Effects of regular ingestion of black tea on haemostasis and cell adhesion molecules in humans

OBJECTIVE: To assess the effects in humans of regular ingestion of black tea on haemostasis-related variables and cell adhesion molecules. DESIGN: Twenty-two subjects were recruited from the general population to a randomised-controlled crossover study. Subjects stopped drinking tea, apart from that provided, for the duration of the study. During a 4-week baseline period all subjects drank 5 cups/day (250 ml) of hot water. The effects of 5 cups/day of black tea for 4 weeks were then compared with hot water. Platelet aggregation in response to three doses of collagen and ADP, plasma concentrations of coagulation and fibrinolytic factors (fibrinogen, factor VII, tPA, PAI-1) and plasma concentrations of cell adhesion molecules (soluble P-selectin, E-selectin, ICAM-1, VCAM-1) were assessed twice, one week apart, at the end of each period. Twenty-four hour urinary concentration of 4-O-methylgallic acid (4OMGA), assessed once at the end of each period, was used as a marker of black tea polyphenol intake. RESULTS: The 24 h urinary excretion of 4OMGA was increased during regular ingestion of black tea in comparison to hot water (P<0.0001). Black tea resulted in lower soluble P-selectin (P=0.01) in comparison to hot water, but did not influence other adhesion molecules. Soluble P-selectin was significantly correlated with mean collagen-stimulated platelet aggregation at baseline (r=0.61, P=0.003), and during regular ingestion of hot water (r=0.70, P<0.0001) and black tea (r=0.51, P=0.01). However, platelet aggregation was not different between the black tea and hot water periods for collagen- or ADP-stimulated aggregation at any dose. Coagulation and fibrinolytic factors were also not different between periods. CONCLUSIONS: The effect of black tea on soluble P-selectin provides a potential mechanism for cardiovascular benefits of regular ingestion of tea. SPONSORSHIP: This study was supported by grants from the Tea Trade Health Research Association and the National Heart Foundation of Australia.     

Can black tea influence plasma total homocysteine concentrations?

BACKGROUND: Polyphenols can act as acceptors of methyl groups during the metabolism of methionine to homocysteine. This may result in elevations in plasma total homocysteine (tHcy) concentrations after ingestion of polyphenol-rich beverages such as tea. OBJECTIVES: Our major objective was to determine whether regular, moderate-to-high intakes of black tea alter tHcy concentrations. We also assessed the relation between the degree of O-methylation of tea-derived polyphenols and the change in tHcy with regular ingestion of tea. DESIGN: Twenty-two subjects completed a randomized, controlled crossover study. Subjects consumed 1250 mL black tea/d (5 cups each containing 2 g tea leaves in 250 mL boiled water) and 1250 mL hot water/d for 4 wk each. Fasting tHcy concentrations and 24-h urinary excretion of 4-O-methylgallic acid (4OMGA, the major O-methylated metabolite of gallic acid) were measured at the end of each period. 4OMGA was used as a marker of overall O-methylation of tea-derived polyphenols. RESULTS: Black tea did not significantly alter mean (+/- SEM) tHcy concentrations (9.9 +/- 0.5 and 10.0 +/- 0.5 micro mol/L for the hot water and black tea periods, respectively). However, the increased excretion of 4OMGA as a consequence of black tea consumption was positively associated with the change in tHcy from the hot water period to the black tea period (r = 0.55, P = 0.008). Subjects in the bottom quartile of increase in 4OMGA excretion had a significant decrease in tHcy (-0.28 +/- 0.10 micro mol/L; P = 0.046), and those in the top quartile had a significant increase in tHcy (0.78 +/- 0.16 micro mol/L; P = 0.005). CONCLUSIONS: Overall, regular ingestion of black tea did not alter mean tHcy concentrations. However, individual differences in O-methylation of polyphenolic compounds may influence the ultimate effects of black tea on tHcy.     

