Comparison of two HPLC systems and an enzymatic method for quantification of soybean sugars

Successful breeding programs need fast and reliable methods for analyzing sugar composition in new soybean (Glycine max (L.) Merrill) lines. The efficiency to quantify the major sugars, including glucose, fructose, sucrose, raffinose, and stachyose, in five soybean lines with two HPLC systems and an enzymatic procedure were compared. Soluble sugars in soybean were extracted with water at a solvent-to-sample ratio of 5:1 at 50 °C for 15 min, and analyzed by high-performance size exclusion chromatography with refractive index detection (HPSEC-RI), high-performance anion-exchange chromatography with pulsed-amperometric detection (HPAEC-PAD), and a raffinose-series oligosaccharides assay procedure. All three methods produced comparable and reproducible results. The HPAEC-PAD method was more sensitive, faster and capable of separating all five major sugars in soybean with improved peak resolution compared with the HPSEC-RI method, and is recommended for soybean breeding programs. The enzymatic procedure required no expensive instrumentation and less sample preparation, but could not quantify individual raffinose and stachyose.