Occurrence of Listeria species in the processing stages of frozen pepper

Abstract

The occurrence of Listeria monocytogenes and other Listeria spp. in a frozen vegetable processing factory was investigated. From May to October 2002, four separate visits were made to the plant and during all of these visits, a total of 216 samples were collected at different stages of the cube and strip pepper processing line. Additionally, 28 swabs were taken from equipment and food-related contact surfaces. The cube and strip pepper processing lines include raw materials, washing, conveyor belt, scalding, cutting, sieving (drying), and the interior sieve (of individually quick frozen (IQF), IQF and finished products. Swab samples were taken from the scalding tank, cooling tank, conveyor belt to IQF interior part of IQF mixing shovel of IQF, transport saddles and packaging materials. No Listeria spp. were isolated from the strip pepper processing stages, however 26 out of 108 (24.1%) samples taken from the cube pepper processing stages were found to be contaminated with Listeria spp. Among these isolates, L. monocytogenes was not identified; however, Listeria welshimeri, Listeria innocua and Listeria ivanovii species were identified in 15, 6 and 5 of the tested samples, respectively. L. welshimeri and L. ivanovii were also isolated from three swab samples. These indicate that even though L. monocytogenes was not isolated, the presence of other Listeria species, particularly L. innocua, in the processing line would be an important criterion for eventual L. monocytogenes contaminations. Thus, periodic controls and application of general hygiene and sanitation principles are necessary in the prevention of possible contaminations.