Pressurized Hot Water Extraction of anthocyanins from red onion: A study on extraction and degradation rates

Pressurized Hot Water Extraction (PHWE) is a quick, efficient and environmentally friendly technique for extractions. However, when using PHWE to extract thermally unstable analytes, extraction and degradation effects occur at the same time, and thereby compete. At first, the extraction effect dominates, but degradation effects soon take over. In this paper, extraction and degradation rates of anthocyanins from red onion were studied with experiments in a static batch reactor at 110 °C. A total extraction curve was calculated with data from the actual extraction and degradation curves, showing that more anthocyanins, 21-36% depending on the species, could be extracted if no degradation occurred, but then longer extraction times would be required than those needed to reach the peak level in the apparent extraction curves. The results give information about the different kinetic processes competing during an extraction procedure.     

An effective method for extracting anthocyanins from blueberry based on freeze-ultrasonic thawing technology

The aim of this study was to develop an effective method for extracting anthocyanins from blueberry Vaccinium spp. (ABVS) using freeze-ultrasonic thawing technology (FUTE). Various parameters including freezing time, ultrasonic time, ultrasonic temperature and liquid–solid ratio were optimized by a single-factor design and multiple response surface methodology. The amounts of extracted anthocyanin and cyanidin-3-O-glucoside were measured by UV and HPLC respectively. The maximum yield of anthocyanins was achieved by freezing the samples for 5.43 min in liquid nitrogen at the liquid–solid ratio of 24.07:1 mL/g, followed by ultrasonic thawing at 41.64 °C for 23.56 min. The yield and antioxidant effects of ABVS extracted using FUTE, ultrasound-assisted extraction (UAE) and freeze-thawing extraction (FTE) were compared in order to determine the overall efficacy of FUTE. In addition to the higher content, FUTE extracted ABVS showed greater ability to scavenge DPPH·, ABTS⁺ and superoxide anions, and inhibit lipid peroxidation compared to the ABVS extracted by UAE or FTE. The reducing power of the FUTE-derived ABVS was intermediate between that of the UAE and FTE samples. Taken together, FUTE can rapidly and effectively extract ABVS and retain its antioxidant capacity.     

Pressurized solvent extraction and monolithic column-HPLC/DAD analysis of anthocyanins in red cabbage

The aim of this work was to develop a fast method for extraction and analysis of anthocyanins in red cabbage. Pressurized hot water containing 5% of ethanol was used as an extremely efficient extraction solvent. HPLC/DAD with a monolithic column was used to accomplish a fast analysis—24 anthocyanin peaks within 18 min. Statistical design was used to optimize the studied extraction parameters: temperature (80–120 °C); sample amount (1–3 g); extraction time (6–11 min); concentration of formic acid in the extraction solvent (0–5 vol.%). The best extraction conditions for a majority of the anthocyanin peaks were 2.5 g of sample, 99 °C (at 50 bar), 7 min of extraction and a solvent composition of water/ethanol/formic acid (94/5/1, v/v/v).     

Q-mode curve resolution of UV-vis spectra for structural transformation studies of anthocyanins in acidic solutions

Chemometric analysis of ultraviolet-visible (UV-vis) spectra for pH values 1.0, 3.3, 5.3, and 6.9 was used to investigate the kinetics and the structural transformations of anthocyanins in extracts of calyces of hibiscus flowers of the Hibiscus acetosella Welw. ex Finicius for the first time. Six different species were detected: the quinoidal base (A), the flavylium cation (AH⁺), the pseudobase or carbinol pseudobase (B), cis-chalcone (C_C), trans-chalcone (C_t), and ionized cis-chalcone (⁻CC). Four equilibrium constant values were calculated using relative concentrations, hydration, pK_h = 2.60 ± 0.01, tautomeric, K_T = 0.14 ± 0.01, acid-base, pK_a = 4.24 ± 0.04, and ionization of the cis-chalcone, pKCC=8.74±1.5×1⁰−2. The calculated protonation rate of the tautomers is KH+=0.08±7.6×10⁻³. These constants are in excellent agreement with those measured previously in salt form. From a kinetic viewpoint, the situation encountered is interesting since the reported investigation is limited to visible light absorption in acid medium. These models have not been reported in the literature.     

High-efficiency high performance liquid chromatographic analysis of red wine anthocyanins

The analysis of anthocyanins in natural products is of significant relevance in recent times due to the recognised health benefits associated with their consumption. In red grapes and wines in particular, anthocyanins are known to contribute important properties to the sensory (colour and taste), anti-oxidant- and ageing characteristics. However, the detailed investigation of the alteration of these compounds during wine ageing is hampered by the challenges associated with the separation of grape-derived anthocyanins and their derived products. High performance liquid chromatography (HPLC) is primarily used for this purpose, often in combination with mass spectrometric (MS) detection, although conventional HPLC methods provide incomplete resolution. We have previously demonstrated how on-column inter-conversion reactions are responsible for poor chromatographic efficiency in the HPLC analysis of anthocyanins, and how an increase in temperature and decrease in particle size may improve the chromatographic performance. In the current contribution an experimental configuration for the high efficiency analysis of anthocyanins is derived using the kinetic plot method (KPM). Further, it is shown how analysis under optimal conditions, in combination with MS detection, delivers much improved separation and identification of red wine anthocyanins and their derived products. This improved analytical performance holds promise for the in-depth investigation of these influential compounds in wine during ageing.     

