over threefold in the L1 group, which may give Zhayu its unique flavor and aroma.

Combined effects of lipase and Lactiplantibacillus plantarum 1-24-LJ on physicochemical property, microbial succession and volatile compounds formation in fermented fish product

BACKGROUND

Studies have shown that either the addition of starter culture or enzyme can improve fermentation in fish or other products. However, little research has been carried out on the effects of coupling starter cultures with lipase on the microbial community and product quality. Suanzhayu is a Chinese fermented fish product that mainly relies on spontaneous fermentation, resulting in an unstable flavor and quality. The present study investigated the impact of lipase and Lactiplantibacillus plantarum 1-24-LJ on the quality of Suanzhayu.

RESULTS

Inoculation decreased pH and 2-thiobarbituric acid reactive substances (TBARS) values, and also helped the dominance of the strain in the ecosystem, whereas lipase addition raised TBARS values and had little effect on pH, water activity (a_w ) and microbiota. The addition of lipase and/or Lpb. plantarum increased the content of alcohols, aldehydes, ketones, esters and umami amino acids. The co-additions with the most significant effect and the total contents of volatile compounds (VCs) and free amino acids (FAAs) were 1801.92 g per 100 g and 21 357.05 mg per 100 g, respectively. Former-Lactobacillus was negatively correlated with pH, a_w and Prevotella, but positively with VCs (ethyl ester of heptanoic acid, ethyl ester of octanoic acid) and FAAs (Tyr, Phe). Furthermore, adding Lpb. plantarum 1-24-LJ alone or in combination with lipase shortened the fermentation process.

CONCLUSION

The present study provides a recommended Suanzhayu process approach for improving product quality and flavor, as well as shortening fermentation time, by adding Lpb. plantarum 1-24-LJ with or without lipase. © 2023 Society of Chemical Industry.

Bacterial Diversity Analysis of Chaozhou Sauerkraut Based on High-Throughput Sequencing of Different Production Methods

In this study, high-throughput sequencing technology was used to analyze the bacterial diversity of sauerkraut produced at home and in factories in Chaozhou. The differences in bacterial community structure among different sauerkraut samples were studied by diversity analysis and heat map analysis, and the dominant bacterial genera were analyzed. The results showed that 54 phyla and 622 genera were identified from 10 Chaozhou sauerkraut samples. The bacterial community structures of Chaozhou sauerkraut produced by five factories were similar, and the dominant bacterial genera were the same, which were Lactobacillus, Pediococcus and Weissella. The dominant genus in the sauerkraut samples produced by three families was similar to that in samples produced by the factories. However, the samples from two other families were quite different, and there may be environmental pollution. The samples may also contain possible pathogenic microorganisms such as Pseudomonas and Vibrio. Overall, there were still some differences in the bacterial community structure of Chaozhou sauerkraut factory-produced and household-handmade samples. To the best of our knowledge, this paper is the first to compare the bacterial diversity of homemade and factory-produced Chaozhou sauerkraut, laying the foundation for further research on Chaozhou sauerkraut.

Further Interpretation of the Volatile, Microbial Community and Edible Quality of Fresh Fermented Rice Noodles with Different Selected Strains

Understanding bacteria and yeasts can reduce unpredictable changes in fresh fermented rice noodles (FFRN). The effects of selected strains (Limosilactobacillus fermentum, Lactoplantibacillus plantarum, Lactococcus lactis and Saccharomyces cerevisiae) on the edible quality, microbial community, and volatile component of FFRN were studied. The results indicated that the fermentation time could be shortened to 12 h when Limosilactobacillus fermentum, Lactoplantibacillus plantarum, and Lactococcus lactis were added, whereas it still required approximately 42 h after adding Saccharomyces cerevisiae. Only a steady bacterial composition was provided by adding Limosilactobacillus fermentum, Lactoplantibacillus plantarum, and Lactococcus lactis, and only a steady fungal composition was provided by adding Saccharomyces cerevisiae. Therefore, these microbial results indicated that the selected single strains cannot improve the safety of FFRN. However, the cooking loss was decreased from 3.11 ± 0.11 to 2.66 ± 0.13 and the hardness of FFRN was increased from 1186 ± 178 to 1980 ± 207 when it was fermented with single strains. Finally, a total of 42 volatile components were determined by Gas chromatography-ion Mobility Spectrometry and 8 aldehydes, 2 ketones, and 1 alcohol were added during the entire fermentation process. The main volatile components were different during fermentation depending on the added strain, and there was the greatest variety of volatiles in the group with added Saccharomyces cerevisiae.

