2.2.3. Quantification of total phenolics
Total phenolic content was measured by Folin–Ciocalteau method following the methodology proposed by Singleton and Rossi (1965). A sample of 0.1 mL was mixed with 7.9 mL of water. Then, Folin– Ciocalteau reagent (0.5 mL) was added and allowed to withstand for 5 min. Sodium carbonate (20% w/v; 1.5 mL) was then added to the mixture. After shaking, the mixture was incubated for 90 min. The absorbance was measured at 725 nm using a Jenway Genova spectrophotometer (Stone, Staffordshire, UK). Different concentrations of gallic acid (GAC) were used for the standard curve and final results were expressed as milligrams of gallic acid equivalents per 100 g of potato peel.