Effects of substrates and suppliers of ingredients on microbial community and metabolites of traditional non-salt Suancai.

Aim: Non-salt Suancai is an acidic fermented vegetable consumed by the Chinese Yi ethnic group. Traditionally, it is produced by fermentation without salt in a cold environment. The present study aimed to investigate the metabolite and microbial characteristics, and the effects of substrates/suppliers ingredients on non-salt Suancai. Methods: A simulated fermentation system of non-salt Suancai was constructed by using different substrates/suppliers' ingredients. The coherence and differential detection of the metabolite and microbial characteristics were done through non-target metabolomic and metagenomic analysis. Results: Lactic acid was the predominant organic acid across all samples. The enumeration of the Lactic acid bacteria showed no discernible differences between study groups, but that of yeast was highest in the mustard leaf stem (Brassica juncea var. latipa). The three major biological metabolic pathways were metabolism, environmental information, and genetic information processing based on the KEGG database. The metabolite diversity varied with the substrate/supplier of ingredients based on the PLS-DA plot. Lactiplantibacillus, Leuconostoc, and Lactococcus were prevalent in all samples but differentially. The microbial diversity and richness varied significantly, with 36~291 species being identified. Among the various substrates collected from the same supplier, 29, 59, and 29 differential species were identified based on LEfSe [linear discriminant analysis (LDA) > 2, P < 0.05]. Leuconostoc citreum, Leuconostoc mesenteroides, Leuconostoc pseudomesenteroides, Lactiplantibacillus plantarum, and Leuconostoc lactis were likely to be used as the species to discriminate samples collected from different suppliers. Conclusions: This research contributed to the exploration of microbial and metabolite characteristics behind the ingredient restriction of non-salt Suancai using traditional technology.

Characterizing the impact of species/strain-specific Lactiplantibacillus plantarum with community assembly and metabolic regulation in pickled Suancai.

To investigate the colonization and impact of the specific Lactiplantibacillus plantarum strains, four isolated strains were applied in pickled Suancai which is a traditional pickled mustard (Brassica juncea). Results showed that strain-8 with the highest lactic acid bacteria (LAB) counts and acetic acid (p < 0.05). There were 11.42 % ∼ 32.35 % differential volatile compounds detected, although nitriles, esters, and acids were predominant. L. plantarum disturbed the microbial community, in which the microbial composition of strain-11 was most similar to the naturally fermented sample. Amino acids, carbohydrate metabolism, and metabolism of cofactors and vitamins were the main functional classes because of the similar dominant microbes (Lactiplantibacillus and Levilactobacillus). The functional units were separated based on NMDS analysis, in which bacterial chemotaxis, amino acid-related units, biotin metabolism, fatty acid biosynthesis, and citrate cycle were significantly different calculated by metagenomeSeq and Benjamin-Hochberg methods (p < 0.05). The contents of most flavor compounds were consistent with their corresponding enzymes. In particular, glucosinolates metabolites were different and significantly related to the myrosinase and metabolic preference of LAB. Therefore, this study revealed the impact mechanism of the specific L. plantarum strains and provided a perspective for developing microbial resources to improve the flavor diversity of fermented vegetables.

Unraveling the contribution of pre-salting duration to microbial succession and changes of volatile and non-volatile organic compounds in Suancai (a Chinese traditional fermented vegetable) during fermentation.

Pre-salting is an important pre-treatment during production of Suancai as it provides flavor precursor and microbial community for subsequent fermentation. To investigate the effect of pre-salting duration on fermentation of Suancai, the physicochemical properties, microbial composition, non-volatile and volatile organic compounds profiles of Suancai pre-salted for 1 month (1 M) and 7 months (7 M) were analyzed during fermentation for 30 days. Results showed that 7 M led to higher salt content, faster depletion of reducing sugars, and more titratable acidity. Additionally, more lactic acid and acetic acid, and less umami amino acid (Glu) and GABA were observed in 7 M. Longer pre-salting duration (7 M) promoted formation of mild-flavor volatile compounds, and significantly reduced isothiocyanates with pungent off-flavor. Moreover, 7 M promoted abundance of genera Chromohalobacter, Vibrio and Pichia, while reducing abundance of Lactobacillus, Debaryomyces and Kazachstania throughout fermentation. These results implicated that longer pre-salting duration facilitated more acidic, milder flavor and less pungent off-odor in Suancai. This study provided a perspective for pre-salting as a control point for improving quality of fermented vegetable.

Comparative evaluation of package types in alleviating textural softening and package-swelling of Paocai during storage: Insight into microbial invasion, cell wall pectinolysis and alteration in sugar and organic acid profiles.

The present study aimed to investigate the effect of initial vacuum package (VP), air package (AP) and salt-solution package (NP) on texture softening and package-swelling of Paocai by comparing the changes in physicochemical properties, pectinolysis, microstructure, microbial profile, as well as sugar and organic acid profiles during storage. Results showed that, when compared with AP and NP, with suppressive microbial invasion and less total pectinase activity, VP could retain more soluble pectin and induce more compact microstructure of Paocai, leading to higher hardness of Paocai during storage. As for package-swelling, VP mitigated gas-production in package by changing the microbial composition and metabolic patterns of sugar and organic acid in Paocai, especially targeted regulating the abundance of genus Kazachstania. This study provided a perspective for appropriate packaging technology to control the pectinase activity as well as cell-invading and gas-producing microorganisms for manufacturing fermented vegetable with better texture and non-package-swelling.

