Folin-Ciocalteu Spectrophotometric Method Research Articles

On the electrochemical biosensing of phenolic compounds in wines

A simple electrochemical sensor based on polyphenol oxidases was proposed for determination of the total phenol content in wine. Application of two oxidases: tyrosinase and laccase (separately) was examined and the results were compared. An analytical characteristic of proposed sensor towards gallic acid was evaluated. The influence of sample matrix components on the sensor response was studied according to Plackett–Burman experimental design. The potential interferents ethanol, tartaric acid, sorbate, sulfate(IV), putrescine, Fe(III) and glucose, which are usually encountered in wines, were taken into account in the examination. Because of the significant matrix effect found, analyses of wine samples towards polyphenol contents were carried out using standard addition method and expressed as gallic acid equivalents. For comparative quantification of phenolic compounds well-established Folin–Ciocalteu spectrophotometric method was applied. Significant inter-method differences were observed in electrochemical behaviour of standard substance – gallic acid – and phenolic constituents of real wine samples in the presence of tartaric acid.

Phenolic Composition and Sensory Properties of Ciders Produced from Latvian Apples

Abstract Polyphenol compounds are very important components of cider – they are responsible for the colour and the bitterness and astringency balance of cider. The polyphenolic profile of apples and apple drinks is influenced by several factors: apple variety, climate, maturity, and technological processes applied. This research paper concerns the influence of apple variety on the phenolic compounds and sensory properties of cider. Fermentation of 12 varieties of apple juice with Saccharomyces cerevisiae yeast ‘71B-1122’ (Lalvin, Canada) was performed in a laboratory of the Faculty of Food Technology of the Latvia University of Agriculture. The total phenol content (TPC) was determined according to the Folin-Ciocalteu spectrophotometric method. Individual phenolic compounds were analysed using HPLC. Sensory properties (clarity, the apple, fruit and yeast aroma, the apple and yeast taste, sourness, astringency, and bitterness) were evaluated by trained panelists using a line scale. Special attention was paid to the use of dessert apples for the production of cider. The most important sensory properties of cider are the aroma and taste of apples and fruit. All cider samples showed the intensity of apple aroma ranging from 5.3 to 7.6 points, and higher results were obtained for cider from the bvariety ‘Auksis’ apples. The TPC in cider samples varied from 792.68 to 3399.78 mg L-1: Among crab apples, the highest TPC was detected in ciders made from the ‘Hyslop’ and ’Riku’ varieties, whereas among dessert apples, the highest TPC was detected in ciders made from the ‘Antonovka’ variety. Among the twelve phenols identified in cider samples, chlorogenic acid and caffeic acid were the dominating ones. Variation in the sensory properties of ciders was dependent on the physicochemical composition of the apples used.

Minor Polar Compounds in Extra Virgin Olive Oil: Correlation between HPLC-DAD-MS and the Folin-Ciocalteu Spectrophotometric Method

Minor polar compounds of 88 extra virgin olive oils were analyzed by HPLC-DAD-MS (high-performance liquid chromatography-diode array detector-mass spectrometry) and by the Folin-Ciocalteu (FC) spectrophotometric method, to validate and evaluate, for olive oils, the linear association between FC and HPLC data. The Pearson correlation coefficients were calculated between HPLC and FC results. The highest, positive R were related with deacetoxyoleuropein aglycone (R = 0.93) and oleuropein aglycone (R = 0.93) as single compounds and with the sum of orthodiphenols (R = 0.94) and the sum of all compounds (R = 0.95), showing that both estimations of total phenols content are reliably correlated, regardless for the absolute contents and are independent of the relative composition of the phenolic fraction. On the other hand the HPLC quantifications of apigenin and lignans showed no significant correlation with FC. These results, supported also by principal component analysis, may suggest caution about the interpretation of FC results to compare olive oils with very different phenolic profiles.

Isolation and characterization of potent bioactive fraction with antioxidant and UV absorbing activity from Aloe barbadensis Miller gel

The methanolic extract of Aloe vera L. gel was subjected to antioxidant guided fractionation with silica gel column chromatography to screen the potent fraction. The antioxidant capacities of different fractions were evaluated using DPPH radical scavenging assay and correlated with total phenol content. Total phenolic contents of different fractions were determined according to the Folin-Ciocalteu spectrophotometric method. The positive correlation was observed between DPPH radical scavenging assay and total phenolic contents indicating that phenolics in Aloe vera L. gel were fundamental contributor of antioxidant activity. Third pooled fraction was identified as potential fraction with highest antioxidant potential. This fraction indicated the presence of well resolved fluorescent components. Characteristic UV–vis absorption and HPLC analysis indicates that aloin take part in antioxidant potential attributed to aloe gel.

