Plant Foods Hum Nutr DOI 10.1007/s11130-015-0499-0
ORIGINAL PAPER
Comparative Thermal Degradation Patterns of Natural Yellow Colorants Used in Foods Pedro J. Giménez 1 & José A. Fernández-López 1 & José M. Angosto 1 & José M. Obón 1
# Springer Science+Business Media New York 2015
Abstract There is a great interest in natural yellow colorants due to warnings issued about certain yellow food colorings of synthetic origin. However, no comparative studies have been reported of their thermal stability. For this reason, the thermal stabilities of six natural yellow colorants used in foods —lutein, riboflavin, curcumin, ßcarotene, gardenia yellow and Opuntia betaxanthins— were studied in simple solutions over a temperature range 30–90 °C. Spectral properties and visual color were investigated during 6 h of heat treatment. Visual color was monitored from the CIEL*a*b* parameters. The remaining absorbance at maximum wavelength and the total color difference were used to quantify color degradation. The rate of color degradation increased as the temperature rose. The results showed that the thermal degradation of the colorants followed a first-order reaction kinetics. The reaction rate constants and half-life periods were determined as being central to understanding the color degradation kinetics. The temperature-dependent degradation was adequately modeled on the Arrhenius equation. Activation energies ranged from 3.2 kJmol−1 (lutein) to 43.7 kJmol−1 (Opuntia betaxanthins). ß-carotene and lutein exhibited high thermal stability, while betaxanthins and riboflavin degraded rapidly as temperature increased. Gardenia yellow and curcumin were in an intermediate position.
* José A. Fernández-López [email protected] 1
Department of Chemical and Environmental Engineering, Technical University of Cartagena (UPCT), Paseo Alfonso XIII 52, E-30203 Cartagena, Murcia, Spain
Keywords Food color . Yellow natural colorants . Thermal degradation . Thermal kinetics
Introduction Since early civilizations, colorants have been used to give a captivating presentation to human-made products, including foods [1]. Experts have long accepted that color plays a crucial role in the taste and perception of food [2]. Furthermore, in recent years, color in food has not only been regarded as a quality trait, but are also associated with health and safety benefits by consumers. The European Food Safety Agency (EFSA) in Europe, the Food and Drug Administration (FDA) in USA, and many other national authorities around the world, have restricted the use of synthetic colorants in foods and beverages because of their confirmed or suspected association with allergic reactions and toxic effects [3]. In addition, a recently published study reported a possible link between hyperactivity in children and the consumption of some synthetic yellow food colorants [4]. The tendency is therefore, for food manufacturers, going progressively toward the use of natural additives, and natural colors provide the further benefit of generally being more internationally accepted, and also some of them even have nutritional and bioactive effects [5]. Nevertheless, in the case of non-alcoholic beverages with added juices some synthetic colorants are mainly used in order to fortify their visual color [6]. The main natural pigments approved as food and drink coloring agents are: curcuminoids, riboflavins, caramels, carotenoids, chlorophylls, anthocyanins, betalains, cochineal, vegetal carbon and inorganic pigments [7]. Nature yellow hues are mainly due to carotenoids, betaxanthins, flavonoids, curcuminoids and riboflavins [5, 8]. There is a great interest in natural yellow colorants due to warnings issued about certain
Plant Foods Hum Nutr
yellow food colorings of synthetic origin [4]. Nevertheless, there are some disadvantages in the application of natural pigments, mainly related with their stability. Curcumin (E100) is the bright golden yellow pigment found in turmeric. Rhizomes produced by the turmeric plant Curcuma longa are dried and ground to produce the spice that contributes to the yellow distinctive color and flavor of mustards, pickles, and curry powder [5]. Riboflavin (E101) is mainly used to fortify foods but can also provide a yellow green color to food. It is particularly sensitive to light, and one example of riboflavin being used is in cake icing [9]. Lutein (E161b) is a natural yellow food colorant obtained from the extraction of marigold flowers. Like other carotenoids, lutein may provide health benefits due to its strong antioxidant properties. It is permitted in the European Union as a food color additive, but is not yet approved in the USA [10]. β-carotene (E160a) is a naturally-occurring pigment that finds widespread use as a colorant in food and beverages. Its shades range from yellow to orange, depending on concentration. It also functions as a safe source of vitamin A and as an antioxidant that contributes to protecting against the damaging effects of free radicals [11]. Gardenia yellow is a rare natural water-soluble colorant, extracted from gardenia fruit (Gardenia jasminoides), that is widely used in Asian countries mainly in colored juice, jelly, candy and noodles. Its chemical structure is postulated as crocetin glycosyl esters [12]. It is not approved as a food colorant in the European Union or in the USA. Betaxanthins are water-soluble vacuolar pigments occurring in plants of most families of the plant order Caryophyllales as Beta vulgaris and Opuntia ficusindica. They exhibit a yellow-orange coloration [13] and are considered bioessential dietary colorants since they are antiradical molecules and introduce essential dietary amino acids into foodstuffs [8]. The thermal processing of foods involves heating at high temperature, depending on the pH of the product and the desired shelf life. The incorporation of a natural colorant in food requires a detailed knowledge of its stability against possible degradation processes and it is also necessary to know the conditions that regulate this alteration in order to take appropriate measures to ensure sufficient stability that will allow the production, storage and transport of the colored product to be optimized. There are no reported comparative studies on the thermal stability of yellow food colorants, and therefore the aim of this study was to monitor the color alteration of selected yellow colorants used in foods upon heating at different temperatures. Since accurate knowledge of kinetic parameters is essential to predicting the quality changes that occur during thermal processing, a further objective was to estimate the degradation kinetic parameters during heat treatment.
