The effect veterinary antibiotic residues in milk have on yoghurt making

The aim of this study was to see if the presence of antibiotics in milk had an effect on yoghurt making. Antibiotics are used in the dairy industry for the treatment and prevention of clinical and subclinical mastitis. The main bacterial pathogens concerned are streptococcus (mainly strep. Uberis), E. coli, and staphylococcus (mainly aureus). The antibiotics used in the study are neomycin and tetracycline, used in a formulation called Mastijet. Before starting the trials validation of the food analytical method was carried out in line with the requirements by the corresponding EU legislation and scientific guidelines. Fifty litres of raw milk was purchased and 48 litres were spiked with the desired level of antibiotics. It was designed to resemble the first second and third days after treatment. It was then homogenised. Forty litres of the milk was then pasturized in the department of food hygiene lab keeping it at 75 C for 30 sec as it is also used in the dairy industry. The appropriate amount of culture was then added to the milk to begin the yoghurt making process. Antibiotic content of the milk and yoghurt samples was analysed using a Shimadzu LCMS-8030 liquid chromatographic-mass spectrometry system consisting of a Shimadzu Nexera HPLC and a LCMS-8030 triple-quadrupole mass spectrometer