Inactivation of Bacillus amyloliquefaciens spores by continuous high-pressure-assisted thermal sterilization in an oil-in-water (o/w) emulsion with 10 % soybean oil

Ultra-high-pressure homogenization (UHPH) offers new opportunities for continuous high-pressure-assisted thermal sterilization of liquids and production of stable emulsions. As relevant indicator, Bacillus amyloliquefaciens spores were suspended in a coarse oil-in-water (o/w) emulsion (pH 7.6) with 10 % soybean oil and 4 % soy protein isolate at the initial concentration of ~106 CFU/mL. The o/w emulsion was subjected to UHPH treatments at 200, 300 and 350 MPa with the inlet temperature at ~80 °C to inactivate the respective bacterial spores and produce fine emulsion simultaneously. After treatment at 350 MPa with the valve temperature higher than 150 °C, a reduction up to 4 log10 CFU/mL of bacterial spores was obtained, and the emulsion was characterized by smaller particle size and narrow particle size distributions, with the D[3, 4] of 0.210 μm and the span of 0.746. No spore germination was found after any of these UHPH treatments. The microstructure of the emulsion was observed under confocal laser scanning microscopy with fluorescein isothiocyanate and Nile red to stain proteins and fats, respectively. UHPH showed potential to combine sterilization and emulsification into one single process.