Herbal infusions bioelectrochemical polyphenolic index: Green tea – The gallic acid interference

An amperometric biosensor containing immobilised laccase from Trametes versicolor was used for the quantification of phenolic compounds in herbal infusions and green tea samples, from nine botanical families. The main purpose of this research was to correlate the bioelectrochemical polyphenolic index (BPI) of the samples with the total phenolic content according to the Folin–Ciocalteu spectrophotometric method (TPC), and the total antioxidant activity (TAA) measured by TEAC (Trolox Equivalent Antioxidant Capacity). A strong correlation between BPI, TPC, and TAA was obtained for 10 herbal infusion samples. However, when a green tea sample was taken into account, a decrease in the linear correlation coefficient (r2) from 0.9949 to 0.2599 and 0.5609 to 0.1086 for the relationship between BPI/TPC and BPI/TAA, respectively, was observed. Thus, we could conclude that the green tea’s matrix affects the laccase-based biosensor response. HPLC–DAD analysis showed the presence of gallic acid only in the green tea sample. The results have indicated that gallic acid inhibited the laccase activity regarding the ABTS oxidation in a concentration-dependent manner. The very strong correlation between BPI/TPC obtained for herbal infusions allow us to conclude that the laccase-based biosensor, used in this research, provides a valuable tool to obtain a valid estimation of the classical Folin–Ciocalteu index, in an uncomplicated and fast way.

Amperometric biosensor based on a high resolution photopolymer deposited onto a screen-printed electrode for phenolic compounds monitoring in tea infusions

An amperometric biosensor based on laccase, from Trametes versicolor (LTV), was developed and optimized for monitoring the phenolic compounds content in tea infusions. The fungal enzyme was immobilized by entrapment within polyvinyl alcohol photopolymer PVA-AWP (azide-unit pendant water-soluble photopolymer) onto disposable graphite screen-printed electrodes (SPE). Sensitivity optimization in terms of pH, temperature and applied potential was carried out. The linear range, detection limit, operational and storage stabilities were also determined. The laccase biosensor (LTV-SPE) was calibrated for o-, m- and p-diphenol as well as caffeic acid. The highest response was found at 0.1M acetate buffer pH 4.7, though it must be added the good reproducibility and operational stability were also obtained. The useful lifetime of the biosensor is estimated to be greater than 6 months. LTV-SPE was used for the determination of the equivalent phenol content (EPC) in tea infusions by the direct addition into the electrochemical cell: the results were compared with those from the Folin-Ciocalteu spectrophotometric method. The amperometric detection exhibits some interesting advantages such as high simplicity, minimal sample preparation and shorter response time. A stable and sensitive amperometric response was obtained toward standard diphenolic compounds and herbal infusions. These biosensors are useful for easy and fast monitoring of EPC that can be related to the antioxidant capacity of natural extracts.

Determination of total phenols in tea infusions, tomato and apple juice by terbium sensitized fluorescence method as an alternative approach to the Folin–Ciocalteu spectrophotometric method

A fast screening of total phenols in tea infusions, tomato and apple juice samples using terbium sensitized fluorescence is described. The proposed method is based on the fluorescence sensitization of terbium (Tb3+) by complexation with flavonols (quercein as a reference standard) (at pH 7.0), which fluoresces intensely with an emission maximum at 545nm when excited at 310nm. Quercetin and terbium cations (at pH 7.0) form a stable complex and the resulted emission at 545nm can be used for the determination of the total phenols concentration expressed in terms of “quercetin equivalent”. Based on the obtained results, a sensitive, simple and rapid spectrofluorimetric method was developed for the determination of total phenols. In the optimum conditions, the calibration graph was linear from 0.01 to 2μgmL−1, with the limit of detection of 0.002μgmL−1. The relative standard deviation values were in the range of 0.75–2.3%. The total concentrations of quercetin equivalent in five tested samples were found in the range of 6.6–27.9μgmL−1 and the results compare favorably with those obtained by spectrophotometric method (r=0.999).