Factors affecting the development of antioxidant properties of malts during the malting and roasting process

Abstract

The total antioxidant activities (taa) of pale and speciality malts were determined. Varieties grown in the U.K. (1998 harvest) did not show differences in the taa when malted under similar conditions. Both the winter and the spring barleys showed similar antioxidant potential.

The processing methods employed during the malting of pale malts were shown to affect the antioxidant yield. Standard malt kilning regimes, with proteolytic and amylolytic rests, did not increase the taa. Under the constraints of the standard kilning regimes, higher modification with quicker drying after the ‘break period’ shows an increase in taa. The antioxidant profile of the barley was very similar to that of the malt, suggesting a major contribution from the natural antioxidants found in barley. The contribution from heat-induced malt antioxidants formed during kilning is minor.

In the case of coloured malts, the taa was found to correlate with colour up to a malt colour of 400°EBC. Above this limit, no further increase in total antioxidant activity was observed. A relationship between temperature and moisture levels during the roasting process and the production of antioxidants was noted. This association was tested for a low colour crystal malt (39°EBC) and a high colour crystal malt (220°EBC). The antioxidant yield dramatically increased at moisture levels below 5%, suggesting that a quicker drying period after the stewing stage would be more favourable for increasing taa. For black malts (1750°EBC), the higher grain temperatures employed during roasting resulted in a higher taa in the malt. Coloured malt antioxidant profile showed that both natural and heat induced antioxidants are present. However the level of antioxidants vary in different malt types.

Limiting the contact with oxygen during mashing and throughout brewing was achieved using a CO₂ blanket. This had the effect of reducing oxidation, thus maintaining antioxidant concentration and reduction potential in the final beer. The use of reducing agents in the brew also helped to maintain taa levels throughout the brewing process. A comparison of antioxidant profiles also showed that most of the antioxidants found in malt were also present in beer. Malt was also found to be the main source of antioxidants in beer.