Monitoring the phenolic profile of sulfite-free white wines obtained by pre-fermentative addition of chitosan

Chitosan is a food adjuvant that demonstrated interesting technological properties, including antimicrobial, chelating and antioxidant activities. Quite recently the use of chitosan in enology, as a clarifying and antimicrobial agent or for the reduction of wine toxins and metal content, has been admitted by EU. However, another intriguing feature of chitosan, e.g. its protecting capacity against phenol oxidation, would deserves to be investigated in wines. The goal of this study was to monitor phenolic compounds and other minor constituents in white wines fermented with sulfur dioxide or two different chitosan formulations. For this purpose a comparative study with control samples was performed and the effect of these winemaking agents on the behavior of the wine constituents over time was determined. White musts were obtained at pilot plant. The different oenological fining agents, potassium metabisulphite, chitosan I and chitosan II, were added to the must at dosage of 80 mg/L, 1g/L and 1 g/L, respectively. Chitosan I and II was removed in finished wines by settling and the obtained wines were stored for 9 months in 50 mL bottles without headspace at room temperature and in darkness. Samples were collected every 30 days and the phenolic compounds and other minor constituents were characterized by High Performance Liquid Chromatography (HPLC) coupled to High Resolution Mass Spectrometry (MS). This analytical procedure provided a complete monitoring of the chemical composition. Indeed, a wide variety of polyphenols belonging to different chemical classes were found in wine samples, pointing out differences between control sample and the three oenological fining agents. The trend of these compounds allowed establishing the effect of each additive in this fraction as well as determining the degree of some chemical reactions with particular emphasis to oxidative phenomena.