Hurdle enhancement of acidic electrolyzed water antimicrobial efficacy on Bacillus cereus spores using ultrasonication

Evaluation of the additive effects of volatile fatty acids and moderate heat treatment for enhancing the inactivation of vegetative cells and spores of Clostridium perfringens by flow cytometry

OBJECTIVES

Clostridium perfringens is a well-known spore-forming bacterium that can resist the environment. A mixture of volatile fatty acids or thermal treatments can interact with these bacteria. The aim of this study was to evaluate the effects of different volatile fatty acid concentrations and moderate heat treatment on Clostridium perfringens sporulation.

METHODS

A pure culture of Clostridium perfringens type A in Duncan Strong medium was treated with a mixture of volatile fatty acids at several concentrations. A thermal treatment was also tested. To evaluate the effects, a double staining method was employed, and treatments on Clostridium perfringens were analysed by flow cytometry.

RESULTS

Moderate heat treatment destroyed vegetative forms but had no effect on sporulating forms. Volatile fatty acids combined with moderate heat treatment inhibited Clostridium perfringens sporulation.

CONCLUSIONS

The use of flow cytometry as an original method for evaluating the treatment of Clostridium perfringens is of interest because of its simplicity, short time to obtain results, and the level of information provided on the microbial population (impact on metabolism). A combination of mild treatments (moderate heat treatment + volatile fatty acids) to decrease the Clostridium perfringens concentration when these bacteria sporulate is a very promising finding for inhibiting Clostridium perfringens propagation.

Proteomics-based analysis of the stress response of Bacillus cereus spores under ultrasound and electrolyzed water treatment

Ultrasound is a green nonthermal technology with promising applications in microbial inactivation. Electrolyzed water has been investigated and found to have a synergistic inactivation effect of ultrasound on spores. This study used a data-independent-acquisition method to analyze the stress response of Bacillus cereus spores following ultrasound combined with electrolyzed water treatment. We identified 197 differentially expressed proteins under ultrasound combined with an electrolyzed water treatment for which the ratio in the metabolic pathway was the highest. Spores downregulated key proteins in energy metabolic and transportation pathways, in particular in phosphotransferase systems and ATP synthase under ultrasound, electrolyzed water, and combined stress. The results of this study revealed that the key proteins in intracellular metabolism decreased after ultrasound treatment, and the expression of small acid-soluble spore protein and cell wall biosynthesis protein increased. Meanwhile, DNA integration, recombination, and inversion protein and small acid-soluble spore protein were upregulated after electrolyzed water treatment. In general, the spores exhibited stress resistance under external stress. The inactivation of spores by further stress was reduced, which we called "cross-protection."

Inactivation mechanisms of atmospheric pressure plasma jet on Bacillus cereus spores and its application on low-water activity foods

Bacillus cereus spore is one of the most easily contaminated bacterial spores in low-water activity foods such as black pepper. Atmospheric-pressure plasma jet (APPJ) has emerged as an emerging and promising method for microbial inactivation in food processing. This study aimed to investigate the efficacy of APPJ in inactivating spores under various treatment parameters and to examine the resulting alterations in spore structures and internal membrane properties. Meanwhile, the practical application of APPJ for spore inactivation in black pepper was also evaluated. The results indicated that air-APPJ had superior spore inactivation capability compared to N₂ and O₂-APPJ. After 20 min of APPJ treatment (50 L/min, 800 W, and 10 cm), the reduction in spore count (>2 log CFU/g) was significantly greater than that achieved by heat treatment (80℃). The damage of inner membranes was considered as the major reason of the dried spore inactivation by APPJ treatment. Moreover, it achieved a reduction in spore count of > 1 log CFU/g on inoculated black pepper without significantly affecting its color and flavor. Although the antioxidant activity of black pepper was slightly reduced, the overall quality of the product was not considerably affected by plasma treatment. This study concluded that APPJ is an effective technique for spore inactivation, offering promising potential for application in the decontamination of low-water activity foods.

Application and potential of multifrequency ultrasound in juice industry: Comprehensive analysis of inactivation and germination of Alicyclobacillus acidoterrestris spores

The majority of acidic fruits are perishable owing to their high-water activity, which promotes microbial activity, thus exhibiting metabolic functions that cause spoilage. Along with sanitary practices, several treatments are used during processing and/or storage to inhibit the development of undesirable bacteria. To overcome the challenges caused by mild heat treatment, juice manufacturers have recently increased their involvement in developing novel non-thermal processing procedures. Ultrasonication alone or in combination with other hurdle technologies may be used to pasteurize processed fruit juices. Multifrequency ultrasound has gained popularity due to the fact that mono-frequency ultrasound has less impact on bacterial inactivation and bioactive compound enhancement of fruit juice. Here, we present and discuss the fundamental information and technological knowledge of how spoilage bacteria, specifically Alicyclobacillus acidoterrestris, assemble resistant spores and inactivate and germinate dormant spores in response to nutrient germinants and physical treatments such as heat and ultrasound. To the authors' knowledge, no prior review of ultrasonic inactivation and germination of A. acidoterrestris in fruit juice exists. Therefore, this article aims to provide a review of previously published research on the inactivation and germination of A. acidoterrestris in fruit juice by ultrasound and heat.

