Abstract: The automated FIA method was based on the enzymatic hydrolysis of lactulose to fructose and galactose followed by the separation of fructose by dialysis and its detection by fructose dehydrogenase (FDH) catalyzed oxidation with ferricyanide as electron acceptor. The manifold allowed a sample stream (0.1 ml/min) to be merged with the reaction buffer stream (0.1 ml/min) containing 185 iu/ml β-galactosidase in phosphate buffer of pH 5. The flow was propelled through a reaction coil (1.3 m x 0.8 mm i.d.) operated at 50°C and the donor channel of the dialysis cell. The acceptor channel (64 mm x 2 mm x 0.5 mm) of the dialysis cell contained stationary 2 mM potassium ferricyanide in phosphate/citrate buffer of pH 5.5. After a dialysis period of 180 s, the acceptor solution was pumped through the FDH enzyme reactor to an amperometric detector where the ferrocyanate was re-oxidized. The amperometric detector was equipped with a screen-printed Pt electrode at +385 mV vs. Pt reference. The method was applied to the analysis of milk samples using a standard-addition calibration procedure. Lactulose concentrations of up to 12.28 mM were measured and these results were confirmed by a photometric method. The sampling frequency for the proposed method was 17 samples/h.

Abstract: The fat and protein from heated milk and reconstituted milk powder are removed by treatment with Carrez I and II solution and filtration. The carbohydrates in the filtrates are determined on a column (7.5 cm x 6 mm) of Dionex DA-X8-11 with a pre-column (5 cm x 9 mm) of Dowex 1-X4, and with gradient elution with (A) 0.15M, 0.2M, 0.4 M (each of pH 8.0), 0.8 M (pH 8.3) and 0.15 M (pH 8.0) borate buffers or (B) 0.2M, 0.3 M (each of pH 8.0), 0.8 M (pH 8.3) and 0.2 M (pH 8.0) borate buffers. Post-column derivatization is effected with Cu(I) bicinchoninate and detection is at 570 nm. By using system A, lactulose and epilactose were determined, even in the presence of large amounts of lactose; use of buffer system B permitted detection of lactulose in the presence of fructose. In addition, other carbohydrates, e.g., ribose, mannose, galactose and glucose, can be determined simultaneously.