Three Phenolic Extracts Regulate the Physicochemical Properties and Microbial Community of Refrigerated Channel Catfish Fillets during Storage

It has been demonstrated that polyphenols have the potential to extend the shelf life of fish products. Thus, the effects of phenolic extracts from grape seed (GSE), lotus seedpod (LSPC), and lotus root (LRPE) were investigated in this study, focusing on the physicochemical changes and bacterial community of refrigerated channel catfish fillets during storage at 4 °C, using ascorbic acid (AA) as reference. As a result, GSE, LSPC, LRPE and AA inhibit the reproduction of microbials in catfish fillets during storage. According to the microbial community analysis, the addition of polyphenols significantly reduced the relative abundance of Proteobacterial in the early stage and changed the distribution of the microbial community in the later stage of storage. After 11 days of storage, the increase in total volatile base nitrogen (TVB-N) in fish was significantly reduced by 25.85%, 25.70%, 22.41%, and 39.31% in the GSE, LSPC, LRPE, and AA groups, respectively, compared to the control group (CK). Moreover, the lipid oxidation of samples was suppressed, in which thiobarbituric acid-reactive substances (TBARS) decreased by 28.77% in the GSE group, compared with the CK. The centrifugal loss, LF-NMR, and MRI results proved that GSE significantly delayed the loss of water and the increase in immobilized water flowability in catfish fillets. The polyphenol-treated samples also showed less decrease in shear force and muscle fiber damage in histology, compared to the CK. Therefore, the dietary polyphenols including GSE, LSPC, and LRPE could be developed as natural antioxidants to protect the quality and to extend the shelf life of freshwater fish.

Relationships between fungal diversity and fruit quality of Yuluxiang pear during low temperature storage

Postharvest decay is an urgent problem that affects the storage of pears. Low temperature storage is one of the most important methods to reduce the prevalence of fruit diseases during storage. In this study, the microbial diversity of postharvest Yuluxiang pear (Pyrus × michauxii "Yu Lu Xiang") fruits stored at low temperature for different lengths of times was analyzed. Illumina MiSeq high-throughput sequencing was used to analyze the composition and diversity of fungal communities. The results showed that the fungi within fruit were classified into 6 phyla, 18 classes, 40 orders, 72 families, and 92 genera based on the 97% sequence similarity level. They belonged to 6 phyla, 18 classes, 40 orders, 72 families, and 92 genera. The highest richness of fungi was obtained after 30 d of treatment. The β-diversity index showed that the fungal community composition of these fruit was significantly different at the beginning of storage compared with the different timepoints of samples at low temperature during storage. The comparison of fungal composition at the phylum level indicated that Ascomycota was dominant in the different timepoints of samples at low temperature, while Alternaria was the primary fungus at the genus level. A correlation analysis was used to further explore the correlation between fungi and fruit firmness, titratable acid, and solid soluble contents at low temperatures during storage. Aureobasidium and Didymella positively correlated with the soluble solids and hardness. Phoma positively correlated with the titratable acid, and Aspergillus positively correlated with titratable acid and hardness. This study can guide the industrial production of Yulu pear and also provide a theoretical basis to prevent and control diseases during the storage period of Yulu pear.

Identification and validation of core microbes associated with key aroma formation in fermented pepper paste (Capsicum annuumL.)