Materials and Methods Materials The commercial food colorants: lutein, ß-carotene, riboflavin and curcumin in powder form were provided by Proquimac Food & Pharma (Barcelona, Spain). Gardenia yellow was from B&K Food Manufacturing Group Co. (Xiamen, China). The Opuntia betaxanthin extract was obtained in our laboratory from Opuntia ficus-indica fruits as indicated previously [13]. All chemicals used were of analytical reagent grade (Merck, Darmstad, Germany). The deionized water used in this study was prepared with a Milli-Q system (Millipore, Bedford, MA, USA). Stock solutions (1000 mg/100 mL) of each colorant in ethanol-water (3:2, v/v) were prepared. In the case of ß-carotene and lutein, drops of acetone were added to completely dissolve the colorant. Successive dilutions were carried out with the same solvent to reach an absorbance of 0.700± 0.05 at the wavelength of maximum absorbance (Table 1) in all the colorant extracts. The final solutions were maintained in the dark at 5 °C, used within 5 days, and shaken before use. Figure 1 shows the yellow shades in the final solutions of the six colorants investigated. Heat Treatment The thermal stability was tested at 30 °C, 50 °C, 70 °C and 90 °C in different experiments. The colorant solutions were distributed in 25 mL borosilicate test tubes (Pobel S.A., Madrid, Spain) sealed with screw caps and placed in a water bath for the required heat treatment. The tubes were wrapped with aluminum foil to avoid exposure to light. The changes in absorbance were monitored between 400 and 700 nm at time intervals of 1, 2, 3, 4, 5, and 6 h. At the end of the heat treatment, the samples were put in ice to stop any further degradation reaction. After 5 min equilibration in ice bath, an aliquot of each sample was passed through a PTFE filter (0.45 μm, Advantec MFS Inc., Dublin, CA, USA) and analyzed in an Agilent 8453 UV-visible photodiode spectrophotometer (Waldbronn, Germany). A non-heat treated sample of each colorant served as control to analyse any color intensity change. The experiments were performed in duplicates. Color Degradation Kinetics A general reaction rate expression for the degradation kinetics can be written as: −
d ½A ¼ k ½Am dt
ð1Þ
where BA^ is the quantitative value of the component under consideration, Bk^ is the reaction rate constant, and Bm^ is the
Plant Foods Hum Nutr Table 1 Color properties in the initial solutions of the selected yellow food colorants
Lutein Riboflavin Curcumin ß-Carotene
L*
a*
b*
λmax (nm)
94.1±0.2b 97.3±0.4e 95.6±0.3c 93.9±0.5b
−14.8±0.3c −17.4±0.3b −19.1±0.1a −14.6±0.3c
75.1±0.2f 69.1±0.4d 53.9±0.2b 70.6±0.4e
445±0.8c 446±0.6c 429±0.5a 448±0.6d
Gardenia yellow 96.5±0.2d −13.8±0.2d 63.2±0.2c 437±0.4b Opuntia betaxanthins 88.0±0.4a −1.3±0.2e 51.2±0.1a 478±0.7e Mean±SD of three determinations. Mean separation by Tukey’s test; values within a column followed by a different letter are significantly different (P
ORIGINAL PAPER
Comparative Thermal Degradation Patterns of Natural Yellow Colorants Used in Foods Pedro J. Giménez 1 & José A. Fernández-López 1 & José M. Angosto 1 & José M. Obón 1
# Springer Science+Business Media New York 2015
Abstract There is a great interest in natural yellow colorants due to warnings issued about certain yellow food colorings of synthetic origin. However, no comparative studies have been reported of their thermal stability. For this reason, the thermal stabilities of six natural yellow colorants used in foods —lutein, riboflavin, curcumin, ßcarotene, gardenia yellow and Opuntia betaxanthins— were studied in simple solutions over a temperature range 30–90 °C. Spectral properties and visual color were investigated during 6 h of heat treatment. Visual color was monitored from the CIEL*a*b* parameters. The remaining absorbance at maximum wavelength and the total color difference were used to quantify color degradation. The rate of color degradation increased as the temperature rose. The results showed that the thermal degradation of the colorants followed a first-order reaction kinetics. The reaction rate constants and half-life periods were determined as being central to understanding the color degradation kinetics. The temperature-dependent degradation was adequately modeled on the Arrhenius equation. Activation energies ranged from 3.2 kJmol−1 (lutein) to 43.7 kJmol−1 (Opuntia betaxanthins). ß-carotene and lutein exhibited high thermal stability, while betaxanthins and riboflavin degraded rapidly as temperature increased. Gardenia yellow and curcumin were in an intermediate position.
* José A. Fernández-López [email protected] 1
Department of Chemical and Environmental Engineering, Technical University of Cartagena (UPCT), Paseo Alfonso XIII 52, E-30203 Cartagena, Murcia, Spain