A Cold Plasma Technology for Ensuring the Microbiological Safety and Quality of Foods

Changing consumers’ taste for chemical and thermally processed food and preference for perceived healthier minimally processed alternatives is a challenge to food industry. At present, several technologies have found usefulness as choice methods for ensuring that processed food remains unaltered while guaranteeing maximum safety and protection of consumers. However, the effectiveness of most green technology is limited due to the formation of resistant spores by certain foodborne microorganisms and the production of toxins. Cold plasma, a recent technology, has shown commendable superiority at both spore inactivation and enzymes and toxin deactivation. However, the exact mechanism behind the efficiency of cold plasma has remained unclear. In order to further optimize and apply cold plasma treatment in food processing, it is crucial to understand these mechanisms and possible factors that might limit or enhance their effectiveness and outcomes. As a novel non-thermal technology, cold plasma has emerged as a means to ensure the microbiological safety of food. Furthermore, this review presents the different design configurations for cold plasma applications, analysis the mechanisms of microbial spore and biofilm inactivation, and examines the impact of cold plasma on food compositional, organoleptic, and nutritional quality.

Research Trends on the Application of Electrolyzed Water in Food Preservation and Sanitation

Electrolyzed water (EW) has been proposed as a novel promising sanitizer and cleaner in recent years. It is an effective antimicrobial and antibiofilm agent that has several advantages of being on the spot, environmentally friendly, cheap, and safe for human beings. Therefore, EW has been applied widely in various fields, including agriculture, food sanitation, livestock management, medical disinfection, clinical, and other fields using antibacterial technology. Currently, EW has potential significance for high-risk settings in hospitals and other clinical facilities. The research focus has been shifted toward the application of slightly acidic EW as more effective with some supplemental chemical and physical treatment methods such as ultraviolet radiations and ultrasound. This review article summarizes the possible mechanism of action and highlights the latest research studies in antimicrobial applications.

Study of the impacts of electro-activated solutions of calcium lactate, calcium ascorbate and their equimolar mixture combined with moderate heat treatments on the spores of Bacillus cereus ATCC 14579 under model conditions and in fresh salmon

Widespread in very diverse environments, the spores of Bacillus cereus are highly resistant to hostile conditions and can contaminate a huge variety of food products, posing a potential health hazard to consumers. Given this significant risk, the objective of this research work was to study the impacts of electro-activated solutions (EAS) made with calcium ascorbate, calcium lactate, and their equimolar mixture on Bacillus cereus ATCC 14579 spores in model conditions and food matrix, the fresh Atlantic salmon. The model conditions consisted of a direct application of the EAS to the spores, which avoided any interference with factors external to those of the solutions. Salmon was chosen as a food model because it is a product sensitive to bacterial spoilage and can be eaten raw. To achieve this, the solutions were prepared by electro-activation using an electric current with an intensity of 750 mA for 30 min, resulting in mean pH values of 1.94 ± 0.15-2.16 ± 0.01 and titratable acidity of 0.102 ± 0.001-0.109 ± 0.001 mol/L, depending on the type of solution. These conditions were chosen because of their excellent antibacterial efficacy previously demonstrated against vegetative cells of B. cereus. The results showed high sporicidal activities of the EAS against B. cereus with a 7 to 9 log reduction, using an initial spore population of 10⁹ CFU/mL, depending on the conditions evaluated, namely: in direct contact (2-30 min), in salmon used as a food matrix (2-7 min), and in combination with moderate heat treatments from 60 to 90 °C (0.5-2 min). In addition, it was observed that the sporicidal capacity of the EAS increased with temperature and the contact time. Otherwise, analysis of the color and lipids of the salmon have not shown any major impacts of the use of EAS as a rinsing solution for this highly perishable food. Furthermore, micrographs taken by scanning and transmission electron microscopy revealed the destructive effects of the EAS used in the vital structures/components of the spores. In general, this study has demonstrated that the electro-activation technology is effective in producing EAS capable of destroying/inactivating B. cereus spores and that they can be used for the improvement of food safety and preservation.

The Bacillus cereus Food Infection as Multifactorial Process

The ubiquitous soil bacterium Bacillus cereus presents major challenges to food safety. It is responsible for two types of food poisoning, the emetic form due to food intoxication and the diarrheal form emerging from food infections with enteropathogenic strains, also known as toxico-infections, which are the subject of this review. The diarrheal type of food poisoning emerges after production of enterotoxins by viable bacteria in the human intestine. Basically, the manifestation of the disease is, however, the result of a multifactorial process, including B. cereus prevalence and survival in different foods, survival of the stomach passage, spore germination, motility, adhesion, and finally enterotoxin production in the intestine. Moreover, all of these processes are influenced by the consumed foodstuffs as well as the intestinal microbiota which have, therefore, to be considered for a reliable prediction of the hazardous potential of contaminated foods. Current knowledge regarding these single aspects is summarized in this review aiming for risk-oriented diagnostics for enteropathogenic B. cereus.