Fermented peppers are usually obtained by the spontaneous fermentation of microorganisms attached to fresh peppers, and the variable microbial composition would lead to inconsistencies in flavor between batches. To demonstrate the roles of microorganisms in flavor formation, the core microbes closely associated with the key aroma compounds of fermented pepper paste were screened and validated in this study. Lactobacillus was the dominant bacterial genus in fermented pepper paste, whereas the main fungal genera were Alternaria and Kazachstania. Nine strains of the genera Lactobacillus, Weissella, Bacillus, Zygosaccharomyces, Kazachstania, Debaryomyces, and Pichia were isolated from fermented pepper paste. Eleven key aroma compounds were identified using gas chromatography combined with olfactometry and relative odor activity values. Correlation analysis showed that Zygosaccharomyces and Kazachstania were positively correlated with the majority of the key aroma compounds, whereas Lactobacillus was negatively correlated with them. Thus, Zygosaccharomyces and Kazachstania were identified as core genera associated with the key odorants. Finally, Zygosaccharomyces bisporus, Kazachstania humilis, and Lactiplantibacillus plantarum were used as starter cultures for fermented peppers, confirming that Z. bisporus and K. humilis were more beneficial for the key aroma compounds (e.g., acetate, linalool, and phenyl ethanol) rather than L. plantarum. This study contributed to understanding the flavor formation mechanism and provided references for the quality control of food fermentation.

Whole-Genome Sequencing of a Potential Ester-Synthesizing Bacterium Isolated from Fermented Golden Pomfret and Identification of Its Lipase Encoding Genes

Microbial ester synthases are regarded as valuable catalysts in the food industry. Here, one strain of Acinetobacter venetianus with ester synthase-production capacity, SCSMX-3, was isolated from traditional fermented golden pomfret. It exhibited good growth in mesophilic, low salt, and slightly alkaline environments. The ester synthase produced by SCSMX-3 displayed maximum activity at pH 8.0 and 35 °C. Genome sequencing revealed that the strain contains one circular chromosome of 336313 bp and two circular plasmids (plasmid A-14424 bp and plasmid B-11249 bp). Six CRISPR structures enhance the genomic stability of SCSMX-3 and provide the opportunity to create new functional strains. Gene function analysis indicated that SCSMX-3 produces the necessary enzymes for survival under different conditions and for flavor substance synthesis. Furthermore, 49 genes encoding enzymes associated with lipid metabolism, including three triacylglycerol lipases and two esterases, were identified through the NCBI Non-Redundant Protein Database. The lipase encoded by gene0302 belongs to the GX group and the abH15.02 (Burkholderia cepacia lipase) homolog of the abH15 superfamily. Our results shed light on the genomic diversity of and lipid metabolism in A. venetianus isolated from fermented golden pomfret, laying a foundation for the exploration of new ester synthases to improve the flavor of fermented fish products.

Exploring the Fungal Community and Its Correlation with the Physicochemical Properties of Chinese Traditional Fermented Fish (Suanyu)

Suanyu is a traditional natural fermented fish product from Southwest China that contains very complex microflora. The main purpose of this study was to explore the fungal community and its relationship with the physicochemical properties of Suanyu. The fungal community structure of Suanyu from the main provinces (Guizhou and Hunan) was studied via high-throughput sequencing. The correlation between dominant fungi and physicochemical characteristics was analyzed via Spearman's correlation coefficient. The results showed that the pH value, total volatile base nitrogen content, and thiobarbituric acid reactive substance content ranges of Suanyu samples were 4.30-5.50, 17.11-94.70 mg/100 g, and 0.61 to 3.62 mg/kg, respectively. The average contents of total volatile base nitrogen, thiobarbituric acid reactive substance, and total BAs in Suanyu from Guizhou were lower than those from Hunan. The main BAs were phenethylamine, putrescine, cadaverine, histamine, and tyramine. Ascomycota was the dominant fungal phylum, and Kodamaea, Debaryomyces, Wallemia, Zygosaccharomyces, and unclassified Dipodascaceae were the dominant fungal genera in different samples. Moreover, high abundance levels of Kodamaea and Zygosaccharomyces were found in Suanyu from Guizhou. According to the correlation analysis, Kodamaea and Zygosaccharomyces were negatively correlated with TBARS (R² = -0.43, -0.51) and TVBN (R² = -0.37, -0.29), and unclassified Dipodascaceae was significant negatively correlated with tyramine (R² = -0.56). This study expands the understanding of the fungal community and the fermentation characteristics of the dominant fungi in Suanyu.

