Inhibition and Mechanism of Citral on Bacillus cereus Vegetative Cells, Spores, and Biofilms.

Bacillus cereus causes food poisoning by producing toxins that cause diarrhea and vomiting and, in severe cases, endocarditis, meningitis, and other diseases. It also tends to form biofilms and spores that lead to contamination of the food production environment. Citral is a potent natural antibacterial agent, but its antibacterial activity against B. cereus has not been extensively studied. In this study, we first determined the minimum inhibitory concentrations and minimum bactericidal concentrations, growth curves, killing effect in different media, membrane potential, intracellular adenosine triphosphate (ATP), reactive oxygen species levels, and morphology of vegetative cells, followed by germination rate, morphology, germination state of spores, and finally biofilm clearance effect. The results showed that the minimum inhibitory concentrations and minimum bactericidal concentrations of citral against bacteria ranged from 100 to 800 µg/mL. The lag phase of bacteria was effectively prolonged by citral, and the growth rate of bacteria was slowed down. Bacteria in Luria-Bertani broth were reduced to below the detection limit by citral at 800 µg/mL within 0.5 h. Bacteria in rice were reduced to 3 log CFU/g by citral at 4000 µg/mL within 0.5 h. After treatment with citral, intracellular ATP concentration was reduced, membrane potential was altered, intracellular reactive oxygen species concentration was increased, and normal cell morphology was altered. After treatment with citral at 400 µg/mL, spore germination rate was reduced to 16.71%, spore morphology was affected, and spore germination state was altered. It also had a good effect on biofilm removal. The present study showed that citral had good bacteriostatic activity against B. cereus vegetative cells and its spores and also had a good clearance effect on its biofilm. Citral has the potential to be used as a bacteriostatic substance for the control of B. cereus in food industry production.

Enhancing UV radiation protection of Bacillus thuringiensis formulations using sulfur quantum dots: synthesis and efficacy evaluation.

Bacillus thuringiensis (Bt) is a widely used microbial insecticide, but its effectiveness is limited due to the degradation of Bt spores and crystals under UV radiation from sunlight. The objective of this study was to develop a novel Bt formulation with improved UV protection by utilizing sulfur quantum dots (SQDs) as stabilizing agents in a Pickering emulsion. The SQDs were comprehensively characterized using FTIR, XRD, TEM, HRTEM, UV, and fluorescence analyses, which confirmed the formation of well-dispersed, spherical SQDs. The microcapsule formulation with SQDs demonstrated superior UV stability, as it maintained 57.77% spore viability after 96 h of UV exposure, in comparison to 33.74% and 31.25% for the SQDs formulation (non-microcapsules) and unprotected Bt formulations (free spore, as a control), respectively. Furthermore, the microcapsule formulation exhibited higher insecticidal activity, resulting in a larval mortality of 71.22%, as opposed to 42.34% and 38.42% for the other formulations. These findings emphasize the effectiveness of microcapsule formulation with SQDs in safeguarding Bt spores and crystals against UV radiation, thereby enhancing their practical application in pest control. This approach presents a promising strategy for the development of biopesticides that are more resilient and have a longer shelf life.

Emulsified and Nanoemulsified Essential Oils in the Control of Clostridium botulinum and Clostridium sporogenes in Mortadella.

Clostridium botulinum is a foodborne pathogen responsible for severe neuroparalytic disease associated with the ingestion of pre-formed toxin in food, with processed meats and canned foods being the most affected. Control of this pathogen in meat products is carried out using the preservative sodium nitrite (NaNO2), which in food, under certain conditions, such as thermal processing and storage, can form carcinogenic compounds. Therefore, the objective was to use nanoemulsified essential oils (EOs) as natural antimicrobial agents, with the aim of reducing the dose of NaNO2 applied in mortadella. The antimicrobial activity of nanoemulsions prepared with mixtures of EOs of garlic, clove, pink pepper, and black pepper was evaluated on endospores and vegetative cells of C. botulinum and Clostridium sporogenes (surrogate model) inoculated in mortadella prepared with 50 parts per million NaNO2. The effects on the technological (pH, water activity, and color) and sensory characteristics of the product were also evaluated. The combinations of EOs and their nanoemulsions showed sporicidal effects on the endospores of both tested microorganisms, with no counts observed from the 10th day of analysis. Furthermore, bacteriostatic effects on the studied microorganisms were observed. Regarding the technological and sensorial characteristics of the product, the addition of the combined EOs had a negative impact on the color of the mortadella and on the flavor/aroma. Despite the strong commercial appeal of adding natural preservatives to foods, the effects on flavor and color must be considered. Given the importance of controlling C. botulinum in this type of product, as well as the reduction in the amount of NaNO2 used, this combination of EOs represents a promising antimicrobial alternative to this preservative, encouraging further research in this direction.

Chemicals and lemon essential oil effect on Alicyclobacillus acidoterrestris viability

Alicyclobacillus acidoterrestris is considered to be one of the important target microorganisms in the quality control of acidic canned foods. There is an urgent need to develop a suitable method for inhibiting or controlling the germination and outgrowth of A.acidoterrestris in acidic drinks. The aim of this work was to evaluate the chemicals used in the lemon industry (sodium benzoate, potassium sorbate), and lemon essential oil as a natural compound, against a strain of A.acidoterrestris in MEB medium and in lemon juice concentrate. The results pointed out that sodium benzoate (500-1000-2000 ppm) and lemon essential oil (0.08- 0.12- 0.16%) completely inhibited the germination of A. acidoterrestris spores in MEB medium and LJC for 11 days. Potassium sorbate (600-1200 ppm) was more effective to inhibit the growth of the microbial target in lemon juice than in MEB medium. The effect of sodium benzoate, potassium sorbate and essential oil was sporostatic in MEB and LJC as they did not affect spore viability.

O uso de esporos de bacillus subtilis ATCC 19659 para avaliar a eficiência do hipoclorito de sódio 2: a açäo do hipoclorito de sódio sobre lotes de esporos produzidos em tempos diferentes / The use of spores of bacillus subtilis ATCC 19659 to evaluate the efficiency of sodium hypochlorite: the accion of sodium hypochlorite on spores produced in different times

A açäo esporicida do hipoclorito de sódio foi avaliada usando-se Bacillus subtilis ATCC 19659. Lotes de esporos produzidos em épocas diferentes näo apresentaram diferenças significativas (P < 0,5) quanto à sua resistencia a hipoclorito de sódio (105 mg/l de cloro residual livre) em pH 9,8 a 30-C nos tempos de contacto de 30, 60, 90, 120, 140, 160 e 180 minutos. A partir dos números de reduçöes decimais chegou-se a equaçäo de regressäo linear simples, Y=0,0351 - 2,073 (r2 de 0,95 e P < 0,05), onde Y representa número de reduçöes decimais e X o tempo de contacto sosanificante com os esporos. Dessa equaçäo obteve-se o tempo de início de morte (tempo necessário para completar-se a fase "lag") e o valor D, parâmetros importantes para se avaliar a açäo do cloro sobre esporos