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Safety concerns in the food industry have increased the demand for natural food colorants. However, the application ranges of natural blue colorants are insufficient because they are scarce in nature, and the currently available natural blue dyes are limited to water-soluble products. In this study, we investigated a fat-soluble azulene derivative isolated from the mushroom Lactarius indigo as a potential candidate for a natural blue colorant. We developed its first total synthesis, where the azulene skeleton was constructed from a pyridine derivative and an ethynyl group was converted into an isopropenyl group using zirconium complexes. Moreover, nanoparticles of the azulene derivative were prepared via reprecipitation method, and their colorant ability was investigated in aqueous solutions. The new candidate food colorant exhibited a deep-blue color in an organic solvent and aqueous dispersion.

This perspective highlights current trends, advances, and challenges related to the replacement of artificial dyes and the insect-based carmine with alternative natural pigments. Briefly reviewing the history of food coloration, key publications and public events leading to diverse concerns about artificial dyes and carmine will be summarized. An overview about promising alternatives in the market and those under development is provided, including a separate section on coloring foodstuffs. The perspective aims at supporting readers to keep abreast with the enormous efforts undertaken by the food and beverage industry to replace certain food dyes.

Synthetic colorants in food can be a potential threat to human health. In this study, surface-enhanced Raman spectroscopy (SERS) coupled with gold nanorods as substrates is proposed to analyze allura red and sunset yellow in beverages. The gold nanorods with different aspect ratios were synthesized, and their long-term stability, SERS activity, and the effect of the different salts on the SERS signal were investigated. The results demonstrate that gold nanorods have a satisfactory stability (stored up to 28 days). SERS coupled with gold nanorods exhibit stronger sensitivity. MgSO 4 was chosen to improve the SERS signal of sunset yellow, and no salts could enhance the SERS signal of allura red. The lowest concentration was 0.10 mg/L for both colorant standard solutions. The successful prediction results using SERS were much closer to those obtained by high-performance liquid chromatography for the sample in beverages. SERS combined with gold nanorods shows potential for analyzing food colorants and other food additives as a rapid, convenient, and sensitive method.

An ultra-high-throughput approach based on ultra-high-performance liquid chromatography with diode array detection (UHPLC-DAD) in combination with simple syringe filtration was successfully developed and validated for the quantitation of nine synthetic colorants in beverages. The recoveries of the colorants from the beverages were found to be dramatically affected by the syringe filter membrane types and pH of the sample solution. The high recoveries of the nine colorants (92.7-105.9%) were achieved by syringe filtration with poly(vinylidene difluoride) membrane following the pH adjustment of sample solution at pH 7.0. The sample treatment procedure was very simple and took only 1 min. The fast chromatographic separation (1 min) of the nine synthetic colorants was achieved by UHPLC-DAD using a C18-core-shell column. This analytical approach (UHPLC-DAD combined with syringe filtration) took only approximately 3 min. The established method was ultrafast, sensitive, precise, accurate, and reliable. The method was successfully applied to rapidly determine the 9 colorants in 17 beverages.

Allura red is a widely used synthetic food dye. In this study, we developed and validated a LC-MS/MS method for the quantification of allura red in three popular takeaway Chinese dishes (braised pork, soy sauce chicken, sweet and sour pork) and human urine samples. High levels of allura red ranging from 2.85 to 8.38 mg/g wet weight were detected in the surveyed Chinese dishes. Of 113 participants who frequently consume the surveyed Chinese dishes (>once a week in the past 2 years), the median of their urinary allura red level was 22.29 nM/mM creatinine (95% CI = 19.48-25.03) . Risk assessment using Cox proportional hazard models showed that a 10-fold increase in urinary allura red was positively associated with high blood pressure (odds ratio of 1.75 (95% CI = 0.78-3.96)). Our findings provide new insights for the potential risk of hypertension for long-term allura red overconsumption.