Effects of chitosan and apple polyphenol coating on quality and microbial composition of large yellow croaker (Pseudosciaena crocea) during ice storage

BACKGROUND

Large yellow croaker (Pseudosciaena crocea) has important commercial value because of its high nutritional value and delicious taste. However, large yellow croaker is readily affected by microorganisms during storage, which causes the corruption of muscle tissue. Both chitosan (CS) and apple polyphenols (APs) are bio-preservatives, which can effectively inhibit the growth of microorganisms and improve the quality of large yellow croaker. The effects of 10.0 and 20.0 g L^-1 CS combined with 1.0 g L^-1 AP coating on the quality and microbial composition of large yellow croaker during ice storage were investigated respectively.

RESULTS

CS + AP coating restrained the increase of total volatile basic nitrogen (TVB-N) and biogenic amines, slowed down the rise of K-value and retarded the growth of microorganisms. The bacteriostatic effect was positively correlated with the concentration of CS. Through the analysis of high-throughput sequencing (HTS), the microbial diversity was changed respectively. The proportion of Shewanella was significantly decreased by CS + AP coating treatment and Pseudomonas was the dominant microorganism in spoiled samples. Compared with the shelf-life of the control group (8 days), 20.0 g L^-1 CS combined with 1.0 g L^-1 AP coating treatment could extend the shelf-life of large yellow croaker for another 8 days.

CONCLUSIONS

CS combined with AP coating may be considered a promising method to delay the biochemical changes of ice stored large yellow croaker and extend its shelf life. © 2021 Society of Chemical Industry.

Microbial Consortium Associated with Crustacean Shells Composting

Soil microbes play an essential role in the biodegradation of crustacean shells, which is the process of sustainable bioconversion to chitin derivatives ultimately resulting in the promotion of plant growth properties. While a number of microorganisms with chitinolytic properties have been characterized, little is known about the microbial taxa that participate in this process either by active chitin degradation or by facilitation of this activity through nutritional cooperation and composting with the chitinolytic microorganisms. In this study, we evaluated the transformation of the soil microbiome triggered by close approximation to the green crab shell surface. Our data indicate that the microbial community associated with green crab shell matter undergoes significant specialized changes, which was reflected in a decreased fungal and bacterial Shannon diversity and evenness and in a dramatic alteration in the community composition. The relative abundance of several bacterial and fungal genera including bacteria Flavobacterium, Clostridium, Pseudomonas, and Sanguibacter and fungi Mortierella, Mycochlamys, and Talaromyces were increased with approximation to the shell surface. Association with the shell triggered significant changes in microbial cooperation that incorporate microorganisms that were previously reported to be involved in chitin degradation as well as ones with no reported chitinolytic activity. Our study indicates that the biodegradation of crab shells in soil incorporates a consortium of microorganisms that might provide a more efficient way for bioconversion.

Illumina-Based Analysis Yields New Insights Into the Fungal Contamination Associated With the Processed Products of Crataegi Fructus

Crataegi Fructus, a medicinal and edible herb in China, has been considered a popular dietary supplement globally. It is used for the treatment of dyspepsia and chronic heart failure according to the Chinese Pharmacopoeia (2020). However, fungal contamination in Crataegi Fructus affects its quality and safety, thus preventing its global promotion. In this study, we comprehensively studied the fungal community in processed products of Crataegi Fructus by high-throughput sequencing. A total of 21 Crataegi Fructus samples were collected from five provinces in China, and the samples were divided into five groups based on collection areas, as well as into three groups based on processing methods. We then targeted the internal transcribed spacer 2 sequence through the Illumina Miseq PE300 platform to investigate fungal composition and diversity. Results showed that all 21 samples were detected with fungal contamination, and Ascomycota was dominant at the phylum level. In the groups based on collection areas, Dothideomycetes, Pleosporaceae, and Alternaria were dominant at the class, family, and genus levels, respectively. In the groups based on processing methods, Dothideomycetes, Aspergillaceae, and Alternaria were the most abundant at the class, family, and genus levels, respectively. Differences in fungal communities between various groups were also observed. Furthermore, a total of 115 species were identified, among which seven were potential toxigenic, namely, Trichothecium roseum, Alternaria tenuissima, Aspergillus carbonarius, Penicillium brevicompactum, Aspergillus fumigatus, Rhizopus microspores, and Pichia fermentans. In conclusion, this study reveals great fungal richness and diversity of Crataegi Fructus, providing references for the prevention and control of fungal contamination of Crataegi Fructus in practical production.

