The secondary structure of human apolipoprotein B at 37 degrees C is estimated to be 24% alpha-helix, 23% beta-sheet, 6% beta-turns, 24% unordered structure, and 24% "beta-strands," characterized by a band around 1618 cm-1, and consistent with extended string-like chains in contact with the lipid moiety not forming beta-sheets. When cooled to a temperature below the cholesteryl ester transition at 30 degrees C, the ordering of the low density lipoprotein core results in reversible changes in the protein conformation, decreasing the apparent amount of alpha-helix, beta-strand, and unordered structure below 30 degrees C and increasing beta-sheet and beta-turns. Lowering the ionic strength affects the core-associated transitions, shifting their temperature from 30 to 20 degrees C, and modifying protein conformation below the transition. An additional thermal event is observed at 75 degrees C, leading to irreversible protein denaturation. In the broad temperature range between the 30 and 75 degrees C transitions, apolipoprotein B is stable toward both temperature and ionic strength changes. After thermal denaturation, the protein retains a certain degree of ordered structure.
In this study, essential oils from wild‐grown caper (Capparis spinosa L.) and sea fennel (Crithmum maritimum L.) from Dalmatia (Croatia) were isolated by hydrodistillation and analyzed by gas chromatography with mass spectrometry. Methyl isothiocyanate (92.06%) was detected as major component of essential oil from caper leaves and flower buds, while limonene (58.37%), sabinene (26.46%), terpinene‐4‐ol (5.59%) and γ‐terpinene (2.81%) were identified as dominant compounds in sea fennel essential oil. Tested essential oils did not exhibit radical‐scavenging activity by 1,1‐diphenyl‐2‐picrylhydrazyl hydrate method, while they showed the antioxidant activity by β‐carotene bleaching method and thiobarbituric acid reactive species assay. In addition, sea fennel essential oil exhibited very high inhibitory effect on the oxidation of human low‐density lipoprotein.
PRACTICAL APLICATIONS
Antioxidants are indispensable for the food preservation from oxidative deterioration, as well as for the protection of unsaturated lipids in animal and human tissues. Therefore, the usage of essential oil in foods, which may act as natural antioxidant preservatives, may prolong the shelf life of relevant food products, as well as influence on health of consumers. Essential oils from caper and sea fennel represent alternative for synthetic antioxidants and potential of functional food.
In this study, the antioxidative capacity effect of essential oils and aqueous tea infusions obtained from oregano, thyme and wild thyme on the oxidation susceptibility of low-density lipoproteins (LDL) has been studied. The results indicate a dose-dependent protective effect of the tested essential oils and aqueous tea infusions on the copper-induced LDL oxidation. The protective effect of essential oils is assigned to the presence of phenolic monoterpenes, thymol and carvacrol, which are identified as the dominant compounds in these essential oils. The strong protective effect of aqueous tea infusions is proposed to be the consequence of large amounts of polyphenols, namely rosmarinic acid and flavonoids (quercetin, eriocitrin, luteolin-7-O-glucoside, apigenin-7-O-glucoside, luteolin, apigenin), with the most pronounced effect in the case of oregano. These findings may have implications for the effect of these compounds on LDL in vivo.
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