Lipid-binding proteins have little effect on flavor stability of beer.

The ability to form a stable head of foam and the flavor characteristics of beer are important factors that influence how a consumer judges beer quality. Both of these characteristics are affected by the lipid content of beer. The oxidation of lipids contributes to off-flavor development, while lipid interactions with the protein films that stabilize the gas bubbles of foam are thought to cause the foam to collapse.

Beer lipids can originate from the malt or yeast, with levels as low as 0.2 to 0.4[micro] g per ml adversely affecting flavor and foam quality. Consumers often return a beer because of problems with off-flavors and foam head. Any reduction in returns would represent significant financial savings to the brewing industry. And, improved product quality and shelf life would assist sales.

Despite its importance in determining beer quality, little is known about the state of lipid in beer-whether it is free or bound to other components, such as proteins and polypeptides-and how that state affects the product's quality. There is evidence that proteins able to bind lipid, such as puroindoline, can aid the recovery of beer foam that has been adversely affected by lipid. Other proteins, such as lipid-transfer proteins (LTPs), play a role in beer foam formation. Protein-bound lipid is not as damaging to foam as free lipid, although scientists do not know the impact effect of protein binding on lipid oxidation.

Scientists at the Institute of Food Research set out to understand the nature and characteristics of lipid-protein interactions in beer and their relation to quality. Identifying any effect of bound lipid on beer quality could lead directly to the development of strategies that can be used to improve beer foam and flavor stability.

The lipid-binding proteins had little effect on flavor stability, but the researchers identified the major lipid binding protein in beer, and it had a positive effect on foam stability. They determined the effect of processing on its functionality and followed its activity through a pilot plant. However the research was never taken further forward, as it was not deemed commercially viable to modify the process for only a potentially small increase in foam stability.

Further information. Dr. Peter Wilde, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, England, U.K.; phone: +44 1603 255000; fax: +44 1603 507723; email: peter.wilde@bbsrc.ac.uk.