Effects of Sodium Chloride or Calcium Chloride Concentration on the Growth and Survival of Escherichia coli O157:H7 in Model Vegetable Fermentations

Brine-Processed Caulerpa lentillifera Macroalgal Stability: Physicochemical, Nutritional and Microbiological Properties

Caulerpa lentillifera is a type of green macroalga that is commonly consumed as fresh seaweed, particularly in Southeast Asia. The effects of different salt types and concentrations on C. lentillifera during brine processing were investigated using table, sea and flower salt at 10-30% levels. The colour and texture of C. lentillifera varied across different treatments. After storage in brine for 12 weeks, lightness (L*) decreased, greenness (a*) decreased and yellowness (b*) increased while firmness increased in all treatments compared to fresh algae. The nutritional composition did not change significantly over time. To ensure the safety and quality of seaweed for consumption, the optimal salt level for brine processing should not exceed 30% table salt. The morphology and elements contained in different types of salt were also observed, and the microbiological safety of seaweed was evaluated. The popularity of Caulerpa macroalgae is rapidly increasing among consumers, leading to a growing demand for ready-to-eat Caulerpa products. However, food safety and security standards must be maintained.

Fermented Vegetables and Legumes vs. Lifestyle Diseases: Microbiota and More

Silages may be preventive against lifestyle diseases, including obesity, diabetes mellitus, or metabolic syndrome. Fermented vegetables and legumes are characterized by pleiotropic health effects, such as probiotic or antioxidant potential. That is mainly due to the fermentation process. Despite the low viability of microorganisms in the gastrointestinal tract, their probiotic potential was confirmed. The modification of microbiota diversity caused by these food products has numerous implications. Most of them are connected to changes in the production of metabolites by bacteria, such as butyrate. Moreover, intake of fermented vegetables and legumes influences epigenetic changes, which lead to inhibition of lipogenesis and decreased appetite. Lifestyle diseases' feature is increased inflammation; thus, foods with high antioxidant potential are recommended. Silages are characterized by having a higher bioavailable antioxidants content than fresh samples. That is due to fermentative microorganisms that produce the enzyme β-glucosidase, which releases these compounds from conjugated bonds with antinutrients. However, fermented vegetables and legumes are rich in salt or salt substitutes, such as potassium chloride. However, until today, silages intake has not been connected to the prevalence of hypertension or kidney failure.

Response mechanisms to acid stress of acid-resistant bacteria and biotechnological applications in the food industry

Acid-resistant bacteria are more and more widely used in industrial production due to their unique acid-resistant properties. In order to survive in various acidic environments, acid-resistant bacteria have developed diverse protective mechanisms such as sensing acid stress and signal transduction, maintaining intracellular pH homeostasis by controlling the flow of H⁺, protecting and repairing biological macromolecules, metabolic modification, and cross-protection. Acid-resistant bacteria have broad biotechnological application prospects in the food field. The production of fermented foods with high acidity and acidophilic enzymes are the main applications of this kind of bacteria in the food industry. Their acid resistance modules can also be used to construct acid-resistant recombinant engineering strains for special purposes. However, they can also cause negative effects on foods, such as spoilage and toxicity. Herein, the aim of this paper is to summarize the research progress of molecular mechanisms against acid stress of acid-resistant bacteria. Moreover, their effects on the food industry were also discussed. It is useful to lay a foundation for broadening our understanding of the physiological metabolism of acid-resistant bacteria and better serving the food industry.

Escherichia coli Contamination of Water for Human Consumption and Its Associated Factors in Peru: A Cross-Sectional Study

The objective of the study was to determine the factors associated with the presence of Escherichia coli contamination in water supplies for human consumption in Peru. A secondary analysis of the Food and Nutrition Surveillance by Life Stages survey (VIANEV) of 2017-2018 was performed. The presence of E. coli contamination in the water samples for human consumption of the households evaluated was defined as a dependent variable. A supply was considered contaminated when there was at least 1 colony-forming unit of E. coli in 100 mL of water for human consumption. Data from 886 participants were analyzed. It was found that 25.2% of household water supply sources for human consumption had E. coli at the time of sampling. Water reservoirs such as buckets or other containers (adjusted prevalence ratio [aPR]: 1.15; 95% confidence interval [CI]: 1.18-1.93), households belonging to a poor wealth quintile (aPR: 1.82; 95% CI: 1.01-3.25), residing in a rural area (aPR: 1.36; 95% CI: 1.01-1.83), and having a low human development index (aPR: 2.12; 95% CI: 1.15-3.91) were more likely to contain E. coli in water supplies for human consumption. However, households with chlorine concentrations of 0.5 mg/L or more in water (aPR: 0.20; 95% CI: 0.11-0.33) and with household members with a higher education (aPR: 0.67; 95% CI: 0.45-0.99) were less likely to contain E. coli in drinking-water supplies. From 2017 to 2018, one in four Peruvians had contamination by E. coli in the water supply to their homes, which was associated with sociodemographic factors, management, and water treatment.

