Determination of L-lactic acid in yoghurt by a bienzyme amperometric graphite-Teflon composite biosensor

L-Lactic acid was determined in cow's milk, goat's milk and whey protein concentrate (WPC)-enriched goat's milk yoghurts by using an amperometric graphite-Teflon biosensor in which peroxidase (HRP), L-lactate oxidase (L-LOD) and the mediator ferrocene were immobilized. The correlation between the L-lactic acid results obtained using the bienzyme biosensor method and a standard colorimetric enzymatic method was 0.95. One- and two-way analyses of variance indicated that the biosensor method was able to discriminate between WPC supplemented and non-supplemented yoghurts, whereas this discrimination could not be accomplished with the colorimetric enzymatic method. The biosensor described in this paper offers considerable advantages to industry because it provides rapid, direct and economical analysis of yoghurt quality.