Acute effects of ingestion of black and green tea on lipoprotein oxidation

BACKGROUND: Tea has been associated with a reduced risk of cardiovascular disease. One proposed mechanism of this risk reduction involves inhibition of lipoprotein oxidation in vivo by antioxidant polyphenolic compounds derived from tea. However, controlled interventions uniformly failed to show that ingestion of tea can inhibit LDL oxidation ex vivo. The absence of effects in previous studies may be due to the isolation of LDL particles from polyphenolic compounds that are present in the aqueous phase of serum. OBJECTIVE: The objective of this study was to examine the acute effects of ingestion of black and green tea on ex vivo Cu(2+)-induced lipoprotein oxidation without prior isolation of lipoproteins from serum. DESIGN: The acute effects of 4 hot drinks-green tea and black tea (each at a dose equivalent to 4 standard cups), water matched to the teas for caffeine content, and water-were assessed in 20 healthy men by using a Latin-square design. The lag time to lipoprotein diene formation, slope of the propagation phase of the oxidation curve, and area under the oxidation curve were calculated. Urinary concentrations of 4-O-methylgallic acid were used as a marker of uptake and metabolism of polyphenolic compounds from tea. RESULTS: Significant increases in urinary 4-O-methylgallic acid for black and green tea (P < 0. 0001) were observed. Caffeine did not significantly influence lipoprotein oxidation. Compared with the water control, there was a greater lag time for black tea (5.4 +/- 2.9 min; P = 0.05) that was of borderline significance and a similar trend for green tea (4.4 +/- 2.8 min; P = 0.17). Slope and area under the oxidation curve were not altered. CONCLUSION: Black tea has a mild acute effect on ex vivo lipoprotein oxidation in human serum. 2000;71:-7.     

Timing of vagal stimulation affects postprandial lipid metabolism in humans

BACKGROUND: Vagal stimulation combined with an oral fat load enhances postprandial lipemia in animals and humans. OBJECTIVE: We assessed whether the observed postprandial increase in plasma lipids could be explained by changes in exogenous (chylomicron) or endogenous (VLDL) lipid metabolism and whether the timing of vagal stimulation in relation to fat intake was important. DESIGN: Vagal stimulation was achieved by using the modified sham feeding (MSF) technique, in which food is tasted and chewed but not swallowed. Seven healthy men consumed an oral fat load (50 g) on one occasion (control protocol). On 2 other occasions, they consumed an oral fat load combined with MSF of an appetizing meal. MSF was performed for either 1 h before or 1 h after the oral fat load. Blood was collected for 7 h and was analyzed for hormones and metabolites. RESULTS: The postprandial triacylglycerol response differed significantly (P < 0.001) between the 3 protocols. Both MSF studies resulted in significantly higher plasma pancreatic polypeptide concentrations compared with the control. Compared with MSF for 1 hour after fat intake, MSF for 1 h before fat intake resulted in significantly higher plasma insulin concentrations (P = 0.013), a more rapid rise in chylomicron triacylglycerol concentrations (P = 0.04), and higher VLDL triacylglycerol and apoliprotein B-100 concentrations. CONCLUSIONS: Vagal stimulation enhanced postprandial lipemia via effects on both chylomicron and VLDL metabolism. MSF before fat intake had more dramatic effects on postprandial lipemia than did MSF after fat intake, possibly because of increased parasympathetic activity at the time of ingestion.     

Tea intake is inversely related to blood pressure in older women

Tea is rich in polyphenols, which have activities consistent with blood pressure-lowering potential. The effects of long-term regular ingestion of tea on blood pressure remain uncertain. We investigated the relationships of tea intake and a biomarker of exposure to tea-derived polyphenols (4-O-methylgallic acid) with blood pressure in a cross-sectional study of 218 women > 70 y old. Clinic blood pressures were measured and tea intake was assessed using a 24-h dietary recall; 4-O-methylgallic acid was measured for the same period in a 24-h urine sample. Mean (95% CI) daily tea intake was 525 (475, 600) mL. Mean systolic and diastolic blood pressures were 138.1 (135.6, 140.6) and 73.5 (72.1, 74.9) mm Hg. Higher tea intake and higher 4-O-methylgallic acid excretion were associated with significantly lower systolic (P = 0.002 and P = 0.040, respectively) and diastolic (P = 0.027 and P < 0.001, respectively) blood pressures. A 250 mL/d (1 cup) increase in tea intake was associated with a 2.2 (0.8, 3.6) mm Hg lower systolic blood pressure and a 0.9 (0.1, 1.7) mm Hg lower diastolic blood pressure. The observed associations for both tea intake and 4-O-methylgallic acid are consistent with the hypothesis that long-term regular ingestion of tea may have a favorable effect on blood pressure in older women.     

