Perspective Cite This: J. Agric. Food Chem. 2018, 66, 3074−3081
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Perspective on the Ongoing Replacement of Artificial and AnimalBased Dyes with Alternative Natural Pigments in Foods and Beverages Ralf M. Schweiggert*,†,‡ †
DSM Nutritional Products, CH-4303 Kaiseraugst, Switzerland Institute of Food Science and Biotechnology, University of Hohenheim, D-70599 Stuttgart, Germany
‡
ABSTRACT: 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. KEYWORDS: carmine, azo-dye, carotenoids, betalains, anthocyanins, spirulina, Genipa, Gardenia, curcumin, carthamine
1. HISTORICAL PERSPECTIVE ON FOOD COLORATION Food processing and preservation often substantially change the original appearance of a food, because most natural pigments present in plant- and animal-derived foods commonly exhibit a comparably poor stability against heat, light, and oxygen exposure.1 Therefore, since ancient times, humans have sought to restore or enhance the colors of food. For instance, the ancient Egyptians were known to color their candy with natural plant extracts and wine as early as 1500 BC.2 In fact, until the middle of the 19th century, food coloration has been carried out with coloring matter supplied by nature, most frequently comprising spices and plant extracts but also animalderived pigments, such as squid ink, as well as brightly colored mineral pigments. The latter included often chronically harmful copper-, lead-, and tin-based pigments.3 In these early times, food coloration was a privilege of the wealthy parts of the population, being widely irrelevant for main parts of the population that produced and prepared their own food at home without the need for color restauration or adaption. However, industrialization and urbanization commencing in the 18th century had also initiated the era of industrial food processing and, consequently, the era of industrial food coloration. The plant- and animal-derived dyestuffs known at that time were often expensive, inhomogeneous, or simply unavailable in large quantities, thus urging food companies to make use of the above-mentioned pigments based on harmful heavy metals.2,3 In 1856, William H. Perkin discovered the first chemically synthesized dyestuff, namely, mauveine (syn. anilin purple and Perkin’s mauve), when aiming at the synthesis of quinine from aniline.4 Subsequently, a large number of artificial dyes were developed from aromatic starting compounds, such as aniline, being derived from coal tar. Thus, numerous artificial dyes were and still are referred to as “coal tar dyes”. Their industrial production skyrocketed after the foundation of companies, such as the later Bayer AG (1863) and “Badische Anilin- und Soda© 2018 American Chemical Society
Fabrik” (BASF, 1865). A particular class of coal tar dyes, the socalled azo-dyes, became rapidly predominant as a result of their extraordinary structural variability, leading to a large range of accessible color hues.5 Simultaneous to the increasing use of artificial dyes, the use of pigments from natural sources declined during the early 20th century, because their chemically synthesized alternatives were less costly, abundantly available at uniform quality, free of any potential off-flavor and, most importantly, provided better stability and higher tinctorial strength. However, the now quasi-unlimited possibilities to color food have rapidly revealed a clear downside. They provided an opportunity to mask the poor quality of foods and, thus, ultimately to easily mislead consumers. In addition, safety concerns about the unregulated use of at that time completely untested food additives were raised. Thus, a need for the legal regulation of food colorants arose. In 1906, the U.S. Federal Food and Drugs Act aimed at “preventing the manufacture, sale, or transportation of adulterated or misbranded or poisonous or deleterious foods [...]”, focusing also on food dyes. Subsequent legislation worldwide aimed at establishing the principle of positive listing regulations; i.e., only compounds that had been tested according to certain specifications should be allowed for use in foods. From the 1950s to 1980s, numerous certified and approved artificial colorants were introduced and broadly used by the food industry. Commencing in the late 1980s and early 1990s, an increasing trend toward the use of “natural” ingredients led to the particular questioning of the use of artificial colorants. Besides purified natural pigments, so-called coloring foodstuffs or coloring foods (see section 4 below) were broadly entering the markets at that time. Being derived from commonly used foods and food Received: Revised: Accepted: Published: 3074
December 18, 2017 March 7, 2018 March 7, 2018 March 19, 2018 DOI: 10.1021/acs.jafc.7b05930 J. Agric. Food Chem. 2018, 66, 3074−3081
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Figure 1. Chemical structures of artificial food dyes investigated by McCann et al. in the so-called Southampton study.
