Inactivation of Bacillus cereus spores in a tsuyu sauce using continuous ohmic heating with five sequential elbow-type electrodes.
OBJECTIVE
The effect of ohmic heating (OH) in a pilot plant system which had a zig-zag shaped (elbow-type) ohmic heater with five sequential voltage electrodes was investigated on Bacillus cereus spores in a commercial tsuyu sauce.


RESULTS
The electrical field was fixed at 26·7 V cm(-1) with an alternating current frequency of 25 kHz. Raw tsuyu sauce (50 l) inoculated with B. cereus spores was submitted in a 4 × 3 factorial design to the OH system and heated at 95, 105, 115, and 125°C each for 30, 60, and 90 s. Survival of B. cereus spores and colour change in the commercial tsuyu sauce were both measured before and after treatment. As the treatment temperature and time increased, the number of surviving B. cereus spores decreased. The OH treatment in a bath-type process at 105°C for more than 30 s resulted in the total inactivation of the inoculated B. cereus spores (average 5·4 log reductions to undetectable levels after treatment). The OH protocol of heating at 105°C for 60 s which ensure complete eradication of the inoculated spores without compromising product quality was chosen and investigated for its suitability for commercial application on bulk quantities of samples (500 l). Reliable and reproducible reductions in B. cereus spore counts of 4·7-5·5 log CFU ml(-1) (mean ± standard deviation = 5·1 ± 0·3 CFU ml(-1) ) were achieved by the selected protocol of the continuous OH treatment (105°C for 60 s).


CONCLUSIONS
This study suggests that OH treatment with five sequential elbow-type electrodes has great potential as an industrial sterilizing method for liquid food contaminated with B. cereus spores.


CONCLUSIONS
This procedure will enhance the microbiological quality of liquid foods while minimizing quality deterioration.
Department of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul, Korea.|Food Safety Research Institute, NONGSHIM Co., Ltd., Seoul, Korea.
J H
JH
Ryang
Department of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul, Korea.
N H
NH
Kim
Food Safety Research Institute, NONGSHIM Co., Ltd., Seoul, Korea.
B S
BS
Lee
Food Safety Research Institute, NONGSHIM Co., Ltd., Seoul, Korea.
C T
CT
Kim
Nutrition Safety Policy Division, Ministry of Food and Drug Safety, Osong, North Chungcheong Province, Korea.
S H
SH
Lee
Food Safety Risk Assessment Division, National Institute of Food and Drug Safety Evaluation, Osong, North Chungcheong Province, Korea.
I G
IG
Hwang
Department of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul, Korea.
M S
MS
Rhee
D001409:Bacillus cereus / Q000502:physiology / Q000528:radiation effects*; D004203:Disinfection / Q000295:instrumentation / Q000379:methods*; D004566:Electrodes; D005516:Food Microbiology / Q000295:instrumentation / Q000379:methods*; D006358:Hot Temperature; D013171:Spores, Bacterial / Q000502:physiology / Q000528:radiation effects; D013696:Temperature
Bacillus; bacterial spores; disinfection; food processing; thermal processes