Abstract: The objective of this study was to determine the bactericidal effect of trans-cinnamaldehyde (TC) combined with mild heating on Cronobacter sakazakii in reconstituted infant formula. Reconstituted infant formula samples with various concentrations of TC (0, 0.1%, 0.2%, 0.3% and 0.4%) were inoculated with a mixture of three C. sakazakii strains (approximately 6.6(lg (CFU/ mL))) followed by incubation at 25, 45, 50 or 55 ℃. The surviving bacteria at different sampling times were enumerated. In order to elucidate the mode of action of the combined treatment, the cell membrane integrity and cell morphology were examined using a LIVE/DEAD? bacterial viability kit and a field emission scanning electron microscope, respectively. TC at 0.4% combined with heat treatment at 25 ℃ for 90 min, at 45 ℃ for 20 min, at 50 ℃ for 10 min or at 55 ℃ for 10 min reduced all pathogens to undetectable levels. Our results demonstrated that the combination of TC and heat treatment significantly reduced (P < 0.05) the number of C. sakazakii compared with either treatment alone, and this effect was dependent on both temperature and TC concentration. The combined treatment inactivated the pathogens partly by damaging cell membrane integrity, leading to cell disruption. These findings suggested that TC combined with mild heating may have potential application to control C. sakazakii infection during reconstitution of infant formula.

Key words: trans-cinnamaldehyde, Cronobacter sakazakii, reconstituted infant formula, mild heating, cell membrane