Simultaneous determination of galactose, glucose, lactose and galactooligosaccharides in galactooligosaccharides raw materials by high-performance anion-exchange chromatography with pulsed amperometric detection

•An enzymatic hydrolysis method was carried out by transforming GOS into galactose and glucose.•Galactose, glucose, lactose and GOS in GOS raw materials could be simultaneously determined by HPAEC-PAD.•The content of GOS in GOS raw materials could be calculated without the k factor.•Detailed calculation formulas were given in the paper. This study describes a method for the simultaneous determination of galactose, glucose, lactose and galactooligosaccharides (GOS) in GOS raw materials (GOS syrups and powdered GOS) by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The GOS raw materials were extracted with phosphate buffer. The extract was then treated with β-galactosidase to hydrolyze GOS and lactose. The total amounts of galactose and glucose released from GOS and lactose were determined in the treated solution. Free galactose, glucose and lactose were determined in the initial solution. The glucose in a β-galactosidase solution was also determined. The content of GOS in GOS raw materials was calculated by the increment of galactose and glucose after GOS were hydrolyzed, and the glucose and galactose also released from lactose were taken into consideration. The validated method has been successfully applied to determine the content of galactose, glucose, lactose and GOS in GOS syrups and powdered GOS.