Ph.D

Evaluation and characterization of selected landraces of rice for bioactive
compounds and validation of its nutraceutical potential through in silico analysis
Abstract
Nearly ninety per cent of the world's production of rice comes from Asian
nations, where it is an often-cultivated crop. The world produced 513.68 million
tonnes of rice in 2022–2023, with China producing the most at 149 million tonnes,
followed by India with 132 million tonnes. Rice is consumed by nearly one-third of
the global population accounting for about 80 per cent of their energy requirements.
In addition to being the staple grain of Asia, rice is quickly taking the lead as the main
diet in Latin America and Africa. Oryza sativa is the most widely grown species of
the available approximately 11,000 rice types and 100,000 landraces as well as
improved cultivars. Existence of such a huge genetic diversity enables humans to
improve the crop’s performance in spite of changing climatic scenarios and
burgeoning population.
Traditional rices are enriched with amino acids, antioxidants, phytochemicals,
vitamin E and other nutrients. In addition to their antioxidant activity, traditional rice
varieties offer anti-diabetic and anti-inflammatory benefits. Epidemiological studies
have shown that regular consumption of whole grain is associated with reduced risks
of chronic diseases such as cardiovascular diseases, type 2 diabetes and some cancers.
Ayurveda considers traditional whole rice grains as nourishing food and medicine.
Brown rice and red rice are great sources of fiber, B vitamins, calcium, zinc, iron,
manganese, selenium, magnesium and other nutrients.
Due to its higher digestibility, nutritional quality, potential health benefits and
biological activity, rice is categorized as the queen of cereals. But these rices are
underexploited and requires a boost in yielding potential, for their commercialization.
In this background, the present study was envisaged to delve into the nutraceutical
superiority of a few selected speciality rice and highlight the significance of
conserving and protecting them.
The study was undertaken as four experiments spread across College of
Agriculture, Vellanikkara, RARS, Pattambi and CFTRI, Mysore. As first part of the
study, a pot culture experiment was conducted for morpho-physio and biochemical
evaluation of the selected twenty-five rice landraces, laid in completely randomised
design. Among the selected landraces, Kavunginpoothala recorded significantly
highest plant height (109.56 cm), followed by Chenkayama (101.51 cm), while
Ithikandapan was the shortest (93.93 cm). The local check Jyothi and Uma showed a
plant height of 96.35 cm and 103.35 cm respectively. Maximum number of tillers
were observed in Palthondi (6) which was on par with Chenkayama, Chuvannavattan,
Thavalakkannan, Rakthasali and Japan Violet. Black jasmine (4) possessed the least
number of tillers and was on par with Kala namak and Krishnakaumudh. Among the
selected landraces, the number of panicles of Palthondi (6) Chenkayama,
Thavalakkannan, Rakthasali, Japan Violet and Chuvanna Vattan were on par with
each other. The local check Jyothi possessed significantly higher number of panicles
per plant. The genotype Kavunginpoothala showed maximum days for 50%
flowering (132) followed by Chenkayama (121), which was on par with Kavuni
(120). The study on physiological aspects showed that the highest net photosynthetic
rate at reproductive stage was exhibited by Kala Namak (28.73 µmol CO2 m-2 s
-1
)
followed by Kothambalarikayama (28.33 µmol CO2 m-2 s
-1
) and the lowest was
shown by Japan Violet (20.87 µmol CO2 m-2 s
-1
).
Chempav possessed highest chlorophyll content (3.25 mg g-1
) which was on par with
Chenkayama (3.20 mg g-1
) and the lowest chlorophyll content was observed in Japan Violet
(1.00 mg g-1
). Highest IAA content at reproductive stage was observed for Kavunginpoothala
(873.60 µg of unoxidized auxin g-1 h-1
) and Ithikandapan (354.87 µg of unoxidized auxin g-1 h1
) exhibited the lowest IAA content. Irrespective of growth stages, Kavunginpoothala
recorded maximum GA content (18.99 mg/g, 20.82 mg/g, 20.87 mg/g). In maturity
stage, Ithikandapan (12.69 mg/g) had lowest GA content. Thavalakkannan and
Chenkayama, showed a purple coloured stem during reproductive stage. At maturity,
Black Jasmine, Ramli, Kala Namak, and Karutha Modan exhibited a black coloured
husk while remaining all other genotypes were in brown colour. Among the entries,
grains for nearly nineteen are red pigmented; five are white pigmented and one being
black pigmented.
The highest average panicle weight was possessed by Chuvanna Vattan
(18.51 g) followed by Rakthasali (18.35 g). The lowest average panicle weight was
for Chenkayama (10.36 g), which was on par with Kavunginpoothala. The local
check Uma and Jyothi exhibited an average panicle weight of 27.46 g and 25.64 g,
respectively. Chuvanna Vattan (26.68 g) exhibited the maximum 1000 grain
weight compared to other genotypes, followed by Njavara (26.26 g). The lowest
1000 seed weight was observed in Rakthasali (16.69 g). The local check Uma and
Jyothi had 1000 weight of 27.46 g and 28.49 g, respectively.
