How to Test Food Coloring?

Food Coloring is an important part of food additives. It is not only used in the food industry to improve the color of food, stimulate people's appetite, and give people a sense of beauty, but is also widely used to color medical and health products, daily chemical products, cosmetics, and the printing and dyeing industry. Although the amount of food coloring used is very small, it has a significant impact on the quality of the food.

Food Coloring is classified according to the chemical structure of its main ingredients, which mainly include chlorophylls, carotenoids, flavonoids, anthocyanins, betalains, tannins, caramel pigments, etc.

Food coloring is usually divided into two main categories: natural pigments and synthetic pigments. Natural pigments for food mainly refer to pigments extracted from animal and plant tissues, including microbial pigments. Most of the natural pigments used are plant pigments such as carotene, chlorophyll, turmeric, etc.; animal pigments such as shellac pigment; and microbial pigments such as riboflavin and red yeast rice pigment. Not only are natural pigments for food safer, but many of them also have certain nutritional value. Synthetic food coloring, also known as synthetic food dye, is mostly made from chemical products such as benzene, toluene and naphthalene through a series of organic reactions such as sulfonation, nitration and azoization. Therefore, synthetic food coloring mostly contains compounds with R- N=N- R′ bonds, benzene rings or xanthene structures, which may be unsafe or harmful to the human body.

1 Overview of the application of food coloring

Before 1981, the Chinese government only approved 14 food coloring agents for use. By 2004, a total of 61 food coloring agents were approved for use in GB2760-1996 (including additional varieties). To date, a total of 65 food coloring agents have been approved for production and use in China. After more than 20 years of development, production, sales and application have reached a certain level and scale. In recent years, the total production of food coloring in China has been about 10,000 t/a, of which synthetic coloring is about 1,000 t/a and natural coloring is about 9,000 t/a. Caramel coloring accounts for more than 80% of natural coloring, and the rest is plant extracts and microbial fermentation products.

1. 1 Synthetic coloring

There were about 100 kinds of chemically synthesized pigments in the world in the 1950s, but now there are only about 60 kinds. Japan once approved the use of 27 kinds of synthetic pigments, but now 16 of them are banned. In the United States, 35 kinds of synthetic pigments were allowed to be used in 1960, but now only 7 kinds remain. Azo pigments have long been banned in Sweden, Finland, Norway, India, Denmark, France, etc., and some countries such as Norway have completely banned the use of any synthetic chemical pigments. In addition, some countries have banned the addition of synthetic pigments to foods such as meat, fish and processed products, fruits and their products, condiments, baby food, and pastries. Among the 65 food colorings allowed to be produced and used in China, 48 are natural pigments and the rest are synthetic pigments. China also has strict restrictions on the addition of synthetic colors to food: artificial synthetic colors cannot be used in meat and its processed products, fish and its processed products, vinegar, soy sauce, fermented bean curd and other condiments, fruits and their products, milk and dairy products, infant foods, biscuits, cakes and pastries. Only soft drinks, cold drinks, confectionery, prepared wines and fruit juices can be used in small amounts.

1. 2 Natural alternative colors

Synthetic β-carotene appeared on the market in 1954 and now has a large market share (about 17% worldwide, 40% in Europe, with an estimated annual global production of over 500 tons). It is mainly used in butter, soft drinks, confectionery and bread processing.

1. 3 Natural colors

Natural colors have been used commercially on a wide scale for 25 years and have made great progress since then. Currently, 13 natural colors are approved for use in Europe, while the US has approved 26. Caramel colors dominate the natural color market, mainly in cola drinks. As the market expands and brown foods grow, the use of caramel colors is also gradually increasing. Other varieties with high production volumes include red yeast rice pigment, paprika red pigment, turmeric yellow pigment, sorghum red pigment, copper sodium chlorophyllin, and rose bengal pigment.

2 Analysis and testing methods for food coloring

2. 1 Chromatography

Shen Shixiu et al. used paper chromatography to identify the adulteration of natural red yeast rice pigment with synthetic pigment carmine in cooked meat products, based on the difference in the distribution coefficients of the components of natural red yeast rice pigment and synthetic pigment carmine. Yan Haoying et al. used a double-wavelength thin-layer scanning method to separate and measure five synthetic food colors: carmine, amaranth, lemon yellow, sunset yellow and brilliant blue.