Regular ingestion of tea does not inhibit in vivo lipid peroxidation in humans.

Prospective studies suggest that tea may protect against cardiovascular disease. A potential mechanism for such an effect involves inhibition of lipid peroxidation by polyphenolic antioxidants derived from tea. Our objective was to determine whether regular ingestion of tea could inhibit in vivo lipid peroxidation. Two controlled intervention studies assessed the effects of regular ingestion of tea on lipid peroxidation determined by measurement of urinary F(2)-isoprostane excretion. Study 1: The effects of 1000 mL/d of green tea and black tea were compared with hot water containing caffeine in 13 subjects with elevated blood pressure using a randomized 3-period (7 d each) crossover design. Study 2: The effects of 1250 mL/d of black tea were compared with hot water in 22 subjects with mildly raised serum total cholesterol concentrations using a randomized 2-period (4 wk each) crossover design. F(2)-isoprostane excretion was not altered after regular ingestion of green tea (273 +/- 48 pmol/mmol creatinine) or black tea (274 +/- 39 pmol/mmol creatinine) in comparison with hot water (263 +/- 47 pmol/mmol creatinine; Study 1), or by regular ingestion of black tea (334 +/- 71 pmol/mmol creatinine) in comparison with hot water (355 +/- 75 pmol/mmol creatinine; Study 2). These results do not support the suggestion that polyphenolic antioxidants derived from tea inhibit in vivo lipid peroxidation.     

Oral exposure to butter, but not fat replacers elevates postprandial triacylglycerol concentration in humans

Oral exposure to dietary fat augments the postprandial triacylglycerol (TAG) concentration. We investigated the TAG response after oral exposure to butter and selected fat replacers. At 2200 h, 17 healthy adults consumed 80 g of almonds and fasted until 0700 h. Safflower oil (50 g in 1-g capsules) was then consumed. Oral stimulation was provided periodically for 2 h as potatoes, potatoes containing butter or one of three fat replacers or no oral stimulation in random order at weekly intervals. Blood was collected at stipulated intervals for 8 h. Oral exposure to butter led to a significantly longer postprandial TAG elevation than the other treatments. The results could not be explained by differential stimulus ingestion, palatability or perceived fat content. There was no significant treatment effect on concentrations of serum oleic acid, apolipoprotein (apo)B-48 or apoB-100, suggesting any oral exposure influence on release of dietary lipid stored in the lacteals or chylomicron and VLDL particle number contributed little to the postprandial TAG rise. In summary, oral exposure to butter elicited a greater postprandial TAG elevation than the tested fat replacers, possibly due to reduced TAG clearance.     

Double-blind controlled study on the effects of dietary diacylglycerol on postprandial serum and chylomicron triacylglycerol responses in healthy humans

OBJECTIVE: The effects of dietary diacylglycerol (DG) on postprandial lipemia in healthy humans were investigated. METHODS: Forty normolipidemic male volunteers ingested fat emulsions containing either DG oil or triacylglycerol (TG) oil, at different doses: 10 g (n = 13), 20 g (n = 10) and 44 g (n = 17). Two test emulsions were given at seven-days intervals in random order. Fatty acid compositions of the test oils had been adjusted to be equal. Fasting and postprandial serum lipid concentrations in each group and plasma lipoprotein lipids in the 20 g-fat ingestion group were measured during the postprandial intervals. RESULTS: When DG emulsion was ingested, serum TG concentrations were significantly lower (p < 0.05) in the late postprandial phase, i.e., 4 hours, 6 hours as compared to the TG emulsion. The magnitude of postprandial lipemia (the area bounded by the curve above the fasting concentration) after ingestion of 44 g-DG emulsion was significantly less than that of 44 g-TG emulsion (6.54 +/- 5.12 and 8.45 +/- 7.54 mmol x h/L, mean +/- SD, respectively). Chylomicron TG, cholesterol, and phospholipid concentrations at 4 hours after ingestion of DG emulsion were significantly lower (p < 0.05) than those after the ingestion of TG emulsion at the same time point. No marked differences were observed for VLDL, LDL and HDL lipids between the test emulsions. CONCLUSION: In the usual range of fat intake (10-44 g), postprandial response after ingestion of DG emulsion was significantly less than that after ingestion of TG emulsion in healthy human subjects.     

