Heated scallop-shell powder treatment for deactivation and removal of Listeria sp. biofilm formed at a low temperature.

The ability of heated scallop-shell powder (HSSP) to work against Listeria sp. biofilm formed at a low temperature was investigated. A biofilm of L. innocua ATCC 33090 was grown on a glass plate at 15˚C for 15 days, then immersed in HSSP slurry. Following treatment, the disinfection ability of the HSSP against the biofilm was non-destructively quantified by conductimetric assay. The biofilm grown at 15˚C was less sensitive than that grown at 37˚C to HSSP treatment and alkaline treatment. The biofilm grown at 15˚C was completely deactivated by 30 min of HSSP treatment (10 mg/mL, pH 12.5). In contrast, after 30 min treatment with alkaline solution at pH 12.5 or sodium hypochlorite (100 ppm), the activity was reduced by only one order of magnitude. The disinfection efficacy of HSSP (10 mg/mL) against L. innocua is similar to or higher than that of sodium hypochlorite (200 ppm). Fluorescence microscopy validated the results of the conductimetric assay. Therefore, HSSP treatment is a potentially powerful alternative control agent against Listeria sp. biofilms that present hazards in the food industry.