What Is the Use of Plant Based Pigments?

Natural pigments mainly include three categories: natural plant pigments, natural animal pigments and natural mineral pigments [1]. Among these, natural plant pigments are the most widely used, and are involved in various industries such as food, textiles, cosmetics, medicine, the leather industry, printing and dyeing, etc. [2]. Natural plant pigments refer to the pigment components found in the roots, stems, leaves, flowers, fruits and bark of plants, such as turmeric, sumac, indigo, safflower, black beans, green walnut skins, etc. Their environmentally friendly characteristics have become the focus of the development of new pigment dyes. Humans have a long history of using natural pigments. In ancient times, people in southern France, northern Spain and northern Africa already used charcoal, ochre and manganese brown clay to paint walls and objects [3-4]; in Korean history, the use of natural inorganic dyes in murals and wooden structures reached a heyday [5].

As early as the Yellow Emperor period (2697 BC – 2599 BC), people in China already knew how to extract the juice from weeds, leaves and branches to dye clothes or paint various patterns [6]. During the Xia, Shang and Western Zhou dynasties, China's dyeing and weaving technology developed rapidly [7]. According to the Book of Rites, the state of Chu (209 BC) even had an official in charge of indigo production called Lan Yin [8]. Until the 19th century, most dyes for textile printing and dyeing came from plants. Since the British chemist Perkin W H invented the first synthetic organic pigment, aniline violet, in 1856 [9], inexpensive chemically synthesized dyes gradually replaced the position of natural plant pigments in the dyeing industry, and natural pigments gradually faded from the historical stage. Synthetic pigments are mainly organic pigments made by artificially synthesizing aniline dyes from petroleum, coal tar and their by-products.

The “grand health” industry is a new “sunrise industry” that has emerged in response to the development of the times, the needs of society and changes in the disease spectrum. “Grand Health” is a broad concept that focuses on people's clothing, food, housing, transportation, birth, aging, sickness and death, and implements a concept of full, comprehensive care for all elements of life. It not only pursues individual physical and health benefits, but also psychological, spiritual, social, environmental and family health. It mainly includes two aspects: one refers to products closely related to human health, such as health foods, health drinks, cosmeceuticals, and healthy household products; the other refers to medical services such as health examinations, preventive healthcare, medical rehabilitation, and community education. In the big health industry, natural plant-derived health products are the core and also the key material basis.

This article mainly reviews the functional applications of natural plant pigments in the big health industry. In recent years, with the enhancement of health and environmental protection and green ecological awareness, natural plant pigments have once again attracted people's attention and returned to the public eye. From an environmental protection perspective, natural plant pigments are obtained from nature, the raw materials are renewable, environmentally friendly, biodegradable, have low toxicity and cause little harm, and are in line with today's theme of “back to nature and green environmental protection” [11]. From a safety perspective, most natural plant pigments are themselves Chinese herbal medicines or materials that can be used for both food and medicine. The vast majority are harmless and will not cause allergies or cancer; a few natural plant pigments also have strong antibacterial, anti-inflammatory and other health-promoting functions [12]. From a dyeing perspective, natural plant pigments have a simple and natural color, an elegant and soft tone, and generally have a special aromatic scent, which can also reflect local/ethnic characteristics.

1. Application of natural plant pigments in food

In traditional diets, people pay more attention to the combination of color, aroma and taste, and prefer things with better sensory qualities [13]. Food coloring can improve the color of food. As an important food additive, it is widely used in food processing and production and research. It is mainly divided into two types: synthetic food coloring and natural food coloring [14]. Synthetic food coloring, such as amaranth, carmine, and lemon yellow, is low in cost, comes in a variety of hues, and produces bright, vivid colors [15]; natural food coloring, such as anthocyanins, lycopene, carotenoids, and cochineal, is derived from plants and animals. However, with the development of modern medicine and the focus on health, people have gradually become aware of the potential risks of synthetic food coloring. Abused synthetic dyes have been successively proven to have varying degrees of toxicity, and some have the risk of causing cancer, teratogenicity and hyperactivity in children [14, 16-17]. For this reason, people have begun to pay attention to the technological development and promotion of natural food coloring [15].

