Rapid lactate oxidase-based assay for lactate content in milk to ascertain its hygienic quality

A rapid method for qualitative and quantitative assaying of L-lactate in milk is described. The method is based on oxidation of lactate by lactate oxidase with the simultaneous formation of H2O2 which subsequently oxidises 2, 4, 6-tribromo 3-hydroxy benzoic acid (TBHBA) in the presence of peroxidase. Oxidised TBHBA then reacts with 4-amino antipyrine to obtain magenta colour (lambda(max) = 523 nm). In the qualitative assay, colour change becomes visible in raw milk samples spiked with 300 mg lactate/L. The absorbance increases linearly up to 1000 mg/L. The method can be used for rapid assessment of the hygienic quality of milk.