José A. Larrauri

A procedure to measure the antiradical efficiency of polyphenols

The kinetic behaviour of polyphenols common in fruits as free radical scavengers was studied using 2,2-diphenyl-1-picrylhydrazyl (DPPH . ). After addition of different standard concentrations to DPPH . (0.025 g litre -1 ), the percentage of remaining DPPH . was determined at different times from the absorbances at 515 nm. The percentage remaining DPPH . against reaction time followed a multiplicative model equation: ln [DPPH . REM ] = b ln t + ln a. The slopes of these equations may be useful parameters to define the antioxidant capacity. The steeper the slope, the lower the amount of antioxidant necessary to decrease by 50% the initial DPPH . concentration (EC 50 ). This parameter, EC 50 , is widely used to measure antioxidant power, but it does not takes into account the reaction time. Time needed to reach the steady state to the concentration corresponding at EC 50 (T EC50 ) was calculated, and antiradical efficiency (AE) was proposed as a new parameter to characterise the antioxidant compounds where AE = 1/EC 50 T EC50 . It was shown that AE is more discriminatory than EC 50 . AE values are more useful because they also take into account the reaction time. The results have shown that the order of the AE (x 10 -3 ) in the compounds tested was: ascorbic acid(11.44) > caffeic acid (2.75) ≥ gallic acid (2.62) > tannic acid (0.57) ≥ DL-α-tocopherol (0.52) > rutin (0.21) ≥ quercetin (0.19) > ferulic acid (0.12) ≥ 3-tert-butyl-4-hydroxyanisole, BHA (0.10) > resveratrol (0.05).

Free radical scavenging capacity and inhibition of lipid oxidation of wines, grape juices and related polyphenolic constituents

Abstract The antioxidant activity of grape juices, wines made from the same lot as juices and their major polyphenolic constituents was measured by the inhibition of lipid oxidation (ferric-thiocyanate) and free radical scavenging (2,2-diphenyl-1-picrylhydrazyl) methods. dl -α-Tocopherol and 3-tertiary-butyl-4-hydroxyanisole (BHA) were used as references. The inhibition of lipid oxidation of the standards followed the order: rutin = ferulic acid > tannic acid = gallic acid = resveratrol > BHA = quercetin > dl -α-tocopherol > caffeic acid. Meanwhile, the free radical scavenging activity of gallic acid was the highest, tannic acid, caffeic acid, quercetin, BHA and rutin activities were intermediate and that for ferulic acid, dl -α-tocopherol and resveratrol were the lowest. Wines had higher activity than the corresponding grape juices and red wine showed the strongest activity among the grape products tested. The antioxidant activity of the samples seems to be based on their free radical scavenging capacity.

Free radical scavenging capacity of selected red, rosé and white wines

The free radical scavenging capacity of selected red, rose and white Spanish wines from different grape varieties was determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH·) method using a new methodology developed at our laboratory. The amount of sample necessary to decrease by 50% the initial DPPH· concentration (EC50), the time needed to reach the steady state at EC50 concentration (TEC50) and the antiradical efficiency (AE = 1/EC50TEC50) were determined in the wine samples. Some differences between rose wines made with Garnacha and Tempranillo grape varieties were observed in the UV-vis spectra and in the free radical scavenging parameters, those from Garnacha variety having the highest antioxidant activity. The antiradical efficiency of the wines followed a decreasing order: red wines (22.44 × 10−6) > rose wines (4.90 × 10−6) > white wines (1.88 × 10−6). There was a correlation between antiradical efficiency and total polyphenol (TP): AE = −3.33135 + 0.0180535TP; the correlation coefficient was r = 0.951454. © 1999 Society of Chemical Industry

Measurement of Health-Promoting Properties in Fruit Dietary Fibres: Antioxidant Capacity, Fermentability and Glucose Retardation Index

The aim of this work was to compare some in uitro health-promoting properties in fruit dietary fibre (antioxidant activity, fermentability and glucose retardation index), which could be useful to predict their physiological effects better than physico-chemical analyses. These properties were evaluated in mango and lemon peel fibre. Mango fibre was better than lemon fibre because of the highest values of antioxidant activity (67.6%) and glucose retardation index (21.5%). Antioxidant activity is proposed as a new health-promoting property associated to dietary fibre.