Buffer Models for pH and Acid Changes Occurring in Cucumber Juice Fermented with Lactiplantibacillus pentosus and Leuconostoc mesenteroides

ABSTRACT

The pH changes that occur during the fermentation of vegetables by lactic acid bacteria depend on the production of weak acids and on the buffering of the fermentation medium. Undefined buffering components of fermentation media make estimates of pH from acid production difficult. The objective of this research was to develop buffer models for a model cucumber fermentation brine system linking pH changes to acid concentrations. A novel titration method was used to measure buffer capacity in cucumber juice medium made from three grades of pickling cucumbers based on diameter. Fermentation of juice made from cucumbers of different sizes resulted in differences in fermentation biochemistry. The results of modeling indicated that the pH of the medium after 24 and 48 h of fermentation by heterolactic Leuconostoc mesenteroides and homolactic Lactiplantibacillus pentosus could be predicted from acid concentrations based on the measured buffer capacity of the corresponding unfermented medium. The differences for all observed and predicted pH values of the fermentation samples, based on measured acid concentrations, had a root mean square error of 0.064 pH units. The buffer models included a quantitative measure of the effect on pH of the malolactic reaction caused by the lactic acid bacteria. These models may have application for assessing the influence of a variety of lactic acid bacteria buffering reactions on pH and fermentation ecology by linking pH to fermentation acid concentrations.

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Effects of a brief blanching process on quality, safety, and shelf life of refrigerated cucumber pickles

Refrigerated pickles are characterized by crisp, crunchy texture, opaque flesh, and fresh flavor. Typically produced without a thermal process, microbial safety relies on preventive controls, brine composition, and sufficient hold time prior to consumption. We hypothesized that brief blanching of whole cucumbers prior to pickling could provide an additional hurdle for pathogenic microbes without negatively impacting finished product quality. Blanch treatments (15, 90, or 180 s) in 80°C water were conducted in duplicate on two lots of cucumbers prior to cutting into spears, acidifying, and storing at 4°C. Enumeration of total aerobes, lactic acid bacteria, and glucose-fermenting coliforms was conducted for fresh and blanched cucumber. Texture, color, cured appearance development, and volatile compound profiles were analyzed for fresh and blanched cucumber and corresponding pickle products during refrigerated storage. The 90 s blanch consistently achieved a minimum 2-log reduction in cucumber microbiota and a predicted 5-log reduction of Escherichia coli O157:H7 up to 1.1 mm into the cucumber fruit. Blanching had no impact on tissue firmness during refrigerated storage for 1 year (p > 0.098). There were no differences in flavor-active lipid oxidation products (E,Z)-2,6-nonadienal and (E)-2-nonenal, and consumers (n = 110) were unable to differentiate between control and 90 s blanched cucumber pickles stored for 62 days. Exocarp color and mesocarp opacity were preserved by the blanching treatment, potentially extending product shelf life. This method offers processors an option for reducing the risk of microbial contamination while maintaining the quality attributes associated with refrigerated cucumber pickles. PRACTICAL APPLICATION: Refrigerated pickles do not undergo thermal processing, which can leave them vulnerable to microbial contamination. This study illustrates that adding a brief blanching step in refrigerated pickle processing can reduce indigenous microbiota without negatively impacting quality attributes. This blanching process could assist pickled vegetable manufacturers in providing additional safeguards for consumers while maintaining a high-quality product.

Sodium Reduction in Traditional Fermented Foods: Challenges, Strategies, and Perspectives

Sodium salt is a pivotal ingredient in traditional fermented foods, but its excessive consumption adversely affects human health, product quality, and production efficiency. Therefore, reducing sodium salt content in traditional fermented foods and developing low-sodium fermented foods have attracted increasing attention. Given the essential role of sodium salt in the safety and quality of fermented foods, appropriate approaches should be applied in the production of low-sodium fermented foods. In this review, the challenges of sodium reduction in traditional fermented foods are presented, including the possible growth of pathogenic bacteria, the formation of hazardous chemicals, flavor deficiency, and texture deterioration. Physical, chemical, and biological strategies are also discussed. This review provides references for improving the quality and safety of low-sodium fermented foods.

Escherichia coli O157:H7 Stationary-Phase Acid Resistance and Assessment of Survival in a Model Vegetable Fermentation System

ABSTRACT

Escherichia coli O157:H7 (STEC) acid resistance may aid the pathogen's ability to cross the human gastric barrier, which makes it an organism of concern in acidic foods. Our objective was to determine how STEC acid resistance may correlate with survival during vegetable fermentations. Seven E. coli O157:H7 strains were screened to assess acid resistance in simulated stomach acid at pH 2. The strains were separated into two groups that differed in acid resistance (P < 0.05), with three being acid sensitive and four acid resistant. The growth rates of these strains were measured in a Luria broth at pH values from 4.2 to 6.8. Two strains having similar growth kinetics, B201 (acid sensitive) and B241 (acid resistant), were selected for further analysis. B201 was found to be missing (compared with B241) two glutamic acid decarboxylase regulatory genes required for acid resistance, gadE and gadX. These strains were challenged in lactic acid (100 mM) solutions, including cucumber juice (CJ) media at pH 3.3. As expected, B201 was more acid sensitive than B241, and a filtered fermented CJ was more inhibitory than similarly acidified CJ. In competitive growth studies with Lactobacillus plantarum LA445 in CJ, B201 or B241 grew from approximately 104 to 108 CFU/mL within 24 h, but the STEC strains were below the limit of detection by 48 h. In all fermentations, L. plantarum reached 108 CFU/mL by 48 h. However, in three of four independent fermentation experiments, strain B201 survived longer than B241. This was possibly due to buffering in B241-LA445 fermentation brines that had increased lactic acid for a given pH compared with B201-LA445. These data indicate that stationary-phase acid resistance may not accurately predict STEC survival during vegetable fermentations.

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