Live yeast in beer increases its antioxidant activity.

Beer is rich in antioxidants, derived from malt and hops. Much research has been conducted concerning the antioxidant activity of beer in relationship to its flavor stability. Yeast possesses enzymatic and non-enzymatic antioxidant systems that defend against oxygen radicals, in addition to scavenging oxygen to promote the synthesis of cells.

It is well-known that bottle-conditioned beer, which contains live yeast, has a longer shelf life in terms of flavor stability and freshness. Scientists at Oregon State University wanted to determine whether bottle-conditioned beer has a higher antioxidant activity than conventional beer. They also wanted to evaluate the contribution of the antioxidant potential provided specifically from yeast.

Beer wort was prepared, and yeast was added and allowed to ferment. The beer was bottle-conditioned when researchers added a second yeast and sugar. The beer also was artificially carbonated, which was followed with the addition of a second yeast without sugar.

The scientists prepared the control samples by artificially carbonating the product without live yeast. Dissolved oxygen, free and total sulfite, yeast viability and antioxidant capacities were determined by the technologists. Then yeast extracts were prepared, and either size-fractionated, heat-treated, protease-treated or lipid-extracted. The investigators analyzed the extracts for antioxidant activity.

Results indicated there were increases in the level of yeast-synthesized sulfite and decreases in the amount of dissolved oxygen and enhanced yeast viability. The antioxidant activities were higher in bottle-conditioned beers compared to the controls. Researchers observed the same trends for all parameters when they compared the artificially carbonated beers containing live yeast to the controls.

Elevations in the antioxidant activities of beer with live yeast present--live beer--were significant. No single yeast component was a major source of antioxidant activity. Rather, several different yeast components contributed to the effect. While the malt and hops components likely play the major role in promoting the antioxidant activity of beer, live yeast in beer provides a significant increase to antioxidant activity. Moreover, the flavor stability and health benefits from beer containing live yeast may be greater.

Further information. Mark Daeschel, Department of Food Science and Technology, Oregon State University, 240-B Wiegand Hall, Corvallis, OR 97331; phone: [phone]; fax: [phone]; email: [e-mail].