antioxidants Review The Potential of High-Anthocyanin Purple Rice as a Functional Ingredient in Human Health Supapohn Yamuangmorn 1 and Chanakan Prom-u-Thai 1,2,* 1 Lanna Rice Research Center, Chiang Mai University, Chiang Mai 50200, Thailand; [email protected] 2 Agronomy Division, Department of Plant and Soil Sciences, Faculty of Agriculture, Chiang Mai University, Chiang Mai 50200, Thailand * Correspondence: [email protected] Abstract: Purple rice is recognized as a source of natural anthocyanin compounds among health- conscious consumers who employ rice as their staple food. Anthocyanin is one of the major an- tioxidant compounds that protect against the reactive oxygen species (ROS) that cause cellular damage in plants and animals, including humans. The physiological role of anthocyanin in plants is not fully understood, but the benefits to human health are apparent against both chronic and non-chronic diseases. This review focuses on anthocyanin synthesis and accumulation in the whole plant of purple rice, from cultivation to the processed end products. The anthocyanin content in purple rice varies due to many factors, including genotype, cultivation, and management as well as post-harvest processing. The cultivation method strongly influences anthocyanin content in rice plants; water conditions, light quantity and quality, and available nutrients in the soil are important factors, while the low stability of anthocyanins means that they can be dramatically degraded under high-temperature conditions. The application of purple rice anthocyanins has been developed in Citation: Yamuangmorn, S.; both functional food and other purposes. To maximize the benefits of purple rice to human health, Prom-u-Thai, C. The Potential of understanding the factors influencing anthocyanin synthesis and accumulation during the entire High-Anthocyanin Purple Rice as a process from cultivation to product development can be a path for success. Functional Ingredient in Human Health. Antioxidants 2021, 10, 833. Keywords: black rice; pigmented rice; rice anthocyanin; rice antioxidant https://doi.org/10.3390/antiox 10060833 Academic Editor: Costantino Paciolla 1. Introduction and Martina Loi Anthocyanins have been demonstrated to reduce the risks of serious diseases such as cancer and obesity, and the compounds have antiviral, anti-inflammatory, and anti-skin Received: 1 May 2021 aging effects [1–6]. In plants, although their function is not completely understood, the Accepted: 17 May 2021 Published: 24 May 2021 major role of anthocyanins has been reported as protecting against free radicals during physiological metabolism; in particular, anthocyanin can alleviate cell damage when plants Publisher’s Note: MDPI stays neutral are grown under biotic and abiotic stresses [7]. Therefore, consumption of naturally with regard to jurisdictional claims in synthesized anthocyanin from plants for the benefit of human health can help reduce the published maps and institutional affil- risk of several major diseases. iations. Rice is one of the world’s major staple food crops, consumed by more than half of the world’s population along with crops such as wheat, maize, and potato; over 90% of the rice production areas and consumption amounts are recorded in Asia [8,9]. At least 175 countries and territories consume rice; the overall consumption is high in the rice-consuming countries, ranging from 100 to 200 kg of paddy rice per person per year Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. according to the FAO. This could be one of the reasons why many international programs This article is an open access article aimed at boosting human nutrition, e.g., the harvest plus biofortification with high zinc, distributed under the terms and iron, iodine, and selenium, are focused on rice crops [10]. Moreover, it is interesting to conditions of the Creative Commons observe that among the staple food crops, rice is recognized as potentially containing high Attribution (CC BY) license (https:// amounts of antioxidant compounds such as anthocyanin, especially in pigmented rice creativecommons.org/licenses/by/ varieties with black (purple) and red pericarp color [11] (Figure1). The purple rice is highly 4.0/). valued, particularly among the health-conscious consumers as a functional compound Antioxidants 2021, 10, 833. https://doi.org/10.3390/antiox10060833 https://www.mdpi.com/journal/antioxidants Antioxidants 2021, 10, x FOR PEER REVIEW 2 of 23 Antioxidants 2021, 10, 833 2 of 21 amounts of antioxidant compounds such as anthocyanin, especially in pigmented rice va- rieties with black (purple) and red pericarp color [11] (Figure 1). The purple rice is highly valued, particularly among the health-conscious consumers as a functional compound for humanfor