Survival of Listeria monocytogenes in Commercially Available Refrigerated Cold-Brewed Coffee
This study examined the survival of Listeria monocytogenes in 18 commercially available cold-brewed coffees with and without added ingredients that had been under refrigeration at 4 °C. The pH of the cold-brewed coffees ranged from 4.97 to 6.14. Each sample was inoculated with a 5-strain mixture of L. monocytogenes and incubated at 4 °C for 60 days. No growth in the L. monocytogenes population was observed; in contrast, a decrease in L. monocytogenes counts was seen in all the cold-brewed coffees evaluated. L. monocytogenes counts reached <1 CFU/ml in 10 of the 18 cold-brewed coffee samples within the 60 days of incubation. Among the 8 samples where L. monocytogenes survived after 60 days, 3 demonstrated >4-log reduction in final counts. The remaining 5 samples did not achieve a 4-log reduction, with the total reduction observed ranging from 1.69 to 3.28 log CFU/ml.
The decrease of L. monocytogenes counts regardless of the concentration and pH of the samples suggests a lack of nutrients for metabolism or possible antimicrobial activity originating from the coffee itself. The comparable reduction in L. monocytogenes counts between cold-brewed coffee with and without added ingredients also suggests the possible antimicrobial activity of the coffee components even in the presence of added dairy or nondairy ingredients. Although there were significant decreases in L. monocytogenes counts, the survival of L. monocytogenes for up to 60 days at 4 °C in some of the cold-brewed coffees we evaluated necessitates the need for good manufacturing practices and hazard analysis critical control point (HACCP) method consideration.
Speaker / Author:
Sujan Acharya, PhD, Department of Nutrition, Dietetics, and Food Science, Utah State University
Brian A. Nummer, PhD, Department of Nutrition, Dietetics, and Food Science, Utah State University