Investigating the antimicrobial activity of pasteurized and raw camel milk against foodborne pathogens: Listeria monocytogenes and E. coli O157:H7

Abstract Text:

Abstract

The objectives of this study were to investigate the antimicrobial activity of pasteurized camel milk against foodborne pathogens (L. monocytogenes and E. coli O157:H7) at different incubation temperatures, and to examine the influence of pasteurization on antimicrobial activity of camel milk at different incubation temperatures. Pasteurized or raw camel milks were inoculated with a cocktail of L. monoctogenes or a cocktail of E. coli O157:H7, separately. Inoculated camel milk was incubated at 10°C, 25°C, and 37°C and sampled at 0, 2, 4, 8, and 24 hours of incubation time. This procedure was exactly applied using pasteurized bovine milk as a control for this experiment. All experiments were repeated at least three times. Chemical compositions of all milks were determined. pHs during incubation, total bacterial count in raw camel milk, and thermoduric bacteria in pasteurized milks were monitored.  During incubation time, L. monocytogenes growth increased dramatically after 2 h when incubated at 25°C and 37°C but no significant growth observed at 10°C. E. coli O157:H7 showed similar behaviour. Interestingly, growth of L. monocytogenes and E. coli O157:H7 in pasteurized camel milk were significantly lower than in pasteurized bovine milk. In general, the growth of L. monocytogenes in camel milk was suppressed by 15 - 18% and 8 - 10% after 8 and 24 h of incubation, respectively. However, growth suppression of E. coli O157:H7 ranged from 5 - 21% and 6 - 14% after 8 and 24 h of incubation time, respectively. Growth suppression of E. coli O157:H7 was influenced significantly by temperature but not suppression of L. monocytogenes growth. In conclusion, our results showed that camel milk possesses antimicrobial activity against foodborne pathogens (Listeria monocytogenes and E. coli O157:H7). Moreover, pasteurization process has insignificant effect on antimicrobial activity of camel milk. Further investigations are need to identify and characterize antimicrobial agents in camel milk.

Keywords: Camel milk, Listeria monocytogenes, E. coli O157:H7, antimicrobial activties