International journal of food microbiology最新文献

Bacillus cereus is a ubiquitous foodborne pathogen commonly found in various foods. Its ability to form spores, biofilms and diarrhoeal and/or emetic toxins further exacerbates the risk of food poisoning. Violacein is a tryptophan derivative with excellent antibacterial activity. However, the knowledge on the antibacterial action of violacein against B. cereus was lacking, and thus this study aimed to investigate the antibacterial activity and mechanism. The antibacterial results demonstrated that minimum inhibitory concentration and minimum bactericidal concentration of violacein were 3.125 mg/L and 12.50 mg/L, respectively. Violacein could effectively inhibit planktonic growth, spore germination and biofilm formation of B. cereus (P < 0.001). Meanwhile, violacein significantly downregulated the expression of toxin genes, including nheA (P < 0.05), nheB (P < 0.001), bceT (P < 0.01), cytK (P < 0.001), hblC (P < 0.001) and hblD (P < 0.001). Results of extracellular alkaline phosphatase, nucleotide and protein leakage assays and scanning and transmission electron microscopy observation tests showed violacein destroyed cell walls and membranes of B. cereus. In addition, 6.25 mg/kg of violacein could significantly inhibit B. cereus in grass carp fillets (P < 0.05). These results demonstrate that violacein has great potential as an effective natural antimicrobial preservative to control food contamination and poisoning events caused by B. cereus.

As a commercially available esterified compound derived from sucrose and palmitoyl acids, sucrose ester palmitic acid (SEPA) has been used as an emulsifier in food processing. It possesses antibacterial activity against vegetative and spore-forming bacteria, including Clostridium, Moorella, Bacillus, and Geobacillus species, prompting the food industry to use it as a food additive to achieve a desirable shelf life; however, the precise mechanism by which the compound affects the physiological processes of bacteria and how it inhibits bacterial growth remains unclear. In this study, we focused on the inhibitory effect of SEPA on the germination-to-outgrowth process of Clostridium perfringens SM101 spores, a strain widely used as a model of C. perfringens. When the isolated spores were exposed to ≧ 20 μg/ml of SEPA on brain heart infusion agar, bacterial colony formation was completely inhibited. Time-resolved phase-contrast microscopy was employed to visualize the effect of SEPA on the entire regrowth process of SM101 spores. SEPA did not affect the “germination stage,” where each spore changes its optical density from phase-bright to phase-dark. In contrast, the presence of SEPA completely blocked the “outgrowth stage,” in which the newly synthesized vegetative cell body emerges from the cracked spore shell. The results demonstrate that SEPA inhibits the revival process of the spores of a pathogenic strain of C. perfringens and that the site of its action is the “outgrowth stage” and not the “germination stage,” as evidenced by single- cell analysis.

The quorum-sensing receptor SdiA is vital for regulating the desiccation tolerance of C. sakazakii, yet the specific mechanism remains elusive. Herein, transcriptomics and phenotypic analysis were employed to explore the response of C. sakazakii wild type (WT) and sdiA knockout strain (ΔsdiA) under drying conditions. Following 20 days of drying in powdered infant formula (PIF), WT exhibited 4 log CFU/g higher survival rates compared to ΔsdiA. Transcriptome revealed similar expression patterns between csrA and sdiA, their interaction was confirmed both by protein-protein interaction analysis and yeast two-hybrid assays. Notably, genes associated with flagellar assembly and chemotaxis (flg, fli, che, mot regulon) showed significantly higher expression levels in WT than in ΔsdiA, indicating a reduced capacity for flagellar synthesis in ΔsdiA, which was consistent with cellular morphology observations. Similarly, genes involved in trehalose biosynthesis (ostAB, treYZS) and uptake (thuEFGK) exhibited similar expression patterns to sdiA, with higher levels of trehalose accumulation observed in WT under desiccation conditions compared to ΔsdiA. Furthermore, WT demonstrated enhanced protein and DNA synthesis capabilities under desiccation stress. Higher expression levels of genes related to oxidative phosphorylation were also noted in WT, ensuring efficient cellular ATP synthesis. This study offers valuable insights into how SdiA influences the desiccation tolerance of C. sakazakii, paving the way for targeted strategies to inhibit and control this bacterium.

