These films are very difficult to remove during the cleaning operation.Microorgan isms that appear to be more of a problem to remove because of biofilm protection are Pseudomonas and L. monocytogenes. Current information suggests that the application of heat appears to be more effective than that of chemical sanitizers,and Teflon appears to be easier to clear of biofilm than does stainless steel.
Biofilms protect against the penetration of water-soluble chemicals such as caustics,bleaches,iodophors,phenols,and quaternary ammonium sanitizers. Therefore, the organisms within them may not be destroyed.According to Kramer (1992), there are no procedural specifications or regulations on the removal and disinfection of biofilms . A biocide may require use at 10 to 100 times normal strength to achieve inactivation.
In tests of sanitizera-including hot water at 82 C;chlorine at 20,50,and 200 ppm;and iodine at 25 ppm-the bacteria on stainless steel chips survived , even after immersion in the sanitizer for 5 minutes.The only true germicide tested was a hydrogen-peroxide-based powder that was found to be effective against biofilms at 3% and 6% solution (Felix,1991).
Relationship of Amount of Contamination,temperature , and Time to Microbial Growth
As temperature decreases, the generation interval (time required for one bacterial cell to become two cells) is increased. This is especially true when the temperature goes below 4 C .the effect of temperature microbial proliferation is illustrated in Fig-ure 3-2.For example , freshly ground beef usually contains approximately l million bacteria/g. When the number of this microbial population reaches approximately 300 million /g,abnormal odor and some slime development , with resultant spoilage,can occur . This trend does not apply to all genera and species of bacteria. However,it can be determined from these data that initial contamination and storage temperature dramatically affect the shelf life of food. The storage life of ground beef that contains l million bacteria/g is approximately 28 hours at 15.5 C.At normal refrigerated storage temperature of approximately -1C to 3C the storage life exceeds 96 hours.
EFFECTS OF MICROORGANISMS ON SPOILAGE
Food is considered spoiled when it becomes unfit for human consumption. Spoilage is usually equated with the decomposition and putrefaction that results from microorganisms.Davidson (2003) defined spoilage as an undesirable change in the flavor,oder,texture,or color of food caused by growth of microorgenisms and ultimately the action of their enzymes.