Reduction in serum total and LDL cholesterol concentrations by a dietary fiber and polyphenol-rich grape product in hypercholesterolemic rats

Abstract The cholesterol lowering effect of a dietary fiber and polyphenols rich product (DFPP) was evaluated in normo- and hypercholesterolemic rats. Four groups of six adult male Wistar rats were fed a purified cholesterol-free diet and 1g/100 g cholesterol-added diets, containing 5 g/100 g diet cellulose or 10 g/100 g diet DFPP as a source of dietary fiber for 4 weeks. Feeding the cholesterol-free diets supplemented with DFPP had no effect on serum cholesterol nor in LDL-cholesterol concentrations. On the contrary, HDL-cholesterol concentration was significantly higher in rats fed DFPP than in the unsupplemented group. In hypercholesterolemic rats, serum total cholesterol and LDL-cholesterol concentrations were significantly lower in the DFPP-supplemented group than in the unsupplemented group. HDL-cholesterol concentrations were not affected by feeding of DFPP in hypercholesterolemic diets. No effect of DFPP on serum triglycerides was observed. In both diets, HDL:LDL ratio tended to be higher and atherogenic index ([Total cholesterol − HDL-cholesterol] × HDL-cholesterol −1 ) lower in the DFPP-fed groups as compared to their controls. These results indicate that the DFPP reduce serum total cholesterol and LDL-cholesterol, as well as the atherogenic index, in hypercholesterolemic rats.

Principales métodos para la determinación de la oxidación lipídica Main methods used in lipid oxidation determination

Main spectrophotometric and chromatographic methods for determination of lipid oxidation in foods and biological systems are reviewed. A new classification, according to the compounds produced in the oxidation phases, is suggested as follows: measurement of oxygen absorption, conjugated dienes, peroxide values, and decomposition of lipid peroxides. Both conjugated dienes (propagation phase) and thiobarbituric acid (termination phase) methods are the most used, despite their interferences; however, chromatographic methods are more precise and selective. Determination of bioavailability and metabolic pathway of the antioxidants in the human body are problems to be solved in the devel opment of new biological antioxidants.

Seasonal Changes in the Composition and Properties of a High Dietary Fibre Powder from Grapefruit Peel

Seasonal changes in composition and properties of a high dietary fibre product from grapefruit peel were studied. Total dietary fibre decreased in January as compared to September (586-686 g kg -1 ). Main constituents from soluble fibre were: uronic acids (172-233 g kg -1 ), arabinose (13-41 g kg -1 ), galactose (4-11 g kg -1 ), glucose (5-10 g kg -1 ) and xylose (2-3 g kg -1 ). Insoluble dietary fibre (385-392 g kg -1 ) did not significantly change during the season. Its main constituents were: Klason lignin (29-37 g kg -1 ), uronic acids (33-70 g kg -1 ) and neutral sugars: glucose (149-196 g kg -1 ), mannose (45-50 g kg -1 ), xylose (25-38 g kg -1 ), galactose (20-22 g kg -1 ) and arabinose (16-45 g kg -1 ). Total neutral sugars from dietary fibre decreased over the harvest period (315-383 g kg -1 ) and an inverse trend was observed in total free-sugars from samples (49-85 g kg -1 ). Both, water holding capacity (7.0-9.3 g water g -1 dry sample) and glucose retardation index (7.0-25.3%) decreased from early stages in fruit development until late in the harvest season. Seasonal changes in grapefruit peel should be taken into account, in order to standardise the quality of rich fibre products.