Total phenols of cake extracts were determined according to the
method of Jun et al. (2012) with minor modification. Each extract
(500 mg) was dissolved in 80% (v/v) methanol (6 mL) using an
ultrasonic bath with 40 kHz for 5 min, and then the volume was
adjusted to 10 ml. Folin-Ciocalteu's phenol reagent (0.4 mL) was
added to each sample (0.2 mL), and stood for 1 min. Then, 6 mL of
5 g/100 mL sodium carbonate solution was added to the mixture,
and stood for 1 h in dark place. The absorbance was measured at
760 nm using a spectrophotometer (U-1800, Hitachi Hightechnologies
Co., Tokyo, Japan), with gallic acid used as a standard.
The content of total phenols was calculated on the basis of the
calibration curve of gallic acid [the equation of standard curve:
absorbance at 760 nm ¼ 0.0037 Cgallic acid (mg/ml) þ 0.0173,
R2 ¼ 0.9996]. Results were expressed as milligram of gallic acid
equivalents (GAE) per gram of cake extract.