Michael H. Gordon

Antioxidant activity and mechanism of action of thymol and carvacrol in two lipid systems

The autoxidation of purified triacylglycerols of lard and sunflower oil (TGL and TGSO) containing 0.02, 0.05, 0.10 and 0.20% thymol and carvacrol was studied at ambient temperature. The results obtained with the inhibited lipid systems (thymol - TGL; carvacrol - TGL; thymol - TGSO and carvacrol - TGSO) showed that thymol had the highest antioxidant effectiveness and activity during TGSO oxidation. Thymol and carvacrol participated in one side reaction during inhibited TGL oxidation, and thymol took part in two side reactions during TGSO oxidation. Carvacrol molecules did not participate in side reactions during TGSO oxidation. Thymol and carvacrol contributed to chain initiation to a higher degree during TGSO oxidation than during TGL oxidation. Thymol radicals did not participate in chain propagation during TGL and TGSO oxidation. Carvacrol radicals took part in one reaction of chain propagation in both lipid systems. In general, during autoxidation of lipids at ambient temperature, thymol is a more effective and more active antioxidant than carvacrol. Both antioxidants differ in the mechanism of their inhibiting action which depends on the character of the lipid medium. Thymol is a better antioxidant in TGSO than in TGL, whereas the activity of carvacrol in the two lipid systems does not differ significantly.

Antioxidants in Food : Practical Applications

Part 1 Antioxidants and food stability: The development of oxidative rancidity in foods Inhibiting oxidation Measuring antioxidant activity. Part 2 Antioxidants and health: Cardiovascular disease and nutritional phenolics Antioxidants and anti-tumour properties Predicting the bioavailability of antioxidants in food: the case of carotenoids. Part 3 Natural antioxidants: Introducing natural antioxidants Sources of natural antioxidants: oilseeds, nuts, cereals, legumes, animal products and microbial sources Sources of natural antioxidants: vegetables, fruits, herbs, spices and teas. Part 4 Practical applications: Regulation of antioxidants in food Use of natural antioxidants in food products Preparation of natural antioxidants Natural antioxidant functionality during food processing.

Antioxidants in food

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Effect of antioxidants on losses of tocopherols during deep-fat frying

Abstract The changes in tocopherol content of oil used for deep-fat frying of potatoes have been studied. It has been found that α-tocopherol is lost much faster than β-, γ- or δ tocopherol, with a reduction of 50% α-tocopherol after 4–5 frying operations compared with values of about 7 and 7–8 frying operations for β- and γ-tocopherol, respectively, in the absence of added antioxidants. However, the presence of a rosemary extract or ascorbyl palmitate in the frying oil caused a marked reduction in the rate of loss of the tocopherols.

ANTIOXIDANT ACTIVITY OF QUERCETIN AND MYRICETIN IN LIPOSOMES

The antioxidant activity during storage at 30 degrees C of quercetin, myricetin and alpha-tocopherol in small unilamellar liposomes has been investigated. Myricetin was more effective than alpha-tocopherol as an antioxidant in liposomes under all conditions studied. At pH 5.4 with a concentration of 10(-2) mol/mol phospholipid, myricetin has been shown to be the strongest antioxidant followed by quercetin and alpha-tocopherol. Cupric chloride and ferric chloride strongly reduced the antioxidant activity of myricetin and quercetin with cupric chloride causing a stronger reduction in activity than ferric chloride. At a pH of 7.4, quercetin was less effective than alpha-tocopherol at a concentration of 10(-2) mol/mol phospholipid, but its activity increased more strongly with concentration and it was very effective at a concentration of 5 x 10(-2) mol/mol phospholipid.

Flavonoid-rich fruit and vegetables improve microvascular reactivity and inflammatory status in men at risk of cardiovascular disease—FLAVURS: a randomized controlled trial

BACKGROUND Observed associations between increased fruit and vegetable (F&V) consumption, particularly those F&Vs that are rich in flavonoids, and vascular health improvements require confirmation in adequately powered randomized controlled trials. OBJECTIVE This study was designed to measure the dose-response relation between high-flavonoid (HF), low-flavonoid (LF), and habitual F&V intakes and vascular function and other cardiovascular disease (CVD) risk indicators. DESIGN A single-blind, dose-dependent, parallel randomized controlled dietary intervention study was conducted. Male and female low-F&V consumers who had a ≥ 1.5-fold increased risk of CVD (n = 174) were randomly assigned to receive an HF F&V, an LF F&V, or a habitual diet, with HF and LF F&V amounts sequentially increasing by 2, 4, and 6 (+2, +4, and +6) portions/d every 6 wk over habitual intakes. Microvascular reactivity (laser Doppler imaging with iontophoresis), arterial stiffness [pulse wave velocity, pulse wave analysis (PWA)], 24-h ambulatory blood pressure, and biomarkers of nitric oxide (NO), vascular function, and inflammation were determined at baseline and at 6, 12, and 18 wk. RESULTS In men, the HF F&V diet increased endothelium-dependent microvascular reactivity (P = 0.017) with +2 portions/d (at 6 wk) and reduced C-reactive protein (P = 0.001), E-selectin (P = 0.0005), and vascular cell adhesion molecule (P = 0.0468) with +4 portions/d (at 12 wk). HF F&Vs increased plasma NO (P = 0.0243) with +4 portions/d (at 12 wk) in the group as a whole. An increase in F&Vs, regardless of flavonoid content in the groups as a whole, mitigated increases in vascular stiffness measured by PWA (P = 0.0065) and reductions in NO (P = 0.0299) in the control group. CONCLUSION These data support recommendations to increase F&V intake to ≥ 6 portions daily, with additional benefit from F&Vs that are rich in flavonoids, particularly in men with an increased risk of CVD.