2. 2 Spectrophotometric method

When determining synthetic food coloring in mixtures by spectrophotometry, the multi-wavelength linear regression photometry method using least squares is often used. However, least squares is significantly affected by outliers and has strict requirements on conditions such as the position of the measurement wavelength. Zhou Tong et al. used the excellent analytical performance of partial least squares multivariate calibration combined with the highly sensitive derivative photometry to simultaneously determine four components of mixed pigments (tartrazine, sunset yellow, carmine, and amaranth); Feng Jiang et al. used stable regression-spectrophotometry to simultaneously determine three groups of synthetic food colours, which overcomes the shortcomings of the least squares method, and analysed the lemon yellow, carmine, and mixed fruit green pigment in drinks. Chen Haichun et al. used the double-wavelength K-factor method to analyse the two components of sunset yellow, lemon yellow and carmine.

2. 3 Ultraviolet spectrophotometry

Ultraviolet spectrophotometry is the most commonly used method for quantitative analysis using characteristic absorption peaks. Since substances selectively absorb light, an ultraviolet-visible spectrophotometer is used to scan the absorption spectrum. it was found that different synthetic food colors such as carmine, amaranth, lemon yellow, sunset yellow and brilliant blue have different absorption spectra. By comparing with the standard spectrum, the qualitative analysis can be done visually and quickly. The peak height is proportional to the content at a certain concentration, so it can be quantified. Thus, the UV-Visible absorption spectroscopy method for determining synthetic food colors was established. However, many pigments with similar structures and properties coexist in the same organism, such as the carotenoids lycopene, α-carotene, and β-carotene, and the red yeast rice pigments monascorubrin, monascoxanthin, and monascobianthrin. Accurately determining the content during the extraction and separation process is a problem that needs to be solved in process research, technology development, and production control.

2. 4 Polarography

The molecular structure of synthetic food coloring contains N=N double bonds or C=C double bonds. These groups are electroactive and can be reduced to produce a reduction wave on a mercury drop electrode. The reduction potential of various pigments is different in different bases, so qualitative analysis can be performed. Quantitative analysis can be performed according to the linear relationship between the peak height of the reduction potential and its concentration. Wen Jun et al. used this method to determine erythrosine in a specific buffer solution; Wang Yong used continuous oscillographic polarography to continuously determine six food colors, including amaranth, sunset red, lemon yellow, carmine, erythrrhizine and brilliant blue, in beverages, fruits and other foods; Alghamdi A H used square wave polarography to determine amaranth, used for the determination of the content of azo pigments. Chanlon S et al. separately determined carmine, tartrazine and allura red. Qian Guiping et al. simultaneously determined the four components of lemon yellow, sunset yellow, amaranth red and carmine. Zhang Lei used the MP-1 dissolution analyzer to test the pigments carmine, lemon yellow, sunset yellow, and amaranth, with a recovery rate of between 96% and 100% and a coefficient of variation of 1.0% to 4.5%. The minimum detectable mass concentration was 0.2 μg/mL, which is suitable for the determination of pigments in beverages.

2. 5 High-performance liquid chromatography (HPLC)

High-performance liquid chromatography is a widely used method for determining food color. As most food colors are a mixture of two or more components, this method is highly accurate and reproducible, and is now a national standard method. Qi Guangjian et al. used Hyper-SIL-ODS 24.6×250 mm (4 μm) as the analytical column, MeOH/NH4AC 7/93 as the mobile phase, and successfully determined malachite green in illegally dyed rice at a detection wavelength of 254 nm. with a minimum detection limit of 0.01 mg/kg. Yue Weimin et al. used ion-pair high performance liquid chromatography to determine five commonly used synthetic food colours; Guan Minya et al. used external standard quantitative detection of five mixed colours added to drinks: lemon yellow, amaranth red, carmine, sunset yellow and brilliant blue.

Many domestic and foreign scholars have also used reversed-phase high-performance liquid chromatography to simultaneously analyze a variety of synthetic pigments in food and beverages. He Jibao et al. used reversed-phase high-performance liquid chromatography to separate the five synthetic pigments lemon yellow, amaranth red, carmine red, sunset yellow, and brilliant blue, and established a method for determining a variety of synthetic pigments in food. Ning Shangyong et al. established a method for simultaneous determination of synthetic pigments (acid scarlet GR, acid red 1, and acid red 26) in food shrimp by reversed-phase liquid chromatography. The factors such as the extraction agent, NH4Ac concentration, and ion pair type were optimized, which resulted in the complete separation of the five pigments, and they were completely separated from the six pigments in the national standard on the chromatogram.

