Assisted extraction of bioactive compounds from plum and grape peels by ultrasonics and pulsed electric fields

The industrial use of fruits for the production of juices results in the accumulation of large amounts of by-products such as peels, with are still a good source of phytochemicals such as phenols and anthocyanins. In this work, the impact of two different processing configuration of pulsed electric fields (PEF-I and PEF-II in continuous, with 25 mm and 7 mm of treatment chamber diameter, respectively) and ultrasonication (US25 and US50 in batch, at 25 and 50 °C, respectively) were evaluated in order to assess these technologies as environmental friendly alternatives to water extraction at 70 °C (WE70) in plum and grape peels. US was able to increase the extraction of anthocyanins and flavonoids in plum peels, being less effective than PEF with total phenols. In grape peels, when US was performed at higher temperature (US50), the yields were significantly higher. PEF was more successful when the diameter of the chamber was larger (PEF-I), and consequently the residence time and number of pulses greater. Particularly, PEF allowed to augment several folds the extraction of anthocyanins and flavonoids from grape peels, but was deleterious for ascorbic acid. Principal component analysis (PCA) showed that US50 and PEF-I were clustered and positively correlated with bioactive compounds recovery and antioxidant capacity.