Investigating Pigment Radicals in Black Rice Using HPLC and Multi-EPR

Production, physico-chemical properties and antioxidant activity of melanin from Annulohypoxylon stygium (Lév.) Y.M. Ju, J.D. Rogers and H.M. Hsieh

To obtain higher melanin production in liquid culture, culture conditions of Annulohypoxylon stygium (Lév.) Y.M. Ju, J.D. Rogers and H.M. Hsieh were optimised. The results showed that using single factor experiment and orthogonal test, the optimised production of melanin reached 2.20 g/L, which was 2.06 times higher than that of the control group. In addition, it was speculated that A. stygium melanin (AsM) was 3,4-dihydroxyphenylalanine (DOPA) melanin and showed an amorphous irregular structure. Moreover, it had good solubility in alkaline solution. AsM showed good antioxidant activity at a concentration of 500 mg/L, with DPPH, ABTS and OH radicals scavenging activities of 90.83%, 75.36% and 70.90%, respectively. AsM prevented alcohol-induced oxidative damage and oxidative stress in HepG2 cells by inhibiting the decrease of antioxidant key enzyme activity under alcohol stimulation. It was proved to have a great potential for application as a natural antioxidant and a substitute for synthetic pigments.

Free Radical Scavenging Capability of Various Defatted Sesame Seed Cakes and Hulls Using EPR Compared with In Vitro Testing and HPLC Analysis

The free radical scavenging activities of black and white sesame seed hulls and the powder of black and white sesame seed cakes were investigated using noninvasive continuous wave electron paramagnetic resonance (EPR) and antioxidant assays. With black sesame seed hulls and the powder of black sesame seed cakes, EPR detected the very strong single-line signal intensities that correspond to the stable organic radicals, while the spectrum of the white sesame seed hulls and the white sesame seed cakes showed no signal. The in vitro antioxidant activities of black and white sesame seed cake extract were evaluated by DPPH free radical scavenging activity, hydrogen peroxide scavenging activity, and ferric reducing antioxidant power (FRAP) assay. The results indicated that the extract from black sesame seed cake possessed a greater DPPH radical inhibitory activity and hydrogen peroxide inhibitory activity than white sesame seed cake extract, with IC₅₀ values of 0.847 ± 0.011 mg/mL and 0.338 ± 0.007 mg/mL, respectively. Black sesame seed cake extract also showed a strong reducing power with a FRAP value of 1.307 ± 0.037 mM Fe (II)/g of extract weight and an EC₁ value of 0.683 ± 0.002 mg/mL. The main compounds from the black and white sesame seed cake extracts were analysed using high-performance liquid chromatography (HPLC). The results revealed that the main compounds in black and white sesame seed cake extracts were in a group of water-soluble lignans, mainly sesaminol triglucoside and sesaminol diglucoside. However, sesaminol diglucoside was found in large amounts in the black sesame seed cake extract, while it was found in a very small amount in the white sesame seed cake extract. Therefore, these results demonstrated considerable antioxidant capacity of the sesame seed, especially in the black strain.

Investigation of Pigments in Thai Purple Rice Using Electron Paramagnetic Resonance Imaging and HPLC

Paramagnetic species (radicals) related pigments in Thai purple rice were investigated by electron paramagnetic resonance (EPR), X-band (9 GHz) EPR imaging (EPRI), and HPLC. The location and distribution of the paramagnetic species in purple and white rice were determined by EPR and EPRI. EPR primarily detected three paramagnetic species in purple rice, which were identified as organic radicals, Mn²⁺, and Fe³⁺ based on the g-values and hyperfine components of the EPR signals. Noninvasive two-dimensional (2D) EPRI revealed that these stable radicals are primarily located in the pigmented region of purple rice, while very few radicals were observed in the interior of the rice. HPLC revealed that the major compounds were cyanidin-3-O-glucoside and peonidin-3-O-glucoside. EPR, EPR imaging, and HPLC results indicate that the stable radicals contain the radical state of anthocyanins and are mostly found within the pigmented embryo region of purple rice. They could be either associated with antioxidant activities or could be one of the products of their oxidative decomposition.

EPR and HPLC Investigation of Pigments in Thai Purple Rice

We investigated the pigments in Thai purple rice using electron paramagnetic resonance (EPR), X-band (9 GHz) EPR imaging (EPRI), and HPLC. The location and spatial distribution of the paramagnetic species in purple and white rice were determined by EPR and EPRI. EPR primarily detected three paramagnetic species in purple rice, which were identified as stable radicals, Mn²⁺, and Fe³⁺ based on the gvalues and hyperfine components of the EPR signals. Subsequent noninvasive two-dimensional (2D) EPRI revealed that these stable radicals are primarily located in the pigmented region of purple rice, while very few radicals were observed in the interior of the rice. HPLC revealed that the major compounds were cyanidin-3-O-glucoside and peonidin-3-O-glucoside. Scavenging activities, EPR, and EPR imaging results indicate that the stable radicals contain the radical state of anthocyanins and are mostly found within the pigmented embryo region of purple rice. They could be either associated with scavenging activities or could be one of the products of their oxidative decomposition.