A new method for the determination of 2-acetolactate in dairy products

Haemin, Fe 3+ and Cu 2+ caused significant decarboxylation of 2-acetolactate (ALA) to diacetyl during steam distillation of milk at pH 6.5. In the absence of these compounds, maximum conversion (28%) of ALA to diacetyl occurred at pH 3.5. Addition of 1.5 m m CuSO 4 at this pH increased the conversion to 100%. Based on this result, a new method for the determination of ALA was developed, in which interference from pre-formed acetoin was minimised. Comparison of this method with the previous method (Jordan and Cogan, Irish Journal of Agricultural and Food Research 34, 39–47, 1995), with which high concentrations of acetoin interfere, was excellent ( R 2=0.96). Breakdown of ALA to diacetyl in the absence of Cu at pH 0.5 and 6.5 were 0.8 and 2.5%, respectively, implying that samples for diacetyl analysis should be adjusted to pH 0.5 before distillation if ALA is also suspected to be present. In quarg (pH 4.5) held at 4°C, ALA was degraded at a rate of 6.9–16.9 μmol L -1 day -1 and from 32 to 50% of the degraded ALA was converted to diacetyl during extended storage.