30A-33 |
Partitioning of d-tocopherol in aqueous mixtures of triacylglycerols and isolated membranes |
H. SIGFUSSON, Food and Agricultural Products Research & Technology Center, Oklahoma State University, FAPC RM 106, Stillwater, OK 74078-6055 and H. O. Hultin, Department of Food Science, University of Massachusetts, Amherst, UMass Marine Station, 932 Washington St., Gloucester, MA 01930. Antioxidants are added to foods to retard oxidative deterioration. The antioxidant partitioning between the different food components is important as this determines its efficiency. The objective was to determine partitioning of d-tocopherol in aqueous suspensions of membrane lipids, mixtures of membranes and triacylglycerols (TAG), and the exchange of tocopherol between these lipids. TAG were obtained by heating minced chicken depot fat in a thermostated water bath for 30 min at 45°C. Membranes were isolated from minced, enzyme-treated muscle by collecting the fraction obtained between 10,000 g for 20 min and 130,000 g for 30 min, followed by suspension in buffer (pH 7.5). d-Tocopherol was mixed either with an aqueous membranes suspension, or an aqueous mixture of membranes and TAG. After mixing, the different lipids were then separated by centrifugation. Protein content of lipid suspensions was determined by means of the Biuret reaction. Total lipids were determined by weight after extraction with organic solvents and phospholipids were estimated by determining the phosphorus content of the lipid extract. Tocopherols were separated and quantified using normal-phase HPLC with fluorescence detection. When added to aqueous suspension of membranes, the d-tocopherol in the membranes increased linearly with tocopherol concentration. The membranes incorporated or bound up to 50% of the added tocopherol. The tocopherol partitioning in this system was independent of incubation temperature in the range of 0-37°C. Studies with the mixed lipid systems suggested a low exchange of tocopherol between the different lipid fractions when the tocopherol resided initially in one lipid fraction. Adding d-tocopherol in ethanol favored its incorporation into the membranes; there was little incorporation of antioxidant into membranes when it was added to the suspensions in oil. The results suggest that partitioning of exogenous d-tocopherol between TAG and membrane lipids in foods may be controlled by proper selection of the antioxidant.
Session 30A, Food Chemistry: Lipids
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