Health benefits of black rice-A review

Balasuramaniam Jaya Prasad,Pazhaniyandi Suramania Sharavanan,Rengaraj Sivaraj

a Department of Botany,Annamalai University,Annamalai Nagar 608002,India

b Department of Botany,Govt Arts College,Mannargudi 614001,India

c Department of Pharmacology,Annamalai University,Annamalai Nagar 608002,India

Keywords:

Black rice

Cyanidin-3-O-glucoside

Diabetes

Dragon eyeball 100

Insulin resistance

Oryza sativa

A B S T R A C T

Rice has been a staple food across the globe since time immemorial.Generally,different types of rice,such as white,purple,red,brown,and black rice,are named following the physical appearance of the rice bran.The color of the rice bran differs due to the presence of pigments in the rice varieties.Apart from general uses like cooking and fodder for cattle,rice has also been extensively involved in the field of medicine,some of which have been scientifically addressed.Although pigmented rice varieties have a history of heritage and are admired all over the world,awareness concerning the benefits of consuming these types of rice is limited.The main theme of this research article is to define the scientifically proven medicinal properties of black rice.The health properties of black rice are experimentally renowned,and gathered empirical data regarding the physiological and pharmacological activity of black rice remarkably supports the use of black rice in nutritional therapy.

1.Introduction

Before the green revolution,pigmented rice varieties were in use as a potential food source by the common people of India and in almost all rice eating parts of the world.These rice varieties contain more amounts of micro-,macro-nutrients and secondary metabolites.They are named after the pigments present in the rice bran.Many pigmented gluey rice varieties were used in the manufacture of commercial healthy food supplements, due to its high secondary metabolite contents and high antioxidant activity[1].Owing to higher nutritive content and metabolites,dieticians strongly advise pigmented rice for peoples with metabolic disorders including diabetics[2].Black rice comprises numerous rice varieties with an extensive historical background on cultivation in Southeast Asian countries such as China,India,and Thailand[3].China and India are the major producers of black rice,followed by Thailand,Bangladesh,Vietnam,and Indonesia (Table 1).Anthocyanin (cyanidin-3-glucoside) turns the color of the rice to black color and,hence it is called black rice[4,5].The rice kernel bran layer has a towering intensity of pharmacological compounds such as γ-oryzanol,anthocyanins,phenolic,and flavonoid compounds.Many studies have shown that these compounds are able to improve the lipid profiles,are anti-inflammatory,anticancerous[6]and reduce oxidative stress[7],may help to fight heart disease,and prevent diabetes[8].Black rice is used as a dietary supplement for the treatment of various diseases such as diabetes,cancer,lipid disorders,and gastrointestinal diseases according to the folklore medicine of India.

Table 1 Top ten rice producing countries in the world according to the Economic Research Service,United States Department of Agriculture 2017/2018.

2.Amino acids in black rice and their role in physiological action

Nitrogen contributes the necessary safeguards for life and this is donated by amino acids [9].A deficiency of amino acids in the diet results in decreased production of protein and then leads to nutritional imbalance.It is necessary to find the amino acids content of food for better health[10].Moreover,rapamycin complex 1 pathway is directly related to the growth of bone,muscles,internal organs,immune factors,and the energy balance of a person and it is gracefully responsive to amino acid accessibility.An imbalance of amino acid results in stunted growth[11].Amino acids have a chief responsibility of adapting numerous functions connected to gene expression,which includes modulation of the physiology of the proteins that intervene and messenger RNA(mRNA)conversion[12].

Black rice contains superior protein and essential amino acids compared with ordinary rice [13].Amino acid and the mineral content of black rice (Dragon eyeball 100, Heukjinjubyeo, Heukgwangbyeo,Heuknambyeo,and Josaengheukchal)and white rice(Hwayoungbyeo).Comparatively, high amino acid contents (ng /mg of rice) were found in Heuknambyeo (black rice variety), in which alanine (53.45± 0.34), arginine (55.76 ± 0.30), asparagine (242.89 ± 0.16),aspartic acid (107.53 ± 0.14), glutamine (14.90 ± 0.09), glutamic acid (193.81 ± 0.09), glycine (21.72 ± 0.03), histidine (16.29 ±0.01),isoleucine (5.27±0.01),leucine(5.72±0.01),lysine(10.39± 0.03), methionine (6.70 ± 0.00), phenylalanine (6.97 ± 0.00),proline (28.57 ± 0.07), serine (29.27 ± 0.07), threonine (11.61 ±0.07), tyrosine (11.72 ± 0.01), and valine content was found to be (15.79 ± 0.02), whereas cysteine and tryptophan were found to be absent.Among these asparagines, aspartic acid and glutamic acid were found to be high when compared with other amino acids[14].

Amino acids play a vital role in body development via protein metabolism.Excess amino acids are converted into ammonia by the removal of the amine group in the liver.They play a key role in an individual's diet in modifying risk to pre-diabetes[15].The organic acids are changed to glucose(gluconeogenesis)or are used directly in metabolism.However,glutamate is deaminated in the kidneys[16].Asparagine synthetase makes the amino acid asparagine,which is needed to make proteins in the cells.Drugs that alter the availability of asparagine in the body might also be useful to treat sarcomas with mutant forms of Ras[17].By silencing the activity of asparagine synthetase,amidotransferase suppress the tumor growth in a molecular genomic sequencing screen of rat tumor cells generated by oncogenic Kras and interruption of Cdkn2a[18].Asparagine-linked glycosylation has appeared to be indispensable in controlling the enzymatic modification of protein to the channels connected to the plasma membrane functioning properties [19].Aspartic acid stimulates the production of Streptomyces platensis,which in turn produces antibiotics[20].

