Identification, heat resistance and growth potential of mesophilic spore-forming bacteria isolated from Algerian retail packaged couscous

Abstract

Abstract Aims In this study, species taxonomy, heat resistance and growth potential of mesophilic aerobic spore-forming Bacillus strains isolated from commercially available couscous were determined. Methods and results Aerobic spore-forming bacteria were isolated from three Algerian retail couscous samples heated at 80 °C for 10 min. Plate counting of spore-forming bacteria showed a mean concentration of 20 CFU/g. By monitoring 16S gene sequencing, ten Bacillus strains were identified, belonging to 3 different species: five Bacillus licheniformis strains, four Bacillus cereus group strains sensu lato and one Bacillus subtilis strain. According to the panC gene sequencing, the four B. cereus strains were assigned to the group IV (mesophilic and heat resistant group, associated with cases of foodborne illness). B. cereus cells growth kinetics in moistened couscous semolina showed a specific growth rate of 0.33 h −1 at 30 °C, confirming their growth ability in this media. The heat resistance ( δ value i.e. the first decimal reduction time) and heat sensitivity ( z T values i.e. the temperature increase leading a ten-fold reduction of the δ value) of spores of B. cereus and B. subtilis strains were determined using Weibull and Bigelow models, respectively. δ 100 °C values are ranged from 0.14 to 7.90 min and estimated z T values ranged from 7.52 °C to 10.38 °C. Moreover, the estimate four decimal reduction times at 90 °C ( t 4D) of spores of isolated B. cereus strains were from 0.58 h to 3.73 h. Conclusions B. cereus strains isolated from retail packaged couscous semolina are resistant to heat treatment both during the industrial food process and can easily grow in moistened couscous semolina. These observations could explain numerous B. cereus outbreaks associated with couscous semolina consumption.