occurred in March 2012 when Starbucks’ “Soy Strawberry & Crème Frappuccino” was blamed to be non-vegan, because it had contained cochineal extract as colorant. The filed petition to stop “using bugs to color” the strawberry-flavored drinks as well as a strikingly broad media response urged the Starbucks Corporation to replace the natural but undesired carmine with the natural carotenoid lycopene. Lycopene might be derived from tomato or the fungus Blakeslea trispora, being also accessible by chemical synthesis. Noteworthy, the issues associated with the use of carmine are not only related to its nauseating “non-vegan” origin but also to the undesired aluminum content of carmine lakes, frequent microbiological issues, and its ability to induce allergic reactions. In addition, as the insects are often collected in the wild and harvest yields are prone to enormous fluctuations, the highly volatile costs of carmine impose enormous pressure on food and beverage manufacturers operating under cost pressure. As a further drawback, the dietary rules of several religious authorities, e.g., of Jewish and Islamic religions, do not allow for the consumption of the insect-derived carmine.9 The major available forms are carminic acid as well as the aluminum- and calcium-based complexes of carminic acid, commonly referred to as “carmine” (Figure 2A). The color of carminic acid depends upon the used pH (pH < 4.5, orange; 4.5 < pH < 7.0, orange−reddish; and pH > 7, red), whereas the color of the aluminum complex is less pH-sensitive, still displaying bright red colors at pH < 7. An unfavorable precipitation of the complexed carmine forms occurs at pH < 3.5, for instance being easily reached in acidic premixes used during beverage or fruit preparation production. At such low pH values, the carboxyl group of carminic acid becomes protonated, leading to a dramatic loss of polarity and water solubility. Overcoming this issue, a further derivative of carminic acid has been developed, the so-called “acid-stable carmine” based on 4-aminocarminic acid (Figure 2B). The introduced amino function prevails protonated at low pH values, thereby mediating sufficient hydrophilicity to prevent precipitation. Despite its potential, the use of 4-aminocarminic acid is currently not allowed in the EU and many other regions. Nevertheless, alarming observations reported by Sabatino et al.
ingredients without a selective enrichment of the pigments, these are considered ingredients instead of additives and, thus, are not burdened with labeling an E number in the European Union (EU). Products with such a “clean label” are often preferred by consumers.3 This trend is still ongoing to date, because new scientific insights and public scandals have fueled the concerns about artificial food colorants in the past 2 decades.
2. CONCERNS REGARDING ARTIFICIAL DYES AND CARMINE 2.1. Artificial Dyes. A landmark study boosting the increasing trend toward “natural” pigments was the so-called “Southampton study”.6 The consumption of six artificial colorants (Figure 1) and sodium benzoate was associated with adverse effects on the hyperactivity and attention in children. The affected colorants were the azo-dyes Allura Red (E129), carmoisine (E122), Ponceau 4R (E124), Sunset Yellow (E110), tartrazine (E102), and quinophthalone Quinoline Yellow (E104), as depicted in Figure 1. Although not disproving or discrediting the reported results, the study has been criticized with regard to several aspects, e.g., “the lack of a biologically plausible mechanism for induction of behavioral effects from consumption of food additives”.7 Nevertheless, since 2010, the use of these artificial colorants has been burdened with an obligation to include a warning label (“may have an adverse effect on activity and attention in children”) on the food product when marketed in the European Union [Regulation (EC) No. 1333/2008]. Noteworthy, potential relationships between hyperactivity in children and the consumption of artificial food additives had already been proposed earlier, resulting, e.g., in the development of the socalled “Feingold diet”, in which artificial colors and flavors as well as foods containing salicylate are to be avoided.8 2.2. Carmine Problem. Besides artificial dyes, a particular naturally occurring pigment has been criticized harshly worldwide, the bright red pigment carmine. The pigment is derived from cochineal, a scale insect (Dactylopius coccus Costa). Although it has been used for decades in numerous foods, a major event fueling the awareness of the public 3075
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Figure 2. Molecular structure of (A) carmine, an aluminum−calcium chelate comprising two molecules of carminic acid complexed by a central aluminum ion (Al3+), and (B) 4-aminocarminic acid.
revealed that more than 50% of the examined E120-labeled redcolored beverages and food additives had contained nonauthorized 4-aminocarminic acid.9,10 Despite the concerns described above, carmine presents a number of clear advantages when compared to other available natural pigments, such as anthocyanins and betalains. Its bright red color is stable over a wide pH range and withstands the exposure of heat, light, and oxygen comparably well.9 As a consequence, numerous food and beverage producers are suffering from the enormous efforts to be invested into finding, testing, and large-scale sourcing of potential alternatives. Frustratingly, tediously developed color solutions may then often be suitable only for single products and applications, while only slight changes of recipes may have a dramatic effect on the color hue and stability of potential alternatives.