Keywords Food color . Yellow natural colorants . Thermal degradation . Thermal kinetics
Introduction Since early civilizations, colorants have been used to give a captivating presentation to human-made products, including foods [1]. Experts have long accepted that color plays a crucial role in the taste and perception of food [2]. Furthermore, in recent years, color in food has not only been regarded as a quality trait, but are also associated with health and safety benefits by consumers. The European Food Safety Agency (EFSA) in Europe, the Food and Drug Administration (FDA) in USA, and many other national authorities around the world, have restricted the use of synthetic colorants in foods and beverages because of their confirmed or suspected association with allergic reactions and toxic effects [3]. In addition, a recently published study reported a possible link between hyperactivity in children and the consumption of some synthetic yellow food colorants [4]. The tendency is therefore, for food manufacturers, going progressively toward the use of natural additives, and natural colors provide the further benefit of generally being more internationally accepted, and also some of them even have nutritional and bioactive effects [5]. Nevertheless, in the case of non-alcoholic beverages with added juices some synthetic colorants are mainly used in order to fortify their visual color [6]. The main natural pigments approved as food and drink coloring agents are: curcuminoids, riboflavins, caramels, carotenoids, chlorophylls, anthocyanins, betalains, cochineal, vegetal carbon and inorganic pigments [7]. Nature yellow hues are mainly due to carotenoids, betaxanthins, flavonoids, curcuminoids and riboflavins [5, 8]. There is a great interest in natural yellow colorants due to warnings issued about certain
Plant Foods Hum Nutr
yellow food colorings of synthetic origin [4]. Nevertheless, there are some disadvantages in the application of natural pigments, mainly related with their stability. Curcumin (E100) is the bright golden yellow pigment found in turmeric. Rhizomes produced by the turmeric plant Curcuma longa are dried and ground to produce the spice that contributes to the yellow distinctive color and flavor of mustards, pickles, and curry powder [5]. Riboflavin (E101) is mainly used to fortify foods but can also provide a yellow green color to food. It is particularly sensitive to light, and one example of riboflavin being used is in cake icing [9]. Lutein (E161b) is a natural yellow food colorant obtained from the extraction of marigold flowers. Like other carotenoids, lutein may provide health benefits due to its strong antioxidant properties. It is permitted in the European Union as a food color additive, but is not yet approved in the USA [10]. β-carotene (E160a) is a naturally-occurring pigment that finds widespread use as a colorant in food and beverages. Its shades range from yellow to orange, depending on concentration. It also functions as a safe source of vitamin A and as an antioxidant that contributes to protecting against the damaging effects of free radicals [11]. Gardenia yellow is a rare natural water-soluble colorant, extracted from gardenia fruit (Gardenia jasminoides), that is widely used in Asian countries mainly in colored juice, jelly, candy and noodles. Its chemical structure is postulated as crocetin glycosyl esters [12]. It is not approved as a food colorant in the European Union or in the USA. Betaxanthins are water-soluble vacuolar pigments occurring in plants of most families of the plant order Caryophyllales as Beta vulgaris and Opuntia ficusindica. They exhibit a yellow-orange coloration [13] and are considered bioessential dietary colorants since they are antiradical molecules and introduce essential dietary amino acids into foodstuffs [8]. The thermal processing of foods involves heating at high temperature, depending on the pH of the product and the desired shelf life. The incorporation of a natural colorant in food requires a detailed knowledge of its stability against possible degradation processes and it is also necessary to know the conditions that regulate this alteration in order to take appropriate measures to ensure sufficient stability that will allow the production, storage and transport of the colored product to be optimized. There are no reported comparative studies on the thermal stability of yellow food colorants, and therefore the aim of this study was to monitor the color alteration of selected yellow colorants used in foods upon heating at different temperatures. Since accurate knowledge of kinetic parameters is essential to predicting the quality changes that occur during thermal processing, a further objective was to estimate the degradation kinetic parameters during heat treatment.
