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A biocontroller to eliminate Listeria monocytogenes from the food processing environment

Schöbitz, Renate, González, Carla, Villarreal, Katherine, Horzella, Mariela, Nahuelquín, Yanina, Fuentes, Ricardo
Food control 2014 v.36 no.1 pp. 217-223
Carnobacterium piscicola, Enterococcus mundtii, Listeria monocytogenes, biofilm, disinfection, food processing, nisin, pathogens, refrigeration, regrowth, salmon, stainless steel, storage time, temperature, viability
Conventional disinfection methods have not been successful in eliminating Listeria monocytogenes from biofilms, which has caused difficulty in eradicating the pathogen from the food processing environment. The aim of this study was to formulate and design a biocontroller for application in the food processing environment and to evaluate its inhibitory capacity against biofilms from L. monocytogenes grown in vitro and in situ in floor gutters in a salmon processing plant. The biocontroller consisted of the thermally treated fermentate (TTF) from two Carnobacterium maltaromaticum strains (ATCC PTA 9380 and ATCC PTA 9381), a strain of Enterococcus mundtii (ATCC PTA 9382), plus nisin at a concentration of 1000 IU/mL. These components were entrapped in an alginate matrix supported by a mesh-type fabric. The activity of the biocontroller was analyzed during three weeks of storage at 4 °C by the plate antagonism test against a pool of five strains of L. monocytogenes. Effectiveness against L. monocytogenes was also tested on biofilms grown in vitro on stainless steel chips with coupons of the biocontroller placed on the chips and tested for 5 days. Loss of viability was confirmed by L. monocytogenes counts (cfu/cm2). Tests were also performed on biofilms grown in situ in floor gutters in a salmon processing plant. The biocontroller was fixed to the floor gutters for 48 h, and afterward, sampling by the sponge method for the presence of L. monocytogenes was performed. The results showed that the antagonistic activity of the biocontroller did not change significantly (p > 0.05) during the three weeks of storage at refrigeration temperature. The biocontroller coupons placed on a biofilm of five strains of L. monocytogenes grown on stainless steel chips reduced the counts from Log 3.7 cfu/cm2 to Log<1.0 cfu/cm2 after 24 h of contact, and no regrowth of the pathogen was observed for up to five days of contact. The in situ-tested biocontroller was able to inhibit or destroy L. monocytogenes in five out of seven trials, and the failures were due to loss of contact of the biocontroller with the side wall of the floor gutter. These in situ results confirmed the laboratory findings and proved the effectiveness of the biocontroller against L. monocytogenes.