3 Development trend of food coloring

Although China is currently in a situation where synthetic and natural colors coexist, with the development of society and people's increasing awareness of food safety, the development of natural colors is the general trend of the world's food coloring development, and the promotion and application of natural colors is also the main direction of China's development of food coloring.

3.1 Developing new varieties of multi-functional natural colors

Generally speaking, natural pigments are relatively safe for the human body. Some natural pigments are nutrients in themselves, with nutritional effects, and some also have certain pharmacological effects. At the same time, natural pigments can better imitate the colors of natural substances, and the hue when coloring is more natural. For example, lycopene has a variety of physiological functions such as antioxidant properties, anticancer properties, enhancing the body's immune function, lowering blood lipids and preventing atherosclerosis; zeaxanthin can protect body tissue cells by quenching singlet oxygen and scavenging free radicals, thereby protecting the biological system from the potentially harmful effects of excessive oxidative reactions; curcumin, in addition to its anti-tumor, antioxidant and antimutagenic properties, it also has a variety of physiological functions such as lowering blood lipids and preventing atherosclerosis, as well as promoting blood circulation, fighting infection and preventing the formation of age spots. Tea pigments contain a large amount of chemically active ingredients such as active phenolic hydroxyl groups, which have strong free radical scavenging and antioxidant effects, and can prevent cancer, protect against ultraviolet radiation, prevent atherosclerosis, prevent tooth decay and protect teeth, as well as having a variety of other physiological functions. China is rich in animal and plant resources and agricultural and sideline products, so there is a bright future for the development of natural food coloring with health-promoting functions and certain nutritional value.

3. 2 Developing new technologies for stabilizing natural pigments

Natural pigments are safe and reliable, but their low coloring power and poor stability to light, heat, oxygen, pH, etc. greatly limits their scope of use. Therefore, developing new technologies for stabilizing natural pigments can greatly improve these shortcomings. For example, adding stabilizers during the processing and storage of natural pigments can extend their shelf life and improve their heat and light resistance. Microencapsulation technology is also very important for improving the stability of natural pigments. Applying microencapsulation technology can improve the solubility of pigments, effectively reduce the impact of the external environment on pigments, reduce the diffusion of pigments to the outside, etc. According to the different ways in which the instability of different pigments is expressed, pigments can be used in combination to improve the stability of the pigment, etc. At present, the stabilization technology of natural food coloring is still very imperfect, and its stability is affected by many factors. It is necessary to develop more complete and advanced technology to improve the stability of natural food coloring, so that natural pigments can be used in a wider range of applications.

References

[1] COLLIER S W, STORM J E. BRONAUGH R L, Reduction of azodyes during in vitro percutaneous absorption [J]. Toxicology and Applied Pharmacology, 1993 (118): 73-79.

[2] SHEN S X, FU X R. Identification of red yeast rice pigment and carmine by paper chromatography [J]. Food and Fermentation Industry, 2001, 22(7): 79- 80.

[3] Yan Haoying, Zhang Jun, Li Shuhua. Thin-layer chromatography scanning analysis of five synthetic food colorings [J]. Modern Preventive Medicine, 1997, 24(2): 192- 194.

[4] Zhou Tong, Zhong Jiayue. Simultaneous determination of mixed pigments by second derivative spectroscopy PLS method [J]. Chinese Journal of Health Inspection, 2002, 12(6):680.

[5] Feng Jiang, Zhou Jianmin, Huang Peng, et al. Stable regression - simultaneous determination of three groups of food colorants by spectrophotometry [J]. Chinese Journal of Public Health, 2002, 18 (4): 494-495.

[6] Chen Haichun. Simultaneous determination of sunset yellow and lemon yellow by dual-wavelength K-factor spectrophotometry [J]. Chemical Reagents, 2003, 25(2): 98-99.

[7] Chen Haichun. Simultaneous determination of sunset yellow and carmine in beverages by dual-wavelength compensation calculation [J]. Chemical Analysis and Measurement, 2005, 14(1): 54- 55.

[8] Li Bibin, Zhang Haixia, Pan Lianfu. Qualitative and quantitative determination of synthetic food coloring by ultraviolet-visible absorption spectroscopy [J]. Chinese Journal of Sanitary Inspection, 2001, 11(1): 58- 59.