Food processing effects on residues: penicillins in milk and yoghurt

Milk samples spiked with benzylpenicillin, cloxacillin, oxacillin, dicloxacillin, ampicillin or nafcillin at and above maximum residue limit concentrations were used to produce yoghurt according to the typical industrial process. As expected, coagulation was negatively influenced by increasing concentrations of residual penicillins. On the other hand, the concentration of the penicillins was reduced due to various parameters of the production process. The temperature during heat treatment (90 degreesC, 15 min) of the milk before the yoghurt cultures were added, the binding of the penicillins to milk proteins, the fermentation time and temperature, and the influence of the starter cultures proved to be main factors leading to the decrease of residual penicillins. Main degradation products of penicillin G as identified by liquid chromatography-tandem mass spectroscopy (LC-MS/MS) were penillic, penicilloic, and penilloic acids. (C) 2002 Elsevier Science B.V. All rights reserved.