As one of the rarely allowable azo dyes, ponceau 4R can be added in some foods in some countries. However, it is necessary to develop a credible and rapid analytical method for its monitoring, because of its potentially harmful risk. The hapten of ponceau 4R was first designed and synthesized by introducing a primary amine group into the structure of ponceau 4R. Based on the well-prepared hapten, the immunogen of ponceau 4R was prepared using glutaraldehyde to link ponceau 4R to the carrier protein. The triggered polyclonal antibody was obtained and tested by ELISA to optimize the proper dilution. An icELISA was developed for ponceau 4R, and the IC50 of the method is 36.82 ng/mL. The limit of detection is 0.80 ng/mL, and the linear range is 1-10000 ng/mL. Five selected structural analogues have no cross-reactivity with the anti-ponceau 4R polyclonal antibody (<0.3). In three food samples (grape juice, carbonated beverage, and RIO cocktail), the assay exhibits good stability and reproducibility with a recovery range of 93.87-103.77%, and the intra- and interassay coefficients of variation were <11.73%. The results indicate that the proposed icELISA is sensitive, accurate, specific, and simple, which provides an alternative for the detection of ponceau 4R in foods.

The food and beverage industry is seeking to broaden the palette of naturally derived colorants. Although considerable effort has been devoted to the search for new blue colorants in fruits and vegetables, less attention has been directed toward blue compounds from other sources such as bacteria and fungi. The current work reviews known organic blue compounds from natural plant, animal, fungal, and microbial sources. The scarcity of blue-colored metabolites in the natural world relative to metabolites of other colors is discussed, and structural trends common among natural blue compounds are identified. These compounds are grouped into seven structural classes and evaluated for their potential as new color additives.

The multiequilibrium system of reactions of cyanidin 3-glucoside at acidic and mildly acidic pH values was studied in the presence of caffeine as a copigment. The thermodynamic and kinetic constants were determined using the so-called direct and reverse pH jump experiments that were followed by conventional UV-vis spectroscopy or stopped flow coupled to a UV-vis detector, depending on the rate of the monitored process. Compared with that of free anthocyanin, the copigmentation with caffeine extends the domain of the flavylium cation up to less acidic pH values, while in a moderately acidic medium, the quinoidal base becomes more stabilized. As a consequence, the hydration to give the colorless hemiketal is difficult over the entire range of pH values. At pH 1, two adducts were found for the flavylium cation-caffeine interaction, with stoichiometries of 1:1 and 1:2 and association constants of 161 M⁻¹ (K₁) and 21 M⁻¹ (K₂), respectively.

This study describes a new method for determining FD&C Blue No. 1, FD&C Blue No. 2, FD&C Green No. 3, FD&C Red No. 3, FD&C Red No. 40, FD&C Yellow No. 5, and FD&C Yellow No. 6 in food products. These seven color additives are water-soluble dyes that are required to be batch certified by the U.S. Food and Drug Administration (FDA) before they may be used in food and other FDA-regulated products. In the new method, the color additives are extracted from a product using one of two procedures developed for various product types, isolated from the noncolored components, and analyzed by liquid chromatography with photodiode array detection. The method was validated by determining linearity, range, precision, recovery from various matrices, limit of detection, limit of quantitation, and relative standard deviation for each color additive. A survey of 44 food products, including beverages, frozen treats, powder mixes, gelatin products, candies, icings, jellies, spices, dressings, sauces, baked goods, and dairy products, found total color additives ranging from 1.9 to 1221 mg/kg. FDA intends to use the new method for conducting a rigorous, comprehensive dietary exposure assessment of certified color additives in products likely to be consumed by children.

The new ionic liquid modified polymeric microspheres (ILPM) were synthesized by precipitation polymerization using 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) as the functional monomer, divinylbenzene (DVB) as the cross-linker, and a mixture of toluene and acetonitrile as the dispersant solvent. The obtained ILPM showed good adsorbability to the four kinds of Sudan dyes and were successfully applied as a special sorbent of solid-phase extraction (SPE) coupled with high-performance liquid chromatography (HPLC) for the simultaneous isolation and determination of four Sudan dyes from foodstuff samples. Compared with the traditional SPE adsorbents such as neutral alumina and C18, the ILPM sorbents provided higher recovery with a significant purification effect. Good linearity was obtained in a range of 0.05-4.0 μg/g (r(2) ≥ 0.9996) for the four kinds of Sudan dyes, and the average recoveries at three spiked levels ranged from 92.5% to 106.1% with the relative standard deviations ≤ 5.7%. The proposed ILPM-SPE-HPLC method could be potentially applied to rapid isolation and determination of Sudan dyes in complicated food samples.