Direct photothermal techniques for rapid quantification of total anthocyanin content in sour cherry cultivars

The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (PAS) and of optothermal window (OW) method for quantification of total anthocyanin concentration (TAC) in five sour cherry varieties is compared to that of the spectrophotometry (SP). High performance liquid chromatography (HPLC) was used to identify and quantify specific anthocyanins. Both, PAS and OW are direct methods that unlike SP and HPLC obviate the need for the extraction of analyte. The outcome of the study leads to the conclusion that PAS and OW are both suitable for quick screening of TAC in sour cherries. The correlation between the two methods and SP is linear with R² = 0.9887 for PAS and R² = 0.9918 for OW, respectively. Both methods are capable of the rapid determination of TAC in sour cherries without a need for a laborious sample pretreatment.     

Anthocyanins HPLC-DAD and MS Characterization,Total Phenolics,and Antioxidant Activity of Some Berries Extracts

Extracts of indigenous wild blackberries, mulberries, bilberries, and blackthorns were analyzed for anthocyanin composition, anthocyanin content, total phenolics, and antioxidant capacity. Anthocyanins extraction with acidified methanol in ultrasonic condition (59 kHz, 60 min., 25°C) was carried out. The extracts were analyzed by high-performance liquid chromatography (HPLC) using a Dionex Ultimate 3000 apparatus equipped with photodiode array detector for qualitative characterization of the anthocyanins. The chromatograms revealed the presence of a large number of anthocyanins in fruits extracts: blackberries, 4 compounds; mulberries, 3 compounds; bilberries, 18 compounds; and blackthorns, 5 compounds. The most abundant anthocyanins were cyanidin-3-glucoside in blackberry, mulberry, and bilberry, and cyanidin-3-rutinoside in blackthorn extract. Structural information about anthocyanins was obtained by using a mass spectrometric method based on fully automated chip-nanoelectrospray ionization (nanoESI) high capacity ion trap (HCT). Anthocyanin content was quantified by the pH differential method and total phenolics were determined by Folin-Ciocalteu method. A Jasco V 530 UV-VIS spectrophotometer was used for absorbance measurements. The free radical scavenging activity of the berries extracts was performed by using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. The reduction of DPPH was followed by a spectrophotometric method. Also, a correlation of the antioxidant capacities of the extracts with their anthocyanin content and total phenolics was attempted.     

Complex Formation and Flower Colors

The pigment of the blue cornflower, protocyanin, is a complex of high molecular weight. Iron(III) and aluminum ions combine with the anhydro base of the cyanin to form deep-blue complexes, which are stable in the physiological pH range. Complexes of this type also have been synthesized. Alkali metal salts play no part in blue flower pigments. Formation of blue complexes can be prevented by sequestration of the metal ions with stronger complexing agents, e.g. flavonols. The variation of flower colors can be explained to a large extent on the basis of the complex formation of anthocyanins. In delphinidin glycosides, the color base or anhydro base is stable even in slightly acidic media.     

Phenolic potential of Tannat, Cabernet-Sauvignon and Merlot grapes and their correspondence with wine composition

The phenolic potential of Tannat, Cabernet-Sauvignon and Merlot grapes was evaluated in 2001 and 2002 and its correspondence with the colour and composition of the respective wines was established. Three vineyards of each variety, situated in the south of Uruguay were considered. Two samples of each vineyard were taken at the moment of the harvest. Phenolic richness, extractable anthocyanins contents and total potential in anthocyanins of the grapes were estimated. Two fermentations on skins were carried out for each vineyard using 50 kg of grape in each one. The anthocyanic and total polyphenols contents of the musts were analysed every 24 h, and skins extractions were carried out in parallel in the laboratory. The duration of the maceration for each variety was decided in function of the analytical results in the grapes, musts and skins extractions. Wines were analysed 2 months after the alcoholic fermentation, determining its phenolic composition and colour. Tannat grapes presented anthocyanic and total polyphenols contents significantly higher in both years. Therefore, wines from this variety presented colour intensity and phenolic contents statistically higher than Cabernet-Sauvignon and Merlot. The correlations between the phenolic contents of the grapes, skins, musts and wines were very significant. Colour intensity and phenolic contents of the wines were highly correlated with the total polyphenols of the grapes and with anthocyanins of the grapes, skins, musts and wines. The estimate of the phenolic potential of the grapes and the extractability of the pigments allows to manage more adequately the fermentation on skins and is an interesting tool to predict the colour and the composition of the wines.