Effect of liquid smoke and chitosan treatment on inhibition of Listeria monocytogenes in fish model system

Abstract

Fish and fishery products which are considered as an excellent source of nutrition can also act as vehicles for the transmission of food borne pathogens. In the present study, the inhibition effects of liquid smoke alone and a combination of liquid smoke and chitosan to inhibit Listeria monocytogenes was investigated. The total phenolic content of liquid smoke was determined according to the Folin-Ciocalteu method and the value observed was 20.7 milligram per millilitre. To study the effect of liquid smoke alone, cold smoking of Pangasianodon hypophthalmus was done with 5 per cent liquid smoke and inoculated with L. monocytogenes. Further, the combined effect of liquid smoke and chitosan was studied by dipping cold smoked P. hypophthalmus pieces in different concentrations (1%, 1.5% and 2%) of chitosan solution for 10 minutes and inoculated with L. monocytogenes. After 14 days of survival study, liquid smoke-treated fish showed reduced bacterial count from 8 log units to 2 log units. However, fish treated with liquid smoke and 1.5% chitosan showed a significant reduction in the bacterial count from 8 log units to 1 log unit. Hence, from the present study, it can be concluded that the combined treatment of liquid smoke and 1.5 per cent chitosan can inhibit L. monocytogenes considerably than liquid smoke alone.