A reliable gas capillary chromatographic determination of lactulose in dairy samples

A gas capillary chromatography of silylated carbohydrates on SPB-17 phase (50% diphenyl/50% dimethylsiloxane) method for the determination of lactulose has been developed. The method has been evaluated for precision and accuracy using phenyl-beta-D-glucoside as internal standard with satisfactory results and, then, applied to 27 commercial milk samples (pasteurized, UHT, sterilized, powder, condensed and chocolate-based milks). Results showed that it was suitable for the determination of lactulose in milks subjected to heat treatments of different intensity, giving good chromatographic resolution, as well as precise and reproducible results. Thus, lactulose levels found in pasteurised milk (n = 6) ranged from 13.0-32.1 mg L-1, UHT milk (n = 10) ranged from 95.6-437.1 mg L-1, sterilized milk (n = 2) above 622.7 mg L-1 and reconstituted powder milk (n=3) ranged from 24.4 to 48.8 mgL(-1)were similar to those previously reported. In addition, this method provided a good separation between sucrose and lactulose/lactose peaks which allowed the suitable quantification of lactulose in samples such as condensed and chocolate-based milks which contain a high concentration of sucrose.