Inactivation kinetics of Geobacillus stearothermophilus spores by a peracetic acid or hydrogen peroxide fog in comparison to the liquid form.

The aim of this study was to compare the sporicidal effect of the disinfectants peracetic acid (PAA) or hydrogen peroxide (H2O2) applied as a fog or as a liquid. The efficacy of fogging of the disinfectants was tested in a closed isolator cabinet using highly heat and chemical-resistant spores of Geobacillus stearothermophilus. Fogging of a 0.06% solution of PAA resulted in over 5-log reduction of spores in 10 min, whereas for PAA used in liquid form the same reduction was achieved in 4.5 min. The inactivation curves for fog and liquid were fitted using three different models (Linear with shoulder, Weibull, Gauss-Eyring). This showed a shoulder for the fog with an estimated length of 4.1 min, but the D values, calculated for the linear parts of the curves, were not significantly different (1.1 and 0.8 min for the PAA fog and solution, respectively). Similar results were obtained for a 12% H2O2 solution, albeit that H2O2 was less effective compared to PAA, requiring 60 min to reach 3-log reduction when applied as a fog, with an estimated shoulder of 18.5 min. Fogging of a 0.06% peracetic acid solution effectively inactivated G. stearothermophilus spores. Overall, the data show that fogging can be an effective method of applying disinfectants but that a shoulder in the inactivation curves should be considered in process design. This study provides inactivation kinetics for disinfection using PAA or H2O2-based fog, which can aid in selection and validation of process parameters for disinfection of contained areas by fogging.

The effect of pulsed electric fields on carotenoids bioaccessibility: The role of tomato matrix.

Tomato fractions were subjected to pulsed electric fields treatment combined or not with heating. Results showed that pulsed electric fields and heating applied in combination or individually induced permeabilization of cell membranes in the tomato fractions. However, no changes in ß-carotene and lycopene bioaccessibility were found upon combined and individual pulsed electric fields and heating, except in the following cases: (i) in tissue, a significant decrease in lycopene bioaccessibility upon combined pulsed electric fields and heating and heating only was observed; (ii) in chromoplasts, both ß-carotene and lycopene bioaccessibility significantly decreased upon combined pulsed electric fields and heating and pulsed electric fields only. The reduction in carotenoids bioaccessibility was attributed to modification in chromoplasts membrane and carotenoids-protein complexes. Differences in the effects of pulsed electric fields on bioaccessibility among different tomato fractions were related to tomato structure complexity.

Inactivation of chemical and heat-resistant spores of Bacillus and Geobacillus by nitrogen cold atmospheric plasma evokes distinct changes in morphology and integrity of spores.

Bacterial spores are resistant to severe conditions and form a challenge to eradicate from food or food packaging material. Cold atmospheric plasma (CAP) treatment is receiving more attention as potential sterilization method at relatively mild conditions but the exact mechanism of inactivation is still not fully understood. In this study, the biocidal effect by nitrogen CAP was determined for chemical (hypochlorite and hydrogen peroxide), physical (UV) and heat-resistant spores. The three different sporeformers used are Bacillus cereus a food-borne pathogen, and Bacillus atrophaeus and Geobacillus stearothermophilus that are used as biological indicators for validation of chemical sterilization and thermal processes, respectively. The different spores showed variation in their degree of inactivation by applied heat, hypochlorite, hydrogen peroxide, and UV treatments, whereas similar inactivation results were obtained with the different spores treated with nitrogen CAP. G. stearothermophilus spores displayed high resistance to heat, hypochlorite, hydrogen peroxide, while for UV treatment B. atrophaeus spores are most tolerant. Scanning electron microscopy analysis revealed distinct morphological changes for nitrogen CAP-treated B. cereus spores including etching effects and the appearance of rough spore surfaces, whereas morphology of spores treated with heat or disinfectants showed no such changes. Moreover, microscopy analysis revealed CAP-exposed B. cereus spores to turn phase grey conceivably because of water influx indicating damage of the spores, a phenomenon that was not observed for non-treated spores. In addition, data are supplied that exclude UV radiation as determinant of antimicrobial activity of nitrogen CAP. Overall, this study shows that nitrogen CAP treatment has a biocidal effect on selected Bacillus and Geobacillus spores associated with alterations in spore surface morphology and loss of spore integrity.