The effect of water activity and temperature on the inactivation of Enterococcus faecium in peanut butter during superheated steam sanitation treatment

The objective of this study was to investigate the inactivation kinetics of Enterococcus faecium in peanut butter under different water activities (aw) and superheated steam temperatures. Peanut butters were prepared at 4 different initial water activities (0.19, 0.40, 0.60, and 0.80) and E. faecium was inoculated into the peanut butter (7.4–8.7 log CFU/g). The inoculated peanut butter samples were exposed at 4 different superheated steam temperatures (125 °C, 175 °C, 225 °C, and 250 °C). Survivor data were modelled using Weibull and log-linear models to describe the inactivation kinetics of E. faecium. The decimal reduction times (D-value), temperature sensitivity (zT) and aw sensitivity (zaw) of the D-value were determined from a log-linear model, and inactivation parameters from the Weibull model were also evaluated. An increase in aw of peanut butter and superheated steam temperature decreased the D-value of E. faecium. The zaw-value and zT-value were determined to be 0.60 ± 0.09 and 194.66 ± 40.69 °C, respectively (R2 > 0.89). The inactivation kinetics of E. faecium on surfaces contaminated with peanut butter can provide comprehensive information to superheated steam sanitation treatment which may be applied to environmental surfaces for effective microbial inactivation without the introduction of water.