3. POTENTIAL ALTERNATIVES TO ARTIFICIAL DYES AND CARMINE 3.1. Potential Alternatives for Yellow, Orange, and Red Color Hues. 3.1.1. Anthocyanins. Imparting red colors to numerous fruits and vegetables, such as strawberries, cherries, and red radish, anthocyanins represent a class of abundantly occurring, water-soluble natural plant pigments (Figure 3A). They are commercially available as purified pigments (E163), mainly from grapes, and they represent the main tinctorial principle in many coloring foodstuffs, e.g., prepared with black carrot or purple sweet potato. The molecular structure of the more than 700 known anthocyanins is highly variable by nature, exerting a significant effect on color hues and stability. While the hydroxylation and glycosylation pattern of the basic anthocyanidin core also slightly influences color hue and stability,11 a most striking feature increasing color stability and shifting color toward more purplish tonalities is the presence of aromatic acyl moieties, such as feruloyl and sinapoyl moieties.12 Such aromatic acyl moieties were found to form intramolecular sandwich-type complexes with the aromatic flavylium ring system mainly driven by π−π
Figure 3. Examples of naturally occurring red, orange, and yellow pigments, being considered for the ongoing or future replacement of artificial dyes and carmine.
interactions. As a consequence, anthocyanidin is sterically shielded against the detrimental influence of nucleophilic and electrophilic reactants. In addition, electronic interactions between the two delocalized electron systems lead to a bathochromic shift of the absorption band. Generally, acylated anthocyanins are most abundant in vegetable sources, such as red and purple radish (Raphanus sativus L.), purple sweet potato [Ipomoea batatas (L.) Lam.], and red cabbage (Brassica oleracea L.), representing natural tissues with a rather neutral vacuolar pH. Acylated anthocyanins are less frequently found in fruit sources, where the natural pH is often more acidic.11 3076
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(E161b), and lycopene (E160d). β-Carotene is available from chemical synthesis as well as from solvent-based extraction from natural sources, e.g., from orange carrots, the fungus B. trispora, and the algae Dunaliella salina. Lutein is commercially extracted from Tagetes flower petals. Lycopene is available from chemical synthesis as well as from solvent-based extractions from natural materials, e.g., from tomato and the microorganism B. trispora.21,22 In addition to pure carotenoid preparations, a number of carotenoid-rich coloring foodstuffs are in use, such as concentrates and preparations based on carrot, mango, and squash. As a result of the poor water solubility of pure carotenoids, they often require sophisticated formulation technologies to make them applicable to aqueous food types. For lipid-based food systems, such as margarines and oils, powdered or oil-based concentrated formulations are available for direct use. For application in aqueous food types, liquid and powdered water-dispersible formulations are commercially available. In addition to simply solubilizing the pigment, the applied formulation technology has substantial impact on color hue and stability as well as carotenoid bioavailability. Horn and Rieger23 have summarized in great detail how the color of nanodispersed β-carotene formulations can be adjusted from bright yellow to orange−reddish color hues by technological measures. These striking differences in color hues produced from one single carotenoid were mainly related to the particle size and the aggregate form (J or H type) of the carotenoid formulation. While the particle size largely impacts color by modulating physical light scattering, the aggregate form influences supramolecular interactions of the delocalized conjugated electron systems (chromophores) of neighboring carotenoid molecules.23,24 When being wellformulated, their color strength and stability are fully sufficient to already cover a wide range of food and beverage applications requiring yellow, orange, and red hues. Future developments extending the accessible color range of carotenoids may not only include the utilization of new carotenoids for food use but may also be based on new formulation strategies and technologies. Besides its importance for solubilization, color, and stability, the applied formulation technology and, thus, also the physical state and the isomeric form of the carotenoid largely impact carotenoid bioavailability. For instance, lipid-dissolved (Z)isomers of lycopene were shown to be substantially more bioavailable than crystalline (all-E)-lycopene from highly similar matrices.25 The ability to tailor carotenoid bioavailability is of particular interest, because carotenoids do not only provide color but also a number of widely accepted and further potential health benefits. The most prominent health benefit of carotenoids is presumably the metabolic conversion of provitamin A carotenoids, such as β-carotene, to vitamin A, exerting essential functions for sound growth and development as well as for the functioning of the visual system. Although only a few among over 700 known carotenoids can be metabolized to vitamin A, relevant provitamin A carotenoids, such as α- and β-carotene as well as β-cryptoxanthin, are abundantly present in many carotenoid-rich fruits and vegetables.26 In addition, lutein and zeaxanthin have been found in high concentrations in the macula lutea of the human retina, where they are believed to play a protective role as a result of their antioxidant as well as their ultraviolet (UV)- and blue-light-filtering properties.27 3.1.4. Curcumin. Curcumin represents an oil-soluble diarylheptanoid (Figure 3D) derived from turmeric (Curcuma longa
