The Interactions Between Rapeseed Lipoxygenase and Native Polyphenolic Compounds in a Model System

The focus of the present research was to study inhibition of lipoxygenase activity by rapeseed native polyphenols and the interactions between those compounds and the enzyme. The enzyme and polyphenolic compounds (polyphenols, phenolic acids) were extracted from rapeseed (Brassica napus) varieties Aviso and PR45DO3. The total phenolic compounds concentration in tested rapeseed was 1,485–1,691 mg/100 g d.m. (dry matter) and the free phenolic acids content in both rapeseed varieties was about 76 μg/100 g d.m. The isolated proteins showed lipoxygenase activity. Prooxidant properties of phenolic compounds in the presence of lipoxygenase and linoleic acid were observed rather in the case of extracts containing a relatively high concentration of miscellaneous polyphenols. Antioxidant properties were recorded in the case of phenolic acid extracts which contain only 1.4–1.9% of phenolics present in raw phenolic extracts. We propose that the prooxidant effect of phenolic compounds comes from quinone and oxidized polyphenols formation. The observed antioxidant activity of phenolic acid extracts is probably due to their ability to scavenge free radicals formed from linoleic acid. However, reduction of lipoxygenase ferric to ferrous ions, which prevent the activation of the enzyme and inhibited its activity, was also observed

Antioxidant synergism and antagonism between tocotrienols, quercetin and rutin in model system

The aim of the study was to reveal antioxidant synergism or antagonism between quercetin, rutin and selected tocotrienols in linoleic acid emulsion. The oxidative stress was generated by 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) or CuSO4; the increase of the concentration of peroxidation products was monitored using fluorescence probe 2,7-dichlorofluorescein (DCF). The antioxidant activity of tested substances depends on the form of the antioxidant (aglycone, glycoside), its concentration, localization in the emulsion, and the factors generating oxidative stress. The synergistic effect occurred when the effectiveness of individual antioxidant was relatively weak and mainly when the concentration of antioxidants was in the physiologically significant range of 1 μM. We suggest that tocotrienols were regenerated by flavonoids. The synergism benefitted from the proximity of the localization of interacting antioxidants (e.g. the presence of one of the antioxidants at the oil-water interface)

Chemical Composition of Seed Oils Recovered from Different Pear (Pyrus communis L.) Cultivars

Lipophilic bioactive compounds in oils recovered from the seeds of eight pear (Pyrus communis L.) cultivars were studied. Oil yield in pear seeds ranged between 16.3 and 31.5 % (w/w) dw. The main fatty acids were palmitic acid (6.13–8.52 %), oleic acid (27.39–38.17 %) and linoleic acid (50.73–63.78 %), all three representing 96–99 % of the total detected fatty acids. The range of total tocochromanols was between 120.5 and 216.1 mg/100 g of oil. Independent of the cultivar, the γ-tocopherol was the main tocochromanol and constituted approximately 88 %. The contents of the carotenoids and squalene were between 0.69–2.99 and 25.5–40.8 mg/100 g of oil, respectively. The β-sitosterol constituted 83.4–87.6 % of total sterols contents, which ranged between 276.4 and 600.1 mg/100 g of oil. Three significant correlations were found between oil yield and total contents of sterols (r = −0.893), tocochromanols (r = −0.955) and carotenoids (r = −0.685) in pear seed oils