An evaluation of different microbial and rapid tests for determining inhibitors in milk

The study focuses on the evaluation of different tests for determining inhibitors in raw cows’ milk, these being the LPT, MaI-1, Copan, Valio T 101, Penzym S, β-STAR, SNAP and ROSA tests. Milks, artificially contaminated with selected concentrations of inhibitory substances (antibiotics, detergents), naturally contaminated samples (i.e., containing inhibitors) of raw milk and 10,000 “routine” samples, were analysed. LPT, MaI-1 and Copan tests were sensitive to all β-lactams at EU maximum residue limits (MRLs), the other tests (Valio T 101, Penzym S, β-STAR, SNAP and ROSA) – to 2–4 of β-lactams investigated. All microbial tests were sensitive to the same detergents: TAAB-1, TAAB-2 and PESETTI ANTIBACT. The results of enzymatic and immuno/receptor tests in many cases could not be evaluated because of abnormalities in colours or testing procedure. Therefore, it was possible to suspect the possibility of the presence of detergent residues in tested milk. The results of investigating the naturally contaminated raw milk samples showed that there were no differences between LPT–Copan and MaI-I–Copan tests. Differences were found, however, between MaI-1 and other tests. Comparison of the tests, according to the method of use, showed that the Copan test was simple to use and interpret, had a long shelf life and was sensitive to all β-lactams. Since the penicillins were determined to be the main group of inhibitors found in raw cows’ milk in Lithuania (86% of the “positive” samples), the rapid tests for β-lactams can be successfully used for screening milk at the milk processing plants.