Study on the Antioxidant Black Rice Anthocyanin

1  Introduction

Anthocyanin is a plant polyphenol widely distributed in nature. With people's increasing awareness of health care, anthocyanin is becoming more and more popular among scientists for its strong physiological activities such as anti-oxidation, anti-cancer, vision protection and anti-aging. Recent research has found that black rice anthocyanin has strong free radical scavenging and anti-oxidation activities, and is an important source for developing natural antioxidants. The topic of this paper is the research literature on the antioxidant activity of black rice anthocyanins by scientific researchers in recent years. It is the object of study, and its collection, collation, induction and summary are carried out to clarify the current research progress on the antioxidant mechanism and physiological functions of black rice anthocyanins. Black rice is abundant in resources, and anthocyanin is a characteristic substance of black rice. Understanding the current research status of the antioxidant activity of black rice anthocyanins has a certain guiding significance for the development and comprehensive utilization of black rice.

2 Current status of research on the antioxidant activity of black rice anthocyanins

2.1 Black rice anthocyanin compounds have antioxidant activity

There have been many reports on research into the substance basis of plant antioxidants, but the results are not the same. It may be the result of the action of a particular vitamin, enzyme or other active substance, or it may be the result of the combined action of several enzymes and substances. Due to the complex composition of black rice skin, it is rich in pigments belonging to the anthocyanin class of compounds, as well as unsaturated fatty acids and active ingredients such as vitamins and trace elements. Experiments have found that the ethyl acetate, n-butanol and aqueous fractions of black rice skin extract have significantly stronger antioxidant capacity than the petroleum ether and chloroform fractions.

Combining the research of previous researchers, it is believed that the main component is anthocyanin-type substances [1]. In other words, the antioxidant capacity of anthocyanin compounds in black rice bran is significantly stronger than that of unsaturated fatty acids. It can therefore be concluded that anthocyanin compounds in black rice bran are the main active ingredients responsible for their antioxidant effects. Anthocyanins in black rice are the main substance basis for their antioxidant effects. The 3-ring formation of black rice anthocyanins forms a conjugated system, which is a polyconjugated aromatic system with high biological activity. As for which anthocyanin compounds should exhibit antioxidant activity, further research is needed to accurately discover them, and this is also a research trend for the future antioxidant activity of black rice anthocyanins.

Many diseases are related to excess free radicals, and the hydroxyl group structure of anthocyanin compounds themselves gives them a strong ability to capture and remove active oxygen free radicals. By removing free radicals, they can protect against free radical-induced damage to biological macromolecules, maintain the fluidity of cell membranes and the conformational structure of proteins, and have a significant effect in inhibiting cardiovascular diseases such as hyperlipidemia and atherosclerosis. It also helps to eliminate excess water, toxins and excess fat in the body, balance the body's metabolic functions, enhance kidney function, fully regulate various bodily functions, warm the internal organs, improve the body's constitution, promote metabolism, slow down aging, and prevent various diseases. Research results show that the in vitro inhibition rates of hydroxyl radicals and superoxide anions and the total antioxidant activity of black rice anthocyanin capsules and black rice anthocyanin increase with their concentration. The scavenging rate of hydroxyl radicals and superoxide anions in black rice anthocyanin capsules is significantly lower than that of black rice anthocyanin, and the total antioxidant activity is significantly lower than that of black rice anthocyanin and vitamin C [2]. In summary, black rice anthocyanin capsules have certain antioxidant physiological functions, but due to the addition of effective components of traditional Chinese medicine such as stilbenes and bacterial polysaccharides, the in vitro antioxidant and free radical scavenging abilities of anthocyanin capsules have been reduced. This may be related to the addition of effective components of traditional Chinese medicine, which changes the efficacy of black rice anthocyanin capsules.