An ultrahigh-performance liquid chromatography (UHPLC) tandem mass spectrometric (MS/MS) method was developed for the simultaneous quantification of 2-acetyl-4-tetrahydroxybutylimidazole (THI), 2- and 4-methylimidazoles (2-MI and 4-MI), and 5-hydroxymethylfurfural (HMF) in beverage samples. A C30 reversed-phase column was used in this method, providing sufficient retention and total resolution for all targeted analytes, with an MS/MS instrument operated in selected reaction monitoring (SRM) mode for sensitive and selective detection using isotope-labeled 4-methyl-d(3)-imidazole (4-MI-d(3)) as the internal standard (IS). This method demonstrates lower limit of quantification (LLOQ) at 1 ng/mL and coefficient of determination (r(2)) >0.999 for each analyte with a calibration range established from 1 to 500 ng/mL. This method also demonstrates excellent quantification accuracy (84.6-105% at 5 ng/mL, n = 7), precision (RSD < 7% at 5 ng/mL, n = 7), and recovery (88.8-99.5% at 10, 100, and 200 ng/mL, n = 3). Seventeen carbonated beverage samples were tested (n = 2) in this study including 13 dark-colored beverage samples with different flavors and varieties and 4 light-colored beverage samples. Three target analytes were quantified in these samples with concentrations in the range from 284 to 644 ng/mL for 4-MI and from 706 to 4940 ng/mL for HMF. THI was detected in only one sample at 6.35 ng/mL.

The influence of a pulsed electric field (PEF) treatment of grape berries at pilot-plant scale on the evolution of the chromatic and phenolic characteristics of Cabernet Sauvignon red wines during aging in American oak barrels and subsequent storage in bottle has been studied. Results obtained in this investigation confirm that the better chromatic characteristics and higher phenolic content obtained due to the PEF treatment after the fermentation process remain or even increase during aging in oxidative conditions in American oak barrels and their subsequent storage in bottle. No sensory differences in color and bouquet were detected after 8 months of aging in bottle by triangle tests. According to the results, PEF is a promising enological technology to obtain wines with the high phenolic content necessary for the production of high quality oak aged red wines.

In the analysis of food additives, past emphasis was put on the development of chromatographic techniques to separate target components from a complex matrix. Especially in the case of artificial food colors, direct spectrophotometric measurement was seen to lack in specificity due to a high spectral overlap between different components. Multivariate curve resolution (MCR) may be used to overcome this limitation. MCR is able to (i) extract from a complex spectral feature the number of involved components, (ii) attribute the resulting spectra to chemical compounds, and (iii) quantify the individual spectral contributions with or without a priori knowledge. We have evaluated MCR for the routine analysis of yellow and blue food colors in absinthe spirits. Using calibration standards, we were able to show that MCR equally performs as compared to partial least-squares regression but with much improved chemical information contained in the predicted spectra. MCR was then applied to an authentic collective of different absinthes. As confirmed by reference analytics, the food colors were correctly assigned with a sensitivity of 0.93 and a specificity of 0.85. Besides the artificial colors, the algorithm detected a further component in some samples that could be assigned to natural coloring from chlorophyll.

A chemiluminescence method based on the luminol-H2O2 system with flow injection technology was proposed for the determination of sudan I in hot chilli sauce. It was found that sudan I could enhance chemiluminescence intensity generated from the luminol-H2O2 system. The increment of chemiluminescence intensity was proportional to the concentration of sudan I, giving a calibration graph linear over the concentration from 10 pg mL-1 to 7 ng mL-1 (R 2 = 0.9980) with the detection limit of 3 pg mL-1 (3sigma) and the quantification limit of 7.5 pg mL-1. At a flow rate of 2.0 mL min-1, one analysis cycle, including sampling and washing, could be accomplished in 60 s with a relative standard deviation of <5.0%. The method has been applied successfully to the determination of sudan I in Pixian douban, Golden Mark guilin chilli sauce, and Golden Mark satay sauce, and the recovery was 90.6-110.0%.

