Many plant-derived compounds with high antioxidant activity are widely used in food applications. Among various methods for measuring antioxidant activity, such as FRAP, ORAC, ABTS, and ESR, DPPH (2,2-diphenyl-1-picrylhydrazyl) is the most commonly employed, despite the difficulties in comparing the results obtained with different DPPH concentrations across assays. To address this difficulty, Sherer and Godoy (2009) proposed using a new indicator, the Antioxidant Activity Index (AAI), calculated as the initial DPPH concentration divided by the EC50, accounting for the variation in the aforesaid DPPH concentration. In this study, we aimed to isolate and quantify antioxidant compounds from fruits and vegetables and compare them to known standards using the AAI index. For this purpose, extracts were prepared at 37°C using 1% HCl in ethanol. Samples were analyzed in triplicate, determining EC50 (ppm of dry sample needed to reduce the initial 50 ppm DPPH concentration by 50%) and calculating the Antioxidant Activity Index (AAI) as a ratio of the initial DPPH concentration to the EC50. AAI was assessed in extracts from various fruits, including grapes, apples, figs, peaches, plums, pears, and berries, along with standards such as gallic acid, ascorbic acid, ferulic acid, rutin, chlorogenic acid, and caffeic acid. Plums exhibited the highest AAI (1.06), followed by berries, with calafate (1.04) and maqui (0.96) standing out. Red grapes had an AAI of 0.59, apples and pears had lower values (0.33 and 0.29), and figs had the lowest (0.08). Standards showed significantly higher AAI values, ranging from 29.9 (gallic acid) to 6.23 (ferulic acid). These results suggest that these fruit and vegetable matrices could serve as sources of antioxidant compounds, adding value to local production and contributing to developing functional foods with health benefits beyond traditional nutritional requirements. Finally, we regard the usage of the AAI index as helpful when comparing results among assays and matrices.