Influence of thermal treatment on phenolic compounds and antioxidant properties of oak acorns from Serbia |
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Authors: | Sveto Raki? Silvana Petrovi? Jelena Kuki? Milka Jadranin Vele Teševi? Dragan Povrenovi? Slavica Šiler-Marinkovi? |
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Affiliation: | 1. Department of Food Technology and Biochemistry, Faculty of Agriculture, Nemanjina 6, 11080 Belgrade, Zemun, Serbia and Montenegro;2. Institute of Pharmacognosy, Faculty of Pharmacy, Vojvode Stepe 450, 11221 Belgrade, Serbia and Montenegro;3. Institute for Chemistry, Technology and Metallurgy, Njegoševa 12, 11000 Belgrade, Serbia and Montenegro;4. Faculty of Chemistry, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia and Montenegro;5. Faculty of Technology and Metallurgy, Karnegieva 4, 11000 Belgrade, Serbia and Montenegro |
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Abstract: | The aim of the present work was to investigate and compare phenolic compounds and antioxidant activity of methanol extracts of Quercus robur and Quercus cerris acorn kernels obtained before and after thermal treatment. Content of total phenolics, tannins, non-tannin phenolics and flavonoids was determined spectrophotometrically and content of gallic acid with HPLC. Antioxidant activity of the samples was assayed through FRAP (Ferric Reducing Antioxidant Power), DPPH scavenging test and inhibition of Fe2+/ascorbate induced lipid peroxidation. Extracts of native and thermally treated kernels showed high antioxidant activity, with extracts of thermally treated kernels being more active than extracts of native ones. Hydrolysable tannins and gallic acid were identified in all samples. Non-tannin phenolics, including gallic acid, were present in significantly higher quantities in thermally treated samples, whilst tannin content decreased. This indicates that during thermal treatment hydrolysable tannins were degraded. As the result of this degradation and consequent increase of non-tannin phenolics content, and amongst them especially gallic acid, thermally treated samples possess higher antioxidant activity than do the native ones. The obtained results have provided further grounds for establishing Q. robur and Q. cerris acorn kernels as a source for functional food preparation. |
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Keywords: | Quercus robur Quercus cerris Acorn kernel Antioxidant activity FRAP DPPH Lipid peroxidation Gallic acid |
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