Purple Rice - Types and Benefits

Introduction

Purple rice contains an antioxidant, namely anthocyanins. Health-conscious individuals mainly consume this as a part of their staple food because anthocyanins possess antiviral and anti-inflammatory properties. Anthocyanins reduce the risk of severe diseases like cancer and obesity and show anti-aging effects. Anthocyanins are found in a wide variety of rice, and only a few forms are accepted as commercial varieties. Their commercial integration depends upon their yield, cooking quality, and other functional properties. The article evaluates the part of anthocyanin biosynthesis genes, the stability, and the utilization of anthocyanin in purple rice.

Where Does Purple Rice Come From?

Rice is considered the world’s dominant food harvest that is consumed by more than fifty percent of the world's population. Around ninety percent of the rice is mainly harvested and consumed in Asia. Purple rice is mainly cultivated in Asian countries like China, Thailand, Japan, Korea, Laos, Vietnam, Sri Lanka, Indonesia, India, and Nepal. The international rice market has turned its head towards pigmented rice, more likely purple rice that will be cultivated not only in Asian countries but in other countries like France, Russia, Italy, and Australia.

What Are the Types of Purple Rice?

Purple rice has been classified into two types based on the endosperm involved:

• Non-glutinous Endosperm: It does not contain gluten and does not become sticky when cooked.

• Glutinous Endosperm: Also known as sticky rice.

Purple rice shows the appearance of color from deep purple to black. The following factors regulate this color separation during the process of harvesting:

1. Quality and duration of sunlight.

2. The temperature of day and night.

3. Moisture content.

4. Rainfall.

5. Nutritional value of the soil.

6. Water availability in the ground.

What Is Anthocyanin Biosynthesis?

Anthocyanin biosynthesis is regulated by the biosynthetic genes that induce or inhibit the expression of their structural and functional components. The following are the structural genes involved in the process of anthocyanin biosynthesis:

• Phenylalanine ammonia-lyase (PAL): Found only in the plant's stem.

• Chalcone Synthase (CHS): Found in the roots of the plant.

• Chalcone Isomerase (CHI): Found in the origins of the plant.

• Anthocyanidin Synthase (ANS): Found in the roots of the plant.

• UDP- glucosyl Transferase (UGT): Found in the plant's roots.

• Dihydroflavonol 4-reductase (DFR): Found in the plant's roots.

• Cinnamate 4-hydroxylase (C4H): Found in the plant's roots.

• Flavanone 3- hydroxylase (F3H): Found in the plant's roots.

In the rice grain, anthocyanin is modulated by two genes- a bHlH (basic helix-loop-helix) gene and a myeloblastosis gene (MYB). While in leaves, a gene called plr4 is present that regulates the color of the purple rice plant.

How Do the Environmental Factors Control Anthocyanin Synthesis?

The following are the environmental factors responsible for anthocyanin biosynthesis:

• Water - Several studies have shown that anthocyanin synthesis is independent of the water regime, but the degree of water stress depends upon the biosynthesis of anthocyanin in rice crops.

• Light - According to a study, it has been shown that anthocyanin synthesis increases up to nine times at a fifty percent shading level as compared to the non-shading condition. But there is a decline in the grain yield. Blue or red LED lights contain higher amounts of anthocyanin in the seedlings of the rice plants.

• Temperature - Studies claim that higher temperatures (over 27 degrees Celsius) enhance the gene expressions of anthocyanin in purple rice plants due to the building up of cyanidin, cyanidin-3-glucoside, and peonidin-3-glucoside. The lower temperature (21-24 degrees Celsius) reduces the expression level of anthocyanin biosynthesis genes.

What Are the Benefits of Anthocyanin on Human Health?

• Reduces Obesity: Anthocyanin lowers glucose uptake and inhibits the formation and proliferation of adipocytes, resulting in reducing the risk of obesity.

• Anti-Inflammatory Effects: Anthocyanins show anti-inflammatory effects and anti-metastatic effects on interleukin-1-beta-stimulated human chondrocytes and on HER-2-positive mammary gland cancer.

• Pharmaceutical Production: Anthocyanin found in the purple rice plant acts as an excellent component to be used in the pharmaceutical industry.

• Cosmetic Industry: Rice plants containing anthocyanin exhibit anti-aging properties due to the inhibition of reactive oxygen species. It is used in the production of cosmetic ingredients useful to prevent skin photoaging.

• Anti-hypoglycemic Effects: There is a reduction in blood glucose levels because of the consumption of purple rice enriched with anthocyanin

• Anti-osteoporosis Effects: Anthocyanin suppresses inflammatory effects and decreases oxidative stress leading to declination in the process of bone absorption.

• Immunity Enhancer: Anthocyanins present in purple rice help in enhancing immunity as they improve the number of cells responding to provide the ability to fight against diseases. Such cells are leukocytes, lymphocytes, and neutrophils. Purple rice promotes phagocytic activities and thus helps in boosting immunity.

• Prevention Against COVID: Studies have shown that anthocyanin exhibits anti-viral properties and functions against the protease enzymes associated with COVID-19.

What Are the Applications of Anthocyanins in Functional Food?

Following are the different applications of purple rice anthocyanins in functional food :

1. Bread made from purple rice enriched with anthocyanin increases postprandial plasma glucose. It also enhances the antioxidant status in healthy controls.

2. Rice flour made from anthocyanin-rich purple rice is useful in baking gluten-free bread that can also exhibit antioxidant ability like FRAP (the ferric reducing ability of plasma).

3. Anthocyanins present in bread made from purple rice show a low digestion rate.

4. Xanthan gum, as an adjuvant with anthocyanin-rich beverages, shows high thermal stability.

5. Improved sensory characteristics are seen in the germinated purple rice.

6. Purple rice shows increased anthocyanin in the crispy rice bar.

7. Noodles made from purple rice show FRAP antioxidant therapy: the ferric reducing ability of plasma.

8. Pasta manufactured by adding fifteen percent of anthocyanin in purple-rich rice exhibits diphenyl picrylhydrazyl and ferric-reducing ability of plasma.

9. Purple rice sprouts have high anthocyanin and are used for manufacturing natural health products.

10. 0.25 % of anthocyanin-rice purple rice extract added to yogurt decreases postprandial glucose levels and enhances plasma antioxidant capacity in healthy controls.

11. In whey-protein-stabilized food emulsions, 0.06 % of purple rice anthocyanin extract suppresses lipid and protein oxidation.

Other Functions

1. In vitro use of anthocyanin extract in cream exhibits antioxidant activity and in vivo anti-aging activity on human skin.

2. The antioxidant properties of rice bran help in manufacturing cosmetic formulations due to the antioxidant properties.

3. In colorimetric sensing of aluminum ions, anthocyanin is used.

4. In freshness monitoring, purple rice bran anthocyanins are used.

Conclusion

Anthocyanins present in purple rice can be used directly as a food and also as an alternative product. These exhibit both antioxidant and anti-inflammatory properties as well. These also prove beneficial to study in vivo and in vitro characteristics of chronic diseases. While the researchers are going on to study the effects of anthocyanins in the case of non-chronic diseases. Therefore anthocyanins are of great importance to human health depending on their bioavailability and metabolic potential. The article reviews the phenomenon of biosynthesis of anthocyanins and also the factors influencing the process.