Recent developments in off-odor formation mechanism and the potential regulation by starter cultures in dry-cured ham

Foul-smelling odors are main quality defects of dry-cured ham, which are connected with the excessive degradation of the structural proteins and excessive oxidation of lipids caused by the abnormal growth of spoilage microorganisms, threatening the development of dry-cured ham industry. Characterizing the key microorganisms and metabolites resulted in the spoilage of dry-cured ham, and discussing the relationship between spoilage microorganisms and metabolites are the key aspects to deeply understand the formation mechanism of off-odor in dry-cured ham. Until now, there is no detailed discussion or critical review on the role of spoilage microorganisms in developing the off-odor of dry-cured ham, and the regulation of off-odor and spoilage microorganisms by starter cultures has been not discussed. This review shows the recent achievement in the off-odor formation mechanism of dry-cured ham, and outlines the potential regulation of off-odor defects in dry-cured ham by starter cultures. Results from current research show that the abnormal growth of Lactic acid bacteria, Micrococcaceae, Enterobacteriaceae, Yeasts and Molds plays a key role in developing the off-odor defects of dry-cured ham, while the key spoilage microorganisms of different type hams are discrepant. High profile of aldehydes, acids, sulfur compounds and biogenic amines are responsible for off-odor development in spoiled dry-cured ham. Several starter cultures derived from these species of Staphylococcus, Penicillium, Debaryomyces, Pediococcus and Lactobacillus show a great potential to prevent microbiological hazards and improve flavor quality of dry-cured ham, whereas, the ecology, function and compatibility of these starter cultures with the processing parameters of dry-cured ham need to be further evaluated in the future.

Effect of fermented foods on some neurological diseases, microbiota, behaviors: mini review

Fermented foods are among the traditional foods consumed for centuries. In recent years, awareness of fermented foods has been increasing due to their positive health benefits. Fermented foods contain beneficial microorganisms. Fermented foods, such as kefir, kimchi, sauerkraut, and yoghurt, contain Lactic acid bacteria (LAB), such as Lactobacilli, Bifidobacteria, and their primary metabolites (lactic acid). Although studies on the effect of consumption of fermented foods on diabetes, cardiovascular, obesity, gastrointestinal diseases on chronic diseases have been conducted, more studies are needed regarding the relationship between neurological diseases and microbiota. There are still unexplored mechanisms in the relationship between the brain and intestine. In this review, we answer how the consumption of fermented foods affects the brain and behavior of Alzheimer's disease, Parkinson's disease, multiple sclerosis disease, stroke, and gut microbiota.

Diversity of a Lactic Acid Bacterial Community during Fermentation of Gajami-Sikhae, a Traditional Korean Fermented Fish, as Determined by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Gajami-sikhae is a traditional Korean fermented fish food made by naturally fermenting flatfish (Glyptocephalus stelleri) with other ingredients. This study was the first to investigate the diversity and dynamics of lactic acid bacteria in gajami-sikhae fermented at different temperatures using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). A total of 4824 isolates were isolated from the fermented gajami-sikhae. These findings indicated that Latilactobacillus, Lactiplantibacillus, Levilactobacillus, Weissella, and Leuconostoc were the dominant genera during fermentation, while the dominant species were Latilactobacillus sakei, Lactiplantibacillus plantarum, Levilactobacillus brevis, Weissella koreensis, and Leuconostoc mesenteroides. At all temperatures, L. sakei was dominant at the early stage of gajami-sikhae fermentation, and it maintained dominance until the later stage of fermentation at low temperatures (5 °C and 10 °C). However, L. plantarum and L. brevis replaced it at higher temperatures (15 °C and 20 °C). The relative abundance of L. plantarum and L. brevis reached 100% at the later fermentation stage at 20 °C. These results suggest that the optimal fermentation temperatures for gajami-sikhae are low rather than high temperatures. This study could allow for the selection of an adjunct culture to control gajami-sikhae fermentation.

