Total phenolic content (TPC)
Fruit juice samples of berries from clusters was removed and frozen in liquid nitrogen The total phenolic content
in juice grape was measured according to the Folin–Ciocalteu method (Slinkard and Singleton, 1977). Gallic acid
was used as a standard phenolic compound. Extraction was performed by 2 mg fruit juice and then the extract was
filtered with No.1 filter paper Fifteen hundred μL diluted Folin– Ciocalteau (Merck) reagent (1:10 with distilled water)
was added to 300 μL extract solution and mixed thoroughly. After five minutes, 1200 μL Na
2CO3
(7%) was added
and then the mixture was shake for 1.5 h. The absorbance was measured using UV/Vis spectrophotometer (Carry
100, Varian, USA) at the wavelength of 765 nm. The concentration of total phenolics was expressed as the mg
Gallic acid equivalents per gram of fresh weight (FW).