Ultrasound assisted extraction of phenolic compounds from grapes

A new ultrasound-assisted extraction method was developed for the determination of phenolic compounds present in grapes. Several extraction variables including extraction temperature (0-75°C), output amplitude (20, 50 and 100%), duty cycle (0.2 s, 0.6 s and 1 s), the quantity of sample (0.5-2 g), and the total extraction time (3-15 min) were evaluated. One of the most widely used extraction methods of polyphenol extraction has been used as reference method. Three parameters were compared: total amount of phenolic compounds, total amount of anthocyanins and total amount of tannic components. The resulting method produced similar or higher recoveries for these three parameters; however a much shorter extraction time was needed: 6 min (ultrasound assisted extraction method) instead of 60 min (reference method). Analytical properties for the new method were established, including limit of detection, limit of quantification, repeatability and reproducibility. The developed method was applied to two different types of grapes in different ripening degree.