Exogenous pigments produced by ascomycetous filamentous fungi belonging to the genera Penicillium, Epicoccum, and Monascus, preselected based on chemotaxonomic knowledge, have been extracted and characterized by quantitative colorimetry. The color characteristics of the fungal extracts were compared to water soluble natural colorants derived from sources currently in use. The tested fungal extracts also included some commercially available Monascus colorants. The a values for the fungal extracts were found to be both positive and negative, the b values were found to be positive, while the hue angles of the fungal color extracts ranged from 40 to 110 indicating the color distribution of fungal extracts over the red-orange-yellow region of the CIELAB color space. The fungal extracts exhibited additional color hues in the red spectrum and similar hues in the yellow spectrum as compared to the reference natural colorants. They were also found to be similar or brighter in terms of chroma to some of the reference natural colorants. Principal component analysis was performed to group and distinguish different colors based on the a and b values. The fungal color extracts could be grouped in accordance with the similarity or difference in the color to those of the existing natural colorants. The diversity of colors was not only found among different fungal genera and/or species but also within the same species on changing the media. There was a marked change in the color composition of the extracts resulting in relatively different hues. Our results, thus, indicate that there exists pigment-producing genera of ascomycetous fungi other than Monascus that produce color shades in the red and the yellow spectra in addition or similar to reference colorants. These color shades could add to the color palette of the natural colorants currently in use. In addition, the multivariate approach in distinguishing and classifying the colorants was shown to be a very useful tool in colorimetric comparison of colorants.

The commercial value of a cochineal (Dactylopius coccus Costa) sample is associated with its color quality. Because the cochineal is a legal food colorant, its color quality is generally understood as its pigment content. Simply put, the higher this content, the more valuable the sample is to the market. In an effort to devise a way to measure the color quality of a cochineal, the present study evaluates different parameters of color measurement such as chromatic attributes (L*, and a*), percentage of carminic acid, tint determination, and chromatographic profile of pigments. Tint determination did not achieve this objective because this parameter does not correlate with carminic acid content. On the other hand, carminic acid showed a highly significant correlation (r = - 0.922, p = 0.000) with L* values determined from powdered cochineal samples. The combination of the information from the spectrophotometric determination of carminic acid with that of the pigment profile acquired by liquid chromatography (LC) and the composition of the red and yellow pigment groups, also acquired by LC, enables greater accuracy in judging the quality of the final sample. As a result of this study, it was possible to achieve the separation of cochineal samples according to geographical origin using two statistical techniques: cluster analysis and principal component analysis.

The colorant properties of pigments from Opuntia stricta, Opuntia undulata, and Opuntia ficus-indicafruits were studied. The pigments were extracted with different solvents and identified by high-performance liquid chromatography. On the basis of their visible light spectra, the pigments were identified as betalains. In O. undulata and O. ficus-indica fruits, both betacyanins and betaxantins were identified, while in O. stricta fruits only betacyanins (betanin and isobetanin) were detected. O. stricta fruits showed the highest betacyanin content (80 mg/100 g fresh fruit). The thermal stability of the pigment extracts was dependent on the pH, with the maximum stability being at pH 5, as expected for betacyanins. At this value and a storage temperature of 4 degrees C, a deactivation half-life time of more than 1 year, with no added stabilizers, was determined. According to these studies, cactus pears from O. stricta may well be considered as a potential source of natural red colorants.

Five synthetic and five natural colorants were determined in lyophilized dairy products and fatty foods using an automatic method based on lixiviation and a solid-phase extraction process that includes cotton and RP-C(18) columns for the sequential retention of synthetic colorants and natural colorants, respectively. The lyophilization of the sample coupled with the separation procedure provides clean extracts despite the complexity of the matrices studied. In addition, the lyophilization process preserves the sample for at least 2 months without changes in the concentrations of the colorants. Identification and determination of synthetic and natural colorants were carried out using a liquid chromatograph equipped with a diode array detector. The detection limits achieved for all of the colorants (0.03-75 microg/g of lyophilized sample) allowed their determination within the limits established by the European Union, with good precision (approximately 4.5%). In addition, colorants spiked to different foods provided average recoveries (spiked at three concentration levels in four types of dairy samples and in three types of fatty foods) near 94 +/- 4%.