A large number of domestic and foreign studies have found that natural food coloring derived from plants is not only highly safe, abundant in source, and has a soft hue, but that some pigments also have certain physiological activities, such as health care, nutrition, and anti-aging, which improves consumer trust in food safety [18-19]. At present, many countries around the world are vigorously researching, developing, and utilizing natural food coloring. Japan is the most advanced country in the development of natural food coloring, followed by the United States [20]. In recent years, the annual growth rate of sales of natural food colors on the international market has remained above 10%. The production of natural food colors in China has begun to take shape, and there are more than 40 types of natural colors that are allowed to be produced and used, with an annual output of over 10,000 tons [20-21].

The development of the modern food industry requires more natural food colors to beautify foods, increase appetite, and enhance the value of goods [22]. According to the different colors of the pigments, they are divided into green, red, yellow, and black, which are the most widely used pigments. The latest applications of some representative natural food colors of plant origin are summarized in Table 1. As can be seen from the table, there are many plants that contain red and yellow pigments and are widely used, mainly in non-staple foods such as beverages, ice cream, candy, biscuits, canned food, etc.; green and black pigments have fewer sources and are mainly used in staple foods such as pastries and baked goods. These plant pigments not only have a rich color to improve the color of the food, but also can be used as seasonings to meet people's needs for food. With the improvement of the extraction process and the reduction of the cost of natural pigments, natural pigments have a very broad future and development potential, and will become one of the priority food additives in the future, and there is a trend to completely replace synthetic pigments [23].

2. The application of natural plant pigments in cosmetics

“Everyone loves beauty,” and since the dawn of human civilization, people have used natural plants as cosmetics for beauty and skin care [24]. In primitive society, some tribal clans would smear various colors collected from nature on their faces during various totem worship rituals, painting them in the shape of totems to show their closeness to the gods. From the 5th century BC to the 7th century AD, there were also many legends and records from various countries about the production and use of cosmetics, such as the ancient Egyptian queen using patina to trace the eye circles, and the ancient Greek beauty Aspazi using fish glue to conceal wrinkles. In ancient China, people liked to use rouge to highlight the beauty and charm of their faces. Rouge, duck egg powder, hair oil and sachets were the four main types of ancient Chinese cosmetics. According to the “Zhonghua Gujin Zhu” (Notes on Ancient and Modern China), “Yan Zhi (rouge) is made from sealing wax, mixed with the sap of red orchids, and used to adorn women's faces.

Since the end of the Shang Dynasty, people in ancient China have used primitive plants to invent rouge for women to apply to their cheeks. During the Wei, Jin, Southern and Northern Dynasties, Ge Hong of the Jin Dynasty compiled the “Emergency Treatment Manual”, which already contained a large number of anti-aging and skin care formulas. During the Tang Dynasty, cosmetics experienced unprecedented development. Sun Simiao compiled the “Qian Jin Yi Fang” and “Emergency Qian Jin Fang”, which contained a large number of plants that could be used for beauty as well as beauty formulas. Li Shizhen's Compendium of Materia Medica from the Qing Dynasty records many methods of using Chinese herbal medicine to remove wrinkles, lighten spots, fight aging, prevent hair loss, and whiten skin, among other skin care and beauty treatments [25]. With the rapid development of the petroleum industry, synthetic cosmetics were born, with mineral oil as the main ingredient and added fragrances, synthetic pigments and other chemical additives, in order to satisfy people's pursuit and desire for beauty.