3.Phyto-chemical profiles of black rice

Phytochemical profiling of methanolic crude extract of black rice bran powder consists of glycoside,steroid, phenol, protein,carbohydrate, tannin,phlobatannin,terpenoid,alkaloid,and flavonoid[21].Anthocyanin pigment is the major content of black rice [22].Previously,many researchers have found the free radical quenching ability of black rice using in vitro and in vivo models[23,24].Fig.1 illustrates that phenolic and flavonoid compounds such as cyanidin-3-glucoside,which is responsible for the black color of the rice,malvidin 3 glucoside, cyanidin-3-rutinoside, γ-aminobutyric acid, peonidin 3 glucoside, cyanidin 3,5-diglucoside, and petunidin-3-glucoside were found to be higher in black rice than in the normal rice varieties[25-28].Moreover, cyanidin-3-glucoside constitutes 80% of the total anthocyanin content of black rice[29].

4.Scientifically proven health benefits of black rice

There are many other terrestrial and marine medicinal plants pharmacological activities are also reported previously by many researchers [30-34].But this article is in the review of black rice, we have focused only on the scientifically proven pharmacological activities of black rice.Black rice has been proven scientifically for its various pharmacological activities.Research has also confirmed the antioxidant activity [35-41], antitumor [42], anti-inflammatory[43], antiproliferative [44], anticancer [44,45], anti-diabetes and hyperlipidemia [46-48], and anti-atherosclerosis activity [49,50]of black rice, the cholesterol and lipid metabolism [51], and the tyrosinase inhibitor activity [52].All this may be due to the presence of the secondary metabolites present in it.α-Glucosidase and α-amylase are the key enzymes directly linked to the postprandial glucose level and the anthocynanin isolated from the black rice inhibits the aforesaid enzyme levels; thus, it could be used in the management of diabetes[53,54].Germinated black rice possesses stronger antidiabetic and antioxidant activity than the normal black rice extract[55].

Black rice extract reduces the glycemic index more than wheat flour, and reduces the level of α-glucosidase more than the standard drug acarbase [56].Cyanidin-3-glucoside content present in the Stevia rebaudiana leaf extract also possessed strong antioxidant and antidiabetic activity [57].Fig.2 represents mechanism of action of cyanidin-3-O-glucoside ameliorates palmitate-induced insulin resistance.Cyanidin-3-glucoside proficiently ameliorates oxidative damage, inflammation, metabolic dysfunctions, apoptosis pathways,and controls diabetic cardiomyopathy.From these, it can be concluded that cyanidin-3-glucoside, an anthocyanin compound, is capable of controlling diabetes [58].Intestinal epithelium actively contributes to the mucosal immune system.TNF-α and interferon are the inflammatory causing agents in the intestine [59].The movement of leukocytes in the inflamed region of the intestine creates an unbalanced response to the microorganisms and causes chronic inflammatory bowel disease [60].Anthocyanins present in the natural form can reach the colon of the intestine and it could be the appropriate candidates for nutritional therapy for the gastrointestinal tract disorders [61].Cyanidin-3-O-glucoside modulates the inflammation that appears in the intestinal cell lines and, thus,it could be effective in the management of chronic gut inflammatory diseases [62].

Skin cancer is found to be more common in the developed countries;ultraviolet radiation(UV)disrupts the immune mechanism and promotes skin carcinogenesis.UV radiation causes inflammation to the surface,which in turn mediates the phosphorylation of protein kinases [63]and damages the DNA level[64]by the increased production of reactive oxygen species in the form of cyclobutane pyrimidine dimmers [65].External application of cyanidin-3-O-glucoside inhibits the UV-caused epidermal thickening and decreases the mRNA and protein expression of proliferating cell nuclear antigen and cyclin by regulating UV-induced inflammation-mediated signaling pathways such as phosphorylation of extracellular-signal-related protein kinases, stress-activated protein kinases [66].Anthocyanins immersed in the intestine might be distorted as phenolic acids via gut microbial ring cleavage, dehydroxylation, and methylation reactions [67].These phenolic acids have been proven to motivate the growth of beneficiary bacteria and restrain the production of harmful bacteria[68].Bifidobacteria and lactobacilli are the intestinal bacteria that are beneficiary to humans and animals; they are proven probiotics [69].Anthocyanin isolated from purple sweet potato induces the growth of the beneficiary bacteria present in the human intestine [70].Cyanidin-3-O-glucoside connects with β-glucoside and provides energy to the bacteria and results in the enhanced growthlike prebiotic activity [71].Anthocyanins are the chemical compounds that can reach the brain [72] within 10 min as soon as it reaches the stomach [73] and gets accumulated in the cerebellum,cortex, hippocampus, and striatum [74] and in the rat brain [75].Cyanidin-3-glucoside enhances exercise performance by up-regulating the skeletal muscle peroxisome proliferators activated receptorgamma co-activator[76].

Fig.1.Major bioactive compounds in black rich which are have number of health benefits to humans.

5.Conclusion

Black rice is one of the traditional rice varieties which have been used in most of the Southeast Asian countries.It consists of a variety of micro and macro nutrients,amino acids,phytochemicals,and secondary metabolites.A number of scientific studies have discussed about the anthocyanin content and its derivatives cyanidin-3-O-glucoside.Black rice possesses various pharmacological properties and,moreover,the amino acid in it gives complete nourishment.Awareness among the public toward consuming black rice will give way for a healthier life.

Fig.2.Mechanism of action of cyanidin-3-O-glucoside ameliorates palmitate-induced insulin resistance.

Declaration of competing interest

Authors declare that they do not have any conflict of interest.

Acknowledgement

Author Balasubramaniam Jaya Prasad would like to thank Department of Science and Technology,Government of India,for providing INSPIRE Fellowship and authorities of Annamalai University for providing necessary support.