Jan Kyselka

Antioxidant effect of mono- and dihydroxyphenols in sunflower oil with different levels of naturally present tocopherols

Antioxidant properties of mono- and dihydroxyphenolic acids and their alkyl esters were examined, with emphasis on the relationship between their molecular structure and antioxidant activity. Test media with different tocopherol level were used for determining the oxidative stability: original refined sunflower oil (total tocopherols 149.0 mg/kg), partially tocopherol-stripped sunflower oil (total tocopherols 8.7 mg/kg) and distilled fatty acid methyl esters (FAME) as a tocopherol-free medium. The chemical reaction of tocopherols with diazomethane tested for the purpose to eliminate their antioxidant activity failed due to the negligible degree of methylation of hydroxyl group in the tocopherol molecule. Caffeic acid and protocatechuic acid (3,4-dihydroxyphenolic acids) and their alkyl esters were found to be more active antioxidants than monohydroxyphenolic acid (p-hydroxybenzoic acid), 2,5-dihydroxyphenolic acid (gentisic acid), 3-methoxy-4-hydroxyphenolic acids (vanillic and ferulic acids) and their corresponding alkyl esters. Naturally present tocopherols in refined sunflower oil proved to have a synergistic effect on gentisic acid but not on its alkyl esters. In contrast, tocopherols showed an antagonistic effect on alkyl esters of caffeic acid, because their protection factors decreased with increasing level of tocopherols in the test medium. Moreover, the antioxidant activity of these alkyl esters decreased with increasing length of their alkyl chain in conformity with the polar paradox hypothesis. Practical applications: Tocopherols as naturally present antioxidants influence considerably the antioxidant activity of other antioxidants added to plant oils used as a test medium. Distilled fatty acid methyl esters prepared from refined sunflower oil may serve as an optimal tocopherol-free test medium. Some alkyl esters of phenolic acids were evaluated to be applicable as natural more lipophilic antioxidants in comparison with phenolic acids.

Antifungal Polyamides of Hydroxycinnamic Acids from Sunflower Bee Pollen

The aim of the bioassay-guided fractionation was the selection of the most potent group of compounds responsible for the protection of sunflower bee pollen grains. Synthesis of prospective antifungal polyamides of hydroxycinnamic acids was based on previous structural elucidation of ethanol soluble fraction by 1H,1H-PFG-COSY, 1H,13C-HSQC, FT-IR, FT-Raman, and LC-MS experiments. The main compounds found were tri- p-coumaroylspermidines accompanied by other HCAA of spermidine and putrescine. Several model HCAA derivatives were prepared to test their antifungal activity against widespread spoilage fungi ( A. niger 42 CCM 8189, F. culmorum DMF 0103, and P. verrucosum DMF 0023). A. niger CCM 8189 and F. culmorum DMF 0103 exhibited higher resistance to the antifungal effects of hydroxycinnamic acid amides, whereas P. verrucosum DMF 0023 was the most sensitive strain. It has been discovered the effect of HCAA polarity on the role of secondary metabolites in the microbial protection of pollen grains. The combination of bioassay-guided fractionation, structural elucidation, selection of prospective compounds, and their synthesis to determine their antifungal properties could be considered as an original approach.

Preparation of conjugated linoleic acid enriched derivatives by conventional and biphasic isomerisation

Kyselka J., Thomes L., Remišová S., Dragoun M., Berčíková M., Filip V. (2016): Preparation of conjugated linoleic acid enriched derivatives by conventional and biphasic isomerisation. Czech J. Food Sci., 34: 511–521. The preparation of conjugated linoleic acid (CLA)-enriched free fatty acids by industrial processes compared with our biphasic isomerisation experiments in a special designed reactor enabling the preparation of CLA esters was evaluated. Our experiments further revealed the main disadvantage of semi-synthetic alkali isomerisation to be the formation of conjugated E,E-octadecadienoic acid isomers (2.92–3.44%) and the bioavailability of free fatty acid products. Urea fractionation technology improved the quality of the reaction mixture, but at the same time the yield of rumenic acid was decreased on purification. Therefore, we decided to apply complexes of noble metals in order to isomerise linoleic acid ester derivatives. The known Wilkinson’s hydrogenation catalyst, RhCl (PPh3)3, was found to be the most effective. We investigated the preparation of bioavailable CLA-enriched triacylglycerols. Special attention was paid to recycling of Wilkinson’s catalyst.