Antioxidant alternatives to sulfur dioxide in white wine production

Wine, considered by many to be the elixir of life, undergoes a meticulous process of vinification before gracing our tables. One of the significant concerns for vintners in white wine production is the browning of the grape must, an undesired outcome that alters the wine's appearance and quality. Historically, sulfur dioxide has been the go-to solution for preventing this browning. However, in light of contemporary health concerns and evolving consumer preferences, the wine industry is keen to explore alternative antioxidants that could potentially replace or reduce sulfur dioxide usage.

A recent study published in the European Food Research and Technology journal delved into this very concern. The research aimed to understand how different antioxidants influence the kinetics of oxygen consumption and the intensity of browning in grape must.

The researchers analyzed two distinct scenarios: grape must from healthy grapes and grape must enriched with laccase to mimic the condition when grapes are infected by the fungus Botrytis cinerea.

Measuring Oxygen Consumption and Browning Intensity

The experimental design was orchestrated to measure the speed of oxygen consumption and the browning intensity prompted by polyphenol oxidases, tyrosinase, and laccase. Predictably, the grape must consumed oxygen and showed browning at a rapid pace, with the presence of laccase accelerating both processes.

The findings corroborated that sulfur dioxide effectively prevents browning, even in grape musts exhibiting high laccase activity levels. Contrastingly, solely utilizing ascorbic acid led to increased oxygen consumption and browning, suggesting its best application in tandem with sulfur dioxide.

Alternative Antioxidants and Their Efficacy

The researchers evaluated alternative antioxidants, such as pure glutathione, inactivated dry yeasts rich in glutathione, and the non-Saccharomyces yeast, Metschnikowia pulcherrima, which acts as a bioprotective agent. These alternatives presented promising avenues for shielding grape must against browning, possibly even lowering sulfur dioxide usage, especially in healthy grapes.

Specifically, both glutathione and the inactivated dry yeast abundant in glutathione diminished oxygen consumption and lessened browning intensity when laccase was absent. However, their efficiency dwindled in the presence of laccase. It is hypothesized that glutathione's protective mechanism against enzymatic browning lies in its ability to combine with orthoquinones produced by polyphenol oxidase action, halting the browning process and depleting the medium's substrates available for these enzymes.

Interestingly, Metschnikowia pulcherrima also mitigated browning intensity. However, its action differs from that of glutathione. This non-Saccharomyces yeast safeguards by proficiently consuming oxygen, thereby reducing its availability for the polyphenol oxidases.

As the wine industry ventures to align with the global call for healthier consumables and a reduction in potentially harmful additives, these promising alternatives to sulfur dioxide warrant further exploration and research.