Optimization of the determination of organic acids and sugars in fruit juices by ion-exclusion liquid chromatography

An HPLC method for the determination of the main organic acids and sugars in fruit juices is proposed. Nine acids (including oxalic, citric, malic, quinic, galacturonic, ascorbic, succinic, and fumaric acid) and three sugars (sucrose, glucose and fructose) were separated by ion-exclusion chromatography using a resin-based Aminex HPX 87H column after a sample clean-up with Sax cartridges. In spite of the suitable chromatographic conditions, quantification of ascorbic and dehydroascorbic acids was affected by on-column degradation of the former into the latter. For all the other analytes the method showed a good precision and linearity and, as an application, eighteen commercial juices from 4 different fruits were tested. Independently from the fruit, citric and malic acids were the main acids in juices, with amounts varying from 0.05 to 3.23 g/L and from 0.52 to 5.61 g/L, respectively. Compared to other fruits, pears demonstrated the highest content of succinic acid, possibly due to the coelution of relatively high quantities of shikimic acid. In some juices, small amounts of quinic, fumaric and galacturonic acids were also found. Finally, peach juices were demonstrated to be the richest in sugars, with apple juices being the poorest.