Mustafa Bener

Antioxidant/antiradical properties of microwave-assisted extracts of three wild edible mushrooms.

A microwave-assisted extraction (MAE) process for polyphenols from three wild edible mushrooms was studied. The optimal extraction conditions were found to be methanol concentration of 80%, extraction temperature of 80 °C, and extraction time of 5 min. Different antioxidant assays (i.e., total antioxidant capacity (TAC) and total phenolic content (TPC)) were utilized to evaluate the antioxidant capacity of the methanolic extracts of Terfezia boudieri Chatin, Boletus edulis, and Lactarius volemus. The reactive species scavenging activities of these extracts were also investigated in vitro. High contents of phenolic and flavonoid compounds may be the major contributors to the observed high antioxidant activities of these extracts. B. edulis showed the higher TAC and TPC; highest inhibitory effect on DPPH and on other studied reactive oxygen species (ROS). MAE showed obvious advantages of high extraction efficiency with lower solvent consumption in terms of high antioxidant capacity/activity of extracts achieved within the shortest time.

Cupric ion reducing antioxidant capacity assay for antioxidants in human serum and for hydroxyl radical scavengers.

Tests measuring the combined antioxidant effect of the nonenzymatic defenses in biological fluids may be useful in providing an index of the organisms capability to counteract reactive species known as pro-oxidants, resist oxidative damage, and combat oxidative stress-related diseases. The selected chromogenic redox reagent for the assay of human serum should be easily accessible, stable, selective, and respond to all types of biologically important antioxidants such as ascorbic acid, alpha-tocopherol, beta-carotene, reduced glutathione (GSH), uric acid, and bilirubin, regardless of chemical type or hydrophilicity. Our recently developed cupric reducing antioxidant capacity (CUPRAC) spectrophotometric method for a number of polyphenols and flavonoids using the copper(II)-neocuproine reagent in ammonium acetate buffer is now applied to a complete series of plasma antioxidants for the assay of total antioxidant capacity of serum, and the resulting absorbance at 450 nm is recorded either directly (e.g., for ascorbic acid, alpha-tocopherol, and glutathione) or after incubation at 50 degrees C for 20 min (e.g., for uric acid, bilirubin, and albumin), quantitation being made by means of a calibration curve. The lipophilic antioxidants, alpha-tocopherol and beta-carotene, are assayed in dichloromethane. Lipophilic antioxidants of serum are extracted with n-hexane from an ethanolic solution of serum subjected to centrifugation. Hydrophilic antioxidants of serum are assayed in the centrifugate after perchloric acid precipitation of proteins. The CUPRAC molar absorptivities, linear ranges, and TEAC (trolox equivalent antioxidant capacity) coefficients of the serum antioxidants are established, and the results are evaluated in comparison with the findings of the ABTS/TEAC reference method. The intra- and inter-assay coefficients of variation (CVs) are 0.7 and 1.5%, respectively, for serum. The CUPRAC assay proved to be efficient for glutathione and thiol-type antioxidants, for which the FRAP (ferric reducing antioxidant potency) test is basically nonresponsive. The additivity of absorbances of all the tested antioxidants confirmed that antioxidants in the CUPRAC test do not chemically interact among each other so as to cause an intensification or quenching of the theoretically expected absorbance, and that a total antioxidant capacity (TAC) assay of serum is possible. As a distinct advantage over other electron-transfer based assays (e.g., Folin, FRAP, ABTS, DPPH), CUPRAC is superior in regard to its realistic pH close to the physiological pH, favorable redox potential, accessibility and stability of reagents, and applicability to lipophilic antioxidants as well as hydrophilic ones. The CUPRAC procedure can also assay hydroxyl radicals, being the most reactive oxygen species (ROS). As a more convenient, efficient, and less costly alternative to HPLC/electrochemical detection techniques and to the nonspecific, low-yield TBARS test, we use p-aminobenzoate, 2,4- and 3,5-dimethoxybenzoate probes for detecting hydroxyl radicals generated from an equivalent mixture of [Fe(II)+EDTA] with hydrogen peroxide. The produced hydroxyl radicals attack both the probe and the water-soluble antioxidants in 37 degrees C-incubated solutions for 2 h. The CUPRAC absorbance of the ethylacetate extract due to the reduction of Cu(II)-neocuproine reagent by the hydroxylated probe decreases in the presence of (.)OH scavengers, the difference being proportional to the scavenging ability of the tested compound. The developed method is less lengthy, more specific, and of a higher yield than the classical TBARS assay.