Study on taste characteristics and microbial communities in Pingwu Fuzhuan brick tea and the correlation between microbiota composition and chemical metabolites

Pingwu Fuzhuan brick tea (PWT) is considered the "Sichuan western road" border-selling tea. The taste and quality of Fuzhuan brick tea (FBT) is greatly influenced by microorganisms. Considering the dearth of studies on the taste and microbial community of PWT, this study aimed to investigate the taste characteristics using electronic tongue system and microbial community structures using high-throughput sequencing, followed by comparison with FBT from other regions and determining the correlation between microbial communities and chemical compositions. The taste strengths of sweetness, bitterness, umami and astringency in PWT were all at lower level compared to other regions FBT. Regarding microbial diversity, the fungal communities in PWT were distinct from those of other regions FBT in terms of taxonomic composition and abundance. Unclassified_k_Fungi and Aspergillus were the most dominant fungal genera in PWT. Candidatus_Microthrix, norank_f_Saprospiraceae, and norank_c_C10-SB1A were dominant bacterial genera in PWT, only distinct from those in Hunan FBT (HNT). Principal component analysis results showed that fungal or bacterial community structures of PWT and other regions FBT were distinctly different. Correlation analysis revealed important links between the top 50 microbial populations and metabolites.

SUPPLEMENTARY INFORMATION

The online version of this article contains supplementary material available at (10.1007/s13197-021-04976-y).

Influence of Tissue Type on the Bacterial Diversity and Community in Pork Bacon

In current study, bacterial diversity and community in different tissues of pork bacon were determined using high-throughput sequencing. In total, six phyla and 111 bacterial genera were identified. Among them, three dominant genera (Staphylococcus, Acinetobacter, and Macrococcus) were shared by all bacon samples. The linear discriminant analysis showed that 24 bacterial taxa significantly differentiated between the tissues. Results of non-metric Multidimensional Scaling and redundancy analysis showed that physicochemical characteristics of the tissue prominently structured the bacterial communities. Network analysis also illustrated that tissue type was an important factor impacting the bacterial interactions in different types of tissue. The results of current study can add valuable insights to the traditional homemade pork bacon.

Effects of ultra-long fermentation time on the microbial community and flavor components of light-flavor Xiaoqu Baijiu based on fermentation tanks

Microbial structure and succession of fermented grains play a significant role in Baijiu's flavor and quality. In this study, high-throughput sequencing (HTS) coupled with headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) were used to analyze the microbial community structures and flavor components in the fermented grains at the end of fermentation from different fermentation time of light-flavor Xiaoqu Baijiu. HTS results showed that Lactobacillus acetotolerans, Lactobacillus helveticus, Lactobacillus buchneri, Wickerhamomyces, Saccharomyces, and Condenascus were identified as the dominant microbes, but Lactobacillus (96.28%) exhibited obvious advantages at the end of ultra-long fermentation time (day 98). HS-SPME-GC-MS analysis revealed that esters and alcohols had the most abundance in fermented grains of day 98, containing high concentrations of ethyl acetate, diethyl succinate, phenylethyl alcohol, isoamyl alcohol, and n-propanol, which were related to the succession of Lactobacillus and yeast communities. Interestingly, the content of n-propanol in the ultra-long fermentation time samples (day 98) was 6 times of that in normal fermented grains (day 14), which may be caused by higher abundance of Lactobacillus in day 98 samples. Monte Carlo permutation test showed residual starch, acidity, and amino nitrogen (p < 0.05) were important factors affecting the microbial community. Together, these results shed light on the physicochemical changes, microbial dynamics, and key flavor components of fermented grains at the end of fermentation from different fermentation time and provide a strategy for further improvement of Baijiu quality.

