The effect of superheated steam on the inactivation kinetics of Enterococcus faecium inoculated in peanut butter at different water activities

Research poster
Hyeon W. Park
V. M. Balasubramaniam
Department of Food Science and Technology

Superheated steam is an emerging sanitation technology for treatment of food plant surfaces that offers minimal water and chemical utilization while providing enhanced efficacy against biofilms compared to other dry sanitation technologies. However, limited data is available on the mediating effects of food soil residues present on environmental surfaces as they impact microbial inactivation.
The objective of this study was to investigate the inactivation kinetics of Enterococcus faecium in peanut butter as a function of superheated temperatures and peanut butter water activity.
E. faecium NRRL B-2354 was inoculated in peanut butter (7.96 logCFU/g±0.63) adjusted to different aw (0.18, 0.40, 0.60, and 0.80), then coated (31.5mm—20.0mm—0.60mm) onto aluminum foil of 0.016mm thickness. The steam treatment was conducted at 125°C, 175°C, 225°C, and 250°C. The coated samples were placed in a custom coupon holder inside the treatment chamber, treated for a given time interval, and then quickly removed and immediately transferred to peptone water to stop the thermal process. Survivors were recovered by plating on agar media.
The temperature was stable at the steady-state for each target temperature (SD<1.12°C). As aw increased from 0.18 and 0.80, D125°C-values decreased from 123.46s to 8.13s. Similarly, D250°C-values were 18.83s and < 0.58s, respectively. The zaw-value and zT-value were 0.52±0.12 and 157.71°C±40.76, respectively (R2>0.87).
While low aw food matrixes offer a protective effect and organic material often minimizes sanitizer efficacy, these results indicate that superheated steam may be an effective alternative technology achieving up to 5-log reduction on peanut butter coated surfaces in 94.16s at 250°C.