title: Tocopherol and tocotrienol analysis in raw and cooked vegetables: a validated method with emphasis on sample preparation.
abstract: Vegetables can be important dietary sources of vitamin E. However, data on vitamin E in raw and cooked vegetables are in part conflicting, indicating analytical pitfalls. The purpose of the study was to develop and validate an HPLC-FLD method for tocochromanol (tocopherols and tocotrienols) analysis equally suitable for raw and cooked vegetables. Significant instability of tocochromanols was observed in raw broccoli and carrot homogenates. Tocochromanols could be stabilized by freeze-drying or ascorbic acid addition prior to homogenization. The optimized protocol for tocochromanol analysis included knife and ball milling of freeze-dried vegetable pieces. Direct acetone extraction of vegetable powders allowed for satisfactory recoveries and precisions. A significant decrease of tocochromanols in baked compared to raw vegetables was shown, the extent of which varied largely between vegetables. For some raw vegetables, such as spinach or broccoli, underestimation of vitamin E in nutrient databases cannot be ruled out and should be examined.
authors.affiliation: Department of Safety and Quality of Fruit and Vegetables, Max Rubner-Institut, Federal Research Institute of Nutrition and Food, Haid-und-Neu-Straße 9, 76131 Karlsruhe, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Knecht
authors.affiliation: Department of Nutritional Behavior, Max Rubner-Institut, Federal Research Institute of Nutrition and Food, Haid-und-Neu-Straße 9, 76131 Karlsruhe, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Sandfuchs
authors.affiliation: Department of Safety and Quality of Fruit and Vegetables, Max Rubner-Institut, Federal Research Institute of Nutrition and Food, Haid-und-Neu-Straße 9, 76131 Karlsruhe, Germany.
authors.forename: Sabine E
authors.initials: SE
authors.lastname: Kulling
authors.affiliation: Department of Safety and Quality of Fruit and Vegetables, Max Rubner-Institut, Federal Research Institute of Nutrition and Food, Haid-und-Neu-Straße 9, 76131 Karlsruhe, Germany. Electronic address: diana.bunzel@mri.bund.de.
authors.forename: Diana
authors.initials: D
authors.lastname: Bunzel
mesh_terms: D001205:Ascorbic Acid / Q000032:analysis; D001937:Brassica / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003296:Cooking; D004032:Diet; D018724:Spinacia oleracea / Q000737:chemistry*; D024505:Tocopherols / Q000032:analysis*; D024508:Tocotrienols / Q000032:analysis*; D014675:Vegetables / Q000737:chemistry*; D014810:Vitamin E / Q000032:analysis
chemical_list: D024508:Tocotrienols; D014810:Vitamin E; D001205:Ascorbic Acid; D024505:Tocopherols
keywords: Enzyme activity; Nutrient databases; Sample preparation; Tocopherol; Tocopherol oxidase; Tocotrienol; Vegetable; Vitamin E