Efficacy of fungoid chitosans from Aspergillus niger and Agaricus bisporus in controlling the oxidative browning of model white wines

The efficacy of two water-insoluble chitosans from Aspergillus niger and Agaricus bisporus, in controlling the browning of model white wine solutions was assessed and compared with respect to sulfite addition (70 mg/L). A water-soluble oligomeric preparation from Agaricus bisporus was also included to test the effect of solubility and reduced molecular weight on the antibrowning capability of the polysaccharide. Chitosans were added at 0.5 g/L and 1 g/L. Color development, iron oxidoreductive equilibrium and generation of phenolic intermediates were monitored. Results demonstrated a significant and comparable anti-browning efficacy of both insoluble formu-lations (up to 85% reduction in browning development with respect to control samples), which mainly acted by chelating iron (up to around 4.4 mg/g of chitosan) and shifting its oxidoreductive equilibrium toward the reduced form. Oligomeric chitosan was ineffective for this purpose as it completely lacked chelating activity, which it is proposed, depended on its negligible interaction with tartaric acid. Data on browning and oxidation-related phenolic intermediates also revealed that sulfite promotes browning once it is completely oxidized.Industrial relevance: Following its very recent European authorization as novel food, chitosan from Agaricus bisporus has been evaluated for the first time and compared in wine-like conditions with the already known water-insoluble chitosan from Aspergillus niger. A further novelty are the data on water-soluble chitosan prepa-rations, not yet permitted in wine but potentially interesting due to the potentially higher specific surface once in solution. The results, apart from providing information on a recently introduced source for enological chitosan, can be useful to producers and winemakers in deciding among fungoid preparations aimed to control the browning of products.