Rapid Estimation of Tocopherol Content in Linseed and Sunflower Oils-Reactivity and Assay.
The reactivity of tocopherols with 2,2-diphenyl-1-picrylhydrazyl (DPPH) was studied in model systems in order to establish a method for quantifying vitamin E in plant oils. The method was optimized with respect to solvent composition of the assay medium, which has a large influence on the course of reaction of tocopherols with DPPH. The rate of reaction of α-tocopherol with DPPH is higher than that of γ-tocopherol in both protic and aprotic solvents. In ethyl acetate, routinely applied for the analysis of antioxidant potential (AOP) of plant oils, reactions of tocopherols with DPPH are slower and concentration of tocopherols in the assay has a large influence on their molar reactivity. In 2-propanol, however, two electrons are exchanged for both α- and γ-tocopherols, independent of their concentration. 2-propanol is not toxic and is fully compatible with polypropylene labware. The chromatographically determined content of tocopherols and their molar reactivity in the DPPH assay reveal that only tocopherols contribute to the AOP of sunflower oil, whereas the contribution of tocopherols to the AOP of linseed oil is 75%. The DPPH assay in 2-propanol can be applied for rapid and cheap estimation of vitamin E content in plant oils where tocopherols are major antioxidants.
Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, Ljubljana 1000, Slovenia. Tjasa.Prevc@bf.uni-lj.si.
Tjaša
T
Prevc
Department of Animal Science, Biotechnical Faculty, University of Ljubljana, Groblje 3, Domžale 1230, Slovenia. Alenka.Levart@bf.uni-lj.si.
Alenka
A
Levart
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, Ljubljana 1000, Slovenia. irena.kralj-cigic@fkkt.uni-lj.si.
Irena Kralj
IK
Cigić
Department of Animal Science, Biotechnical Faculty, University of Ljubljana, Groblje 3, Domžale 1230, Slovenia. janez.salobir@bf.uni-lj.si.
Janez
J
Salobir
Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, Ljubljana 1000, Slovenia. natasa.poklarulrih@bf.uni-lj.si.
Nataša Poklar
NP
Ulrih
Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, Ljubljana 1000, Slovenia. blaz.cigic@bf.uni-lj.si.
Blaž
B
Cigić
D019840:2-Propanol / Q000737:chemistry; D000085:Acetates / Q000737:chemistry; D000975:Antioxidants / Q000032:analysis; D001681:Biological Assay / Q000379:methods*; D001713:Biphenyl Compounds / Q000737:chemistry; D019597:Flax / Q000737:chemistry*; D007700:Kinetics; D010084:Oxidation-Reduction; D010851:Picrates / Q000737:chemistry; D010938:Plant Oils / Q000737:chemistry*; D012997:Solvents; D000074242:Sunflower Oil; D024505:Tocopherols / Q000032:analysis*; D014810:Vitamin E / Q000032:analysis; D024502:alpha-Tocopherol / Q000032:analysis; D024504:gamma-Tocopherol / Q000032:analysis
D000085:Acetates; D000975:Antioxidants; D001713:Biphenyl Compounds; D010851:Picrates; D010938:Plant Oils; D012997:Solvents; D000074242:Sunflower Oil; D014810:Vitamin E; C007650:ethyl acetate; D024504:gamma-Tocopherol; C004931:1,1-diphenyl-2-picrylhydrazyl; D024502:alpha-Tocopherol; D019840:2-Propanol; D024505:Tocopherols
DPPH; antioxidants; plant oil; solvent; vitamin E; α-tocopherol; γ-tocopherol