This study investigated the influence of food contact surface materials on the biofilm formation of Vibrio parahaemolyticus while attempting to minimize the impact of environmental factors. The response surface methodology (RSM), incorporating three controlled environmental factors (temperature, pH, and salinity), was employed to determine the optimal conditions for biofilm formation on stainless steel (SS) and polypropylene (PP) coupons. The RSM results demonstrated that pH was highly influential. After minimizing the impacts of environmental factors, initially V. parahaemolyticus adhered more rapidly on PP than SS. To adhere to SS, V. parahaemolyticus formed extra exopolysaccharide (EPS) and exhibited clustered stacking. Both PP and SS exhibited hydrophilic properties, but SS was more hydrophilic than PP. Finally, this study observed a higher transfer rate of biofilms from PP to fish fillets than from SS to fish fillets. The present findings suggest that the food industry should consider the material of food processing surfaces to prevent V. parahaemolyticus biofilm formation and thus to enhance food safety.

Shewanella putrefaciens, commonly found in seafood, forms tenacious biofilms on various surfaces, contributing to spoilage and cross-contamination. Bacteriophages, owing to their potent lytic capabilities, have emerged as novel and safe options for preventing and eliminating contaminants across various foods and food processing environments. In this study, a novel phage SPX1 was isolated, characterized by a high burst size (43.81 ± 3.01 PFU/CFU) and a short latent period (10 min). SPX1 belongs to the Caudoviricetes class, exhibits resistance to chloroform, and sensitivity to ultraviolet. It shows stability over a wide range of temperatures (30–50 °C) and pH levels (3−11). The genome of phage SPX1 consists of 53,428 bp with 49.72 % G + C composition, and lacks tRNAs or virulence factors. Genome analysis revealed the presence of two endolysins, confirming its biofilm-removal capacity. Following the treatment of shrimp surface biofilm with the optimal MOI of 0.001 of phage SPX1 for 5 h, the bacterial count decreased by 1.84 ± 0.1 log₁₀ CFU/cm² (> 98.5 %). Biofilms on the surfaces of the three common materials used in shrimp processing and transportation also showed varying degrees of reduction: glass (1.98 ± 0.01 log₁₀ CFU/cm²), stainless steel (1.93 ± 0.05 log₁₀ CFU/cm²), and polyethylene (1.38 ± 0.1 log₁₀ CFU/cm²). The study will contribute to phage as a novel and potent biocontrol agent for effectively managing S. putrefaciens and its biofilm, ensuring a reduction in spoilage bacteria contamination during the aquaculture, processing, and transportation of seafood products.

Like in many developing countries, the traditional Ethiopian diet relies mainly on starchy staple foods and often lacks sufficient animal-sourced foods which are crucial for cobalamin intake. Furthermore, the concentration of folate in traditionally prepared injera, an Ethiopian cereal-based fermented staple food, is highly variable and injera contains biologically inactive corrinoids. This study aimed to improve the cobalamin and folate content of injera by using cobalamin-producing Propionibacterium freudenreichii and folate-producing Lactiplantibacillus plantarum strains, both individually and combined. Since injera is fermented using backslopping, we also assessed the ability of these strains to produce cobalamin and folate consistently across successive fermentation batches. Changes in the microbial ecosystem were monitored using real-time PCR. The theoretical contribution of the injera prepared using the selected strains to the cobalamin and folate intake of children and women of reproductive age was also calculated. Results showed that using the selected bacterial strains individually increased cobalamin (up to 19.2 μg/100 g of dry matter) and folate (up to 180.2 μg/100 g of dry matter) levels in the injera dough over several backslopping fermentation batches. Regular consumption of the injera with enhanced vitamin content produced using each strain alone would be capable of fulfilling the entire recommended nutrient intake for cobalamin and up to 29 % of the recommended intake for folate for children and women of reproductive age. However, when the strains were used together, the production of both vitamins was reduced. The presence of certain common endogenous bacterial species and genera exhibited significant variability, highlighting the complex response of the native microbiota to the different inoculation strategies employed. Future experiments should consider selecting a microbial consortium comprising non-competing microorganisms to ensure the simultaneous production of cobalamin and folate in fermented foods.

