Abstract:
Rice (Oryza sativa L.) is the dietary staple over half of the world’s population and wide range of
rice varieties are available worldwide with varing physicochemical and bioactive properties. Rice
bran is a by-product of the rice milling process and currently numerous applications worldwide in
functional foods and nutraceutical industries. In Sri Lanka, rice is the dietary staple and reported
to have many Sri Lankan traditional rice varieties. In the traditional knowledge of Sri Lanka,
some of these varieties are claimed to have varing physicochemical and functional properties.
However, there is no single comprehensive study conducted in the country to date, to evaluate
physicochemical and bioactive properties of these varieties. This study therefore, was undertaken
to investigate the selected physicochemical and bioactive properties for selected Sri Lankan
traditional rice varieties.
Twenty three (23) red and white rice varieties were selected for the study. The selected varieties
were studied for grain size, shape, color, moisture, crude protein, crude fat, ash, total
carbohydrate, amylose content, gelatinization temperature and gel consistency as
physicochemical properties of the rice grain. These properties were studied for the whole grains
or the brown rice (endosperm and bran). As bioactivities anti-diabetic, anti-inflammatory,
anticancer, anti-oxidant and anti-hypertension properties were studied using wide variety of
enzymatic, non enzymatic and cell based bioassays in vitro. Anti-hyperglycemic activity also
studied using in vivo rat model (lg/kg body weight) as an anti-diabetic property. Screening of
selected varieties was performed based on anti-diabetic property (a-amylase inhibitory activity
and anti-glycation activity) and rest of the bioactivities were conducted only for the highly
biologically active varieties selected at the screening process. Seventy percent ethanolic extract of
the rice bran (concentration range: 1 - 400 pg/ml) was used in all the bioactivities. Antiinflammatory
and anti-cancer properties were studied also for rice bran fractions, by partitioning
70 % ethanolic extracts using hexane, dichlromethane and butanol. Effect of rice bran protein
hydrolysates (concentration range: 250 - 1200 pg/ml) were studied only for anti-hypertension and
anti-cancer properties.
Physicochemical properties studied indicated that out of 23 varieties 20 varieties are red rices and
size and shape were mostly short bold (56 %) and medium bold (30 %). Moisture, crude protein,
crude fat, ash and the total carbohydrate contents ranged from 10.42 ± 0.25 - 12.33 ± 0.02 %,
10.59 ± 0.12 - 13.27 ± 0.32 %, 2.18 ± 0.10 - 4.12 ± 0.28 %, 1.30 ± 0.14 - 1.92 ± 0.05 % and
81.42 ± 0.25 - 85.66 ± 0.24 % respectively and varied significantly (p < 0.05) among the
varieties. Among the varieties studied 95 % of the varieties were high amylose rices (> 25 %).
Gelatinization properties studied indicated that gel consistency was mostly medium (48 %) and
soft (39 %) and gelatinization temperature was mostly intermediate (65 %). The highly
biologically active varieties selected at the screening process were Sudu Heeneti, Goda Heeneti,
Masuran and Dik Wee and these four varieties are red rices. These four varieties had antidiabetic,
anti-oxidant, anti-inflammatory and anti-cancer properties. Anti-diabetic property of
these varieties was mediated by multiple mechanisms which inclue a-amylase inhibitory activity,
anti-glycation activity, glycation reversing ability and acetyl and butyrylcholinesterase enzyme
inhibitory activities. Further, Masuran, Sudu Heeneti and Dik Wee varieties had low in vitro
starch digestion rate indicating that these varieties may be low glycemic index rices. Brans of
Masuran variety also showed in vivo anti-hyperglycemic activity. Anti-inflamatory activity of
selected varieties was too mediated by multiple mechanisms. These mechanisms include
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reduction of oxidative burst of human whole blood, and isolated immune cells including
polymorphonuclear cells and macrophages, inhibition of nitric oxide and pro inflammatory
cytokines, TNF-a and IL-1 p without mediating cytotoxicity to normal cells. As anti-cancer
property the selected four varieties showed cytotoxicity on human lung cancer cell line NCIH460
and human cervical cancer cell line HeLa. All these varieties had high glutathione Stransferase
enzyme inhibitory activity and indicate its potential to be used as adjuvant in
managing cancer patients during chemotherapy. Anti-oxidant property of these varieties are
multifaceted and mediated by prescence of polyphenolic antioxidants, scavenging of free
radicals, DPPH, ABTS, superoxide and nitric oxide and ferric reducing antioxidant power.
However, all these varieties did not show anti-hypertension activity tested via ACE inhibition.
Seventy % ethanolic extracts showed significantly high activity compared to rice bran protein
hydrolysates in different bioactivities tested in this study. Fractionation results indicated that
synergistic as well as anatoganistic effect. However, generally non polar fractions were more
biologically active compared to polar fractions of the rice bran. Among the bioactivities studied
a-amylase inhibitory activity, anti-glycation activity, glycation reversing ability and oxidative
burst inhibitory activity showed potent activity while other bioactivities showed moderate
activities compared to standard drugs used in the study and other rice varieties worldwide.
In conclusion, Sri Lankan traditional rice possesses desirable physicochemical and bioactive
properties. In terms of physicochemical properties both red and white rice had desirable
properties. However, in terms of biological activities red rice is superior to white rice. Brans of
selected red rice showed the potential of isolating active compounds for developing promising
novel drugs for managing diabetes, cancer and inflammatory diseases. It also shows the
possibility of using rice and rice bran in functional foods and nutraceuticals industries.
Collectively, this research added value to the rice bran, a cheap source and a byproduct of the rice
milling industry. Finally, the findings of this study may essentially help to promote Sri Lankan
traditional rice especially red rice as a healthy staple food for Sri Lankans and thought out the
world and make it a profitable industry to the country.
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