**1. Introduction**

Rice *(Oryza sativa* L.) is a cereal food and consumed, providing energy and nutrients for more than half of the world's population, particularly in Asian countries [1]. An increasing in rice consumption in Africa and Latin America has been observed in the past decade, mainly due to urbanization and changes in eating habits. In addition, European, US and Australian citizens are eating more rice, possibly due to an increased interest in global traveling and Asian cuisines. The world production of rice (paddy) was 782.00 million metric tons in 2018 [2]. The most common rice consumed by human is white rice (85%) and the rest is pigmented rice.

Rice paddy consists of hull and caryopsis. The hull or the outer layer constitutes about 20% of the total paddy rice contain minerals and cellulose. The hulling process also separated the hull from the grain or kernel. After removing of husk, whole-grain rice is the unpolished version of the grains consisting of the germ (2-3%), bran (6-7%), and endosperm (about 90%), and is also called brown rice [3]. Consequently, the process of milling is carried out to obtained white rice, also referred to as milled or polished rice, by removing 8-10% of external layers (mainly bran) from brown rice [4]. The endosperm of rice contains water 12%, carbohydrate 75–80%, and protein 7% [5]. Rice carbohydrate is primarily a starch which is made

up of linear amylose and branched amylopectin [6–8]. According to the amylose content in rice, rice cultivars can be classified into five groups including waxy (1-2%), very low (2-9%), low (10-20%), intermediate (20-25%) and high (25-33%) [9].

White rice is a common source of starches and phtochemicals including phenolic compounds, sterols, γ-oryzanol, tocotrienols and tocopherols which locate particularly in the outer layer such as pericarp and aleurone of rice grains [10]. In addition, pigmented or colored rice including black, red and dark purple rice is well known by the rice pericarp or grain having a black, red brown or dark purple color in its covering layers. The pigments, which are located in the aleuronic layer of rice grain, have been reported to consist of a mixture of anthocyanin compounds [6, 10–13]. The pigmented rice has been cultivated and consumed in Asia including China, Japan, Korea, and South East Asian countries for a long time and is widely known as "forbidden rice." Royal families and kings used to consume these special varieties of rice in order to have their health improvement and to enhance their wealth [14]. In addition, many varieties of dark pigmented rice including Japonica black rice, Chinese black rice, Thai black rice and Indonesian black rice have been widely studied. Similar to white rice, pigmented rice is found in short-grained and long-grained, waxy (glutinous) and non-waxy (non-glutinous), husked and early maturing stages. The black and red rice have been used as a functional food and their extracts are also used as food colorants in breads, ice cream and liquor [8, 15].

Interestingly, an increased incidence in non-communicate including heart disease, Type II diabetes, obesity, and cancers in both developing and developed countries has been observed. Recently, pigmented rice varieties have gained an increase in attention from consumers due to its high nutritional value and bioactive compounds, providing its potential health benefits including antioxidant, anti-inflammatory, anticancer, and antidiabetic [8, 11, 16, 17]. In addition, many epidemiological and interventional studies have reported that the consumption of fruits and vegetables, cereal, whole grains, wine, cocoa, coffee and tea can reduce the risks of non-communicable disease including obesity, neurodegenerative diseases, Type II diabetes, and cardiovascular diseases [18, 19]. For the most part, the biological functional effects in acute and chronic diseases of plants have been traced to their phenolic compounds. Various studies have shown that phenolic compounds act as antioxidants [20]. Antioxidants control and reduce the oxidative damage in foods by delaying or inhibiting oxidation caused by reactive oxygen species (ROS), extending the shelf-life and quality of food products [21]. In addition, beta carotene, ascorbic acid, and phenolic compounds play important roles in delaying aging, reducing inflammation, and preventing certain cancers in human. The health benefits of whole grains are mainly contributed by one of its major constituents of phenolic compounds including phenolic acids, anthocyanins, and proanthocyanidins, which are the most common secondary metabolites in cereal grains, exist in pigmented grains and are considered to be the most effective antioxidants in nature [12]. Therefore, the objective of this chapter is to provide an up-to-date coverage of pigmented rice in regard to bioactive constituents, extraction and analytical methods, and their potential health benefits. Special attention is paid to bioactivities of pigmented rice and its main anthocyanins.

