**2.3 Various bioactive compounds present in red rice**

Red rice was characterized by a high quantity of oligomeric procyanidins (0.2 mg/g) with more than 60% of total phytochemicals found in the rice seeds. Proanthocyanidins are high molecular weight polymers or complex flavan-3-ol polymers that consist mainly of catechin, epicatechin, gallocatechin, and epigallocatechin units that can also be found in rice germ and bran, particularly in pigmented rice. The degree of polymerization varied, and the reddish colored test was associated with the presence of a class of polymeric compounds of the proanthocyanidins. These could be in the sum class of the oligomer and polymer contents of the total proanthocyanidins present in the red rice bran extract fraction. The degree of polymerization and galloylation can affect their bioactivity and proanthocyanidin profiles differently depending on the food sources [27, 48]. Proanthocyanidins can be classified into several classes depending on the degree of hydroxylation of the constitutive units and the linkages between them. Our research group has reported on the type of proanthocyanidins found in the red rice that was collected from Dok Khamtai

*Phytochemicals in Human Health*

recorded elsewhere [27].

**2.2 Various bioactive compounds present in black rice**

Another extraction technique is the subcritical water extraction method that has been developed for the extraction of bioactive compounds from pigmented rice through the use of hot water at temperatures between 100 and 374°C under high pressure to maintain a liquid status. This technique is considered to be very friendly to the environment because no organic solvents are used, and this can potentially alleviate some of the problems associated with the conventional methods [36, 37]. There were differences in the extraction procedure and the varieties of the rice cultivars that were used to detect the amounts of bioactive compounds in different portions of rice such as in the whole grains, kernels, endosperm, husks, rice, and bran. More than 1000 published studies have been reviewed to make up the cited data based on this information. Some data on rice composition have been selectively

Phytochemical profiles of black rice are characterized by the presence of anthocyanins, which are a group of reddish to purple flavonoids that exist in black rice and other pigmented cereal grains. The main anthocyanins in black rice were found to be present in quantities more than 95% and were cyanidin 3-O-glucoside (2.8 mg/g) and peonidin-3-O-glucoside (0.5 mg/g) followed by flavones and flavonols (0.5 mg/g) and flavan-3-ols (0.3 mg/g) [38]. The concentrations of total anthocyanins in black rice cultivars significantly varied from one report to another, while much higher concentrations of anthocyanins were detected in Chinese black-purple rice that contained cyanidin 3-O-glucoside (6.3 mg/g) and peonidin 3-O-glucoside (3.6 mg/g) [39]. The variations of the anthocyanin content in the reports on black rice might be due to the use of different cultivars and the variety of differing growing conditions. The anthocyanidins or aglycons, the basic structure of anthocyanins, consist of an aromatic ring (A) that is bonded to a heterocyclic ring (C) that contains oxygen, which is bonded by a carbon–carbon bond to a third aromatic ring (B). When the anthocyanidins are bonded to a sugar moiety in the glycosidic linkage, they are known as anthocyanins. More than 500 different anthocyanins and 23 anthocyanidins have been reported. Anthocyanins exist as mono-, di-, or tri-O-linked glycosides and acyl glycosides of anthocyanidins in plants. The sugar moiety may be substituted by aliphatic, hydroxybenzoic, or hydroxycinnamic acids. The structural characteristics of anthocyanins make them highly reactive toward the reactive oxygen species (ROS) [27]. The basic structure of this is shown in **Figure 2**. Major flavone and flavonol glycosides present in black rice are taxifolin, quercetin, apigenin, and luteolin, which are comprised of monomeric and oligomeric constituents. The concentrations of the flavone and flavonol contents were

**6**

**Figure 2.**

*General structure of anthocyanins.*


#### **Table 1.**

*Phytochemical content of black rice extract (polar fraction).*

cultivar, Northern Thailand, as a type B proanthocyanidin. The monomeric units of proanthocyanidin in the acid hydrolysis of the red rice extract fraction were found to be catechins, epicatechins, gallocatechins, and epigallocatechins [16]. The results revealed that the proanthocyanidin types were procyanidin (catechin and/or epicatechin) and prodelphinidin (gallocatechin and/or epigallocatechin), while the degree of polymerization was recorded at approximately 4. Interestingly, the majority of proanthocyanidins in our red rice extract were of the oligomer with the same degree of polymerization that was found in grape seed extracts [49]. As has been mentioned previously, red rice has a high content of catechins and proanthocyanidins, but some of the black rice cultivars found in France and Canada have revealed the presence of catechins in their black rice cultivars (four times less than the red rice cultivars). It is worth mentioning that many other records have shown that procyanidins have been typically observed in red but not black rice varieties, including in the Northern Thai black rice cultivar obtained from Doi Saket, Chiang Mai [31]. The general structure of proanthocyanidins is shown in (**Figure 3**).