Release and Degradation of Anthocyanins and Phenolics from Blueberry Pomace during Thermal Acid Hydrolysis and Dry Heating

In this study, blueberry pomace was soaked in pH 1, 4, or 7 solution for 10 min followed by boiling hydrolysis. Nine anthocyanins and 11 other phenolic compounds were released after acid hydrolysis. The highest anthocyanin release (4.70 mg/g) was achieved by boiling at pH 1 for 15 min followed by 3.94 mg/g at pH 4 and 3.46 mg/g at pH 7. Phenolics were released more quickly than anthocyanins during boiling. The change of antioxidant activity of the pomace during boiling was correlated with the total phenolic content but not anthocyanin content. The degradation rate of anthocyanins during boiling eventually surpassed the release rate from the pomace. Protocatechuic acid and catechin continuously increased during heating. Dry heat resulted in continuous degradation of anthocyanins and other phenolics in the pomace. The reduction in antioxidant activity of the pomace during dry heating was correlated with both the phenolic and anthocyanin contents.

Novel Optical Fiber Reflectometric CUPRAC Sensor for Total Antioxidant Capacity Measurement of Food Extracts and Biological Samples

A novel fiber optic sensor was developed for screening the total antioxidant capacity (TAC) based on the use of cupric-neocuproine (Cu(II)-Nc) immobilized onto a Nafion cation-exchange membrane with reflectance spectrometric measurement. The reflectance change associated with the formation of the highly colored Cu(I)-Nc chelate on the membrane as a result of reaction with antioxidants was measured at 530 nm by using a miniature reflectance spectrometer. The calibration graph of trolox (TR) was linear with a slope of 3.40 × 10(3) L mol(-1) mm(-1). The limit of detection (LOD) and limit of quantification (LOQ) for TR in the reflectometric cupric reducing antioxidant capacity (CUPRAC) method were found as 0.53 and 1.76 μM, respectively. The trolox equivalent antioxidant capacities (TEAC) of various antioxidant compounds using the proposed method were comparable to those of the main CUPRAC assay. This assay was validated through linearity, additivity, precision, and recovery. The developed reflectance sensor was used to screen the TAC of some commercial fruit juices and mice tissue homogenates without preliminary treatment. The method is rapid, inexpensive, versatile, and nonlaborious, uses stable reagents on the sensor, and enables the in situ estimation of antioxidant capacity of food extracts and biological samples.

The CUPRAC Methods of Antioxidant Measurement for Beverages

In this chapter, total antioxidant capacity (TAC), ascorbic acid content, and reactive oxygen species (ROS) scavenging activity of beverages (orange, pomegranate, red grape, apple, cherry, and apricot juices) were investigated. TAC was spectrophotometrically determined by using the main and sensor-based cupric reducing antioxidant capacity (CUPRAC) methods. The modified CUPRAC methods were used to determine the ROS (hydrogen peroxide, hydroxyl and superoxide radical) scavenging activity. The ascorbic acid (AA) content of beverages was measured by La-CUPRAC method. This study showed that the antioxidant capacities of beverages, unlike their ROS scavenging activities, are correlated with their ascorbic acid contents. The TAC values and AA contents of freshly squeezed fruit juices were higher than those of ready-to-drink juices. In addition, the scavenging activities of ready-to-drink juices showed irregular variations with respect to the type of ROS scavenged. This report aims to summarize the measurement of TAC, AA, and ROS scavenging activity of various fruit juices, together with correlation of data and possible effects of processing.

Novel Spectroscopic and Electrochemical Sensors and Nanoprobes for the Characterization of Food and Biological Antioxidants

Since an unbalanced excess of reactive oxygen/nitrogen species (ROS/RNS) causes various diseases, determination of antioxidants that can counter oxidative stress is important in food and biological analyses. Optical/electrochemical nanosensors have attracted attention in antioxidant activity (AOA) assessment because of their increased sensitivity and selectivity. Optical sensors offer advantages such as low cost, flexibility, remote control, speed, miniaturization and on-site/in situ analysis. Electrochemical sensors using noble metal nanoparticles on modified electrodes better catalyze bioelectrochemical reactions. We summarize the design principles of colorimetric sensors and nanoprobes for food antioxidants (including electron-transfer based and ROS/RNS scavenging assays) and important milestones contributed by our laboratory. We present novel sensors and nanoprobes together with their mechanisms and analytical performances. Our colorimetric sensors for AOA measurement made use of cupric-neocuproine and ferric-phenanthroline complexes immobilized on a Nafion membrane. We recently designed an optical oxidant/antioxidant sensor using N,N-dimethyl-p-phenylene diamine (DMPD) as probe, from which ROS produced colored DMPD-quinone cationic radicals electrostatically retained on a Nafion membrane. The attenuation of initial color by antioxidants enabled indirect AOA estimation. The surface plasmon resonance absorption of silver nanoparticles as a result of enlargement of citrate-reduced seed particles by antioxidant addition enabled a linear response of AOA. We determined biothiols with Ellman reagent−derivatized gold nanoparticles.