As synthetic cosmetics can be mass-produced on a large scale, they are cheaper and have a stable supply, so they quickly became popular in society at the time. However, synthetic cosmetics are a hodgepodge of a wide variety of chemical raw materials and synthetic pigments, and they contain potentially harmful chemical additives. Long-term use can damage the skin and cause chronic toxicity in the body[26-27]. This phenomenon has aroused great concern among people who care about beauty. Nowadays, when choosing cosmetics, especially lipsticks, lip glosses, eye shadows, foundations, blushes, rouge and hair dyes, people not only demand bright colors, but also pay more attention to safety and harmlessness [28]. With the progress of society and the development of the economy, people's awareness of the pursuit of natural, healthy and safe is increasing day by day. Cosmetics are no longer a luxury for a few people. More and more consumers are beginning to pay attention to the care and maintenance of skin and hair. Beauty makeup has almost become an essential part of modern people's daily lives [29-30]. This paper summarizes some of the natural plant pigments that are currently used in cosmetics, as shown in Table 2. With the continuous improvement of modern extraction and separation technology, the application prospects of natural plant pigments in cosmetics are very broad.

3. Application of natural plant pigments in healthcare

With the development of medicine and people's increasing awareness of health, many people have come to realize that disease prevention is an effective means of promoting and protecting health. Some natural plant pigments not only have therapeutic effects on various human diseases such as hypertension and diabetes, but also have preventive and healthcare functions because they also contain the unique active ingredients of traditional Chinese medicine. In the “12th Five-Year Plan for the Development of Medical Science and Technology,” the traditional health preservation concept of “treating diseases before they occur” was proposed for the first time. The earliest origin of “treating diseases before they occur” is the strategy of disease prevention and health preservation proposed in the Huangdi Neijing (Yellow Emperor's Internal Classic), which is an important part of China's traditional Chinese medicine culture and the “prevention first” ideology that is still followed by China's medical and health community today [34]. In recent years, through continuous in-depth research on natural plant pigments, it has been discovered that plant pigments have a wide range of biological activities, including antioxidant, anti-aging, anti-radiation, free radical scavenging, anti-cancer, anti-tumor, anti-atherosclerosis, prevention of coronary heart disease, protection of cardiovascular function, and enhancement of immunity. They have broad prospects for development and application in disease prevention and health care.

Wang Wei [36] studied the antioxidant activity of 14 commonly used natural pigments such as anthocyanins, flavonoids, carotenoids and quinones. The research showed that natural pigments with a diketone structure, flavonoid structure and anthocyanin structure, such as turmeric pigment, sorghum pigment, grape skin pigment and onion pigment, can be developed into antioxidants and anti-aging health products. The flavonoids in black rice pigment, such as anthocyanins, not only have strong oxygen free radical scavenging and antioxidant functions, but also significantly inhibit the peroxidation of egg yolk lipoproteins [37]. At present, natural black pigments and red pigments are also widely used in healthcare. Among them, paprika red is currently the world's best-selling natural food coloring, which can be used as a coloring agent for sugar-coated medicines and also has health benefits [26].

Gao Xiang [38] conducted a study on chili-based health foods at home and abroad, concluding that chili can not only be used to develop weight-loss health foods, but also health foods that protect against radiation. At the same time, capsanthin also has a certain inhibitory effect on the occurrence of cancer and tumors [39]. Many spicy ethnic groups and countries have a lower chance of developing cancer than Western countries [26]. Shikonin belongs to the naphthoquinone class of compounds. Studies have shown that it has anti-inflammatory and anti-tumor effects. Its anti-tumor effect not only directly poisons tumor cells, but also inhibits tumor angiogenesis and thus hinders the supply of nutrients to the tumor, thereby inhibiting tumor growth [40-42].

Therefore, the development and application of natural plant pigments is imperative. Not only are they abundant in source and have a natural color, they also have a variety of biological activities, satisfying the modern yearning for health. Natural plant pigments are divided into seven categories according to their different pharmacological effects. The application of natural plant pigments in healthcare is summarized and categorized in Table 3. As can be seen from the table, plant pigments with the most active functions include those that scavenge free radicals, those that have antioxidant properties and those that have anti-aging properties. This coincides with the current focus on the prevention of aging and health maintenance. There are also relatively many plant pigments that can prevent cancer and lower the “three highs” (high blood pressure, high blood sugar, high blood lipids). There are relatively few plant pigments that can protect against radiation and relieve visual fatigue, but they are closely related to human health. The vigorous development of natural plant pigments provides support and protection for China's healthcare industry and public health.

