The Effect of Temperature-Assisted High Hydrostatic Pressure on the Survival of Alicyclobacillus acidoterrestris Inoculated in Orange Juice throughout Storage at Different Isothermal Conditions

Effect of high hydrostatic pressure treatment on the inactivation and sublethal injury of foodborne pathogens and quality of apple puree at different pH

The objectives of this study were to evaluate the survival of high hydrostatic pressure (HHP)-treated Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes in apple puree, as well as to determine the levels of HHP-induced cell injury according to the pressure level, holding time, and pH of apple puree. Apple puree was inoculated with three foodborne pathogens and treated at pressures of 300-600 MPa for up to 7 min at 22 °C using HHP equipment. Increasing the pressure level and lowering the pH of apple puree led to larger microbial reductions, and E. coli O157:H7 showed higher resistance compared to S. Typhimurium and L. monocytogenes. Besides, approximately 5-log injured cells of E. coli O157:H7 were induced in apple puree at pH 3.5 and 3.8. HHP treatment at 500 MPa for 2 min effectively achieved complete inactivation of the three pathogens in apple puree at pH 3.5. For apple puree at pH 3.8, more than 2 min treatment of HHP at 600 MPa is seemingly needed to achieve complete inactivation of the three pathogens. Transmission electron microscopy analysis was conducted to identify ultrastructural changes in the injured or dead cells after HHP treatment. Plasmolysis and uneven cavities in the cytoplasm were observed in injured cells, and additional deformations, such as distorted and rough cell envelopes, and cell disruption occurred in dead cells. No changes in solid soluble content (SSC) and color of apple puree were observed after HHP treatment, and no differences were detected between control and HHP-treated samples during 10 d of storage at 5 °C. The results of this study could be useful in determining the acidity of apple purees or the treatment time at specific acidity levels when applying the HHP processing.

Strategy for Avoiding Alicyclobacillus acidocaldarius Contamination of Apple Juice by Adding Magnetosomes/Antibacterial Peptide Composites

The survival of Alicyclobacillus acidocaldarius (A. acidocaldarius) in fruit juice after pasteurization results in high economic losses due to unpalatability. The present work addressed this issue by inhibiting the growth of A. acidocaldarius in apple juice by the addition of MN@IDR-1018 composites formed of innate defense regulator 1018 (IDR-1018) antibacterial peptides that are coupled on the surfaces of magnetosomes (MN) via amidation reactions. MN@IDR-1018 was demonstrated to provide excellent antibacterial activity against A. acidoterrestris with a minimum inhibitory concentration of 100 μg mL-1, which led to cell death via membrane dissolution and rupture. In addition, this concentration of MN@IDR-1018 was proved to present low toxicity in mice and had no discernible effect on the color, flavor, and aroma of apple juice. This enables the active material to be extracted from the apple juice by the application of a magnetic field, thereby avoiding the development of antibiotic resistance.

Effectiveness of a Phage Cocktail as a Potential Biocontrol Agent against Saprophytic Bacteria in Ready-To-Eat Plant-Based Food

This study aimed to evaluate the effectiveness of the phage cocktail to improve the microbiological quality of five different mixed-leaf salads: rucola, mixed-leaf salad with carrot, mixed-leaf salad with beetroot, washed and unwashed spinach, during storage in refrigerated conditions. Enterobacterales rods constituted a significant group of bacteria in the tested products. Selected bacteria were tested for antibiotic resistance profiles and then used to search for specific bacteriophages. Forty-three phages targeting bacteria dominant in mixed-leaf salads were isolated from sewage. Their titer was determined, and lytic activity was assessed using the Bioscreen C Pro automated growth analyzer. Two methods of phage cocktail application including spraying, and an absorption pad were effective for rucola, mixed leaf salad with carrot, and mixed leaf salad with beetroot. The maximum reduction level after 48 h of incubation reached 99.9% compared to the control sample. In washed and unwashed spinach, attempts to reduce the number of microorganisms did not bring the desired effect. The decrease in bacteria count in the lettuce mixes depended on the composition of the autochthonous saprophytic bacteria species. Both phage cocktail application methods effectively improved the microbiological quality of minimally processed products. Whole-spectral phage cocktail application may constitute an alternative food microbiological quality improvement method without affecting food properties.