The Processing Status of Natural Coloring in China

In recent years, China's natural coloring industry has developed rapidly, and the development of natural coloring has become one of the development trends in industries such as pigments and medicine. China's natural pigment production is increasing year by year. At present, there are 65 kinds of pigments used in food in China, including 48 kinds of plant pigments. Natural pigments account for 90% of the pigments produced each year [2]. China's paprika red, gardenia yellow, red yeast rice and other pigments have already achieved large-scale production and have entered the international market [3].

However, due to the disadvantages of natural pigments, such as poor stability and weak coloring, as well as the backward processing level, China is still in a state where synthetic pigments and natural coloring coexist and develop at the same time. At the same time, China's pigment industry is facing a severe situation with frequent outbreaks of pigment quality problems, and there is a large gap between the needs of the industry's development. Improving the quality and processing level of natural coloring is an urgent issue that needs to be addressed. This paper analyzes the problems in the processing of natural coloring in China, discusses and proposes measures to improve the processing level of natural coloring in China.

1 Problems with natural coloring during processing

Most natural colorings are highly safe, and some also have the advantages of natural coloring and physiological activity, making natural colorings more acceptable and the mainstream of pigment industry consumption. However, due to the disadvantages of poor stability and weak coloring, coupled with the traditional processing technology and backward technology, simple processing equipment and other reasons, there are still many problems in the natural coloring processing industry, which restricts the rapid development of natural coloring processing.

1.1 Outdated processing technology

The traditional natural coloring processing process mainly includes crushing, extraction, separation and purification, concentration and drying. After years of development, natural coloring processing technology has made considerable progress, and extraction processes such as supercritical fluid extraction and microwave extraction, as well as separation processes such as column chromatography and membrane separation, have emerged, promoting the development of natural coloring processing. However, due to the limited scope of application of new processes, they cannot completely replace traditional processes. In addition, natural coloring itself has shortcomings, and there are still some problems with natural coloring processing. For example, traditional processes cannot effectively solve problems such as the low purity, poor stability, and low extraction rate of natural coloring. Some pigments cannot avoid problems such as color transfer, which greatly reduces the added value and technological content of pigment products and limits the development and utilization of natural coloring in a diversified direction [4]. China has introduced and developed many advanced processing technologies, but due to high costs and imperfect technology, their scope of application is limited, making it difficult to meet consumer demand and restricting the development of natural coloring processing in China. The attached table lists the advantages and disadvantages of several common natural coloring extraction and separation processes.

Most natural coloring processing enterprises in China still use traditional drying techniques, and microwave drying technology has not yet become widespread. Traditional drying techniques have low processing efficiency, and the extraction and separation of natural coloring is overemphasized during processing, while the reuse of resources is neglected, resulting in huge waste of resources. A large amount of waste water is discharged during processing, and the treatment of waste water has not been effectively resolved, which not only increases energy consumption and reduces the added value of products, but also causes serious environmental pollution.

There are also safety risks in the extraction and separation of natural coloring. At present, natural coloring is still extracted using organic solvents such as hexane, methanol solution, and acetone. Some companies even use toxic solvents such as benzene. The safety of these solvents and their residues in subsequent processes will have a certain impact on the safety of natural coloring. In addition, the safety of natural pigments extracted from microorganisms has yet to be verified. For example, although red yeast rice extract has excellent product performance, its safety is still a major obstacle to its development.

1.2 Outdated processing equipment

Most of China's natural coloring processing enterprises are currently small township enterprises with low processing capacity, simple processing equipment, high energy consumption, weak technical capabilities, and poor risk resistance. This results in poor product quality, high raw material consumption, high prices, and low added value. In addition, processing enterprises have not standardized or serialized their products. With the exception of a few individual products, there are no standardized products, making it difficult to enter the international market. For example, the processing equipment required for solvent extraction is very simple, but the extracted natural coloring has poor quality and low purity, which affects the scope of application of the product. Supercritical fluid extraction has the advantages of strong processing capacity, high efficiency and environmental protection, but its processing equipment has the problems of complex and expensive operation and high operating costs, so its scope of application is relatively narrow. Therefore, although natural coloring has a bright future, its processing equipment has not kept pace, which limits the rapid development of natural coloring processing.

1. 3 Irregular processing

There are many irregularities in the processing of the coloring industry. Companies do not take effective measures to control the quality of natural coloring during the processing. However, natural coloring has a complex composition, some of which may be toxic, and the chemical structure of some may change during extraction. In addition, it may be contaminated during processing. Therefore, toxicological tests must be carried out on natural coloring during the processing [5]. Only after it is determined that its quality meets the standards can it be processed, and the processing process must be strictly controlled to avoid secondary pollution. There are many problems in the processing of natural coloring, which restricts its development and requires further standardization.

2 New developments in the processing of natural coloring

In recent years, China's pigment industry has developed rapidly, and the country has proposed a development policy of “natural, nutritious, and multifunctional” for the pigment industry. Natural coloring has high nutritional value and certain biological activity. These advantages determine that natural coloring will inevitably replace synthetic coloring and become the mainstream of consumption. In GB 2760-2011 “Food Additive Use Standards,” there are already more than 40 types of natural coloring allowed for use in China. After years of competition and structural adjustment, China's coloring industry has begun to operate on a large scale, with relatively concentrated production and significantly improved competitiveness. A number of domestic natural coloring processing enterprises have rapidly emerged, and a number of well-known enterprises have appeared[6].

The processing technology for natural coloring has made significant progress, and the scope of application of new processing technologies is gradually expanding. For example, extraction processes such as microwave and enzymatic extraction, as well as separation processes such as membrane separation and column chromatography, have been applied to natural coloring, which has greatly saved resources and improved processing efficiency. Microwave extraction has the advantages of uniform heating, energy conservation and emission reduction, environmental protection and low cost [7], and can improve the yield of natural pigments and the purity of extracts. Microwave extraction overcomes the shortcomings of supercritical extraction and solvent extraction, meets environmental requirements, reduces operating costs, and has good development prospects. Wang Weihua [8] et al. found that the use of microwave extraction of lycopene can achieve an extraction rate of 95% under optimal process conditions, thereby greatly shortening the extraction time. Li or [9] and others used microwaves to extract the yellow pigment from wild chrysanthemums. Compared with the solvent method, the extraction rate increased from 88.6% to 91.1%, and the extraction time was reduced from 12h to 450s, greatly improving the extraction efficiency.

The application of enzymatic extraction has also promoted the development of natural coloring processing. Enzymatic extraction does not damage plant components and can increase the extraction rate of active ingredients. For example, Yu Qing [10] and others developed a method for extracting the pigment from the leaves of the Chinese evergreen tree by adding cellulase and pectinase, which increased the extraction rate by 13.2% compared to the traditional method.

Separation processes such as membrane separation and column chromatography have also promoted the development of natural coloring. Membrane separation is a simple and highly effective process that can be used to separate pigments such as cocoa pigments and red yeast rice pigments. It can remove more than 90% of macromolecular substances such as pectin, and can achieve 100% retention of pigments at room temperature. Macroporous adsorption resins have a good adsorption and purification effect on natural coloring. The adsorption and screening effect of macroporous adsorption resins can be used to achieve the purpose of separating substances.

The purification process for natural coloring is also developing rapidly. The introduction of advanced separation and purification technology to purify natural coloring can improve its performance and expand its scope of use. At present, the main purification technologies used for natural coloring are: ultrafiltration purification, adsorption resin purification, gel chromatography, and other technologies. With the advent of advanced technologies such as biotechnology and nuclear magnetic resonance technology, China should apply these advanced technologies to the refining process of natural coloring, thereby greatly improving the processing efficiency of natural coloring and increasing the comprehensive utilization rate and added value of the product.

Poor stability and weak coloring strength have always been important factors limiting the development of natural coloring in a wider market. In recent years, China has carried out various explorations to solve the problem of poor stability of natural pigments, and has achieved remarkable results. For example, the use of microencapsulation technology can improve the stability of natural coloring; the use of biotechnology can change the hue of natural coloring to improve its stability, solubility and coloring power; appropriate processing conditions can be controlled, such as avoiding high-temperature heating and stabilizing the optimal pH value of the pigment; in 2011, Harbin Institute of Technology developed a natural coloring separation and purification system and a stabilisation technology for anthocyanin pigments, solved the technical problems of low extraction rate, poor stability and substandard purity in the processing of natural coloring in the past, and promoted the development of natural coloring processing. However, the problem of poor stability of most natural coloring is still difficult to solve. China needs to continue to increase investment, research and explore new technologies to solve the technical problems of poor stability of natural coloring.

3 Countermeasures for the development of natural coloring processing

3.1 Establish a modern processing concept

Traditional natural coloring processing places too much emphasis on the quality of natural coloring and ignores the reuse of resources, resulting in a low comprehensive utilization rate of by-products and low added value. This is no longer in line with modern natural coloring processing requirements, and a modern processing concept must be established. The modern processing concept requires that, while ensuring the quality of natural coloring, the comprehensive utilization rate of by-products be increased, and zero emissions be achieved during the processing, so as to conserve resources and increase the added value of the product. In line with the concept of a circular economy, we should establish a sense of efficiency, environmental protection and energy conservation, actively develop a modern processing model with low consumption, low emissions and high efficiency, strengthen energy conservation and environmental protection, reduce resource consumption, reduce waste emissions, improve the comprehensive utilization of natural coloring resources, and increase product added value [11]. We should build a modern natural coloring processing system that is safe, environmentally friendly, efficient, low-consumption and high value-added, and promote the development of natural coloring processing in China.