2.2 Black rice anthocyanin antioxidant mechanism

If the body is overfed, especially with a large amount of simple sugars and saturated fats, metabolism will produce a large amount of reactive oxygen species and reactive nitrogen species, which can oxidize and damage biological macromolecules such as DNA, proteins and lipids, and trigger various diseases, including diabetes, tumors and atherosclerosis. Anthocyanins can scavenge free radicals by forming stable free radicals with stored free radicals due to their molecular structure containing multiple phenolic hydroxyl groups, chelate metal ions that initiate lipid peroxidation, and participate in a synergistic antioxidant effect. By terminating the free radical chain reaction and chelating metal ions, they can remove active oxygen and thus reduce or eliminate the damaging effects of free radicals on body tissues and organs. In addition to its strong free radical scavenging ability, black rice anthocyanin has also been shown to significantly increase the activity of superoxide dismutase and catalase in the liver of mice, which may be another mechanism by which anthocyanin exerts its antioxidant effect in the body [3].

The phenolic radical structure of anthocyanin compounds, especially the ortho phenolic radical of catechol or hydroquinone, can be easily oxidized to the hydroxyl radical structure. The oxidation reaction proceeds faster in the presence of enzymes, sufficient moisture and a higher pH value, thereby consuming oxygen in the environment. Its phenolic structure gives it a strong ability to capture free radicals such as reactive oxygen species. If it can bind to lipid free radicals produced by oxidation, will reduce or prevent the oxidation process in tissues, which gives it strong antioxidant and free radical scavenging abilities. The mechanism of action of anthocyanins in scavenging free radicals and antioxidants is that it prevents the three stages of free radical production in the body: reaction with oxygen radicals to prevent free radicals from being initiated; sequestering with metal ions to prevent hydroxyl radical formation; and reacting with lipid peroxyl radicals to prevent lipid peroxidation.

The antioxidant and free radical scavenging properties of anthocyanins are the basis for their physiological activity. In summary, the mechanism of the antioxidant activity of black rice anthocyanins is related to phenol-quinone balance and the formation of stable free radicals. On the one hand, due to the conjugation effect, the hydrogen atom on the phenolic hydroxyl group becomes more active and is easily removed to become a hydrogen donor, and a quinone reaction occurs to achieve phenol-quinone balance; On the other hand, as a hydrogen donor, it can react with lipid compound radicals to form phenolic radicals. The unpaired electron on the phenolic radical's oxygen atom is dispersed throughout the conjugated system, which is stable, thereby reducing the rate of transfer of the autocatalytic oxidation chain reaction and inhibiting further oxidation of lipids [4].

2.3 The physiological effects of black rice anthocyanin

2.3.1 Enhances the body's immune system

Anthocyanin can activate the immune system, protect serum immunoglobulins from free radicals, activate macrophages, and enhance the body's immune system. In the past, as humans were often plagued by traditional diseases such as lung disease and infections, the research on antibiotics was once the focus of people's research. Later, due to the improvement of human health awareness, the research on vitamins was listed as a key research topic. Humans have entered the era of vitamins from the era of antibiotics. However, it has now been discovered that despite the in-depth research on antibiotics and vitamins, they cannot solve modern diseases such as cardiovascular and cerebrovascular diseases, diabetes, cancer, and the improvement of sub-health conditions, nor can they solve the problem of people living longer and anti-aging. The existence of these problems is related to the damage caused to the human body by free radicals. Free radicals are related to more than 100 diseases, and the length of human life directly depends on the strength of people's ability to resist oxidation and free radicals. Anthocyanin can resist free radicals and prevent various diseases caused by free radicals. It is the most effective antioxidant discovered by humans today, and also the most effective free radical scavenger. Anthocyanin's antioxidant properties are 50 times higher than those of vitamin E and 20 times higher than those of vitamin C [5].

2.3.2 Delay aging and prevent cardiovascular and cerebrovascular diseases

Black rice anthocyanins can effectively scavenge superoxide radicals and hydroxyl radicals, significantly inhibit the oxygenation of low-density lipoprotein and platelet aggregation, which are the main factors causing atherosclerosis. Black rice anthocyanins can help with the absorption and utilization of vitamin C and vitamin E, enhance antioxidant capacity, protect blood vessels, enhance blood vessel resistance, reduce the fragility of capillaries, maintain blood vessel permeability, enhance the function of capillaries, veins, and arteries, improve the circulatory system, and reduce the incidence of cardiovascular diseases; improve varicose veins and edema; and reduce the risk of diabetes and the development of complications [6].

2.3.3 Anti-cancer effect

Black rice anthocyanin has been shown in many ways to reduce the proliferation of cancer cells and inhibit tumor formation. It can induce apoptosis in breast cancer cells and inhibit their metastasis; inhibit prostate cancer; prevent colon cancer from worsening; and prevent skin cancer. The ability of black rice anthocyanins to affect the cancer process may be related to multiple mechanisms such as their effective antioxidant capacity and inhibition of cyclooxygenase. Black rice anthocyanins inhibit tumorigenesis by blocking the active cyclin-dependent kinase pathway [7].

2.3.4 Promoting a virtuous cycle of lipid metabolism

Lipids are one of the most important nutrients in our bodies. On the one hand, our bodies cannot do without lipids, which not only provide us with energy, but are also a component of cells. Lipids are not only a major component of brain nerves, but are also essential for many important physiological functions in the body, such as adrenal cortical hormones, prostaglandins, sex hormones, etc.; on the other hand, unreasonable fat intake can also bring many health hazards, such as the effect of blood fat levels on the cardiovascular system. Black rice anthocyanins not only protect lipids, which are cell components, from the effects of oxidation, but also affect the concentration of free lipids, thereby maintaining good health [8].

2.3.5 Hypoglycemic effect

Diabetes is an endocrine metabolic disease caused by the interaction of genetic and environmental factors, leading to insufficient or relative insufficiency of insulin, which in turn causes metabolic disorders of sugar, protein, lipids, etc. in the body. The main manifestation is persistent hyperglycemia. Long-term hyperglycemia can cause various complications such as dysfunction of the body and even damage to organs. In terms of diabetes treatment, there is an urgent need to find new hypoglycemic drugs that are highly effective, low in toxicity, and can effectively prevent the occurrence of diabetes complications [9]. Previous studies have shown that black rice anthocyanins have a significant effect on diabetes prevention. Black rice anthocyanins can significantly improve the symptoms of “three highs and one low” in diabetic rats, slow down the trend of weight loss in rats, improve the ratio of kidney, liver and pancreas in the model group, and can significantly reduce blood glucose in diabetic rats, improve the phenomenon of glycation in the blood, especially the therapeutic effect of the medium dose group is obvious [10].

2.3.6 Anti-inflammatory and antibacterial effects

An inflammatory response, commonly known as inflammation, refers to the physiological response triggered by stimuli such as trauma, bleeding or pathogenic infection in biological tissues. This includes symptoms such as redness, swelling, heat and pain. Black rice anthocyanins have an inhibitory effect on inflammation caused by pathogenic infection due to their antibacterial effect. The antibacterial effect of black rice anthocyanins has multiple mechanisms of action: black rice anthocyanins can destroy the integrity of cell walls and cell membranes, causing microorganisms to release intracellular components and die; inhibit protein synthesis, causing bacteria to die; destroy the structural components of the bacteria, change the morphology of the bacteria, rupture the spore walls, and kill the bacteria [11].

2.3.7 Protect the liver

The liver is an organ in the body that is mainly responsible for metabolic functions, and it also plays a role in the body in functions such as deoxidation, storing glycogen, and secreting proteins. Modern people's better lifestyles place a greater burden on the liver, and black rice anthocyanins can greatly relieve this burden [12]. Treating mouse liver cells with peroxide can cause oxidation of liver fat and liver cell toxicity, while the addition of anthocyanins can significantly reduce the decrease in liver function activity caused by peroxide. Pathological histology showed that black rice anthocyanin capsules can significantly improve the fatty degeneration of liver cells. At the same time, the suspension agent has no effect on the effect of the drug. Black rice anthocyanin compound capsules can play a certain role in the treatment of alcoholic liver damage [13].

2.3.8 Improve memory

Learning and memory are advanced brain functions that are essential to the functioning of the human brain. Studies have shown that learning and memory are accompanied by complex neurophysiological and biochemical mechanisms involving a variety of substances. The central nervous system plays an important role in the learning and memory process, including the acquisition, storage, maintenance and retrieval of information. In spontaneous behavior, mice treated with bacterial lipopolysaccharide showed a significant decrease in spontaneous activity and spatial learning and memory ability, which was significantly different from the blank control group. After being treated with black rice anthocyanin, the mice's spontaneous activity and learning and memory abilities improved, indicating that black rice anthocyanin enhances the learning and memory of mice to a certain extent. Some scholars have also found that black rice anthocyanin penetrates the blood-brain barrier and has a scavenging effect on free radicals in brain tissue. It is pointed out that the inhibition of free radical production and the scavenging of free radicals by black rice anthocyanin are an important mechanism for protecting brain neurons and improving memory ability [14].

2.3.9 Protecting eyesight

The initial step in visual formation is that the photoreceptor cells of the retina receive light signal stimulation. However, when there are a large number of free radicals, a peroxidation chain reaction occurs, forming reactive oxygen species, which directly act on the membrane structure of the photoreceptor cells, causing apoptosis of the photoreceptor cells and impaired visual function [15]. Chen Wei studied the antioxidant effect of black rice anthocyanin in photochemical injury of the rat retina and found that black rice anthocyanin can reduce the content of lipid peroxides in retinal tissue cells and increase the activity of antioxidant enzymes in retinal tissue cells, thereby protecting photoreceptor cells. Chen Wei found in subsequent experiments that black rice anthocyanin can inhibit the apoptosis of photoreceptor cells in retinal tissue and protect against photochemical injury to the retina. This effect may be related to its downregulation of the activity of key enzymes.

3 Summary and outlook

As a natural food coloring, black rice anthocyanin is safe and non-toxic, has a bright color and is abundant in resources. It also has a wide range of disease prevention and health promotion effects, and has great application potential in the fields of food and medicine. At present, research on black rice anthocyanin is still in its infancy. There are certain differences in the content and composition of anthocyanin between different varieties, and its health effects and mechanisms are not yet fully understood. In the past 20 years, research on reactive oxygen species and free radicals has become a hot topic in modern life sciences, and evaluating and screening natural resources with strong antioxidant activity has become a new trend in biological, medical and food science research.

Research on black rice anthocyanins has now made great strides at home and abroad. We are already familiar with its mechanism of action and its various antioxidant physiological functions, and have developed some food and drugs. However, there is no unanimous conclusion on the regulatory enzymes that synthesize anthocyanins. In addition, the photosensitive pigment that regulates enzyme activity has not yet been isolated, and its regulatory mechanism is not yet clear. At present, humans have begun to use genetic engineering methods to regulate anthocyanin synthesis, and scholars in this field have conducted a large amount of research work, but so far, there is still no unanimous conclusion.

3.1 Increase research efforts to develop the antioxidant activity of black rice anthocyanins

In the past 10 years, we have conducted in-depth research on the composition, antioxidant properties and other important physiological functions of black rice anthocyanins, as well as the process of extracting and testing anthocyanins. As a natural food colouring agent, black rice anthocyanins are safe and non-toxic, brightly coloured and abundant in resources. They also have a wide range of disease prevention and health promotion effects, and have great potential for application in the food and pharmaceutical fields.

3.2 Cultivating high-quality black rice, increasing the anthocyanin content of black rice, and increasing the extraction of black rice anthocyanins

There are certain differences in the content and composition of anthocyanins between different varieties, and their health benefits and mechanisms are not yet fully understood. Therefore, future research should focus on screening and breeding black rice varieties with higher anthocyanin content, improving the extraction process to obtain anthocyanins with high purity and good stability, the dose-effect relationship of anthocyanins on animal and human disease intervention, and the regulation of gene expression.

3.3 Improving the extraction process of black rice anthocyanin and extracting black rice anthocyanin with the highest antioxidant activity

At present, the antioxidant properties of black rice anthocyanin are well known, but its extraction process and processing methods still need to be improved. Continue to explore the extraction process of black rice anthocyanin, aiming to further improve the extraction rate of functional ingredients in raw materials and further improve the utilization rate of raw materials, thereby further increasing the added value of black rice deep processing.

3.4 Development of safe health foods using the antioxidant activity of black rice anthocyanins

Black rice anthocyanins are safe, non-toxic, abundant in resources, and have considerable nutritional and pharmacological effects, with a wide range of effects on human health. Anthocyanins can be used not only as nutritional enhancers in food, but also as a substitute for synthetic preservatives such as benzoic acid as a food preservative, and can also be used as a food coloring agent in ordinary drinks and foods, in line with people's general requirements for natural, safe and healthy food additives.

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