Ferric reducing power (FRP) of carrot juice and yoghurt
The FRP of carrot juice extract was determined according to
Oyaizu (1986). An extract (100 mL) of carrot juice or yoghurt was
mixed with 2.5 mL of 0.2 M phosphate buffer (pH 6.6), 1% potassium
ferricyanide (2.5 mL) and the mixture was incubated in a
water bath at 50 C for 20 min. Trichloroacetic acid (2.5 mL, 10%)
was added to the mixture and centrifuged (3000 rpm, 10 min). The
upper layer (2.5 mL) was mixed with distilled water (2.5 mL) and
freshly prepared 0.1% ferric chloride solution (0.5 mL). Absorbance
was measured at 700 nm. After subtracting absorbance of a blank
sample (prepared from distilled water), FRP was determined from
ascorbic acid (AA) calibration standard as AA equivalents in milligram
per kilogram of carrot juice or yoghurt.