4. Other applications of natural plant pigments

Natural plant pigments are also widely used in textiles, feed, the paper industry and the leather industry. There are already a large number of natural dye textiles on the market, which not only have a natural colour, but also have certain functions such as UV protection [49]. Japan, South Korea and India have all established research institutes for plant dyes. Their research shows that silk underwear and pajamas dyed with pigments extracted from madder, indigo, tulip and safflower pigments to dye silk underwear and pajamas can both protect against insects and bacteria and protect the skin [12]; in feed, natural plant pigments have extremely high application value. For example, paprika red pigment is important for improving the appearance and flavor of animal products, and can be used to color and enhance the color of animal skin, egg yolks, fish, shellfish, etc. [50].

Capsanthin is currently widely used at home and abroad to improve the color and flavor of rainbow trout meat, etc. [51-52]; in papermaking, the use of natural plant pigments is also very important. White paper can cause visual fatigue and reduce work efficiency after prolonged use. People also widely use colored paper, but long-term use of paper dyed with synthetic dyes can cause harm to the human body. Therefore, it is particularly important to create a colorful and safe paper use environment. Natural pigment dyes have been used to dye paper. For example, natural redbud pigment not only has good coloring ability, but also meets environmental requirements for packaging materials[49]. In the leather industry, natural plant pigments can not only give leather a rich color and full luster, but also meet various market demands and people's pursuit of beauty. Their advantages of being environmentally friendly and renewable make natural pigments more widely used. For example, thick-skinned fragrant, casuarina, safflower, madder, bayberry, etc. have been used for tanning and dyeing. These natural dyes can not only be used as tanning dyes, but also as leather fungicides. For example, plant pigments such as turmeric and rhubarb have good antibacterial activity. Therefore, the development of natural plant pigments will become an important part of eco-friendly and human health development, and the market prospects are broad [53].

5 Prospects

China is a vast country with abundant plant resources, which lays a solid foundation for the further development, utilization and research of natural plant dyes. Natural plant pigments have unique advantages over chemically synthesized pigments and are attracting more and more attention in the pigment industry. In particular, with the deepening of people's understanding of the concepts of healthy and safe living, natural plant pigments will gradually replace synthetic pigments with toxic side effects and become the new direction of development of the domestic pigment industry in the future. However, research on natural pigments has stalled for the time being, mainly because natural plant pigments are generally secondary metabolites of plants. They have complex pigment compositions, low extraction rates and are difficult to separate, have low pigment contents and poor stability. Therefore, efficient extraction and separation techniques and the development of a highly stable source of plant pigments are urgent problems that need to be solved.

The author believes that the following aspects can be considered: firstly, improving the extraction process. The extraction of natural pigments is affected by many factors, such as temperature, time and pH, which may affect the extraction rate of pigments. Combining traditional boiling extraction methods with new extraction methods to develop extraction and separation techniques that are both efficient and economical is the key. The second is to strengthen research on the structure, properties and physiological activity of natural plant pigments, to provide a guarantee for the development of high-quality plant pigments and to improve the comprehensive utilization rate of pigments. The third is to improve the production process to ensure product quality. Actively adopting advanced production technology to improve product competitiveness is also a key focus of natural pigment development. Fourth, it is to broaden the application fields of natural pigments, to further expand the international market based on the domestic market, to make full use of the advantages of China's abundant plant resources, and to continuously improve the quality of products with the help of high technology. It is believed that in future development and application, natural plant pigments will serve mankind better with their natural characteristics, high safety, health benefits, and lower cost, and will be more widely used in food, cosmetics, medicine and health care.

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