Quantitation determination of chlorogenic acid in cider apple juices by 1H NMR spectrometry

This article introduces a method for the determination of chlorogenic acid in apple juices by measuring its signal at 7.20 ppm in the H-1 NMR spectrum. The method is direct and does not need any previous derivatization. The addition to the juice of 1,3,5-benzenetricarboxylic acid as internal standard allows the determination of the absolute concentration of chlorogenic acid. Ascorbic acid is also added to prevent enzymatic oxidation of the phenolic compounds and to adjust the pH to 2.74, since the chemical shifts of some compounds vary with the pH. A standard addition method performed with the juices of three different varieties of apples gave recoveries between 91 and 107%. The precision of the method was tested for repeatability (n = 5) and reproducibility (n = 15), obtaining coefficient of variation of 5.7 and 7.5 %, respectively, for a sample of Gezamina apple juice (586 mgl(-1) chlorogenic acid). (C) 2003 Elsevier Science B.V. All rights reserved.