Inhibitory effect of edible natural compounds with di- and tri-carboxyl moiety on endogenous protease inducing disassembly and degradation of myofibrils from grass carp (Ctenopharyngodon idella).

Inhibition of endogenous protease is a rapid and feasible approach to control the proteolysis proceeding of post mortem fish flesh. In the present study, the in vitro inhibitory effects of common edible di- and tri-carboxylic acids and salts on endogenous proteolytic activities as well as myofibrillar disassembly and degradation mediated by crude enzyme of grass carp muscle were investigated. The results showed that among the compounds tested, maleic acid, fumaric acid, tartaric acid and malic acid were the most effective inhibitor for cathepsin B, L and calpain, with IC50 ranging from 7.76 to 30.13 mM, from 32.38 to 65.12 mM, from 1.06 to 6.76 mM, respectively. Also, relatively lower Ki (ranging from 1.04 to 43.21 mM) of these compounds were found towards cathepsin B, L and calpain. Incubation of myofibrillar protein with crude enzyme in the presence of di- and tri-carboxylic compounds could remarkably suppress the dissociation and degradation of myosin heavy chain (MHC), and ameliorate the loss of heat shock protein (HSP) in myofibrils, with tartaric acid and fumaric acid proved more effective than other compounds, possibly implicating their application as potential and efficient inhibitors for quality control of fish muscle products.

Divergent role of abiotic factors in shaping microbial community assembly of paocai brine during aging process.

Microbial communities in fermented food are shaped by a myriad of abiotic factors. The respective roles of abiotic factors in shaping the dynamic bacterial community of paocai during aging remain unclear. In the present study, 100 paocai samples (pH: 2.95-5.23; NaCl content: 0.13-15.41%; total acid: 6.61-18.33 mg/mL; total sugars: 7.96-487.90 µg/mL; total viable count: 3.55-8.99 LogCFU/mL; aging time: 5 day-15 year) were analyzed through high-throughput sequencing and the results revealed five dominant bacterial genera across different samples, including Lactobacillus, Pediococcus, Leuconostoc, Lactococcus and unclassified genera. Both NaCl and total acid (TA) were the major factors regulating bacterial community divergence in paocai. Based on these results, the microbial communities were reconstructed by manipulating the TA and NaCl contents in vitro to validate the effectiveness of these factors in shaping microbial communities during paocai fermentation. Results showed that roles of abiotic factors differentiated during fermentation. At the early stage, salt was the first abiotic filter, mainly working through promoting the abundance of Lactococcus and Leuconostoc. As the TA content increased, the selective role of salt weakened while acid became the dominant at the later stage, as evidenced by the increased abundance of Lactobacillus and Pediococcus following the increase of TA content.

Antimicrobial resistance and resistance genes in Salmonella strains isolated from broiler chickens along the slaughtering process in China.

A total of 189 Salmonella isolates were recovered from 627 samples which were collected from cecal contents of broilers, chicken carcasses, chicken meat after cutting step and frozen broiler chicken products along the slaughtering process at a slaughterhouse in Sichuan province of China. The Salmonella isolates were subjected to antimicrobial susceptibility testing to 10 categories of antimicrobial agents using the Kirby-Bauer disk diffusion method. Those antibiotics-resistant isolates were further investigated for the occurrence of resistance genes, the presence of class 1 integron as well as the associated gene cassettes, and the mutations within the gyrA and parC genes. Consequently, the prevalence of Salmonella was 30.14% (47.96% for cecal content, 18.78% for chicken carcasses, 31.33% for cutting meat and 14.00% for frozen meat, respectively). The predominant serotypes were S. Typhimurium (15.34%) and S. Enteritidis (69.84%). High resistance rates to the following drugs were observed: nalidixic acid (99.5%), ampicillin (87.8%), tetracycline (51.9%), ciprofloxacin (48.7%), trimethoprim/sulfamethoxazole (48.1%), and spectinomycin (34.4%). Antimicrobial resistance profiling showed that 60.8% of isolates were multidrug resistant (MDR), and MDR strains increased from 44.7% to 78.6% along the slaughtering line. 94.6% (n=157) of beta-lactam-resistant isolates harbored at least one resistance gene of blaTEM or blaCTX-M. The relatively low prevalence of aminoglycoside resistance genes (aac(3)-II, aac(3)-IV, and ant(2″)-I) was found in 49 (66.2%) of antibiotic-resistant isolates. The tetracycline resistance genes (tet(A), tet(B), tet(C), and tet(G) and sulfonamide resistance genes (sul1, sul2, and sul3) were identified in 84 (85.7%) and 89 (97.8%) antibiotic-resistant isolates respectively. floR was identified in 44 (97.8%) florfenicol-resistant isolates. Class 1 integron was detected in 37.4% (n=43) of the MDR isolates. Two different gene cassettes, blaOXA-30-aadA1 (19 isolates) and blaOXA-30-aadA1/drfA1-orfC (2 isolates), were identified in class 1 integron-positive isolates. 97.9% (184/188) of quinolone-resistant isolates had at least one mutation within gyrA or parC. Overall, antimicrobial resistance showed an increasing trend along the slaughtering process. The results showed that broiler chicken products in the slaughterhouse were contaminated with MDR Salmonella, which might originate from food producing animals to some extent, and cross-contamination during slaughter, and facilitate the dissemination of the resistance genes to consumers along the production chain, which suggests importance of controlling Salmonella during slaughter for public health, underlying strict hygiene method and HACCP management to reduce cross-contamination.