Anthocyanin content
The analysis method for anthocyanin content was modified from the method used by Hosseinian et al (2008). The pigmented rice extract (20 μL) was added into 2 mL of potassium chloride buffer (0.03 mol/L, pH 1.0) and 2 mL of sodium acetate buffer (0.4 mol/L, pH 4.5). Each of them was left for 15 min before taking an absorption measurement using spectrophotometer (Libra S22, Biochrom, England) at 550 nm and 700 nm. Distilled water was used as a blank. The anthocyanin concentration (mg/L) of sample was calculated according to the following formula and expressed as Cyanidin-3-glucoside equivalents: