NMR and MS characterization of apple juice and partial removal of sugar by diananofiltration process

Apple is one of the most consumed fruit worldwide as well as its juice. However, while consumption of whole apples can improve vascular function, decrease systolic blood pressure and reduce cholesterol levels, clear apple juice has been associated with adverse effects, mainly related to its high fructose and low fiber content [2]. Therefore, the partial removal of sugar in apple juice without changing the rest of the natural composition and bio-functional properties is a remarkable technical challenge [3]. In the present work, apple juice was characterized using Nuclear Magnetic Resonance (NMR) and Mass spectrometry (MS) coupled with HPLC-UV. In order to reduce the sugar content and to preserve its phenolic composition, the juice was first clarified by ultrafiltration and then nanofiltered through a combination of diafiltration and batch concentration processes. Three different nanofiltration membranes with MWCO in the range of 200-600 Da were tested. For all selected membranes, the recovery rate of both sugars and phenolic compounds decreased in the retentate by increasing the diafiltration volume; however, the separation factor between phenolic compounds and sugars remained almost unchanged during the diafiltration process. Among the investigated membranes, a thin-film composite membrane with the lowest MWCO (200-300 Da) showed the highest retention of phenolic compounds in both diafiltration and concentration processes. More than 70% of phenolic compounds were recovered in the retentate stream of this membrane at a volume reduction factor of 4, while recoveries of glucose and fructose were 41 and 44%, respectively. Therefore, the combination of diafiltration and batch concentration with this membrane represented a good compromise to remove up to 60% of sugars from apple juice with minimal losses of phenolic compounds.