Investigate oxidative stability of phytosterols.

Phytosterols are plant-derived compounds that are similar in structure and function to cholesterol. Although early human diets were rich in phyotosterols, as much as 1 g per day, the typical Western diet currently is relatively low in phytosterol content. Phytosterols inhibit the intestinal absorption of cholesterol. Numerous clinical trials have demonstrated that consuming foods, on a daily basis, that are enriched with at least 0.8 g of plant sterols or stanols lowers serum LDL cholesterol.

The oxidative stability of phytosterols as lipid compounds can be defined as their resistance to oxidation. Phytosterol oxidation products (oxyphytosterols) may be formed during the processing and storage of foods. Researchers in Finland studied the oxidative stability of phytosterols that occur during the processing and long-term storage of phytosterol-enriched milk powder and heat-treated milk, and in microcrystalline phytosterol suspensions in different fats and oils.

All of these products were stable, in spite of the heat treatments used in their processing and long-term storage, even at slightly elevated temperatures. The largest change in the phytosterol oxide content was found in phytosterol-enriched milk powder that had been stored at 38 C for 12 months. During this period, the amount of phytosterol oxidation grew from 0.03% to 0.07%. The investigators concluded that the formation of phytosterol oxides did not seem to be a limiting factor for the manufacture and subsequent storage of the food products they tested.

Some epidemiological studies have found that a higher intake of plant foods containing phytosterols is associated with a decreased risk of cancer. But it is not clear whether phytosterols or other compounds in plant foods are the protective sources.

Further information. Vieno Piironen, Department of Applied Chemistry and Microbiology, University of Helsinki, Latokartanonkaari 11, P.O. Box 27, 00014, Helsinki, Finland; phone: [phone]; fax: [phone]; email: [e-mail].