Effect of tea catechins on postprandial plasma lipid responses in human subjects

Epidemiological surveys suggest that a higher intake of tea may be associated with a lower risk of CHD. There is accumulating evidence that postprandial lipaemia makes a substantial contribution to the incidence of CHD. Our aim was, therefore, to evaluate the effect of tea catechins (major ingredients in green tea) on postprandial lipid responses in human subjects after the consumption of test meals. In a randomized triple-crossover design, nine male subjects with mild or borderline hypertriacylglycerolaemia consumed 10 (control), 224 (moderate dose) and 674 mg (high dose) of the assigned tea catechins three times each along with a standardized light meal consisting of a piece of bread spread with 20 g butter. Plasma lipids were measured in the fasting state and 1, 2, 3, 4 and 6 h after consuming the light meal. Results showed that, compared with the control, moderate and high doses of tea catechins reduced the incremental area under the plasma triacylglycerol curves by 15.1 and 28.7%, respectively. Next, the rapid elevation of remnant-like particle cholesterol was significantly inhibited by a high dose of tea catechins 2 h after consuming the light meal (P<0.01). In the range of tea catechin dosages, no significant differences were observed in the postprandial responses for plasma total cholesterol or NEFA at any time point. In conclusion, this trial demonstrated that tea catechins attenuated the postprandial increase in plasma triacylglycerol levels following a fat load. These results may provide evidence for one of the possible mechanisms involved in lowering the incidence of CVD, and may prove useful in further studies on the beneficial health effects of tea drinking.     

Acute Effects of Kawakawa (Piper excelsum) Intake on Postprandial Glycemic and Insulinaemic Response in a Healthy Population

Background: Piper excelsum (kawakawa) is an endemic shrub of Aotearoa, New Zealand, of cultural and medicinal importance to Māori. Its fruits and leaves are often consumed. These tissues contain several compounds that have been shown to be biologically active and which may underpin its putative health-promoting effects. The current study investigates whether kawakawa tea can modulate postprandial glucose metabolism. Methods: We report a pilot three-arm randomized crossover study to assess the bioavailability of kawakawa tea (BOKA-T) in six male participants with each arm having an acute intervention of kawakawa tea (4 g/250 mL water; 1 g/250 mL water; water) and a follow-up two-arm randomized crossover study to assess the impact of acute kawakawa tea ingestion on postprandial glucose metabolism in healthy human volunteers (TOAST) (4 g/250 mL water; and water; n = 30 (15 male and 15 female)). Participants consumed 250 mL of kawakawa tea or water control within each study prior to consuming a high-glycemic breakfast. Pre- and postprandial plasma glucose and insulin concentrations were measured, and the Matsuda index was calculated to measure insulin sensitivity. Results: In the BOKA-T study, lower plasma glucose (p < 0.01) and insulin (p < 0.01) concentrations at 60 min were observed after consumption of a high-dose kawakawa tea in comparison to low-dose or water. In the TOAST study, only plasma insulin (p = 0.01) was lower at 60 min in the high-dose kawakawa group compared to the control group. Both studies showed a trend towards higher insulin sensitivity in the high-dose kawakawa group compared to water only. Conclusions: Consuming kawakawa tea may modulate postprandial glucose metabolism. Further investigations with a longer-term intervention study are warranted.     

