Detecting antibiotics in milk according to its pH level and type of test used

The aim of the research was to ascertain the extent to which changes in the pH acidity of milk influence the possibility of using fast acting diagnost ic tests to discover traces of antibiotics. The research were carried out o n antibiotic-free milk having 5 different pH levels: 6.0; 6.3; 6.6-6.8 (nor mal pH level of milk); 7.3; 7.5. For the purpose of the research the absolu te minimally detectable level of antibiotics according to classifications o f test manufacturers as well as an amount less than this minimum was added to the milk. The following antibiotics were used: penicillin, tetracycline, streptomycin and neomycin; and the following tests: Delvotest P (Gistbroca des, Holland), BR-test (Gist-brocades), STD (Abiotest, Poland), Valio T 101 (Valio, Finland) and Penzym (UCB-Bioproducts, Belgium). The research revealed that the possibility of detecting antibiotics in milk using fast-acting tests depends to a significant extent on the pH of milk, type of antibiotic and test. The above tests used on milk with a normal pH level also revealed traces of antibiotics even in cases when they were at less than a minimum level. Generally, detecting antibiotics was more satisf actory in the 7.3-7.5 alkaline pH range than acid (6.0-6.3), Nevertheless, some tests in the 7.3-7.5 pH range gave false positive results in milk not containing antibiotics, which made identification impossible.