Determination of Carbohydrates in Soluble (Instant) Coffee by Anion-Exchange Chromatography with Pulsed Amperometric Detection: Summary of Collaborative Study

Abstract

Abstract A collaborative study was conducted to validate a liquid chromatographic (LC) method for determining free and total (after acid hydrolysis) carbohydrate profile of soluble (instant) coffee. Carbohydrates were separated on a pellicular anion-exchange column with pure water as mobile phase and detected by pulsed amperometry. Precisions in determining free and total carbohydrates were very similar. Average RSDr and RSDR values were 4.5 and 14.3%, respectively, for carbohydrate levels >0.3%, with individual values ranging, respectively, from 2.2 to 4.6% and 9.9 to 24.2% for mannitol, 1.6 to 7.3% and 4.9 to 21.1 % for arabinose, 1.7 to 8.1 % and 4.1 to 12.9% for galactose, 2.4 to 8.7% and 6.1 to 24.3% for glucose, 1.8 to 6.8% and 10.0 to 11.6% for sucrose, 3.7 to 7.4% and 22.5 to 27.8% for xylose, 2.0 to 7.0% and 10.6 to 24.4% for mannose, and 2.9 to 5.2% and 15.5 to 18.4% for fructose (free form only). The technique's precision was considered good, taking into account the usual peak integration problems always encountered in LC procedures, the low levels of free carbohydrates, the hydrolysis step, and the relative lack of experience of most participating laboratories. Except for the pair rhamnose/arabinose, the method allows good and reproducible separation of carbohydrates found in soluble coffee and, therefore, is suitable for routine analysis. The anion-exchange chromatographic method with pulsed amperometry for determining carbohydrates in soluble (instant) coffee has been adopted first action by AOAC INTERNATIONAL.