Changes in LDL particle composition after the consumption of meals containing different amounts and types of fat

BACKGROUND: Remodeling of lipoprotein particles in the postprandial period is considered to be an important source of atherogenic particles, but acute changes occurring after meals have been little studied. OBJECTIVE: We sought to characterize changes in LDL particle composition occurring after a single meal, with particular reference to potential lipid exchange with particles carrying dietary fatty acids. DESIGN: In a balanced design, 8 healthy subjects ingested isoenergetic meals of different fat content: low-fat, rich in saturated fatty acids (SFAs), and rich in polyunsaturated fatty acids (PUFAs). We investigated changes in LDL composition 4 and 6 h after meal ingestion. RESULTS: The LDL triacylglycerol-to-protein ratio closely mirrored the plasma triacylglycerol concentrations after each of the meals, and there was a strong association between these variables in both the fasting and postprandial states (P < 0.001). A postprandial increase in LDL triacylglycerol was associated with a decrease in LDL cholesterol. There were no effects of the ingestion of a single meal on the LDL density profiles for protein or for any of the lipid components. The fatty acid composition of total LDL lipids changed in the postprandial period, with an enrichment in PUFA after the PUFA-rich meal and in SFA after the SFA-rich meal. CONCLUSIONS: The changes observed in LDL composition after single meals are in accord with the proposition that there is neutral lipid exchange in the postprandial period, with triacylglycerol enrichment of LDL particles at the expense of cholesteryl esters. The change in the fatty acid composition of LDL particles implies significant lipid exchange with particles containing dietary fat.     

Ingestion of red wine significantly increases plasma phenolic acid concentrations but does not acutely affect ex vivo lipoprotein oxidizability

BACKGROUND: Reduced lipoprotein oxidizability by red wine phenols has been proposed as the basis for a relatively lower incidence of coronary heart disease in red wine drinkers. We showed previously that caffeic and protocatechuic acids isolated from red wine exhibit antioxidant activity in vitro. However, there is no information in the literature on the absorption of these compounds after red wine ingestion. OBJECTIVES: We sought to determine whether certain phenolic acids can be detected in the circulation after red wine consumption and if their presence has an acute effect on serum and LDL oxidation ex vivo. DESIGN: Twelve healthy male nonsmokers consumed red wine, phenol-stripped red wine, dealcoholized red wine, or water, each at a separate visit, in random order and 1 wk apart. Beverages were consumed over 30 min and blood was sampled just before beverage consumption and 1, 2, and 4 h after consumption. Plasma caffeic, protocatechuic, and 4-O-methylgallic acids were measured by gas chromatography-mass spectrometry. We also measured copper-induced serum and LDL oxidizability ex vivo and serum uric acid. RESULTS: Caffeic acid and 4-O-methylgallic acid concentrations increased significantly (P < 0.025) after consumption of red wine and dealcoholized red wine compared with water or phenol-stripped red wine. Uric acid increased significantly (P < 0.001) after ingestion of red wine, phenol-stripped red wine, and dealcoholized red wine. There was no effect on ex vivo serum or LDL oxidation after any of the beverages. CONCLUSION: Although red wine and dealcoholized red wine consumption acutely increase plasma phenolic acid and serum uric acid concentrations, the increase is insufficient to influence ex vivo lipoprotein oxidation.     

Prior exercise does not affect chylomicron particle number following a mixed meal of moderate fat content

Background  

A single session of exercise has been reported to reduce fasting and postprandial triacylglycerol concentrations on the subsequent day. It is possible that exercise also reduces chylomicron particle number, which may underlie the observed reduction in postprandial triacylglycerol concentration. In the present study we aimed to determine whether a single session of exercise reduces fasting and postprandial chylomicron particle number on the subsequent day. In a randomised crossover design eight lean and healthy male and female subjects attended two postprandial testing days. On the previous day the subjects either performed 90 minutes of moderate intensity exercise or did not perform any exercise. Fasting blood samples were then collected prior to ingestion of a moderate fat mixed meal (0.44 g fat, 0.94 g carbohydrate, 0.27 g protein/kg body weight), blood was then collected after 1 h, 2 h, 4 h, 6 h, and 8 h.     

