Review: Biofilm as a major factor in contamination of milk and dairy products with thermoduric bacteria

Abstract

The primary source of thermoduric bacteria for contamination of milk and dairy products is raw milk. Contamination sources of raw milk are the surface of udder, milking-, cooling- and storage equipments. Inadequate cleaning and storage of milking equipment may cause formation of biofilm on the surfaces which are in contact with milk. Thermoduric bacteria are divided on the basis of their physiological characteristics from thermophilic, mesophilic and psychrophilic bacteria. Thermoduric bacteria in biofilm have favourable conditions for reproduction. Bacteria in biofilm are much more resistant to temperatures and chemicals used on cleaning of equipment. Characteristics of bacteria cells, the cell-surface properties and the properties of fluid suspending bacteria influenced binding of bacteria in biofilm formed on the surface of the equipment. Outgrowth of thermoduric bacteria and contamination of processed milk take place from biofilm formed on the surfaces of regeneration and cooling sections of pasteurizes and from biofilms formed on the surfaces of separators and buffer tanks, which were in contact with milk. Thermoduric bacteria in raw milk undergo the necessary heat treatment and after it, reproducing in biofilms which formed on the surfaces of equipment, they can turn now to the product. Thermoduric bacteria have often negative impact quality of dairy products.

Keywords

• biofilm
• thermoduric bacteria
• milk and dairy products