Dietary supplementation with a natural carotenoid mixture decreases oxidative stress

Objective: To determine whether dietary supplementation with a natural carotenoid mixture counteracts the enhancement of oxidative stress induced by consumption of fish oil.Design: A randomised double-blind crossover dietary intervention.Setting: Hugh Sinclair Unit of Human Nutrition, School of Food Biosciences, The University of Reading, Whiteknights PO Box 226, Reading RG6 6AP, UK.Subjects and intervention: A total of 32 free-living healthy nonsmoking volunteers were recruited by posters and e-mails in The University of Reading. One volunteer withdrew during the study. The volunteers consumed a daily supplement comprising capsules containing fish oil (4 × 1 g) or fish oil (4 × 1 g) containing a natural carotenoid mixture (4 × 7.6 mg) for 3 weeks in a randomised crossover design separated by a 12 week washout phase. The carotenoid mixture provided a daily intake of β-carotene (6.0 mg), α-carotene (1.4 mg), lycopene (4.5 mg), bixin (11.7 mg), lutein (4.4 mg) and paprika carotenoids (2.2 mg). Blood and urine samples were collected on days 0 and 21 of each dietary period.Results: The carotenoid mixture reduced the fall in ex vivo oxidative stability of low-density lipoprotein (LDL) induced by the fish oil (P=0.045) and it reduced the extent of DNA damage assessed by the concentration of 8-hydroxy-2′-deoxyguanosine in urine (P=0.005). There was no effect on the oxidative stability of plasma ex vivo assessed by the oxygen radical absorbance capacity test. β-Carotene, α-carotene, lycopene and lutein were increased in the plasma of subjects consuming the carotenoid mixture. Plasma triglyceride levels were reduced significantly more than the reduction for the fish oil control (P=0.035), but total cholesterol, HDL and LDL levels were not significantly changed by the consumption of the carotenoid mixture.Conclusions: Consumption of the natural carotenoid mixture lowered the increase in oxidative stress induced by the fish oil as assessed by ex vivo oxidative stability of LDL and DNA degradation product in urine. The carotenoid mixture also enhanced the plasma triglyceride-lowering effect of the fish oil.Sponsorship: The study was supported by funding from the Greek Studentship Foundation and from Unilever Bestfoods plc. Carotenoids were contributed by Overseal Foods plc.

Antioxidant activity of extracts from old tea leaves

Abstract The effect of methanolic extracts of old tea leaves (OTL) (leaves numbers 5–8 of the shoots) on the stability of rapeseed oil during heating at 60°C and deep-fat frying of potato crisps at 180°C was determined. The OTL extract was effective in retarding oil deterioration at 60°C, with activity increasing with concentration in the range 0.02–0.25%. At a concentration of 0.25% the OTL extract was similar in activity to a rosemary extract added at 0.1%. The OTL extract (0.1%) was as active in retarding the deterioration of oil as a rosemary extract (0.1%) during repeat frying of potato crisps. Hence it is clear that old tea leaves, which at present are often considered as agricultural waste, contain antioxidants that may usefully be extracted and added to foods.

A comparison of oil stability based on the metrohm rancimat with storage at 20°C

The induction time for oxidative stability by the Rancimat method has been compared with peroxide development during storage at 20°C for six edible oils and rapeseed oil samples with added metal ions, antioxidants or phosphatidylethanolamine. The Rancimat method correlated highly (r=0.966;P=0.000) with oil stability measured by peroxide development for all samples except the oils containing added phosphatidylethanolamine or added butylated hydroxytoluene.

Absorption and metabolism of olive oil secoiridoids in the small intestine

The secoiridoids 3,4-dihydroxyphenylethanol-elenolic acid (3,4-DHPEA-EA) and 3,4-dihydroxyphenylethanol-elenolic acid dialdehyde (3,4-DHPEA-EDA) account for approximately 55 % of the phenolic content of olive oil and may be partly responsible for its reported human health benefits. We have investigated the absorption and metabolism of these secoiridoids in the upper gastrointestinal tract. Both 3,4-DHPEA-EDA and 3,4-DHPEA-EA were relatively stable under gastric conditions, only undergoing limited hydrolysis. Both secoiridoids were transferred across a human cellular model of the small intestine (Caco-2 cells). However, no glucuronide conjugation was observed for either secoiridoid during transfer, although some hydroxytyrosol and homovanillic alcohol were formed. As Caco-2 cells are known to express only limited metabolic activity, we also investigated the absorption and metabolism of secoiridoids in isolated, perfused segments of the jejunum and ileum. Here, both secoiridoids underwent extensive metabolism, most notably a two-electron reduction and glucuronidation during the transfer across both the ileum and jejunum. Unlike Caco-2 cells, the intact small-intestinal segments contain NADPH-dependent aldo-keto reductases, which reduce the aldehyde carbonyl group of 3,4-DHPEA-EA and one of the two aldeydic carbonyl groups present on 3,4-DHPEA-EDA. These reduced forms are then glucuronidated and represent the major in vivo small-intestinal metabolites of the secoiridoids. In agreement with the cell studies, perfusion of the jejunum and ileum also yielded hydroxytyrosol and homovanillic alcohol and their respective glucuronides. We suggest that the reduced and glucuronidated forms represent novel physiological metabolites of the secoiridoids that should be pursued in vivo and investigated for their biological activity.