#### **2. Phytochemicals in cereal grains**

Cereal grains are composed of nutrients and phytochemicals. Phytochemicals are bioactive, non-nutritional plant compounds, which typically occur in small quantities in plants foods, for example, fruits and vegetables, whole grains and cereals. The most important groups of dietary phytochemicals can be divided into general categories as phenolics, alkaloids, nitrogen-containing compounds, organosulfur compounds,

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**Figure 1.**

*The chemical structures of the main phenolic acids.*

*Phenolic Compounds and Potential Health Benefits of Pigmented Rice*

phytosterols, and carotenoids [18]. In addition, bioactive compounds including phenolic compounds, phytosterols, tocols, dietary fibers (mainly beta-glucan), lignans, alkylresorcinols, phytic acid, γ-oryzanols, avenanthramides, inositols and betaine are obtained from whole grain cereals [19, 22]. Some bioactive compounds are quite specific to certain cereals, for example, γ-oryzanol in rice, avenanthramide and saponins in oats, beta glucans in oats and barley and alkylresorcinol in rye, although these are also present in other cereals like wheat but relatively in fewer amounts.

Phenolics compounds or polyphenols contain one or more aromatic rings with

Phenolic acids in rice grain present in two forms including soluble and insoluble forms. The soluble form, including free and conjugated forms, the former of which can be extracted by solvent, such as aqueous methanol, ethanol, and acetone, and the latter can be hydrolyzed from soluble phenolics by alkali. However, the insoluble form, also called bound phenolics, which esterify to the cell walls. Among these three phenolic fractions, the most abundant is insoluble bound phenolic acids, followed by soluble conjugated phenolic acids and the least is soluble free phenolic acids [25]. In addition, phenolic acids mainly exist in rice bran with trace amounts in endosperm in different rice genotypes. Phenolic acids are widely distributed into two sub-classes including hydrobenzoic and hydroxycinnamic acids and derivatives. **Figure 1** shows the structure of some common phenolic acids detected in rice. Hydroxybenzoic acid derivates include *p-*hydroxybenzoic, protocatechuic acid, vannilic, syringic and gallic acids. In addition, hydroxycinnamic acid derivates like *p*-coumaric, caffeic, ferulic and sinapic acids. Phenolic acids in many plants are

one or more hydroxyl groups and generally are categorized as phenolic acids, flavonoids, stilbenes, coumarins and tannins [18]. Phenolic compounds are the secondary metabolites plants, providing essential function in the reproduction and growth of the plant, acting as defense mechanisms against pathogens, parasites and environments (light, chilling, pollution, etc.), and contributing to the color of plant [23, 24]. In addition to their roles in plants, phenolic compounds in human diet provide health benefits associated with reduced risk of chronic diseases [22].

*DOI: http://dx.doi.org/10.5772/intechopen.93876*

**3. Phenolic compounds in pigmented rice**

**3.1 Phenolic acids**

*Phenolic Compounds and Potential Health Benefits of Pigmented Rice DOI: http://dx.doi.org/10.5772/intechopen.93876*

phytosterols, and carotenoids [18]. In addition, bioactive compounds including phenolic compounds, phytosterols, tocols, dietary fibers (mainly beta-glucan), lignans, alkylresorcinols, phytic acid, γ-oryzanols, avenanthramides, inositols and betaine are obtained from whole grain cereals [19, 22]. Some bioactive compounds are quite specific to certain cereals, for example, γ-oryzanol in rice, avenanthramide and saponins in oats, beta glucans in oats and barley and alkylresorcinol in rye, although these are also present in other cereals like wheat but relatively in fewer amounts.
