How various antioxidants influence oxygen consumption kinetics and browning intensity in two scenarios were analyzed in this study, recently published by the European Food Research and Technology journal. The first scenario was grape must from healthy grapes while the second was grape must enriched with laccase to reproduce what occurs when the grapes are infected with Botrytis cinerea.
The experimental design measured oxygen consumption kinetics and browning intensity caused by polyphenol oxidases, tyrosinase, and laccase. As expected, the results confirm that grape must consumes oxygen and browns very quickly and that the presence of laccase accelerates both of these processes. The results also confirm that sulfur dioxide is highly effective in preventing browning even in grape musts with high levels of laccase activity. On the other hand, using only ascorbic acid leads to higher oxygen consumption and browning, which indicates that this antioxidant must be used in association with sulfur dioxide.
The other alternative antioxidants—glutathione, both pure and in the form of inactivated dry yeasts, and the non-Saccharomyces yeast, Metschnikowia pulcherrima used as a bioprotective agent—can be interesting tools for protecting grape juice against browning and perhaps for reducing the use of sulfur dioxide, at least in healthy grapes. Specifically, glutathione and inactivated dry yeast rich in glutathione reduced oxygen consumption and reduced the intensity of browning when no laccase was present in the medium. However, their effectivity was reduced in the presence of laccase. The mechanism by which glutathione protects against enzymatic browning and reduces oxygen consumption is probably its capacity to combine with the orthodiquinones formed by the action of the polyphenol oxidases in stopping the browning process and depleting the medium on substrates for these enzymes.
Metschnikowia pulcherrima also reduced browning intensity but its action mechanism is different from that of glutathione. This non-Saccharomyces yeast protects because it consumes oxygen very efficiently, and therefore reduces its availability for the polyphenol oxidases.
More studies are needed to further investigate these promising alternatives to sulfur dioxide since many consumers are searching for healthier wines, and the wine industry is very keen to reduce this unfriendly additive.
Reference Article:
Giménez, P., Just-Borras, A., Pons, P. et al. Biotechnological tools for reducing the use of sulfur dioxide in white grape must and preventing enzymatic browning: glutathione; inactivated dry yeasts rich in glutathione; and bioprotection with Metschnikowia pulcherrima. Eur Food Res Technol 249, 1491–1501 (2023). https://doi.org/10.1007/s00217-023-04229-6