Black Jasmine possessed the significantly high iron (39.65, 24.71 mg/kg)
and zinc (19.21, 17.67 mg/kg) contents in unpolished and polished grains. The
anthocyanin content was found high in Black Jasmine (1110.05 µg/g), followed by
red variety Rakthasali (1058.49 µg/g) and Njavara (1001.51 µg/g). The
nutraceutical components such as gamma oryzanol, tocopherol, total polyphenols
and flavonoids was significantly high in Black Jasmine (72.85 mg/100 g, 5.32
µg/g, 13.13 mg/g and 6.46 mg/g, respectively) followed by Rakthasali (63.12
mg/100 g, 4.33 µg/g, 8.89 mg/g, and 6.25 mg/g, respectively) and Njavara (61.80
mg/100 g, 4.26 µg/g, 8.77 mg/g and 6.17 mg/g, respectively). The cooking and
eating quality of rice was determined by the proximate content and carbohydrate
digestibility. Among the studied genotypes, significantly highest ash (2.53%), fibre
(2.43%), fat (2.64%), lowest digestibility (60%) and high antioxidant activity were
observed in Black Jasmine.
It was also observed that, polishing caused a reduction in bioactive
contents. Due to polishing, nearly 80 and 50 per cent reduction was found in
mineral content and antioxidant activity. Among the selected genotypes, it could be
noted that, black pigmented landraces exhibited significantly high bioactive
compounds followed by red and white. Thus, based on the consistency in bioactive
compounds, HPLC characterization was also carried out at CSIR-CFTRI, Mysore
for a subset of the major compounds to identify and quantify them in nine selected
representatives from the red, black and white rice types. The HPLC analyses
indicated that Rakthasali had the highest chlorogenic acid (14.27 mg/100 g)
content, while Black jasmine had high gallic acid (3.56 mg/100 g). Njavara showed
highest t-cinnamic acid (1.47 mg/100 g) content compared to other varieties. These
sub compounds may be the reason for high nutraceutical potential these pigmented
genotypes. It was also noted that white genotypes had the presence of many sub
compounds, even though white rice is considered inferior to black and red.
In the next phase of the study, the three best promising genotypes
(Rakthasali, Black Jasmine and Njavara) were grown in field during Kharif and
Rabi. The field experiments were laid in randomised block design at RARS,
Pattambi, with an aim to analyse the phenolic content, anthocyanin content and
antioxidant activity. The results indicated that, the grains harvested from the Kharif
season exhibited high phenolic and anthocyanin contents along with high
antioxidant activity compared to the Rabi season crop. Subsequently, all the grains
were subjected to storage (ageing) study to check the bioactive compound activity
during storage. The grains were stored under ambient conditions and bioactive
profiling (total phenolics, anthocyanin, antioxidant activity) was carried out in
grains at harvest, 6, 9 and 12 months after storage. A tremendous reduction was
observed in all the grains stored. Among the genotypes, Rakthasali,
Thavalakkannan and Kattamodan exhibited lowest reduction in phenolic content
(~30 %). Black Jasmine, Japan Violet and Chenkayama had lowest reduction in
anthocyanin content (~ 15 %). Rakthasali, Karutha Modan, Krishnakaumudh and
Njavara showed lowest reduction in antioxidant activity (~ 30 %) among the
selected entries.
Simultaneously, an in silico study was conducted on CB dock platform to
find out the best bioactive compound against receptors of major lifestyle diseases
such as cancer, diabetes and inflammation, based on the interaction dynamics. The
major sub-compounds of phenolics, flavonoids, oryzanols, anthocyanins and tocols
were selected for the docking study. The disease specific target proteins/receptors
were selected for performing the docking assay. Chlorogenic acid was identified as
best phenolic sub-compound against cancer, diabetes and inflammation. Among
the oryzanol sub-compounds, stigmasteryl ferulate, sitostanyl ferulate and
cycloartenyl ferulate exhibited best interaction with receptors, evidenced by
superior docking scores. Among flavonoids, luteolin, myrcetin and fisetin are the
promising drug candidates against these diseases. In case of tocols, strong
interaction with target proteins was noted for gamma toco-trienol, beta toco-trienol
and delta toco-trienol. delphinidin-3-O-galactoside, and cyanidin-3-O-glucoside
are the major sub compounds of anthocyanin which showed best docking scores
with selected target proteins.
From the present study, based on the docking scores and ADMET
properties, the above selected sub compounds which were also pronounced in
Rakthasali, Black Jasmine and Njavara as per their HPLC profiles, were found
promising to combat lifestyle disorders Further validation by wet lab studies is
required to reinforce their promising roles. The study describes rice bran is the
main source of minerals, vitamin E and other bioactive compounds known to
possess medicinal properties. The study highlights the nutraceutical potential of
Rakthasali, Black Jasmine and Njavara and the possibilities for exploiting them by
selecting the apt growing season, ageing stage and targeted extraction of the
relevant bioactive compound (s), for reaping maximum benefits. The relevance of
further examination of these varieties for their stress resilience and marginal yield
increase potential also is a future thrust.