The other active compounds were γ-oryzanol and carotenoids at 27%, whereas flavones, flavonols, and anthocyanins were present in a much less quantity at less than 9% [38]. The main carotenoid detected in red rice bran was lutein, while xanthophylls and zeaxanthin were the carotenoids that were found to be present in lesser quantities. A range of phenolic acids including gallic, protocatechuic, hydroxybenzoic, vanillic, and ferulic acids in red, black, and brown rice have been detected as the dominant phenolic acids present in red and black rice bran [50, 51]. The contents of the phenolic compounds, flavonoids, catechins, anthocyanins, and proanthocyanidins, are summarized in **Table 2** as an example of the phytochemicals that were detected in Dok Khamtai Thai red jasmine rice cultivar. The contents of these bioactive compounds can be used to determine the antioxidant activities that may then provide health benefits.

#### **2.4 Various bioactive compounds present in brown and white rice**

The rice bran of whole grain brown rice (unpolished) has been acknowledged as a potential source of edible oil. Although rice bran oil is not very popular worldwide, its demand is increasing due to numerous reports on its health benefits.

**9**

**Table 2.**

**Figure 3.**

*General structure of proanthocyanidins [16].*

*Values are mean ± S.D., ND = not detectable.*

*Phytochemical content of red rice extract (polar fraction).*

*Anthocyanins and Proanthocyanidins in Natural Pigmented Rice and Their Bioactivities*

Previously, rice bran obtained from brown rice has received a significant amount of attention from the nutraceutical industry as brown rice bran is recognized as the primary source of oil extraction. On this issue, agro-industrial by-products are gaining special attention from the food processing industry because rice bran oil presents a positive fatty acid profile along with the presence of other phytochemicals like ϒ-oryzanol, tocopherols, and tocotrienols. Basically, rice bran is rich in carbohydrates (34–62%), lipids (15–20%), proteins (11–15%), and dietary crude fiber (7–11%) [52]. The health benefits of rice bran include the strong antioxidant potential of rice bran oil. This is not only a consequence of the presence of significant quantities of linolenic acid (34%), oleic acid (38.4%), and other unsaturated

**Compounds (mg/g extract)** Total phenolic content 237.78 ± 17.26 Vanillic acid 1.53 ± 0.19 Protocatechuic acid 0.35 ± 0.03 Gallic acid ND Coumaric acid 0.2 ± 0.01 Ferulic acid 0.56 ± 0.04 Chlorogenic acid ND ϒ-Tocotrienol ND ϒ-Oryzanol 1.75 ± 0.23 Anthocyanin ND Catechin 6.65 ± 0.57 Proanthocyanidin 53.45 ± 3.23

*DOI: http://dx.doi.org/10.5772/intechopen.86962*

*Anthocyanins and Proanthocyanidins in Natural Pigmented Rice and Their Bioactivities DOI: http://dx.doi.org/10.5772/intechopen.86962*

*Phytochemicals in Human Health*

*Values are mean ± S.D., ND = not detectable.*

*Phytochemical content of black rice extract (polar fraction).*

**Table 1.**

cultivar, Northern Thailand, as a type B proanthocyanidin. The monomeric units of proanthocyanidin in the acid hydrolysis of the red rice extract fraction were found to be catechins, epicatechins, gallocatechins, and epigallocatechins [16]. The results revealed that the proanthocyanidin types were procyanidin (catechin and/or epicatechin) and prodelphinidin (gallocatechin and/or epigallocatechin), while the degree of polymerization was recorded at approximately 4. Interestingly, the majority of proanthocyanidins in our red rice extract were of the oligomer with the same degree of polymerization that was found in grape seed extracts [49]. As has been mentioned previously, red rice has a high content of catechins and proanthocyanidins, but some of the black rice cultivars found in France and Canada have revealed the presence of catechins in their black rice cultivars (four times less than the red rice cultivars). It is worth mentioning that many other records have shown that procyanidins have been typically observed in red but not black rice varieties, including in the Northern Thai black rice cultivar obtained from Doi Saket, Chiang Mai [31]. The general structure

