Blueberry wine: how processing affects nutritional value

Blueberries are rich in nutritional content, including vitamins, fibre and bioactive compounds, which is one of the reasons why they are ingredients in an increasing number of foods and beverages — including wine. However, the effects of the vinification process of blueberry wine, specifically fermentation and heat, on these compounds and their antioxidant activity (ie, the ability to reduce damaging free radicals) have not been thoroughly studied.

Researchers in ACS Food Science & Technology have now examined fermentation’s effects on the bioactive compounds and antioxidant activity in blueberry wine. The results suggest blueberry wine maintains some of the fruit’s nutrients and the team identifies ways to optimise components.

Maria Serratosa and colleagues started their investigation with 8 L of blueberry juice from fruit grown in southern Spain and separated it into 1 L flasks. The researchers placed four flasks in a 17°C water bath and the other four flasks in a 21°C water bath. Two flasks in each water bath underwent a long (complete) fermentation to produce dry wine, and the other two flasks underwent a short (partial) fermentation to produce sweet wine. The team measured and compared bioactive compound levels in the initial juice and in the final product. They used a common free-radical-scavenging assay to measure and compare the antioxidant activity of the bioactive compounds in the juice and wines.

Specifically, they looked at: anthocyanins: antioxidants responsible for red wine’s colour; flavonols; flavan-3-ols; tannins that produce an astringent flavour in wine; and vitamin C.

The researchers found that anthocyanins, tannins and flavanol concentrations decreased with longer fermentation times. Conversely, levels of flavan-3-ol increased with fermentation time. However, fermentation time did not appear to affect the amount of vitamin C in the wines. Rather, wine kept at 21°C had about half as much vitamin C as wine kept at 17°C. And finally, while antioxidant levels generally decreased, all wines still exhibited higher antioxidant activity than the initial blueberry juice.

Overall, fermenting blueberry juice can create a wine that maintains benefits of the fruit, but temperature and fermentation time can influence the nutrient content of the final product, the researchers said.

The findings have been published in the journal ACS Food Science & Technology.

Image credit: iStock.com/5PH