International journal of food microbiology最新文献

The aim of the present research was to evaluate the effect of Urtica dioica L. (nettle) essential oil (in the forms of Pickering nanoemulsion (NEO) and free (EO)) on microbial, chemical and sensory changes of pizza cheese stored at 4 °C for 12 days. For this purpose, Escherichia coli and Listeria monocytogenes were inoculated into pizza cheese. In all tests, the control group had the lowest score after 12 days of storage. In the antimicrobial assay test in different treatments, NEO4% treatment decreased the growth of E.coli from 4 (0th day) to 3.3 log CFU/g (12th day) and the growth of L. monocytogenes from 3.8 (0th day) to 3.1 log CFU/g (12th day). The minimum inhibitory concentration (MIC) of NEO and EO for E.coli and L. monocytogenes was 0.62 ± 0.01 mg/mL. Additionally, the minimum bactericidal concentration (MBC) of EO and NEO for E. coli was 25 ± 0.1 mg/mL, and for L. monocytogenes was 1.25 ± 0.1 mg/mL. At day 12, almost all treatments (free form and nano) had relatively similar pH. In our study, the minimum and maximum value of DPPH was detected in the treatment of NEO1% (31.25 ± 1.50 %) and BHT200 (96.40 ± 2.5 %), respectively. Also, on the 12th day of the test, the NEO treatment obtained the highest score in all sensory tests (appearance & color, body & texture, odor and overall acceptability). According to the findings of the present study, Pickering emulsion form of nettle EO increases the storage period of pizza cheese.

Jellified materials were observed in spoiled pasteurized apple juice that contained dimethyl dicarbonate (DMDC). Microbiological analysis showed a high microbial load (4-5 log CFU/mL) in the sample. Acetobacter spp. was identified as the spoilage microorganism by 16S rRNA gene sequencing. Metataxonomic analysis showed Acetobacter represented 99 % of the bacterial community. Three Acetobacter isolates (LX5, LX9 and LX16) were selected for whole genome sequencing and characterized for their susceptibility to DMDC. Genome-based phylogeny supported the species-level classification of LX5 as A. fabarum. It also suggested LX9 and LX16 are the same microorganisms from a potentially novel species closely related to A. lovaniensis. The minimum inhibitory concentrations (MICs) of DMDC for Acetobacter isolates in sterile apple juice (pH ∼3) at 30 °C were 46 ppm and 329 ppm for A. fabarum LX5 and Acetobacter LX9/LX16, respectively. The minimum bactericidal concentrations (MBCs) were 250 and 500 ppm for A. fabarum LX5 and Acetobacter LX9/LX16, respectively. The inoculum concentration for the MIC assay was approximately 6 log₁₀ CFU/mL, representing the "worst-case" scenario. When the contamination level was reduced to 500 CFU/mL per US federal regulation (21 CFR 172.133) and the apple juice was refrigerated, Acetobacter isolates did not grow and were completely inhibited by 238 ppm DMDC. Pangenome analysis identified gene clusters that potentially play a role in biofilm development, carbohydrate metabolism, and oxidative stress tolerance, but it also ruled out the involvement of Acetobacter in apple juice gel formation. The investigation concluded that post-pasteurization contamination, high microbial load and ambient storage were factors leading to this spoilage incident.

Acid adaptive response (AAR) is a survival mechanism that allows bacteria to develop enhanced stress tolerance. Our previous research identified AAR in Alicyclobacillus acidoterrestris, a thermo-acidophilic bacterium responsible for fruit juice spoilage. However, the roles of specific acidulants, adaptive temperatures, and acidic juice matrices in triggering AAR remain elusive. In this work, acid adaptation of A. acidoterrestris in broth acidified with various organic acids and in fruit juices was investigated, while also considering the ambient temperature. Results revealed that acid adaptation (at pH values of 3.0, 3.2, and 3.5, adjusted with malic, tartaric, or citric acids, and at pH 3.5 adjusted with lactic, succinic, or ascorbic acids, for 1 h) enhanced acid resistance (pH = 2.2, 1 h) of A. acidoterrestris, across all tested temperatures (45 °C, 35 °C, 25 °C, and 10 °C). Moreover, heat tolerance (65 °C, 5 min) was improved, except when using tartaric acid. Among acidulants used during adaptation (pH 3.5, 45 °C), succinic acid induced the highest level of acid resistance, followed by lactic, citric, malic, ascorbic, and tartaric acids, in descending order. For heat resistance, the ranking was succinic, citric, tartaric, lactic, ascorbic, and malic acids. Furthermore, acid adaptation in apple or orange juices enhanced heat resistance (65 °C) of A. acidoterrestris, and the induced resistance increased with extension of adaptation period. Adaptive temperatures of 25 °C and 35 °C were more effective in promoting resistance than 10 °C. These findings highlight the importance of considering adaptive responses of A. acidoterrestris to different preservation stresses and acidic juice environments during juice processing.

