2.2.2. Determination of Bioactive Compounds
z Preparation of Crude Extract: The test method was modified from [24] soaking powders of rice formulas accepted by consumers (before and after cooking) in 95%-methanol solvent to dissolve in distilled water at a ratio of 1:5 (w/v) for 24 hr. The mixture was then spun with a centrifuge machine at 2,500 rpm for 20 min and filtered with Whatman No.1 filtering paper. Next, the mixture was dried under vacuum conditions with a rotary evaporator at 45°C. The rough extracts obtained were used for further experimentation.
z Determination of Total Phenolic Compounds: TPC amounts were determined by the Folin-Ciocalteu method, an experimentation method modified from [24] and [25]. Rough extracts from rice at a volume of 200 μl were mixed with 1 ml of Folin-Ciocalteu reagents (diluted with disinfected distilled water at a ratio of 1:100) and 800 μl of a 10% Na2CO3 solution was added. Next, the disinfected distilled water was added to adjust the total volume to 5 ml. The mixture was blended and left to react for 2 hr before being measured for light absorption values at a wavelength of 760 nm. The standard antioxidant used to compare with the experiment results was Gallic acid.
z Extraction and Determination of γ-oryzanol and α-tocopherol: The experimentation method modified from [24] and [26] involved 1 g of soaking powder of rice formulas accepted by consumers (before and after cooking) in acetone at a ratio of 1:10 (w/v). The mixture was then spun with a centrifuge machine at maximum speed for 1 min and at 2,500 rpm for 20 min. Supernatants will be obtained after the solvent has been separated. Supernatants were then dehydrated under nitrogen.
Measurement of γ-oryzanol and α-tocopherol levels by the HPLC method was performed by dissolving rough extracts in the mobile phase and filtering by using a syringe-driven filter with a diameter of 0.45 μm. Analysis was performed using a RP-HPLC system machine (Shimadzu). 20 μl of the sample were injected through the security guard-column. Column size was 4.60 × 250 mm, 4 μl. Column temperature was controlled at 45°C. The mobile phase solvent, acetonitrile/methanol (25:75, v/v), was used at a flow rate of 1.5 ml/min. The wavelength was detected at 292 nm for measuring α-tocopherol levels and 325 nm for measuring γ-oryzanol levels.