Phenolic compounds enhancement and sugar reduction in apple juice by diananofiltration

Apple is one of the most consumed fruits in the world because of its availability throughout the year in various products, including fresh fruit, juice and concentrate. Epidemiological studies have shown that apple consumption as fresh fruit can prevent chronic heart and vascular diseases, diabetes, respiratory and pulmonary dysfunctions, obesity, and cancer, among others. All these quality properties are ultimately based on the metabolic composition of the fruit. On the other hand, processing steps for producing ready-to-drink apple juices, including juice extraction and clarification, harm the health-promoting compounds of apples, and clear apple juice has been associated with adverse effects, mainly related to its high fructose and low fiber content. Partial removal of sugars in apple juice without compromising its biofunctional properties represents a significant technological challenge. In the present work, apple juice was initially characterized using Nuclear Magnetic Resonance (NMR) and Mass spectrometry (MS) coupled with HPLC-UV. Three different spiral-wound nanofiltration (NF) membranes with a molecular weight cut-off (MWCO) range of 200-500 Da were tested to reduce the sugar content of the juice and preserve its phenolic composition. In addition, a combination of diafiltration and batch concentration processes was investigated. For all selected membranes, the permeate flux and recovery rate of glucose, fructose, and phenolic compounds were evaluated in both diafiltration and concentration processes. Among the investigated membranes, a thin-film composite membrane with an MWCO of 200-300 Da provided the best results in preserving phenolic compounds in the selected operating conditions. More than 70% of phenolic compounds were recovered in the retentate stream, while the content of sugars was reduced by about 60%.