Effects of varying the carbohydrate:fat ratio in a hot lunch on postprandial variables in male volunteers

1. Healthy male volunteers consumed at noon, hot test meals with four different carbohydrate:fat ratios varying between 2.64 and 0.50, and composed of fried beefsteak, mashed potatoes, French beans, and a dessert of custard with mashed peaches. The energy content of the meals was 40% of the daily intake of the volunteers, estimated from their individual dietary histories. 2. Before, and at different times after the start of the meal, blood samples were taken and a number of indices of carbohydrate and lipid metabolism were determined in the samples, i.e. glucose, insulin, free fatty acid, free and total glycerol, free and total cholesterol, high-density-lipoprotein (HDL)-cholesterol and low-density-lipoprotein (LDL)-cholesterol. 3. Increasing the carbohydrate:fat ratio resulted in higher postprandial peaks of glucose and insulin. In addition, the peak area under the postprandial glucose curve showed a significant increase. The peak area under the postprandial insulin curve had also increased, indicating that a larger amount of insulin was secreted by the pancreas on increasing the carbohydrate content in the meal. There was no significant correlation between the height of the postprandial peak of blood glucose and the size of the meal. 4. All four meals caused elevated postprandial blood triacylglycerol levels. However, the decline of this elevated level took a much longer time after the meals with the lower carbohydrate:fat ratios, i.e. containing larger amounts of triacylglycerols. There was a significant decreasing linear relation between the carbohydrate content of the meals and the peak area under the postprandial triacylglycerol curve. Free glycerol and free fatty acids showed lower postprandial levels in the blood after the meals with the higher carbohydrate:fat ratios, and the peak areas of the postprandial curves of both variables displayed a significant decrease. Little or no effect of the meal carbohydrate:fat ratio was observed on the postprandial concentrations of total cholesterol, unesterified cholesterol, HDL-cholesterol or LDL-cholesterol.     

Postprandial serum triacylglycerols and oxidative stress in mice after consumption of fish oil, soy oil or olive oil: possible role for paraoxonase-1 triacylglycerol lipase-like activity

OBJECTIVE: Postprandial triacylglycerols and oxidative stress responses are influenced by the type of fat consumed. We investigated the effect of individual unsaturated fatty acids or oils (fish, soy, or olive) on postprandial triglyceridemia response in association with serum resistance to oxidation and paraoxonase-1 (PON1) activity. METHODS: Balb/C mice were supplemented with phosphate buffered saline (control), docosahexaenoic acid (omega-3), linoleic acid (omega-6), or oleic acid (omega-9; 500 mug/300 muL of phosphate buffered saline) and with fish, soy, or olive oil (300 muL); blood samples were collected 2 h after feeding. RESULTS: Serum triacylglycerol and oxidative stress responses increased after intake of all unsaturated fatty acids and oil supplements. However, ingestion of fish oil or its major fatty acid, docosahexaenoic acid, induced the most remarkable increase in postprandial serum triacylglycerols and in the susceptibility of serum to in vitro oxidation. Serum PON1 activity was decreased by 24% after fish oil ingestion. The increase in postprandial serum susceptibility to oxidation was lower after soy oil supplementation to PON1-transgenic mice in comparison with Balb/C mice, showing that PON1 attenuates the postprandial serum oxidative response. In parallel, in PON1-transgenic mice, a decreased postprandial triacylglycerol response was noted, suggesting PON1 involvement in triacylglycerol metabolism. PON1 exhibited a triacylglycerol lipase-like activity on chylomicrons. CONCLUSION: PON1 attenuates the postprandial oxidative stress response, and this could have resulted from PON1 lipase-like activity on chylomicron triacylglycerols.     

Double-Blind Controlled Study on the Effects of Dietary Diacylglycerol on Postprandial Serum and Chylomicron Triacylglycerol Responses in Healthy Humans

Objective: The effects of dietary diacylglycerol (DG) on postprandial lipemia in healthy humans were investigated.

Methods: Forty normolipidemic male volunteers ingested fat emulsions containing either DG oil or triacylglycerol (TG) oil, at different doses: 10 g (n = 13), 20 g (n = 10) and 44 g (n = 17). Two test emulsions were given at seven-days intervals in random order. Fatty acid compositions of the test oils had been adjusted to be equal. Fasting and postprandial serum lipid concentrations in each group and plasma lipoprotein lipids in the 20 g-fat ingestion group were measured during the postprandial intervals.

