Fulgencio Saura-Calixto

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).

A starch hydrolysis procedure to estimate glycemic index

Abstract An in vitro procedure to measure the rate of starch digestion in starchy common foodstuffs was developed. A first-order equation that rules the hydrolytic process was found: CC∞ (1−e −kt ). Besides an in vivo assay, to calculate the glycemic index (GI), was carried out on thirty healthy volunteers. This is a simple in vitro method that could be used to estimate the metabolic glycemic response to a food. The best correlated value with in vivo glycemic responses was the percentage of starch hydrolysis at 90 min (r= 0.909, p≤0.05, GI 1 = 39.21 + 0.803(H 90 )).

Analysis of resistant starch : a method for foods and food products

Abstract A method for resistant starch (RS) determination in food and food products is proposed. The main features are: removal of protein; removal of digestible starch; solubilization and enzymatic hydrolysis of RS; and quantification of RS as glucose released. Stomach and intestine physiological conditions (pH, transit time) were approximately simulated. All operations were performed in a 50ml centrifuge tube. Reference materials and food products were analysed by three laboratories. Statistical analysis included repeatability and reproducibility. This procedure is quite satisfactory for starchy foods containing appreciable quantities of RS and it may be useful for nutritional labelling of foodstuffs. For samples containing ⩽ 1% RS, differences are not significant and they can be considered as foods with a negligible RS content.

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.

Tannins: Current knowledge of food sources, intake, bioavailability and biological effects

Tannins are a unique group of phenolic metabolites with molecular weights between 500 and 30 000 Da, which are widely distributed in almost all plant foods and beverages. Proanthocyanidins and hydrolysable tannins are the two major groups of these bioactive compounds, but complex tannins containing structural elements of both groups and specific tannins in marine brown algae have also been described. Most literature data on food tannins refer only to oligomeric compounds that are extracted with aqueous-organic solvents, but a significant number of non-extractable tannins are usually not mentioned in the literature. The biological effects of tannins usually depend on their grade of polymerisation and solubility. Highly polymerised tannins exhibit low bioaccessibility in the small intestine and low fermentability by colonic microflora. This review summarises a new approach to analysis of extractable and non-extractable tannins, major food sources, and effects of storage and processing on tannin content and bioavailability. Biological properties such as antioxidant, antimicrobial and antiviral effects are also described. In addition, the role of tannins in diabetes mellitus has been discussed.

Dietary fiber as a carrier of dietary antioxidants: an essential physiological function.

The literature addresses dietary fiber (DF) and antioxidants (AOX) separately as nonrelated compounds. This paper proposes to show that DF and AOX could be approached jointly in nutrition and health studies because around 50% of the total dietary antioxidants, mainly polyphenolics, traverse the small intestine linked to dietary fiber. These antioxidants have received little attention so far. They release the fiber matrix in the colon by the action of the bacterial microbiota, producing metabolites and an antioxidant environment. The content of polyphenols associated with DF in different foods and their potential health-related properties, including animal experiments and human trials, are reviewed. It is concluded that the transportation of dietary antioxidants through the gastrointestinal tract may be an essential function of DF.

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

Assessment of some parameters involved in the gelatinization and retrogration of starch

Abstract Factors influencing the formation of resistant starch (RS) during gelatinization and retrogradation were studied in starches and flours from cereals (wheat, corn, rice) and potato. RS obtained using a high-pressure autoclave system varied between 3.94 and 21.21% (rice and potato starches, respectively) similar to the values obtained after gelatinization in a boiling water bath. Except for rice, RS was higher in pure starches than in flours. Stirring during gelatinization yielded more homogeneous products than non-stirred samples. Apparently, gelatinization was unaffected by pH values between 3.5 and 10.5. To obtain optimum RS yields during retrogradation, it was necessary to cool down starch gels prior to freezing, followed by thawing at room temperature and drying at 60°C. These conditions ensure good yields in the formation of RS with potential industrial applications. ©

Evaluation of free radical scavenging of dietary carotenoids by the stable radical 2,2-diphenyl-1-picrylhydrazyl

In order to avoid the interference of compounds with a chromophoric system when the 2,2-diphenyl-1-picrylhydrazyl (DPPH·) method is used, a new measure of the decrease in absorbance at 580 nm was performed (correlation coefficient between absorbance and DPPH· concentration, 0.9979; p < 0.01). The antioxidant effectiveness of dietary carotenes and xanthophylls towards the stable free radical DPPH· was measured. The antioxidant activity expressed as the amount of antioxidant able to reduce the initial DPPH· concentration to 50% (EC50), given in terms of moles of antioxidant per mole of DPPH·, ranged from 0.16 ± 0.01 (lycopene) to 3.29 ± 0.31 (lutein). The parameter antiradical efficiency (AE), which involves the potency (1/EC50) and the time taken to reach the steady state at EC50 (TEC50), was calculated to discriminate carotenoids with no significant difference between their EC50. Comparison of the structures of the carotenoids tested revealed that the scavenging ability towards DPPH· was increased by the length of the effective conjugated double-bond system and was modulated by the addition of chemical groups on the terminal rings (xanthophylls). © 2000 Society of Chemical Industry

Comparison between free radical scavenging capacity and oxidative stability of nut oils

Several works have measured free radical scavenging capacity of nut oils, since they may become a significant source of dietary fat. However, they have not considered kinetic parameters, what was the first aim of this work. Also, it was studied the possible relation between values of free radical scavenging capacity DPPH and oxidative stability (Rancimat method) in different nut (hazelnut, peanut, pistachio, walnut and almond) oils. The ranking of antioxidant capacity of nut oils, by both assays, was: pistachio>hazelnut>walnut>almond>peanut. A significant correlation was found between DPPH and Rancimat methods assays. Tocopherols appear to be the responsible compounds of this antioxidant capacity being neglictible the contribution of polyphenols. An interference effect of phospholipids, present in methanolic fraction of nut oils, was observed in the determination of polyphenols in nut oils by Folin and ortho-diphenols assays.