2.6. Determination of total phenol content
The total phenol contents of the apple juice were measured by a modified colorimetric Folin–Ciocalteu method. A volume of apple juice (10 ll) was added to a 96-well plate containing 20 ll of Folin–Ciocalteu reagent and allowed to react for 7 min. Then, reaction mixture was mixed with 80 ll of 700 mM sodium carbonate solution and incubated for 1 h. The optimal density was determined using a plate reader at 760 nm. The result values were compared to a standard curve of prepared gallic acid solutions.