The applicability of coloring foodstuffs made from vegetable sources with highly stable acylated anthocyanins is often hampered by the presence of unpleasant flavor compounds. For instance, red radish (R. sativus L.) extracts contain highly stable acylated anthocyanins13 but also sulfur-containing off-odor compounds, such as methanethiol, dimethyl disulfide, and further compounds derived from the degradation of glucosinolates.14 Preparations with mainly non-acylated anthocyanins, such as those from grapes, are to be used only under more acidic conditions (pH < 3.5). Even then, color stability is often limited. For instance, a challengingly low stability was found for the pelargonidin-based anthocyanins of strawberry. Attempts to enhance shelf life and thermal stability, e.g., by co-pigment or hydrocolloid addition, were only partly successful.13,15 A further still widely unresolved but noteworthy challenge is the instability of anthocyanins in the presence of ascorbic acid,16 being frequently overlooked and underestimated by food processors as a result of the commonly stabilizing effect of ascorbic acid. 3.1.2. Betalains. Betalains are water-soluble pigments divided into the classes of the yellow−orange betaxanthins and the red−purple betacyanins (Figure 3B). The most widely commercially used betacyanin-rich food source is red beet (Beta vulgaris L.), although others, such as pitaya (syn. pitahaya and dragon fruit; Hylocereus spp.) and amaranth (Amaranthus spp.), have also been explored. Examples of betaxanthin sources are prickly pear (Opuntia ficus-indica (L.) Mill., Cactaceae) and yellow beet (B. vulgaris L.). Betalains present an optimum stability in the mildly acidic pH range from 4 to 6.17 Higher pH values may lead to the cleavage of the aldimine bond, releasing betalamic acid and the cyclo-DOPA-glycosides (betacyanins) or the respective amino compound (betaxanthins). Degradation mechanisms under acidic conditions are still widely unclear, although isomerized forms of betanin (isobetanin), deglycosylated forms (betanidin), and 14,15-dehydrobetanin (neobetanin) have been observed after acid treatments. Conditions favoring the stability of betalains are low water activity, low oxygen, light, and temperature exposure, and absence of prooxidative metal ions and decolorizing enzymes. A concise review about further details of betalain stability has been presented by Herbach et al.18 and Martins et al.17 Current applications of betalains include mildly acidic and neutral products with a rather short shelf life, such as meats, sausages, frozen foods, and low-temperature dairy products. The application of red beet juice concentrates is often not only hampered by poor betalain stability but also by the co-presence of aroma-intense off-flavors, such as the earthy geosmin and a number of pyrazine derivatives.19 Earlier, the comparably high nitrate content of red beet has also been criticized,19 particularly with regard to applications in infant nutrition. In contrast, the high nitrate content most recently rendered red beet juice highly attractive for athletes of endurance sports. Nitrate (NO3−) is metabolically converted to a number of reactive nitrogen intermediates, including nitric oxide (NO), increasing the time-trial endurance of athletes presumably as a result of the effect of NO on vasodilation and the resulting more effective oxygen delivery to the muscle.20 3.1.3. Carotenoids. Imparting yellow, orange, and red color hues to many fruits and vegetables, carotenoids represent a class of lipid-soluble natural pigments. A number of carotenoids has been approved in many countries for being used in foods and beverages, such as β-carotene (E160a; Figure 3C), lutein 3077
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Journal of Agricultural and Food Chemistry L.), requiring formulation prior to being used in aqueous food types. Although conveying a very high color brilliance, curcumin is known for its poor light stability at high water activity. Thus, popular applications are commonly those with low water activity, such as high boiling candies, jellies, and gum confectionery. Further information on the use of curcumin as a food colorant has been provided elsewhere.28,29 3.1.5. Carthamine. Extracts of safflower (Carthamus tinctorius L.) are used as coloring foodstuffs, providing the water-soluble yellow−greenish carthamine (Figure 3D). Their color stability is high, but the coloring foodstuff introduces an often undesired flavor that may be noticeable in final applications unless being masked by specific added flavors.28 Example applications may be jellies and gum confectionary, fruit preparations, and fruit-based spreads. In products where different color layers are required, Carthamus extracts and other colors with water-soluble pigments were shown to lead to an undesired migration, which is not observed with carotenoids, e.g., from orange carrot concentrates.29 Further details and application notes are available.22 3.1.6. Microbial Pigments: Azaphilones and Anthraquinones. The fungus Monascus purpureus is known to produce six major azaphilone pigments, i.e., the yellow monascin and ankaflavin, the orange monascorubrin