Epidemiological evidence suggests that a high intake of plant foods is associated with lower risk of chronic diseases. However, the mechanism of action and the components involved in this effect have not been identified clearly. In recent years, the scientific community has agreed to focus its attention on a class of secondary metabolites extensively present in a wide range of plant foods: the flavonoids, suggested as having different biological roles. The antiinflammatory actions of flavonoids in vitro or in cellular models involve the inhibition of the synthesis and activities of different pro-inflammatory mediators such as eicosanoids, cytokines, adhesion molecules and C-reactive protein. Molecular activities of flavonoids include inhibition of transcription factors such as NF-kB and activating protein-1 (AP-1), as well as activation of nuclear factor-erythroid 2-related factor 2 (Nrf2). However, the in vitro evidence might be somehow of limited impact due to the non-physiological concentrations utilized and to the fact that in vivo flavonoids are extensively metabolized to molecules with different chemical structures and activities compared with the ones originally present in the food. Human studies investigating the effect of flavonoids on markers of inflammation are insufficient, and are mainly focused on flavonoid-rich foods but not on pure molecules. Most of the studies lack assessment of flavonoid absorption or fail to associate an effect on inflammation with a change in circulating levels of flavonoids. Human trials with appropriate placebo and pure flavonoid molecules are needed to clarify if flavonoids represent ancillary ingredients or key molecules involved in the anti-inflammatory properties of plant foods.

The purpose of this double-blind study was to investigate the influence of adding a quercetin-containing supplement to the diet on plasma quercetin status, serum/platelet fatty acid levels and risk factors for heart disease. Healthy men and women with cholesterol levels of 4.0-7.2 mmol/L, consumed four capsules daily of either a quercetin-containing supplement (1.0 g quercetin/d) or rice flour placebo for 28 d. Quercetin intakes were approximately 50-fold greater than the dietary intakes associated with lower coronary heart disease mortality on the basis of epidemiologic studies. Subjects consuming quercetin-containing capsules had plasma quercetin concentrations approximately 23-fold higher than those of subjects consuming the control capsules. Quercetin supplementation did not modify serum total, LDL or HDL cholesterol or triglyceride levels. There were also no alterations of other cardiovascular disease or thrombogenic risk factors, including platelet aggregation, platelet thromboxane B2 production, blood pressure or resting heart rate. Furthermore, there was no effect on the levels of (n-6) or (n-3) polyunsaturated fatty acids in serum or platelet phospholipids. In conclusion, supplementation with quercetin-containing capsules markedly enhanced the plasma quercetin concentration but had no effect on other cardiovascular or thrombogenic risk factors.

Total Antioxidant Capacity (TAC) is a biomarker often used in order to investigate oxidative stress in many pathological conditions. Saliva and urine can be collected noninvasively and represent attractive diagnostic fluids for detecting biomarkers of various pathological conditions. The reviewed case-control and intervention studies that measured salivary or urinary TAC revealed that diseases, antioxidant foods, or supplements and age, gender, and lifestyle factors influenced salivary or urinary TAC. Salivary and urinary TAC were particularly affected by oral or renal status, respectively, as well as by infection; therefore these factors must be taken into account in both case-control and intervention studies. Furthermore, some considerations on sample collection and normalization strategies could be made. In particular, unstimulated saliva could be the better approach to measure salivary TAC, whereas 24 h or spontaneous urine collection should be chosen on the basis of the study outcome and of the creatinine clearance. Finally, the uric acid-independent TAC could be the better approach to evaluate red-ox status of body, in particular after nutritional interventions and in diseases associated with hyperuricaemia.

The present study investigated whether storage under modified-atmosphere packaging (MAP) affected the antioxidant properties of fresh lettuce (Lactuca sativa). Eleven healthy volunteers (six men, five women) consumed 250 g fresh lettuce, and blood was sampled before (0 h) and 2, 3 and 6 h after consumption. The protocol was repeated 3 d later with the same lettuce stored at 5°C under MAP conditions (O2–N2(5:95, v/v)). Results showed that after ingestion of fresh lettuce, plasma total radical-trapping antioxidant potential (TRAP), measured as area under the curve, was significantly higher (1·3 (SEM 0·3) MMOL/L PER 6 H;P<0·05) THAN THE VALUE OBTAINED WITH MAP-STORED LETTUCE (0·1 (sem 0·2) mmol/l per 6 h). Plasma TRAP, quercetin andp-coumaric acid were significantly different from baseline values (P≤0·05) 2 and 3 h after fresh lettuce ingestion. Caffeic acid increased significantly at 3 h (P<0·05). Plasma β-carotene levels increased significantly at 6 h (P<0·05). Vitamin C concentrations (mg/l) rose from 10·9 (sem 2·0) to 12·7 (sem 3·0) (P<0·001), 12·7 (sem 2·0) (P<0·01) and 12·9 (sem 3·0) (P<0·05) at 0, 2, 3 and 6 h respectively. No changes were observed after ingestion of MAP-stored lettuce for all the measured markers. Our present results showed that ingestion of MAP-stored lettuce does not modify plasma redox status in healthy subjects. Further research is needed to develop post-harvesting techniques able to preserve the bioactive molecule content of plant food.

Strawberries contain many antioxidant phytochemicals such as vitamin C, carotenoids and phenolic compounds including anthocyanins (ACN). In the present study, antioxidant composition of fresh strawberries (FS) and stored strawberries (SS) and the bioavailability of the main strawberry bioactive compounds were determined in human subjects. Thirteen healthy volunteers consumed 300 g of FS and SS on two separate occasions. Blood, before and at different time points from meal consumption, as well as 24 h urine, was collected, and parent compounds and metabolites of the different compounds were determined by HPLC or LC/MS/MS. A reduction in a-carotene plasma concentrations v. baseline values was recorded after the consumption of FS, although the amount of this carotenoid was higher in the SS. On the contrary, a significant increase of plasma vitamin C after 2, 3 and 5 h (P,0·05) of FS and SS consumption was recorded. No quercetin and ACN were found in plasma, while coumaric acid, 4-hydroxybenzoic acid (4HBA, 56 and 54 % of pelargonidin-3-glucoside (Pel-glc) ingested with FS and SS, respectively) and protocatechuic acid (59 and 34 % of cyanidin-3-glucoside ingested with FS and SS, respectively) over 8 h from strawberry consumption were retrieved in the plasma. Pelargonidin glucuronide, pelargonidin glucoside and pelargonidin aglycone peaked in urine within 2 h of strawberry consumption, and the 24 h amount excreted was always approximately 0·9 % of the Pel-glc dose ingested. The data indicated that the content of phytochemicals in strawberries may influence the bioavailability of individual compounds. Furthermore, in the present study, the metabolism of Pel-glc was elucidated, and, for the first time, 4HBA was suggested to be a major human metabolite of Pel-glc.