The free radical scavenging capacity (RSC) of antioxidants from sesame cake extract was studied using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH(*)()) on a kinetic model. Pure lignans and lignan glycosides isolated from methanolic extract by preparative HPLC were used in the study. To understand the kinetic behavior better and to determine the RSC of sesame antioxidants, the second-order rate constant (k(2)) was calculated for the quenching reaction with [DPPH(*)] radical. The k(2) values of the sesame antioxidants were compared with those of butylated hydroxytoluene and alpha-tocopherol. The k(2) values for sesamol, sesamol dimer, sesamin, sesamolin, sesaminol triglucoside, and sesaminol diglucoside were 4.00 x 10(-)(5), 0.50 x 10(-)(5), 0.36 x 10(-)(5), 0.13 x 10(-)(5), 0.33 x 10(-)(5), and 0.08 x 10(-)(5) microM(-)(1) s(-)(1), respectively.

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Njavara is an important medicinal rice variety of Kerala, India, widely used in Ayurveda as a 'health food' and in the treatment of rheumatoid arthritis, paralysis, neurodegenerative diseases and in rejuvenation therapy. Phytochemical investigations and spectroscopic studies of the diethyl ether fraction of methanolic extract of Njavara Black (NB) rice bran gave three important compounds namely, tricin and two rare flavonolignans- tricin 4'-O-(erythro-β-guaiacylglyceryl) ether and tricin 4'-O-(threo-β-guaiacylglyceryl) ether. The EC(50) values of these compounds in DPPH system were 90.39, 352.04 and 208.1 μg/ml, respectively. Quantification of the compounds by HPLC in NB and staple, non-medicinal rice varieties Sujatha (SJ) and Palakkadan Matta (PM) showed that tricin is present 39.64 and 16.12 fold higher in NB, compared to SJ and PM, respectively. This is the first report on the occurrence of tricin at significantly higher levels in Njavara and occurrence of the two flavonolignans in Oryza sativa species. Of the three compounds, tricin and the threo- form of flavonolignan showed anti-inflammatory effect of >65% after 5 h, at 2 mg/kg, in carrageenan-induced, paw edema experiments in rats. The results of the study corroborate with the preferential use of Njavara in indigenous medicine, over staple varieties.

Chemical indices, antioxidant and anti‐inflammatory activity of extracts of bran of medicinal rice – Njavara “black glumed” type (NBb) and its rice (NBr), were studied in comparison with bran and rice of staple varieties: Sujatha and Palakkadan Matta. Total oryzanol, phenolic, flavonoid, proanthocyanidin and phytate contents of NBb (1.84 mg/g, 27.16 mg of gallic acid/g, 4.50 mg of quercetin/g, 0.98 mg of catechin/g and 8.77 mg/g dry weight of bran, respectively) were higher compared with NBr and staple varieties. NBb showed greater reducing power and significantly higher scavenging activity with 2, 2‐diphenyl‐1‐picryl hydrazyl radical, superoxide and hydrogen peroxide with values of concentration of NBb required to scavenge 50% of respective radicals (IC50): 84.66, 203.16 and 73.55 µg/mL, respectively. The anti‐inflammatory effect (in vivo) of NBb was 83.3%, whereas NBr and staple varieties showed activity in the range 16–66%. The higher oryzanol content, chemical indices, antioxidant and anti‐inflammatory activity for Njavara compared with staple varieties corroborates with its medicinal use in Ayurveda. PRACTICAL APPLICATIONS Medicinal plants are a source of antioxidants and bioactive compounds responsible for the prevention of oxidative stress that leads to many degenerative diseases and conditions. The present study indicates that the extracts of “Njavara” (black glumed), a medicinal rice variety, contains significant amounts of oryzanols, phenolic acids, flavonoids, proanthocyanidins and phytic acid compared with staple varieties. These extracts are potential free radical scavengers and have anti‐inflammatory effect compared with staple varieties. Njavara, identified as a source of bioactive compounds, can be consumed as a health food in addition to its medicinal uses; thus, benefiting consumers. Higher oryzanol content in Njavara is beneficial for lowering plasma cholesterol, reducing platelet aggregation, nerve imbalances and aortic fatty streak formation. Higher antioxidants in Njavara are also beneficial against the diseases initiated by free radicals. These promising results also open up newer areas of research for developing improved varieties of rice containing more bioactive compounds.

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Structural, electronic, and energetic characteristics of tricin, tricin-4'-O-(erythro-β-guaiacylglyceryl)ether (TEGE), and tricin-4'-O-(threo-β-guaiacylglyceryl)ether (TTGE), isolated from "Njavara" rice bran have been studied using DFT to explain their experimentally determined radical scavenging activity (EC(50) values) in comparison with known standards such as quercetin, myricetin, and catechin. Among the three mechanisms proposed for explaining the antioxidant activity, proton coupled-electron transfer (PC-ET), sequential proton loss electron transfer (SPLET), and electron transfer-proton transfer (ET-PT), our results support the second one. The O-H bond dissociation enthalpy (BDE) and the spin density on the oxygen with the radical character are excellent descriptors of radical scavenging activity. BDE (in kcal/mol) increased in the order myricetin (74.6) < quercetin (78.1) < catechin (78.3) < tricin (81.5) < TTGE (90.6) < TEGE (91.1), while the EC(50) increased exponentially with increase in BDE, 20.51, 42.98, 45.07, 90.39, 208.01, and 352.04 μg/mL for myricetin, quercetin, catechin, tricin, TTGE, and TEGE, respectively.

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