Materials and Methods Materials The commercial food colorants: lutein, ß-carotene, riboflavin and curcumin in powder form were provided by Proquimac Food & Pharma (Barcelona, Spain). Gardenia yellow was from B&K Food Manufacturing Group Co. (Xiamen, China). The Opuntia betaxanthin extract was obtained in our laboratory from Opuntia ficus-indica fruits as indicated previously [13]. All chemicals used were of analytical reagent grade (Merck, Darmstad, Germany). The deionized water used in this study was prepared with a Milli-Q system (Millipore, Bedford, MA, USA). Stock solutions (1000 mg/100 mL) of each colorant in ethanol-water (3:2, v/v) were prepared. In the case of ß-carotene and lutein, drops of acetone were added to completely dissolve the colorant. Successive dilutions were carried out with the same solvent to reach an absorbance of 0.700± 0.05 at the wavelength of maximum absorbance (Table 1) in all the colorant extracts. The final solutions were maintained in the dark at 5 °C, used within 5 days, and shaken before use. Figure 1 shows the yellow shades in the final solutions of the six colorants investigated. Heat Treatment The thermal stability was tested at 30 °C, 50 °C, 70 °C and 90 °C in different experiments. The colorant solutions were distributed in 25 mL borosilicate test tubes (Pobel S.A., Madrid, Spain) sealed with screw caps and placed in a water bath for the required heat treatment. The tubes were wrapped with aluminum foil to avoid exposure to light. The changes in absorbance were monitored between 400 and 700 nm at time intervals of 1, 2, 3, 4, 5, and 6 h. At the end of the heat treatment, the samples were put in ice to stop any further degradation reaction. After 5 min equilibration in ice bath, an aliquot of each sample was passed through a PTFE filter (0.45 μm, Advantec MFS Inc., Dublin, CA, USA) and analyzed in an Agilent 8453 UV-visible photodiode spectrophotometer (Waldbronn, Germany). A non-heat treated sample of each colorant served as control to analyse any color intensity change. The experiments were performed in duplicates. Color Degradation Kinetics A general reaction rate expression for the degradation kinetics can be written as: −
d ½A ¼ k ½Am dt
ð1Þ
where BA^ is the quantitative value of the component under consideration, Bk^ is the reaction rate constant, and Bm^ is the
Plant Foods Hum Nutr Table 1 Color properties in the initial solutions of the selected yellow food colorants
Lutein Riboflavin Curcumin ß-Carotene
L*
a*
b*
λmax (nm)
94.1±0.2b 97.3±0.4e 95.6±0.3c 93.9±0.5b
−14.8±0.3c −17.4±0.3b −19.1±0.1a −14.6±0.3c
75.1±0.2f 69.1±0.4d 53.9±0.2b 70.6±0.4e
445±0.8c 446±0.6c 429±0.5a 448±0.6d
Gardenia yellow 96.5±0.2d −13.8±0.2d 63.2±0.2c 437±0.4b Opuntia betaxanthins 88.0±0.4a −1.3±0.2e 51.2±0.1a 478±0.7e Mean±SD of three determinations. Mean separation by Tukey’s test; values within a column followed by a different letter are significantly different (P
![[Analysis of colorants in foods using liquid chromatography-mass spectrometry].](/assets/img/hold.png)
