Identification and Quantitation of Free Neutral Carbohydrates in Milk Products by Gas-Liquid Chromatography and Mass Spectrometry

Abstract

Free carbohydrates in selected milk products were isolated by dialysis and converted to trimethylsilyl ethers. Gas chromatography of the derived sugars from fluid milk resulted in 7 peaks. Comparisons of gas-liquid chromatographic retention times and mass spectral data revealed that the 7 peaks were isomers of glucose, galactose, and lactose. No other sugars were detected in the other products.Quantitative data were obtained both by weighing the dialysate residue after ion exchange and freeze drying, and by comparing gas-liquid chromatographic peak area to internal standards. The sugar contents in chocolate milk, whole milk, and skimmilk were not altered significantly by processing. The sugar in cultured products varied greatly. Cheddar, Trappist, and Brick cheese contained negligible carbohydrate, whereas sour cream still contained 3.7% milk sugars.The free monosaccharide of whole milk was similar to previously reported values. Free glucose and galactose were 13.8 and 11.7 mg/100 ml.