Yeast extracts inhibit lipid oxidation in cooked beef patties.

Many proteins and protein hydrolysates possess antioxidant activity in food model systems. As you may know, yeast extract is the common name for yeast autolysates. These are concentrations of yeast cells that are allowed to die and break up. When this happens, the yeasts' digestive enzymes break their proteins down into simpler compounds.

Yeast autolysates are used in Vegemite, Marmite and Cenovis, three spreads that are popular in Australia, the United Kingdom and Switzerland. Autolyzed yeast extract is also the primary source of monosodium glutamate. Yeast extract is a good source of vitamin B12.

Yeast extracts are natural ingredients that are enjoying vast popularity due to their excellent organoleptic qualities and their role as flavor enhancers. As new hydrolyzed yeasts or yeast extracts are increasingly produced as flavoring agents for food applications, research is needed to evaluate their potential antioxidant activity in food systems.

Scientists at the University of Kentucky wanted to determine the in situ antioxidant activity of two commercial yeast extracts in cooked beef patties. They divided fresh, homogenous salt-free ground beef into five equal portions. One was used to prepare control meat patties that did not contain any yeast extract. Four were treated with yeast extracts A and B at levels of 0.1%, 0.5%, 1.0% or 1.5%.

Thiobarbituric acid-reactive substances (TBARS) were measured in cooked patties while they were refrigerated at 5 C for up to 7 days. The total antioxidant reducing capacity of both yeast extracts was also analyzed using the ferric reducing-antioxidant power (FRAP) assay. The yeast extracts suppressed TBARS formation in the stored cooked beef patties. The amount of yeast extract enhanced the extent of inhibition, but no difference was seen between yeast extracts A and B.

The scientists observed a 17% to 20% reduction in TBARS values, with a 1.5% addition of yeast in beef patties stored for seven days. FRAP values, not affected by sodium chloride, increased as the concentration of yeast extract increased, indicating that both yeast extracts created a dose-dependent inhibitory activity. The antioxidant activity present in both yeast extracts indicates they have potential to improve the oxidative stability of foods, which is an added benefit to their main role as flavor enhancers.

Further information. Youling Xiong, Department of Animal Sciences, Room 206 W. P. Garrigus Building, University of Kentucky, Lexington, KY 40546; phone: [phone]; fax: [phone]; email: [e-mail].