Rice is a staple food for nearly half of the world’s population.
In recent decades, genetic improvement in rice grain quality has
become important in rice breeding and considerable progress has
been made in breeding for quality. Several successful examples of
biofortification of rice to improve its nutritional quality and
combat nutritional deficiencies via a transgenic engineering
approach have been reported. Ye et al. introduced the β-carotene
synthesis pathway into rice endosperm by genetic engineering to
obtain golden rice that produces 0.16 mg/100 g of β-carotene in
the grains (1). Storozhenko et al. reported on the biofortification
of folate content in rice grains by overexpression of two genes
encoding GTP cyclohydrolase I and aminodeoxychorismate
synthase (2). Recently, the R0 and β subunits of soybean β-
conglycinin were expressed in rice seeds to improve the nutritional
and physiological properties of rice as a food (3). However, few
reports have described the biofortification of rice grains to
improve nutritional quality by conventional breeding (4). As
the first step toward achieving this goal, investigating diversity in
phytochemicals among rice varieties is necessary to find a way of
enriching these compositions through breeding.
Some pigmented rice cultivars contain phytochemicals that are
responsible for their color. Generally, these colored compounds
or pigments fall into several large groups, such as chlorophylls,
carotenoids, and flavonoids. The genotypic diversity of some
phytochemicals in rice grains has been characterized. For example,
Shen et al. reported a wide range of total flavonoid contents and
antioxidant capacity in rice grains (5). Jiang et al. reported the
mineral contents and their correlations with other quality traits of
rice (6). However, individual flavonoids and carotenoids have not
attracted as much attention as other components in rice grains and
the phytochemicals in other cereals, fruits, and vegetables (7, 8).
Anthocyanins, a group of reddish purple, water-soluble flavonoids that are the primary pigments in the red and black grains,
have been widely identified and characterized in cereal grains (9,10).
The major components of anthocyanidins in pigmented rice
are cyanidin-3-O-β-glucoside and peonidin-3-O-β-glucoside.
However, few studies have reported on the characterization of
other flavonoids, such as flavonols and flavones, in pigmented
rice (11).
Carotenoids play essential roles in plants, e.g., photoprotective
functions during photosynthesis (12). Anthocyanins in plants also
function as photoprotectants (13). Nagira et al. suggested that
changes in the levels of endogenous abscisic acid (ABA), the
metabolic end product of carotenoid, may play an important role
in the induction of anthocyanin synthesis in regenerated torenia
shoots (14). However, no previous reports have described the
correlations between these pigments, and their contents or compositions in Korean pigmented rice have not been determined.
The present study was performed to determine the flavonoids
and carotenoids in black, red, and white rice grains and to analyze
the relationships among their contents. The results of this study
could provide rice breeders and eventually commercial rice
growers new opportunities to promote the production of rice
with enhanced levels of bioactive compounds.
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