Metagenomic Analysis of Bacterial Diversity in Traditional Fermented Foods Reveals Food-Specific Dominance of Specific Bacterial Taxa

Traditional fermented foods have been recognized by various communities to be good for health since ancient times. There is a provincial legacy of traditional fermented foods among the ethnic population of North-East India. Fermented bamboo shoots (local name: Tuaither), soybeans (Bekang), and pork fat (Sa-um) are famous in the Mizoram state and represent a primary portion of the daily diet. These foods are prepared using methods based on cultural traditions inherited from previous generations, and prepared using a relatively uncontrolled fermentation process. Analysis of the bacterial diversity in these foods can provide important information regarding the flavor and texture of the final products of fermentation. Unfortunately, studies on the microbial composition and health benefits of such traditional fermented foods have rarely been documented. Therefore, the present study aims to highlight this bacterial diversity, along with the proximate composition of different traditional fermented foods (Tuaither, Bekang and Sa-um) primarily consumed in Mizoram state, India. Samples were collected on three different days of fermentation (3rd, 5th and 7th day), and bacterial diversity analysis was performed using the V3-V4 variable region of 16S rRNA gene with Illumina sequencing. Results revealed differences in the bacterial composition of dominant group members among all of the three food types. Firmicutes (82.72–94.00%), followed by Proteobacteria (4.67–15.01%), were found to dominate to varying degrees in all three of the fermented foods. However, at genus level high variation was observed in bacterial composition among these three different types of fermented foods. Lactobacillus (91.64–77.16%), Staphylococcus (52.00–17.90%), and Clostridium (72.48–55.40%) exhibited the highest relative abundances in the Tuaither, Bekang and Sa-um foods, respectively, in descending order from the 3rd to 7th day of fermentation. A few of the bacterial genera such as Lactobacilli were positively correlated with fermented bamboo shoot samples, and Staphylococcus was positively correlated with protein, carbohydrate and crude fiber content in soybean samples. In general, Tuaither, Bekang and Sa-um exhibited distinct differences in bacterial composition. This variation may be due to differences in the raw materials and/or methods used in the preparation of the different fermented food products. This is the first study to describe the bacterial composition of these traditional fermented foods using high-throughput sequencing techniques, and could help to drive research attention to comprehensive studies on improving understanding of the role of microbial communities in the preparation of traditional foods and their health benefits.

Dynamics and correlation of microbial community and flavor in Pixian Douban fermented with closed process of constant temperature

BACKGROUND

As a Chinese traditional flavor condiment, Pixian Douban (PXDB) is produced using a traditional open fermentation process. In this study, an experimental fermentation of PXDB was conducted at 40 °C for 90 days in a closed system, which has not been applied to PXDB production. The flavor, microbial community and correlations of the samples in the closed system were compared with those in the traditional fermentation.

RESULTS

The content of organic acids and free amino acids in the closed fermentation of constant temperature (CFCT) achieved the standards of product quality, although they were lower than those in the traditional fermentation. Of the 140 detected aroma components, 98 were shared in the two fermentation processes. Enterobacter, Bacteroides and Megamonas were the core microbial genera related to 26 flavor components in the traditional fermentation, while Pantoea was the core microbial genus related to 18 flavor components in CFCT. The CFCT has its own unique advantages over traditional fermentation in forming aromas. It produced a greater impact on the succession of fungi than those of bacteria after changing traditional fermentation to CFCT. The influence of microorganisms on the formation of flavor components was relatively more balanced in CFCT, while the changed fermentation process impacted greatly on the functions of Zygosaccharomomyces and Pichia but little on those of Sphingomonas, Megamonas and Parabacteroides.

CONCLUSION

The study indicated that it was feasible to ferment PXDB in the closed system, and provides a basis to realize controllable PXDB production. © 2020 Society of Chemical Industry.