Riboflavin (vitamin B₂) is essential for human beings and it has to be provided by healthy nutrition. The use of fermentation with riboflavin-overproducing lactic acid bacteria (LAB) represents an ideal strategy to generate, by in situ biofortification, functional drinks. These beverages can positively contribute to consumer health and address nutritional deficiencies. In the present work, the functional capabilities of Weissella cibaria BAL3C-5 C120T for riboflavin-overproduction and dextran-production during fermentation of oat-, rice-, soybean- and almond-based drinks have been evaluated. It was confirmed that the strain was capable of producing riboflavin and dextran in the analysed drinks. This property was especially pronounced in the oat-based drink, where after 24 h of fermentation the strain was able to increase riboflavin and dextran levels up to 3.4 mg/L and 3.2 g/L, respectively. Moreover, under optimized conditions the strain was able to enrich the fermented oat-based drinks with the prebiotic oligosaccharide panose (up to 6.6 g/L). In addition, in the oat-based drinks BAL3C-5 C120T showed a good pH-lowering ability (from 7.0 to 3.8) as well as a high 80 % cell viability after one month of storage. Rheological analysis of the resulting fermented oat-based beverages revealed a thixotropic structure related to a gel-like behaviour which was not observed in the non-fermented control drinks. In summary, these results confirmed the unique characteristics of W. cibaria BAL3C-5 C120T strain for the development of biofortified and functional plant-based beverages with improved nutritional and rheological properties. Analysis of the BAL3C-5 C120T strain survival under gastrointestinal conditions and its autoaggregation properties, also indicated its potential use as a probiotic delivered in an oat-based fermented beverage. In this context, this study also promotes the utilization of W. cibaria species in health and food industries where it has not yet been used as a starter or adjunct culture.

The viable but non-culturable (VBNC) state is a survival strategy adopted by microorganisms in response to unfavorable conditions in the environment. VBNC cells are unable to form colonies but still maintain a low level of activity, posing a potential threat to food safety and public health. Therefore, the development of effective strategies to prevent the formation and resuscitation of VBNC cells of microorganisms is a key challenge in food science and microbiology research. However, current research on VBNC cells has primarily focused on bacteria, with relatively limited reports on fungi. This paper provides a comprehensive and systematic review of yeast in the VBNC state, discussing various factors that induce and facilitate resuscitation, along with detection methods and formation and recovery mechanisms. A comprehensive understanding of the induction and resuscitation of yeast in the VBNC state and exploration of its molecular mechanism hold significant implications for food safety and public health. It is imperative to enhance our comprehension of the underlying mechanisms and contributory factors pertaining to VBNC yeast, thereby facilitating the efficient management of the food fermentation process and ensuring the integrity of food quality and safety.

Yeast optimisation has been crucial in improving the quality and efficiency of beer production, one of the world's most widely consumed beverages. In this context, rare mating hybridisation is a promising technique for yeast optimization to generate novel and improved non-GMO strains. The limitation of this technique is the lack of knowledge and comparable data on yeast strains hybridisable to Saccharomyces cerevisiae, probably the most important yeast species in beer production. Yeast from the genera Saccharomyces, Naumovozyma, Nakaseomyces and Kazachstania have been described to be able to form hybrids with S. cerevisiae. In the present study, 242 yeast strains were analysed under brewing conditions, including Saccharomyces species (S. cerevisiae, S. kudriavzevii, S. uvarum, S. eubayanus, S. paradoxus, S. mikatae, S. jurei and S. arboricola) and non-Saccharomyces species (Naumovozyma, Nakaseomyces and Kazaschtania), representing the full genetic variability (species and subpopulations) described up to the start of the study.

The fermentation profile was analysed by monitoring weight loss during fermentation to determine kinetic parameters and CO₂ production. Metabolic analysis was performed to determine the concentration of sugars (maltotriose, maltose and glucose), alcohols (ethanol, glycerol and 2,3-butanediol) and organic acids (malic acid, succinic acid and acetic acid). Maltose and maltotriose are the predominant sugars in beer wort. The ability to consume these sugars determines the characteristics of the final product. Dataset comparisons were then made at species, subpopulation and isolation source level. The results obtained in this study demonstrate the great phenotypic variability that exists within the genus Saccharomyces and within each species of this genus, which could be useful in the generation of optimised brewing hybrids. Yeasts with different fermentative capacities and fermentative behaviours can be found under brewing conditions. S. cerevisiae, S. uvarum and S. eubayanus are the species that contain strains with similar fermentation performance to commercial strains.