Examine oxidation properties of structured lipids.

Structured lipids chemically consist of medium-chain fatty acids and long-chain fatty acids attached to a glycerol backbone. The function and properties of structured lipids depend on the type of fatty acid moieties present and the position of their attachment to the backbone. Long-chain fatty acids offer certain functional properties they impart to the final product or have a biological function once they are ingested. Medium-chain fatty acids are a readily available source of energy that, in general, does not contribute to fat storage.

Structured lipids can be used to replace the oil in nutritional beverages. The structured lipid can be used as a delivery mechanism for essential fatty acids and improved absorption. But it would be necessary to determine if the lipid changes the sensory profile of the nutritional beverage when it is used in place of canola oil, for example. Additionally, the oxidation properties of structured lipid-based oil-in-water emulsions have to be examined before they can be incorporated into commercial beverage formulations. But there are indications that a canola oil-caprylic acid structured lipid may be suitable for use in nutritional beverages.

Scientists at the University of Georgia synthesized a structured lipid from canola oil and caprylic acid in a bioreactor packed with a sn-1,3 specific lipase from Rhizomucor miehei. Differences between beverages formulated with structured lipids and canola oil were determined using a triangle test and quantitative descriptive analysis.

The researchers formulated 10% oil-in-water emulsions with structured lipids, [alpha]-tocopherol, [beta]-carotene, genistein and daidzein, and then stabilized them using 0.5% whey protein isolate (WPI) or sucrose fatty acid ester (SFE). The peroxide values, anisidine values and total oxidation values of emulsions stored at 50 C were measured during a 30-day period.

Substituting the lipids for unmodified canola oil significantly enhanced the perception of sweetness and decreased the formation of bubbles in the emulsions. Significantly less total oxidation occurred in the WPI emulsions compared to their SFE counterparts. [beta]-carotene did not affect the oxidation of WPI emulsions. [alpha]-tocopherol, genistein and daidzein significantly increased secondary oxidation. All four natural compounds exhibited pro-oxidant activity in the SFE emulsions

WPI provided both emulsification and antioxidant properties to the structured lipid-based emulsions. However, [alpha]-tocopherol, [beta]-carotene, genistein and daidzein exhibited pro-oxidant activity in some emulsions.

Further information. Casimir Akoh, Department of Food Science and Technology, University of Georgia, Food Science Building, Athens, GA 30602; phone: [phone]; fax: [phone]; email: [e-mail].