and rubropunctatin, and the red monascorubramine and rubropunctamine (Figure 3E). Although not being approved in many regions worldwide, they are part of the daily diet of more than 1 billion Asian people, being consumed mostly via fermented red rice. A popular fungal anthraquinone was named Arpink Red, later called Natural Red (Figure 3E). An overview on microbial pigments was presented previously.30,31 3.2. Potential Solutions for Blue and Green Hues. 3.2.1. Spirulina. During the past few years, the use of phycocyanin-rich preparations often known as “spirulina” has successfully spread throughout the world. Phycocyanins are proteins (phycobiliproteins) linked with chromogenic tetrapyrrole moieties (Figure 4A). Spirulina is currently applied in foods with low water activity at neutral or slightly acidic pH values (pH > 4.5), such as in sweets, chewing gum, sugar decorations, candies, dairy products, and ice cream. Its performance is poor under conditions that lead to the denaturation of the proteinaceous pigment, e.g., at a pH lower than 4.5 or at ethanol contents greater than 20%.32,33 3.2.2. Anthocyanins. Specific anthocyanins have also been proposed to be used as blue colorants. In particular, complexation of anthocyanins comprising an at least dihydroxylated B ring (e.g., cyanidin and delphinidin) with bi- and trivalent metal ions, such as Al3+ and Fe3+, was shown to yield bright blue colors. Unfortunately, anthocyanin−metal chelates possess poor water solubility and, thus, often precipitate rapidly in aqueous food systems, resulting in significant color fading. Furthermore, the frequent presence of citric acid in foods hampers the formation of metal− anthocyanin complexes as a result of its potent chelating properties.33 3.2.3. Chlorophylls. Single natural compounds exerting stable green shades are rare. Naturally abundant chlorophylls are highly sensitive to heat and acidic conditions, rapidly turning brownish and yellowish. An enhanced stability is found when replacing the central magnesium ion (Mg2+) with a copper ion (Cu2+).35 Commercially available preparations of so-called copper chlorophyllins are obtained by the “addition of copper to the product obtained by saponification of a solvent
Figure 4. Examples of green and blue pigments, being considered for the ongoing or future replacement of artificial dyes.34
extraction of strains of edible plant material, grass, lucerna, and nettle”.36 Major coloring components present in the complex mixtures of diverse compounds are copper chlorines e4 and e6 (Figure 4B). Further information on chlorophylls may be found elsewhere.35 3.2.4. Iridoid-Based Pigments. A class of iridoid-based pigments may be derived from Genipa americana L. and Gardenia jasminoides J. Ellis. The blue color is not present in the intact fruit tissue but rapidly develops when exposing the mashed fruit to oxygen. The contained genipin glycosides will then first be deglycosylated by genuine fruit glycosidases to yield genipin (Figure 4C), a highly reactive iridoid compound. The latter reacts with genuine amino acids of the fruit and oxygen to yield yet widely uncharacterized polymeric blue pigments. Genipa fruits are considered novel food in most regions outside Latin America,34 while Gardenia fruits, extracts thereof, and a pigment named Gardenia Blue are in current use in East Asia, including Japan.33 Further information on natural blue pigments has been recently summarized.32−34 3.2.5. Caffeic-Acid-Ester-Based Pigments. Green colorants derived from caffeic acid esters, such as chlorogenic acid, have 3078
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Table 1. Overview on the Most Relevant Advantages and Disadvantages of Using the Described Artificial Dyes and Natural Pigments in Foods and Beverages artificial food dyes advantages
natural pigments
high stability against heat, light, and oxygen high tinctorial strength
favorable scientific literature available, associating their consumption with health benefits (e.g., anthocyanins, β-carotene, curcumin, lutein, lycopene, and others) “clean labeling” (coloring foodstuffs)
accessibility of all color shades at brilliant and vibrant color saturation at all food-relevant pH values low cost-in-use constant quality commonly not requiring formulation as a result of broad availability of hydro- and lipophilic dyes disadvantages
a
positively viewed by consumersa
negatively viewed by consumers unfavorable labeling required in the EU for certain dyes as a result of potential adverse health effects (“may have an adverse effect on activity and attention in children”) unfavorable scientific literature prominently present, associating their consumption with adverse health effects
comparably low stability against heat, light, and oxygen comparably low color saturation and brilliance not all color shades are accessible at the desired color intensity, in particular, regarding green and blue hues comparably high cost-in-use fluctuating quality and price when sourced from materials grown outdoors interactions with other food ingredients, requiring adaptations of the targeted food composition (e.g., omitting ascorbic acid when using anthocyanins) and, thus, higher costs for development of new foods concomitant non-coloring and undesired compounds (e.g., flavors; mainly coloring foodstuffs) need for complex analytical techniques for authenticity and quality control (mainly coloring foodstuffs)
Except for the insect-derived carmine, as described in section 2.2.