**Compound (mg/g extract)** Total phenolic content 117.6 ± 14.6 Vanillic acid 4.2 ± 0.4 Protocatechuic acid 2.3 ± 0.1 Gallic acid ND Coumaric acid 0.5 ± 0.2 Ferulic acid 1.4 ± 0.0 Chlorogenic acid 1.7 ± 0.3 Total flavonoid content 42.9 ± 2.1 Anthocyanin 8.1 ± 1.9 Catechin ND Proanthocyanidin ND

The other active compounds were γ-oryzanol and carotenoids at 27%, whereas flavones, flavonols, and anthocyanins were present in a much less quantity at less than 9% [38]. The main carotenoid detected in red rice bran was lutein, while xanthophylls and zeaxanthin were the carotenoids that were found to be present in lesser quantities. A range of phenolic acids including gallic, protocatechuic, hydroxybenzoic, vanillic, and ferulic acids in red, black, and brown rice have been detected as the dominant phenolic acids present in red and black rice bran [50, 51]. The contents of the phenolic compounds, flavonoids, catechins, anthocyanins, and proanthocyanidins, are summarized in **Table 2** as an example of the phytochemicals that were detected in Dok Khamtai Thai red jasmine rice cultivar. The contents of these bioactive compounds can be used to determine the antioxi-

of proanthocyanidins is shown in (**Figure 3**).

dant activities that may then provide health benefits.

**2.4 Various bioactive compounds present in brown and white rice**

The rice bran of whole grain brown rice (unpolished) has been acknowledged as a potential source of edible oil. Although rice bran oil is not very popular worldwide, its demand is increasing due to numerous reports on its health benefits.

**8**

Previously, rice bran obtained from brown rice has received a significant amount of attention from the nutraceutical industry as brown rice bran is recognized as the primary source of oil extraction. On this issue, agro-industrial by-products are gaining special attention from the food processing industry because rice bran oil presents a positive fatty acid profile along with the presence of other phytochemicals like ϒ-oryzanol, tocopherols, and tocotrienols. Basically, rice bran is rich in carbohydrates (34–62%), lipids (15–20%), proteins (11–15%), and dietary crude fiber (7–11%) [52]. The health benefits of rice bran include the strong antioxidant potential of rice bran oil. This is not only a consequence of the presence of significant quantities of linolenic acid (34%), oleic acid (38.4%), and other unsaturated


#### **Table 2.**

*Phytochemical content of red rice extract (polar fraction).*

fatty acids but also occurs as a result of the high contents of γ-oryzanol, tocopherols, and tocotrienols that reveal strong oxidative stability along with a range of other health benefits [53, 54].

The protein content present in rice bran of brown rice is characterized as a good source of protein that is nutritionally superior and hypoallergenic in nature. Rice bran is a rich source of essential amino acids such as lysine, which seems to be present in minute quantities in other cereal grains [55, 56]. The proteins in rice bran are highly digestible and can be utilized as an effective food ingredient. Rice bran is rich in dietary fiber, and, consequently, the rice bran by-products of rice processing are now often present in food commodities and functional foods that have been marketed for the ability to add dietary fiber to the diets of consumers and to offer health benefits in terms of daily nutrition. Additionally, brown rice possesses high contents of a variety of nutrients, such as fiber, vitamins, and minerals that are lost during the process of refining and milling in the production of white rice within the rice agro-industry. Notably, brown rice possesses four times as much dietary fiber as white rice [57].

White rice is a major source of energy nourishment for the world's population, especially in Asian countries. However, the carbohydrate content in white rice accounts for 80% of its makeup, which is considered a higher amount than wheat. Wheat is a popular grain among European countries and contains a lessor proportion of carbohydrates (approximately 50–70%) [58]. For this reason, there are concerns that white rice possesses a high glycemic content and that it may not be a suitable source of carbohydrates for people who have weight problems. It is interesting to note that white rice does not contain anthocyanins and proanthocyanidins, which are the important phytochemicals that are found in black rice and red rice, respectively, particularly in portions of rice germ and bran extracts. While total flavonols and phenolic compounds are observed to be significantly high in pigmented rice, nonpigmented rice such as white rice possesses a minute quantity of flavone/ flavanol content [50].
