Whey protein addition and its increased light absorption and tinctorial strength of model solutions colored with anthocyanins.

Anthocyanins (ACN) are pigments with vivid colors, but their application as food colorants is restricted by their limited stability and color expression. Anthocyanins exhibit higher stability in dairy systems than in buffers at similar pH, suggesting that pigments may be able to interact with dairy components such as proteins, resulting in improved performance as colorants. Our objective was to determine the type of interaction between whey proteins (WP) and ACN leading to color enhancements and to determine the role of the ACN chemical structure in this interaction. Model solutions colored with semipurified pigments from sources with different ACN profiles (Berberis boliviana, grape skin, purple corn, black carrot, and red cabbage) were mixed with different concentrations of whey protein isolate (WPI) in pH 3 buffer. Absorption spectra of these solutions were acquired using an absorbance microplate reader, and color parameters were calculated from spectral data. Isolated ACN 3-glucosides were used to determine the role of the aglycone structure in the WP-ACN interaction using visible and fluorescence spectroscopy. In silico modeling was used to visualize potential differences in the interaction between ß-lactoglobulin and ACN. Addition of WPI resulted in hyperchromic shifts at the wavelength of maximum absorption in the visible range (λvis-max) of up to 19%, and a significant increase in tinctorial strength for all ACN sources (ΔE > 5). Moreover, ACN acylation did not seem to play a significant role in the WP-ACN interaction. When using isolated ACN, WPI addition resulted in hyperchromic shifts at the λvis-max only for methoxylated ACN such as petunidin-3-glucoside (up to 24%), and malvidin-3-glucoside (up to 97%). The bimolecular quenching constant values (Kq > 1010M-1s-1) strongly suggested that the predominant type of quenching interaction was static. Analysis of enthalpy, entropy, and Gibbs free energy showed that this binding was spontaneous; depending on the chemical structure of the ACN, the predominant binding forces could be hydrophobic interactions or hydrogen bonding. Modeling suggested that methoxylations in the B ring of the aglycon structure promoted interactions with electron acceptor amino acids. Overall, WP could be used to enhance the tinctorial strength of select ACN depending on their structural characteristics. Therefore, ACN source selection may play a key role for specific applications in dairy products.

Effects of hydroxycinnamic acids on blue color expression of cyanidin derivatives and their metal chelates.

Mechanisms to recreate many anthocyanin blue hues in nature are not fully understood, but interactions with metal ions and phenolic compounds are thought to play important roles. Bluing effects of hydroxycinnamic acids on cyanidin and chelates were investigated by addition of the acids to triglycosylated cyanidin (0-50×[anthocyanin]) and by comparison to hydroxycinnamic acid monoacylated and diacylated Cy fractions by spectrophotometry (380-700nm) and colorimetry in pH 5-8. With no metal ions, λmax and absorbance was greatest for cyanidin with diacylation>monoacylation>increasing [acids]. Hydroxycinnamic acids added to cyanidin solutions weakly impacted color characteristics (ΔE<5); while acylation (covalent acid attachment) resulted in ΔE 5-15. Triglycosylated cyanidin expressed blue color (pH 7-8), suggesting glycosylation pattern also plays a role. Al3+ chelation increased absorbance 2-42× and λmax≳40nm (pH 5-6) compared to added hydroxycinnamic acids. Metal chelation and aromatic diacylation resulted in the most blue hues.

Spectral and colorimetric characteristics of metal chelates of acylated cyanidin derivatives.

Colorants derived from nature are increasingly popular due to consumer demand. Anthocyanins are a class of naturally occurring pigments that produce red-purple-blue hues in nature, especially when interacting with metal ions and co-pigments. The role of various acylations of cyanidin (Cy) derivatives on color expression and stability of Al3+ and Fe3+ chelates in pH 6-7 were evaluated by spectrophotometry (380-700nm) and colorimetry (CIE-L∗a∗b∗) during dark, ambient storage (48h). Increased substitution generally increased λmax of Cy chelates: malonic acid monoacylationferulic-sinapic>sinapic-sinapic)>monoacylated (malonic≈sinapic>ferulic>p-coumaric).

Evaluating the role of metal ions in the bathochromic and hyperchromic responses of cyanidin derivatives in acidic and alkaline pH.

In many food products, colorants derived from natural sources are increasingly popular due to consumer demand. Anthocyanins are one class of versatile and abundant naturally occurring chromophores that produce different hues in nature, especially with metal ions and other copigments assisting. The effects of chelation of metal ions (Mg(2+), Al(3+), Cr(3+), Fe(3+), and Ga(3+)) in factorial excesses to anthocyanin concentration (0-500×) on the spectral characteristics (380-700nm) of cyanidin and acylated cyanidin derivatives were evaluated to better understand the color evolution of anthocyanin-metal chelates in pH 3-8. In all pH, anthocyanins exhibited bathochromic and hyperchromic shifts. Largest bathochromic shifts most often occurred in pH 6; while largest hyperchromic shifts occurred in pH 5. Divalent Mg(2+) showed no observable effect on anthocyanin color while trivalent metal ions caused bathochromic shifts and hue changes. Generally, bathochromic shifts on anthocyanins were greatest with more electron rich metal ions (Fe(3+)≈Ga(3+)>Al(3+)>Cr(3+)).

Determination of color, pigment, and phenolic stability in yogurt systems colored with nonacylated anthocyanins from Berberis boliviana L. as compared to other natural/synthetic colorants.