The approach has been criticized, particularly because the generation of a general reference database for aromatic constituents of food sources is highly intricate as a result of the large variability found in natural foods.3 Limiting the use of coloring foodstuffs, the EU guidelines exclude options for the removal of undesired components, such as off-flavors or even other antinutritive components. For instance, efficient deodorization techniques would be highly useful to expand the applicability of raw materials, such as red cabbage, radish, and red beet. As a further consequence of the EU guidance notes, the labeling of several previously used “coloring foodstuffs” as such has been questioned, such as, for instance, spinach/nettle, carrot, and turmeric oleoresins. Their manufacture includes a “selective” solvent or oil extraction step, presumably leading to enrichment factors greater than 6 in numerous cases.28 The use of coloring foodstuffs often requires high analytical efforts for authenticity and “purity” control. For instance, in 2016, several anthocyanin- and betalain-based coloring foodstuffs were found to be adulterated with a textile dye, namely, Reactive Red 195.38 Despite their comparably high cost, coloring foodstuffs are highly attractive for the food and beverage industry in the EU, allowing labeling the coloring principle as an ingredient rather than as food additives. In brief, the presented perspective aimed at providing a concise overview on academic and industrial developments in the field of food coloration. Because the demand by customers for natural food ingredients is expected to increase further, the use of natural pigments will clearly follow this major trend. Table 1) presents an overview on the above-mentioned advantages and disadvantages of using natural pigments and artificial colorants. Although natural pigments do often not reach the same maximum color brilliance as reached with artificial azo-dyes or carmine, the general trend toward “more natural” and organically produced foods might also change consumer expectations with regard to the color of the foods.
also been considered for food uses. Under alkaline conditions, the caffeoyl moiety is thought to be readily oxidized in the presence of oxygen to yield the respective o-quinone. One such o-quinone may react with a primary amine to give rise to a Schiff base, reacting with a second o-quinone followed by a Diels−Alder-type cyclization to yield a first yellowish benzacridine structure (Figure 4D). The latter is easily oxidized, leading to a greenish oxidation product (Figure 4D).34 Although studies on this pigment are scarce, a rather low stability was found by Brauch,34 who also presented a detailed review on this type of green pigment. Noteworthy, attractive green color shades may be achieved by blending yellow and blue colorants, such as the popular combination of spirulina and Carthamus extracts for the bright green coloration of gelled food types.29
4. PERSPECTIVE ON COLORING FOODS A coloring preparation represents a “coloring foodstuff” when no “selective” enrichment of the coloring principle was carried out during its production. Then, it is treated as an “ingredient” and exempt from the European legislation of food additives, although eventually being subject to a novel food authorization. The term “selective” was only vaguely defined until the release of the EU guidance notes in 2013.37 Whether a product has been selectively extracted or enriched is now being quantitatively defined by the introduction of so-called “enrichment factors”. These were derived from the ratio of the content in pigments to that of nutritive (e.g., sugars) or aromatic constituents (flavor compounds) in the potential coloring food divided by the respective ratios found in the source material. A coloring preparation with an enrichment factor greater than 6 is then considered to be derived from a “selective” production and, thus, to represent a “food additive”. Preparations with enrichment factors lower than 6 would be considered derived by non-selective production and, thus, as “coloring foodstuff”. 3079
