Optimization of a newly established gas-chromatographic method for determining lactose and galactose traces: Application to Pecorino Romano cheese

In this work, we present and validate new gas-chromatographic with flame injection detector method to measure traces of lactose and galactose in cheese. Analytes are first extracted from the matrix by repeated treatments with a 40% (v/v) methanol/water solution, followed by their silanization with a 2:1 mixture of trimethylsilylimidazole and trimethylchlorosilane. Validation parameters show excellent limits of detection and quantification, and very good precision and trueness. The method was tested with a wide sampling of Protected Designation of Origin (PDO) Pecorino Romano sheep cheese (33 samples, different for geographic area of production, seasonality and ripening levels). For all of them, the concentration of lactose and galactose were always below the relevant limits of detection (i.e. 0.54 and 0.90 mg kg−1, respectively). On this basis, PDO Pecorino Romano sheep cheese is, according to both European Community and European Food Safety Authority guidelines, a “lactose free” foodstuff, useful in the dietary management of patients with galactosaemia and of people who are lactose intolerant.