Anthocyanins are of interest to the food industry because of their antioxidant power, attractive color, and stability in high acid foods. Powder from the Peruvian berry Berberis boliviana Lechler, rich in nonacylated anthocyanins (7% to 8% dry weight), was incorporated into yogurt samples containing 3 different fat levels. Color (CIE L, a, b, chroma, and hue angle), pigment (monomeric anthocyanin and polymeric color), and total phenolics were monitored over 8 wk of storage and compared to yogurt treatments containing purple carrot acylated anthocyanins, red beet betalaines, or FD&C Red nr 40. Anthocyanin profiles were analyzed by HPLC coupled to photodiode array and mass detectors. Color of yogurt containing B. boliviana anthocyanins at 20 mg cyanidin-3-glucoside (cy-3-glu) equivalents/100 g yogurt (L*= 65, chroma = 14, and hue angle = 335 degrees ) was similar to commercial blueberry yogurt (L*= 65, chroma = 10.5, and hue angle = 341 degrees ). High color, pigment, and phenolic stability were observed in yogurts colored with B. boliviana, independent of the fat matrix. Acylated anthocyanins from purple carrot extracts exhibited increased stability with higher fat content. Anthocyanin degradation followed 1st-order kinetics. Pigment half-lives were 125 and 104 d for nonacylated anthocyanins at 10 and 20 mg cy-3-glu equivalents/100 g yogurt and 550.2, 232.6, and 128.9 d for acylated anthocyanins at 20 mg of cy-3-glu equivalents/100 g of 4%, 2%, and 0% fat yogurt. Addition of B. boliviana whole berry powder to yogurt matrices produced an attractive, stable anthocyanin-rich product, eliminating the need for industrial colorant extraction.

Effects of extraction conditions on improving the yield and quality of an anthocyanin-rich purple corn (Zea mays L.) color extract.

Purple corn (Zea mays L.) is a rich and economic source of anthocyanin colorants and functional ingredients. However, high levels of anthocyanin-rich waste are generated during processing, reducing the yields and increasing the costs of the final product. This waste has been associated with anthocyanin complexation with tannins and proteins. Our objective was to evaluate anthocyanin extraction methods to reduce purple corn waste. Different solvents (water, 0.01%-HCl-acidified water, and 0.01%-HCl-acidified ethanol), temperatures (room temperature, 50, 75, and 100 degrees C), and times of exposure to the solvents were investigated. Acetone (70% acetone in water) extraction was used as control. Anthocyanins, total phenolics, tannins, and proteins in extracts were measured by the pH differential, Folin-Ciocalteu, protein precipitation, and BCA assay methods. Qualitative analyses were done by HPLC coupled to a PDA detector and SDS-PAGE analysis. Water at 50 degrees C achieved the highest yield of anthocyanins (0.94 +/- 0.03 g per 100 g dry corncob) with relatively low tannins and proteins, comparable to the anthocyanin yield obtained by 70% acetone (0.98 +/- 0.08 g per 100 g dry corncob). Extending the extraction time from 20 to 60 min and using consecutive reextraction procedures reduced anthocyanin purity, increasing the yields of other phenolics. A neutral protease was applied to the extracts and effectively decomposed the major protein that was believed to contribute to the development of anthocyanin complexation and waste generation. Extraction time, consecutive reextraction procedures, and enzyme hydrolysis should be considered for high yield of anthocyanins and waste reduction.

Molar absorptivity and color characteristics of acylated and non-acylated pelargonidin-based anthocyanins.

The effects of glycosylation and acylation on the spectral characteristics, molar absorptivity, and color attributes of purified acylated and non-acylated pelargonidin derivatives were compared. Pigments were obtained from strawberries, radishes, red-fleshed potatoes, and partially hydrolyzed radish pigments. Individual pigments were isolated by using semipreparative HPLC. Spectral and color (CIELch) attributes of purified pigments were measured. Molar absorptivity ranged from 15 600 to 39 590 for pelargonidin-3-glucoside (pg-3-glu) and pg-3-rutinoside-5-glucoside acylated with p-coumaric acid, respectively. The presence of cinnamic acid acylation had a considerable impact on spectral and color characteristics, causing a bathochromic shift of lambda(max). Sugar substitution also played an important role, with a hypsochromic shift caused by the presence of glycosylation. Pg-3, 5-diglu and pg-3,5-triglu possessed a higher hue angle (>40 degrees ) than the other pg derivatives at pH 1.0, corresponding to the yellow-orange region of the color solid. Acylation with malonic acid did not affect lambda(max) and showed little effect on color characteristics. The solvent system had an effect not only on the molar absorptivity, but also on the visual color characteristic of the pigments.

Electrospray and tandem mass spectroscopy as tools for anthocyanin characterization.

The utility of electrospray and tandem mass spectroscopy (ES-MS and MS-MS) in anthocyanin characterization was tested using different anthocyanin extracts. Anthocyanins were semipurified by using a C-18 resin, washed with acidified water followed by ethyl acetate, and recovered with acidified methanol. Samples were directly injected into a mass spectrometer in either aqueous or methanolic solutions. The positive charge of anthocyanins favored fast and effective ES-MS detection of intact molecular ions. Little interference from other compounds was observed when the ethyl acetate cleaning procedure was used. Tandem mass spectroscopy provided clear and characteristic fragmentation patterns. The voltage used affected only the proportions at which these fragments were present. ES-MS may be used as a fast procedure for identification of anthocyanins, requiring minimal sample preparation. In combination with HPLC, ES-MS and MS-MS could be very powerful tools for anthocyanin characterization and monitoring the authenticity of anthocyanin-containing fruit juices and vegetable extracts.