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(11) Andersen, O. M.; Jordheim, M. Basic anthocyanin chemistry and dietary sources. In Anthocyanins in Health and Disease, 1st ed.; Wallace, T. C., Giusti, M. M., Eds.; CRC Press (Taylor and Francis Group): Boca Raton, FL, 2014; Vol. 1, pp 13−90. (12) Sadilova, E.; Stintzing, F. C.; Carle, R. Thermal degradation of acylated and nonacylated anthocyanins. J. Food Sci. 2006, 71, C504− C512. (13) Müller-Maatsch, J.; Bechtold, L.; Schweiggert, R. M.; Carle, R. Co-pigmentation of pelargonidin derivatives in strawberry and red radish model solutions by the addition of phenolic fractions from mango peels. Food Chem. 2016, 213, 625−634. (14) Gao, R.; Jing, P.; Ruan, S.; Zhang, Y.; Zhao, S.; Cai, Z.; Qian, B. Removal of off-flavours from radish (Raphanus sativus L.) anthocyaninrich pigments using chitosan and its mechanism(s). Food Chem. 2014, 146, 423−428. (15) Holzwarth, M.; Korhummel, S.; Siekmann, T.; Carle, R.; Kammerer, D. R. Influence of different pectins, process and storage conditions on anthocyanin and colour retention in strawberry jams and spreads. LWTFood Sci. Technol. 2013, 52, 131−138. (16) West, M. E.; Mauer, L. J. Color and chemical stability of a variety of anthocyanins and ascorbic acid in solution and powder forms. J. Agric. Food Chem. 2013, 61, 4169−4179. (17) Martins, N.; Roriz, C. L.; Morales, P.; Barros, L.; Ferreira, I. C. F. R. Coloring attributes of betalains: A key emphasis on stability and future applications. Food Funct. 2017, 8, 1357−1372. (18) Herbach, K. M.; Stintzing, F. C.; Carle, R. Betalain stability and degradationStructural and chromatic aspects. J. Food Sci. 2006, 71, R41−R50. (19) Stintzing, F. C.; Carle, R. Functional properties of anthocyanins and betalains in plants, food, and in human nutrition. Trends Food Sci. Technol. 2004, 15, 19−38. (20) Jones, A. M. Dietary nitrate supplementation and exercise performance. Sports Med. 2014, 44, 35−45. (21) Wrolstad, R. E.; Culver, C. A. Alternatives to those artificial FD & C food colorants. Annu. Rev. Food Sci. Technol. 2012, 3, 59−77. (22) Handbook on Natural Pigments in Food and Beverages: Industrial Applications for Improving Food Color; Carle, R., Schweiggert, R., Eds.; Elsevier: Amsterdam, Netherlands, 2016; pp 1−509. (23) Horn, D.; Rieger, J. Organic nanoparticles in the aqueous phaseTheory, experiment, and use. Angew. Chem., Int. Ed. 2001, 40, 4330−4361. (24) Hempel, J.; Schädle, C. N.; Leptihn, S.; Carle, R.; Schweiggert, R. M. Structure related aggregation behavior of carotenoids and carotenoid esters. J. Photochem. Photobiol., A 2016, 317, 161−174. (25) Cooperstone, J. L.; Ralston, R. A.; Riedl, K. M.; Haufe, T. C.; Schweiggert, R. M.; King, S. A.; Timmers, C. D.; Francis, D.; Lesinski, G. B.; Clinton, S. K.; Schwartz, S. J. Enhanced bioavailability of lycopene when consumed as cis-isomers from tangerine compared to red tomato juice, a randomized, cross-over clinical trial. Mol. Nutr. Food Res. 2015, 59, 658−659. (26) Food and Agriculture Organization of the United Nations (FAO)/World Health Organization (WHO). Vitamin A. Human Vitamin and Mineral RequirementsReport of a Joint FAO/WHO Expert Consultation; FAO/WHO: Rome, Italy, 2002. (27) Johnson, E. J. Role of lutein and zeaxanthin in visual and cognitive function throughout the lifespan. Nutr. Rev. 2014, 72, 605− 612. (28) Kendrick, A. Coloring aqueous food types. In Handbook on Natural Pigments in Food and Beverages: Industrial Applications for Improving Food Color; Carle, R., Schweiggert, R., Eds.; Elsevier: Amsterdam, Netherlands, 2016; Chapter 7, pp 163−177, DOI: 10.1016/B978-0-08-100371-8.00007-5. (29) Hubbermann, E. M. Coloring of low-moisture and gelatinized food products. In Handbook on Natural Pigments in Food and Beverages: Industrial Applications for Improving Food Color; Carle, R., Schweiggert, R., Eds.; Elsevier: Amsterdam, Netherlands, 2016; Chapter 8, pp 179− 196, DOI: 10.1016/B978-0-08-100371-8.00008-7. (30) Dufossé, L. Current and potential natural pigments from microorganisms (bacteria, yeasts, fungi, microalgae). In Handbook on
For instance, turbid juices and slightly turbid beverages with less vivid colors are becoming more and more popular. The increasing use of most of the natural pigments will require food and beverage producers to invest substantially more efforts into their color-related product development in the future. If properly developed, alternatives to artificial dyes and carmine are broadly available for almost all color shades, and thus, there is no doubt that the future of foods and beverages will be bright and colorful.
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AUTHOR INFORMATION
Corresponding Author
*Telephone: +41-61-815-8615. E-mail: ralf.schweiggert@dsm. com. ORCID
Ralf M. Schweiggert: 0000-0003-0546-1335 Notes
The author declares the following competing financial interest(s): The author works for a manufacturer of carotenoids and carotenoid formulations (DSM Nutritional Products, Kaiseraugst, Switzerland), in addition to serving the University of Hohenheim as lecturer (PD). The views presented in this publication do not necessarily represent the views of DSM.