human health health among among everyday everyday sources sources of carboh of carbohydrateydrate [12]. In [12 other]. In staple other staplefood crops, food anthocyanincrops, anthocyanin has been has reported been reported in purple in purple maize, maize, a variety a variety that is thatrarely is rarelyconsumed consumed in com- in parisoncomparison with withother other non-staple non-staple food foodcrops crops such suchas Brassica, as Brassica, Solanaceous Solanaceous species, species, and some and ediblesome edibleflowers flowers [13–16]. [13 Additionally,–16]. Additionally, anthocya anthocyaninnin can be directly can be directlytaken from taken the from concen- the trateconcentrate in capsules in capsules for convenience, for convenience, but this but can this be quite can be expensive quite expensive [17,18]. [Therefore,17,18]. Therefore, purple ricepurple is an rice advantageous is an advantageous option for option anthocyanin for anthocyanin intake, intake,especially especially when dealing whendealing with a largewith anumber large number of rice consumers of rice consumers worldwide. worldwide. 0.5 cm BB 3 CMU KJ CMU 107 YMCB 3 CMU Figure 1. Characteristic rice kernels with non-pericarp color (BB 3 CMU), purple (KJ CMU 107) and Figurered (YMCB 1. Characteristic 3 CMU) pericarp rice kernels color. with non-pericarp color (BB 3 CMU), purple (KJ CMU 107) and red (YMCB 3 CMU) pericarp color. The anthocyanin-rich rice grains have been recognized as excellent sources of natural and safe food colorants [19–21]. Synthetic colorants can be harmful to humans and the The anthocyanin-rich rice grains have been recognized as excellent sources of natural environment via allergic and toxic reactions [22]; this can raise the demand for naturally and safe food colorants [19–21]. Synthetic colorants can be harmful to humans and the pigmented rice such as purple rice that contains high concentrations of anthocyanin. Thus, environment via allergic and toxic reactions [22]; this can raise the demand for naturally purple rice not only provides enough anthocyanin to fulfill the growing interest but also pigmented rice such as purple rice that contains high concentrations of anthocyanin. Thus, can increase the value of rice products. There are numerous rice varieties containing purple rice not only provides enough anthocyanin to fulfill the growing interest but also anthocyanins, but only some are accepted as commercial varieties due to yield potential, can increase the value of rice products. There are numerous rice varieties containing an- cooking quality, and other functional properties that may be less acceptable. This review thocyanins, but only some are accepted as commercial varieties due to yield potential, will focus on the purple rice market trend, the possible sources of anthocyanin from cooking quality, and other functional properties that may be less acceptable. This review different plant parts of purple rice, the significant role of anthocyanin in plants and humans, will focus on the purple rice market trend, the possible sources of anthocyanin from dif- and factors controlling anthocyanin in rice plants. We also examine the role of anthocyanin ferent plant parts of purple rice, the significant role of anthocyanin in plants and humans, biosynthesis genes in the regulation of anthocyanin in rice, the stability of anthocyanin andin rice factors and controlling rice products, anthocyanin and the utilization in rice plants. of anthocyanin We also examine in purple the role rice of for anthocya- different ninpurposes. biosynthesis Thus, genes this review in the regulation should be of useful anthocyanin for understanding in rice, the stability the entire of anthocyanin processes of inpurple rice and rice rice production products, and and postharvest the utilization management, of anthocyanin from in product purple processingrice for different to the purposes.benefits to Thus, consumers’ this review health. should be useful for understanding the entire processes of purple rice production and postharvest management, from product processing to the ben- efits2. Purple to consumers’ Rice’s Market health. and Trend Rice is the dominant cereal and staple food in many countries. Whilst non-pigmented 2.rice Purple (no pericarp Rice’s Market color) is and widely Trend consumed throughout the world, pigmented rice varieties, e.g.,Rice purple is the rice, dominant are also gainingcereal and interest staple in food many in regions.many countries. Purple rice Whilst is traditionally non-pigmented culti- ricevated (no in pericarp Asian countries color) is such widely as China,consumed Japan, throughout Korea, Thailand, the world, Laos, pigmented Vietnam, rice Indonesia, varie- ties,India, e.g., Sri purple Lanka, rice, and