Transcriptomic studies have become an essential tool to understand the response of yeast to stimuli. The present work analyses the reaction of eight Saccharomyces cerevisiae strains with varying competitive abilities against a competitor (CR85, Saccharomyces kudriavzevii) in co-cultured fermentations. RNA sequencing (RNAseq) was performed at three very early time points after strains coinoculation in fermentation to delimit exactly when S. cerevisiae's response is triggered. A rapid response to its competitor, including activation of the glycolytic pathway, ribosomal metabolism, and nucleotide synthesis, is crucial for the dominance of S. cerevisiae strain in mixed fermentations. Additionaly, the study highlights the necessity of investigating individual yeast strains rather than a holistic species view, as significant variations in responses are observed among strains of the same clade.

Since cefixime and tellurite are known to inhibit most bacteria belonging to Enterobacterales, we found that addition of tellurite inhibited E. albertii growth in Luria Bertani broth but not in tryptic soy broth (TSB), and addition of phosphate and soy peptone enhanced E. albertii growth in TSB in presence of tellurite. Subsequently, to find the positive factor present in TSB, E. albertii growth was examined in tryptone, soy peptone, glucose, or phosphate deficient tryptic soy agar plates. Phosphate, soy peptone, and/or glucose deficiency indeed decreased E. albertii growth. However, none of the substances are specifically present in xylose-rhamnose-melibiose (XRM)-MacConkey agar and thus, not affecting E. albertii growth. Altogether, a novel E. albertii selective differential medium, XRM-MacConkey medium containing cefixime (C), tellurite (T), phosphate (P), and soy peptone (S) (named CT-PS-XR-MacConkey medium), which differentiate E. albertii (colorless) from E. coli (red) by colony color, has been developed. The CT-PS-XR-MacConkey agar was evaluated with 156 bacterial strains including 65 E. albertii. While all E. albertii strains grew as colorless colonies, 54 strains of 9 different genera belonging to 19 different species were unable to grow on this medium. However, rest of these bacterial strains grew either as colorless or as red colonies. Furthermore, spiking experiments using chicken meat as food samples showed that the CT-PS-XR-MacConkey medium is highly selective for E. albertii than XRM-MacConkey agar. Altogether, the results suggest that the CT-PS-XR-MacConkey agar is indeed a useful selective medium for isolation of E. albertii from food samples.

Yersinia intermedia, Y. frederiksenii, and Y. kristensenii are a group of pathogens that are commonly found in food and are often overlooked in terms of their pathogenic potential. This study conducted a systematic and comprehensive genomic analysis of 114 Y. intermedia genomes, 20 Y. frederiksenii genomes, and 65 Y. kristensenii genomes from public database and our previous study. The results showed that these species were most frequently detected in Europe (56.28 %, 112/199), followed by in Asia (20.6 %, 41/199). Additionally, 33.17 % (66/199) genomes were isolated from food. Y. intermedia were grouped into Bayesian analysis of population structure (Baps) groups 3 and 4, demonstrating significant genomic diversity. This species has a high proportion of accessory genes (79.43 %), approximately 50 % of which have unknown functions, indicating a high degree of genomic plasticity. The three species carried a large number of mobile genetic elements (MGEs), including plasmids such as ColRNAI_1, ColE10_1, Col440II_1, Col440I_1, and Col (Ye4449) _1; insertion sequences (ISs) like MITEYpe1, MITEEc1, and IS1635; genomic islands (GIs); and prophages. In Y. intermedia, the following antibiotics resistance genes (ARGs) were detected: qnrD1 in 3.51 % (4/114), aph(3')-Ia in 2.63 % (3/114), bla_A in 1.75 % (2/114), and catA1, vat(F), and tet(C) each in 0.88 % (1/114). In Y. kristensenii, vat(F) was present in 98.46 % (64/65), bla_TEM-116 in 7.69 % (5/65), and aph(3')-Ia in 1.54 % (1/65). However, only one Y. frederiksenii genome carried vat(F). There were differences in the virulence gene composition of the three species, with Y. kristensenii having the highest number of virulence genes, particularly its complete cytotoxic genes (yaxA and yaxB) and flagellar motor proteins genes (motA and motB). The pathogenic mechanisms of Y. intermedia and Y. frederiksenii were more similar, especially in the carriage of O-antigen related genes. Y. frederiksenii's unique mechanisms also include the yapC gene, which encodes the autotransporter protein YapC from Y. pestis. After co-cultured with human colonic epithelial cell lines Caco-2 and HT-29, Y. intermedia and Y. kristensenii demonstrated different adhesive and invasive capabilities, particularly the Y. intermedia strain y7, which exhibited stronger adhesion and invasion in both cell lines. In strains y118 and y119 of Y. intermedia, an Arg378del mutation in the UreC protein was identified, resulting in the loss of urease activity. Therefore, this study revealed the pathogenic potential of Y. intermedia, Y. frederiksenii, and Y. kristensenii. Future research should focus on identifying their unknown virulence genes and strengthening public food safety measures to mitigate potential risks.