Results: When DG emulsion was ingested, serum TG concentrations were significantly lower (p < 0.05) in the late postprandial phase, i.e., 4 hours, 6 hours as compared to the TG emulsion. The magnitude of postprandial lipemia (the area bounded by the curve above the fasting concentration) after ingestion of 44 g-DG emulsion was significantly less than that of 44 g-TG emulsion (6.54 ± 5.12 and 8.45 ± 7.54 mmol · h/L, mean ± SD, respectively). Chylomicron TG, cholesterol, and phospholipid concentrations at 4 hours after ingestion of DG emulsion were significantly lower (p < 0.05) than those after the ingestion of TG emulsion at the same time point. No marked differences were observed for VLDL, LDL and HDL lipids between the test emulsions.

Conclusion: In the usual range of fat intake (10–44 g), postprandial response after ingestion of DG emulsion was significantly less than that after ingestion of TG emulsion in healthy human subjects.     

Antioxidant potential of green and black tea determined using the ferric reducing power (FRAP) assay

Tea is one of the most commonly consumed beverages in the world and is rich in polyphenolic compounds collectively known as the tea flavonoids. Tea flavonoids possess antioxidant properties in vitro and have been proposed as key protective dietary components, reducing risk of coronary heart disease and some cancers. The present study aimed to evaluate the possible effects of different preparation methods on the antioxidant properties of green and black tea. Antioxidant potentials of tea infusates were assessed using an assay based upon the reduction of ferric chloride linked to a chromophore. Green tea, black leaf tea and black tea in tea bags were infused with water at 90 degrees C for time periods ranging from 0.25 to 15 min. Green tea infusates possessed approximately 2.5-fold greater antioxidant capacity than both types of black tea infusates. Both green and black teas released significant levels of antioxidants into the hot water within 2 min of infusion. Preparation of teas across a range of temperatures between 20 and 90 degrees C revealed that although antioxidants were liberated from the leaves into the water in cooler infusions, increasing the temperature could increase antioxidant potential by 4 to 9.5-fold. Black tea prepared using tea bags had significantly lower antioxidant capacity than black leaf tea at temperatures between 20 and 70 degrees C, suggesting that tea bag materials may prevent some extraction of flavonoids into the tea solution. The addition of milk appeared to diminish the antioxidant potential of black tea preparations. This effect was greatest where whole cow's milk was used and appeared to be primarily related to the fat content of the added milk. These experiments have considered the effects of commonly used domestic methods of preparation on the in vitro antioxidant potential of tea. It is concluded that maximum antioxidant capacity and hence maximal health benefit may be derived from green tea or from black leaf tea prepared by infusion with water at 90 degrees C for up to 2 min and taken with the addition of either fat-free milk, or without milk addition. Further studies are required to assess the antioxidant actions of tea flavonoids in vivo.     

Sweetener augmentation of serum triacylglycerol during a fat challenge test in humans

OBJECTIVE: High concentrations of fructose enhance postprandial lipemia following lipid loading whereas glucose exerts a negative or minimal effect. This study evaluated the effect of lower sweetener concentrations and the contribution of their sweetness level and palatability. METHODS: At each of four test sessions, twelve male and ten female healthy adults ingested one of four milkshakes containing 108 g dairy cream alone or supplemented with 30 g fructose, 17.5 g glucose or 1 g aspartame. Blood samples were collected at baseline, two, four, six and eight hours after ingestion. Sensory discrimination tests were conducted after the last two sessions. RESULTS: Fructose and glucose led to 37% (p = 0.03) and 59% (p = 0.08) rises in triacylglycerol area under the curve (TG AUC) when compared to the plain milkshake, respectively. Although the sweetened shakes were equisweet and were more palatable than the plain shake, the TG rise after the aspartame milkshake did not differ from the plain milkshake. CONCLUSIONS: These data indicate that low levels of glucose and fructose consumed with lipid enhance postprandial lipemia. Sweetness and palatability did not account for the effect.     

Protein ingestion does not affect postprandial lipaemia or chylomicron-triglyceride clearance

The effects of protein ingestion on postprandial lipaemia and intravenous fat tolerance were examined in 15 normolipidaemic young men and women. Mean postprandial lipaemia was similar after meals containing 100 ml dairy cream (containing 40 g fat) and after meals containing 100 ml dairy cream and 23 g protein (in the form of casein). The rate of disappearance of an intravenous bolus of Intralipid was similar before and after the ingestion of 23 g casein. These findings indicate that dietary protein does not significantly affect postprandial lipaemia or chylomicron-triglyceride clearance.