Abstract
In the present study, the transfer of one of the most widely used antibiotics in dairy cows, cloxacillin, from raw milk to a wide range of dairy products such as yoghurt, kefir, milk curd, cream, rennet cheese, whey, butter, buttermilk, milk powder and whey powder was investigated. Raw milk was fortified with cloxacillin at three different concentration levels: 15 and 30 μg/kg, which correspond of 0.5 and 1 cloxacillin maximum residue level (MRL) and 100 μg/kg. Spiked milk was used to produce 10 different dairy products, according to typical industrial processes. All obtained dairy products were analysed to determine the cloxacillin residues in order to measure the degree of cloxacillin degradation, concentration factor and retention rate during the various treatments. Additionally, the impact of different conditions of storage (in the refrigeration and freezing) on the stability of cloxacillin in the obtained dairy products were tested. The dairy product manufacturing processes were unaffected by the presence of cloxacillin. The cloxacillin residues were determined in all dairy products obtained during 4 different experiments. The highest concentration factor was observed in whey powder (10.0) and milk powder (5.0). The highest reduction in the cloxacillin residual level was observed in yoghurt (35 ± 4%). The lowest amounts of cloxacillin, ranging from 7 to 20%, were transferred to cream, butter, rennet cheese and buttermilk, the highest retention rate was observed for whey (85 ± 4%). In general, the results obtained from this study reveal that stability of cloxacillin in most cases was affected (the relative responses at a range of 45–87%), with the exception of yoghurt, milk powder and whey powder, regardless of storage conditions, the relative response was ≥90%. In most cases, the degradation was about 20%, which indicates that consumers can still be exposed to cloxacillin residues. The dark side of the results showed that the use of milk contaminated with cloxacillin in the dairy industry could affect the safety of dairy products, since most of the investigated industrial processes do not eliminate this antibiotic residue.
Published Version
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