Listeria monocytogenes and Staphylococcus aureus are prevalent foodborne pathogens responsible for poisoning humans with food. The present study was devoted to the establishment of a method based on dual polymerase spiral reaction (dual-PSR) and melting curve analysis for concurrent identification L. monocytogenes and S. aureus. Specifically, the primer pairs were aimed at the conserved hlyA gene of L. monocytogenes and that of S. aureus (nuc). These reactions were carried out isothermally at 65 °C for 45 min within the same reaction vessel, and the amplified products were analyzed in a melting curve. Different average temperatures of melting allow the discrimination in the dual-PSR assay between the two target bacteria. The limits of simultaneous determination of L. monocytogenes and S. aureus in artificially contaminated fresh-cut fruit samples were 1 × 10^-4 ng of genomic DNA and 1 × 10² CFU/g, respectively. This method is characterized by its expeditious nature and simultaneous detection capability, and it promises to be a valuable technology for the monitoring of pathogenic microorganisms around health and quality control of foodstuffs within that industry.

Despite the shortfin squid, Illex argentinus, is one of the most important commercial species for the Argentine fisheries, being the third frozen product exported to Europe, the occurrence and distribution of zoonotic anisakid nematodes is scarcely reported. A total of 712 I. argentinus distributed in 17 samples, corresponding to its three main commercial stocks, caught along its distribution range in Argentine waters were examined for anisakid parasites. In total, 360 nematodes were detected in the viscera, however no infestations in the mantle were observed. According to their morphology, all the larvae (L₃) were assigned to the genus Anisakis. Genetic identification was performed by sequence analysis of the mitochondrial (mtDNA cox2) gene loci resulting in the record of only Anisakis pegreffii. Distance-based multiple linear regressions (DistLM) evidenced that dorsal mantle length (ML) and date of capture (as surrogate of cohort) were the most important predictors of parasite abundance across infrapopulations in I. argentinus. At component population, DistLM analysis showed that ML and latitude (indirectly representing a gradient in water temperature) were the most important variables determining the prevalence of parasites, however, its mean abundance was only influenced by ML. Parasite burdens were temporally inestable, due to variability in recruitment to host populations, being associated with changing hydrographic conditions and the opportunistic feeding behaviour and annual life cycle of the hosts. The genetic identification of A. pegreffii is relevant for both human health and the fishery industry, given its importance as an etiological agent of human anisakiosis. Due to the restriction of larvae to internal organs, the risk of anisakiosis by the consumption of edible parts of I. argentinus is low.

This study aimed to investigate the bactericidal effect of naringenin (NG), a plant-derived flavonoid, and its synergistic effect with mild heat (MH) treatment at 50 °C in peptone water (PW) and ready-to-drink cold brew coffee (RDC). Among various NG concentrations (1-20 mM), 10 mM NG resulted in the greatest inactivation for Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus. In RDC, NG + MH treatment resulted in a 5-8-log reduction in all pathogens after 10 min, except for S. aureus. In contrast, NG or MH treatment alone exhibited only marginal bactericidal effects. From inactivating mechanism analysis, lipid membrane destruction and intracellular enzyme inactivation were the key factors for pathogen inactivation. Cell membrane and enzyme dysfunctions were identified in propidium iodide (PI) uptake test, membrane potential assay, and membrane protein analysis. Furthermore, NG + MH exerted minimal influence on the quality attributes of RDC in pH, color, and total phenolic content. These results indicated that the NG + MH treatment system effectively ensured microbial safety in cold brew coffee while enhancing its nutritional value and preserving quality attributes.