Contamination rate and biofilm formation by psychotrophic bacteria from bulk milk tanks and dairy processing equipments

Psychorotrophs are the heterogeneous group of bacteria that can grow at refrigerator temperatures. Most of these bacteria produce extracellular proteases and lipases which decompose lipids and proteins in milk that leads to undesirable defect in milk. These defects do not disappear even after pasteurization and sterilization. This study aimed to investigate the occurrence rate and diversity of psychotropic bacteria in raw milk tankers and dairy processing equipments as well as the biofilm-forming ability of the isolates. A total of 80 samples including 30 samples of raw milk tanks, 30 samples of dairy product processing equipments and 20 samples from different surfaces of the production line were collected. According to the results, 26.25% of the samples were found contaminated with psychrotrophic bacteria. Amongst, 65% of the surface samples of production line, 23.33% of the raw milk tanks and 3.3% of the processing equipment were positive for psychrotrophic bacteria. Out of 31 isolates, Bacillus genus had the highest contamination rate (32.25%), whilst Alcaligenes showed the lowest rate (3.2%). The results of biofilm formation revealed that 21 isolates (67.75%) were able to produce biofilm. It was concluded that in some cases, current CIP procedure is not efficient for the entire removal of biofilm from the processing equipments. It seems that it is necessary to apply complementary physical/chemical approaches along with the current CIP procedure to complete obliteration of biofilms from dairy industry.