Annatto is a natural food colorant extracted from the seeds of the Bixa orellana L. plant. Annatto is used in Latin American cuisine to add a deep red color as well as distinctive flavor notes to fish, meat, and rice dishes. In the United States, annatto extracts are primarily used to impart orange/yellow hues to cheese and other dairy foods. The objective of this study was to identify and compare volatile compounds present in water- and oil-soluble annatto extracts. Volatile compounds were recovered using dynamic headspace-solvent desorption sampling and analyzed using GC-MS. Compounds were identified by comparison to a mass spectral database, Kovats indexes, and retention times of known standards. Of the 107 compounds detected, 56 compounds were tentatively identified and 51 were positively identified. Volatile profile differences exist between water- and oil- soluble extracts, and annatto extracts contain odorants with the potential to influence food aroma.

The determination of mercury in different types of color food additives using electrothermal atomic absorption spectrometry is proposed. The procedure involves direct introduction of the additive samples as suspensions, and fast-program methodology is used to avoid mercury volatilization losses. Suspensions are prepared in a medium containing 0.1% w/v Triton X-100, 1% v/v concentrated nitric acid, 2% w/v potassium permanganate, and 3% w/v silver nitrate before being directly introduced into the furnace. Calibration uses aqueous standards, and compensation of the background is carried out using the Zeeman device. The characteristic mass is 61 pg and the detection limit is 59 pg. The reliability of the procedure is checked by comparing the results obtained with other results based on microwave-oven sample digestion, and by analyzing a certified reference material.

High-performance liquid chromatography (HPLC) with photodiode array detection was applied for the characterization of anthocyanins in red-fleshed Budd Blood (Citrus sinensis) orange. More than seven anthocyanin pigments were separated within 30 min by using a binary gradient (0.1% H(3)P0(4) in water and 0.1% H(3)PO(4) in acetonitrile) elution on a Prodigy ODS column. Separations by reversed-phase HPLC and semipreparative HPLC on a Prodigy 10-microm ODS Prep column, and acid and alkali hydrolyses were used for identification of anthocyanins. The primary anthocyanins in Budd Blood orange grown in Florida were cyanidin-3-(6"-malonylglucoside) (44.8%) followed by cyanidin-3-glucoside (33.6%). Two other minor pigments were also acylated with malonic acid. Malonated anthocyanins represented the major proportion (>51%) of anthocyanins in Budd Blood orange. Total anthocyanin contents and juice color parameters (CIE L,a,b) were compared with six other Florida-grown blood oranges.

(+)-catechin was separately incubated with furfural or with 5-(hydroxymethyl)furfural, and the formation of new oligomeric bridged compounds having flavanol units linked by furfuryl or 5-hydroxymethylfurfuryl groups was observed. LC/ESI-MS analyses detected four dimeric adducts along with intermediate adducts in each solution, and reaction was faster with furfural than with hydroxymethylfurfural. In addition, new compounds exhibiting the same UV--visible spectra as xanthylium salts with absorption maxima around 440 nm were also detected. When malvidin 3-O-glucoside or cyanidin 3-O-glucoside was added to the mixtures, new oligomeric colorless and colored pigments involving both (+)-catechin and anthocyanin moieties were detected, showing thus that the two polyphenols competed in the condensation process. Among the obtained colored pigment adducts, two dimeric compounds in which the flavanol was bridged to the anthocyanin were observed. Their UV-visible spectra were similar to the spectrum of malvidin 3-O-glucoside, but their maximum in the visible region was bathochromically shifted.

The carotenoid pigment profiles of authentic pure orange juices from Spain and Florida and an industrial paprika (Capsicum annuum) extract used for food coloring were obtained using reversed-phase liquid chromatography with a C18 packed column and an acetone/methanol/water eluent system. The procedure involving the carotenoid extraction is described. Both retention times and spectral properties using photodiode array detection for characterization of the major carotenoids at 430 and 519 nm are given. The influence of external addition of tangerine juice and/or paprika extract on orange juice color is described using the U.S. Department of Agriculture scale and adulterated orange juice. The procedure for quantitation of externally added paprika extract to orange juice is investigated, and the limit of quantitation, coefficient of variation, and recoveries are determined.