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REFERENCES
(1) Delgado-Vargas, F.; Jiménez, A. R.; Paredes-López, O. Natural pigments: Carotenoids, anthocyanins, and betalainsCharacteristics, biosynthesis, processing, and stability. Crit. Rev. Food Sci. Nutr. 2000, 40, 173−289. (2) Downham, A.; Collins, P. Colouring our foods in the last and next millennium. Int. J. Food Sci. Technol. 2000, 35, 5−22. (3) Stich, E. Food color and coloring food: Quality, differentiation and regulatory requirements in the European Union and the United States. In Handbook on Natural Pigments in Food and Beverages: Industrial Applications for Improving Food Color; Carle, R., Schweiggert, R., Eds.; Elsevier: Amsterdam, Netherlands, 2016; Chapter 1, pp 3−27, DOI: 10.1016/B978-0-08-100371-8.00001-4. (4) Filarowski, A. Perkin’s mauve: The history of the chemistry. Resonance 2011, 16, 1140−1145. (5) Plischke, W.; Meier, S. M.; Riedl, B. Von Steinkohlenteer bis zu Krebsmedikamenten. Chem. Unserer Zeit 2014, 48, 124−132. (6) McCann, D.; Barrett, A.; Cooper, A.; Crumpler, D.; Dalen, L.; Grimshaw, K.; Kitchin, E.; Lok, K.; Porteous, L.; Prince, E.; SonugaBarke, E.; Warner, J. O.; Stevenson, J. Food additives and hyperactive behaviour in 3-year-old and 8/9-year-old children in the community: A randomised, double-blinded, placebo-controlled trial. Lancet 2007, 370, 1560−1567. (7) EFSA Panel on Food Additives, Flavourings, Processing Aids and Food Contact Materials (AFC).. Assessment of the results of the study by McCann et al. (2007) on the effect of some colours and sodium benzoate on children’s behaviour [1]Scientific Opinion of the Panel on Food Additives, Flavourings, Processing Aids and Food Contact Materials (AFC). EFSA J. 2008, 6, 660. (8) Feingold, B. F. Hyperkinesis and learning disabilities linked to the ingestion of artificial food colors and flavors. J. Learn. Disabil. 1976, 9, 551−559. (9) Müller-Maatsch, J.; Gras, C. The “Carmine Problem” and potential alternatives. In Handbook on Natural Pigments in Food and Beverages: Industrial Applications for Improving Food Color; Carle, R., Schweiggert, R., Eds.; Elsevier: Amsterdam, Netherlands, 2016; Chapter 18, pp 385−428, DOI: 10.1016/B978-0-08-100371-8.00018X. (10) Sabatino, L.; Scordino, M.; Gargano, M.; Lazzaro, F.; Borzì, M. A.; Traulo, P.; Gagliano, G. Aminocarminic acid in E120-labelled food additives and beverages. Food Addit. Contam., Part B 2012, 5, 295− 300. 3080
DOI: 10.1021/acs.jafc.7b05930 J. Agric. Food Chem. 2018, 66, 3074−3081
Perspective
Journal of Agricultural and Food Chemistry Natural Pigments in Food and Beverages: Industrial Applications for Improving Food Color; Carle, R., Schweiggert, R., Eds.; Elsevier: Amsterdam, Netherlands, 2016; Chapter 16, pp 337−354, DOI: 10.1016/B978-0-08-100371-8.00016-6. (31) Caro, Y.; Anamale, L.; Fouillaud, M.; Laurent, P.; Petit, T.; Dufosse, L. Natural hydroxyanthraquinoid pigments as potent food grade colorants: An overview. Nat. Prod. Bioprospect. 2012, 2, 174− 193. (32) Newsome, A. G.; Culver, C. A.; Van Breemen, R. B. Nature’s palette: The search for natural blue colorants. J. Agric. Food Chem. 2014, 62, 6498−6511. (33) Buchweitz, M. Natural solutions for blue colors in food. In Handbook on Natural Pigments in Food and Beverages: Industrial Applications for Improving Food Color; Carle, R., Schweiggert, R., Eds.; Elsevier: Amsterdam, Netherlands, 2016; Chapter 17, pp 355−384, DOI: 10.1016/B978-0-08-100371-8.00017-8. (34) Brauch, J. E. Underutilized fruits and vegetables as potential novel pigment sources. In Handbook on Natural Pigments in Food and Beverages: Industrial Applications for Improving Food Color; Carle, R., Schweiggert, R., Eds.; Elsevier: Amsterdam, Netherlands, 2016; Chapter 15, pp 305−335, DOI: 10.1016/B978-0-08-100371-8.000154. (35) Roca, M.; Chen, K.; Pérez-Gálvez, A. Chlorophylls. In Handbook on Natural Pigments in Food and Beverages: Industrial Applications for Improving Food Color; Carle, R., Schweiggert, R., Eds.; Elsevier: Amsterdam, Netherlands, 2016; Chapter 6, pp 125−158, DOI: 10.1016/B978-0-08-100371-8.00006-3. (36) EFSA Panel on Food Additives and Nutrient Sources Added to Food (ANS).. Scientific Opinion on re-evaluation of copper complexes of chlorophylls (E 141(i)) and chlorophyllins (E 141(ii)) as food additives. EFSA J. 2015, 13, 4151. (37) European Commission (EC). Guidance Notes on the Classification of Food Extracts with Colouring Properties; EC: Brussels, Belgium, 2013; https://ec.europa.eu/food/sites/food/files/safety/ docs/fs_food-improvement-agents_guidance_additive-eu-rules.pdf. (38) Müller-Maatsch, J.; Schweiggert, R. M.; Carle, R. Adulteration of anthocyanin- and betalain-based coloring foodstuffs with the textile dye ‘Reactive Red 195’ and its detection by spectrophotometric, chromatic and HPLC−PDA−MS/MS analyses. Food Control 2016, 70, 333−338.
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DOI: 10.1021/acs.jafc.7b05930 J. Agric. Food Chem. 2018, 66, 3074−3081