3.2 Improving the processing technology

Improving traditional processing techniques with advanced processing technology is one of the hotspots in the research of natural coloring. Using techniques such as enzyme technology and nuclear magnetic resonance to improve traditional processes has solved the shortcomings of natural coloring, such as stability and color intensity, improved the overall level of natural pigment processing, achieved zero emissions in the processing process, increased the added value of the product, and promoted the rapid development of natural coloring processing. For example, the use of enzyme technology in the processing can reduce the use of chemicals that are harmful to health, save investment in equipment, reduce emissions of pollutants, and is environmentally friendly, meeting the requirements of being “green, efficient and safe”. Another example is the use of the catalytic decomposition of enzymes to remove impurities through enzymatic reactions, which has the effect of refining natural coloring. For example, the extraction of chlorophyll from silkworm cocoons can use an enzymatic refining method to remove unpleasant odors and obtain high-quality chlorophyll [12].

Microwave extraction overcomes the shortcomings of solvent extraction and supercritical extraction methods, reduces operating costs, saves resources, meets the requirements of high efficiency, environmental protection, and energy conservation, and shows good development prospects and great application potential. Some people used microwave processing to treat pomelo peels and found that the efficiency of microwave extraction of natural coloring is about 30 times that of traditional processing methods, and it has higher purity and consumes less energy. It is conducive to industrial production and makes full use of modern microwave technology to promote the rapid development of the natural coloring processing industry.

Establish a scientific management mechanism during the processing of natural coloring to standardize the processing of natural pigments and improve product quality. Implementing HACCP management methods during the processing can maximize the safety of natural coloring products, achieve unified standards from raw material procurement to processing, sales, packaging and other links, and establish feasible process parameters to standardize the processing process, so that it meets the standards of industrial food factories and promote the standardized production of natural pigments [13].

3. 3 Improve the level of processing equipment

On the basis of making full use of modern processing technology and processes, the level of processing equipment should also be improved simultaneously, so as to enhance the overall competitiveness of the natural coloring industry. Continuously update and develop processing equipment required for the entire process, including crushing, extraction, separation and purification, concentration and drying, to improve the processing capacity and efficiency of natural pigments. Through introduction and innovation, research and development of processing equipment that is compatible with advanced processing technology, while researching and developing energy-saving, efficient, environmentally-friendly processing equipment, conserving resources, protecting the environment, and increasing the added value of natural pigment products. By improving the level of natural coloring processing equipment, it will promote the sound and rapid development of natural coloring processing.

3. 4 Strengthen the development of natural coloring with special physiological activities

China has abundant natural coloring resources, and the following have been developed: curcumin, tea pigments, red yeast rice pigments, etc. New natural coloring not only has outstanding advantages, but also has many physiological functions, and is an important resource for the development of functional pigments in China. For example, curcumin has the functions of good coloring strength, anti-oxidation, anti-tumor, and lowering blood lipids. In addition, curcumin has a variety of physiological functions such as anti-inflammatory, anti-infective, anticoagulant, and preventing the formation of age spots [14].

China is rich in tea resources. The processing of tea produces a large amount of pruned leaves, tea dust, and even unsold coarse old tea. If these are not utilized, it will result in a huge waste of resources. If they are used as raw materials for processing tea pigments, it will greatly improve the utilization rate of tea resources and open up a new way for the comprehensive utilization of tea. Tea pigments are rich in vitamins, amino acids, alkaloids, flavonoids, steroidal compounds and other substances, and have high nutritional value. Tea pigments not only have good coloring and stability, but also have certain health functions, such as anti-oxidation, antibacterial, antitumor, and regulating blood sugar and blood lipids. They are widely used in the fields of food and medicine and health[15]. However, the tea pigment extraction process still lacks effective separation and purification techniques. Current research on tea pigments mainly focuses on comprehensive studies of various mixtures, and whether there is a synergistic or antagonistic effect between the components remains to be explored. There is a need to further develop new processes for extracting tea pigments and promote the development and research of natural tea pigments.

Natural coloring has high nutritional value and certain biological activity, and research and development of natural coloring has become a development trend in the coloring industry. At present, there is a strong demand for natural coloring in China, and it is a good time to develop emerging natural coloring. Accelerating research and development of new natural coloring is conducive to developing China's high-quality natural coloring resources, increasing natural coloring production, and helping to meet people's growing nutritional and health needs, promoting the development of the natural coloring industry.

4 Conclusion

With the development of people's respect for nature, the pursuit of health and the field of food toxicology, the development and application of natural coloring will become the trend of development of China's pigment industry. Due to its own advantages, such as diverse varieties, abundant raw materials, high safety and strong functionality, natural coloring is developing very rapidly and has huge market potential. China has abundant natural coloring resources, and the development of natural coloring in China has a bright future. China has always focused on the development and utilization of natural coloring. However, natural coloring has disadvantages such as poor stability and weak coloring, and the low processing level has also limited the rapid development of natural coloring processing. In view of the current processing status of natural coloring, it is necessary to adhere to modern processing concepts, improve traditional processing techniques using advanced processing technologies, update and develop new processing equipment, accelerate the processing of natural coloring, improve processing efficiency, reduce production costs, improve product quality, strive to achieve zero emissions in the processing, improve the comprehensive utilization rate of by-products, and increase the added value of products, thereby improving the overall competitiveness of the natural coloring processing industry and promoting the healthy and rapid development of the natural coloring processing industry.

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