The ultrasound-assisted extraction (UAE) method was used to optimize the extraction of phenolic compounds from pumpkins and peaches. The response surface methodology (RSM) was used to study the effects of three independent variables each with three treatments. They included extraction temperatures (30, 40 and 50 ̊C), ultrasonic power levels (30, 50 and 70 %) and extraction times (10, 20 and 30 min). The optimal conditions for extractions of total phenolics from pumpkins were inferred to be a temperature of 41.45 ̊C, a power of 44.60 % and a time of 25.67 min. However, an extraction temperature of 40.99 ̊C, power of 56.01 % and time of 25.71 min was optimal for recovery of free radical scavenging activity (measured by 1, 1-diphenyl-2-picrylhydrazyl (DPPH) reduction). The optimal conditions for peach extracts were an extraction temperature of 41.53 ̊C, power of 43.99 % and time of 27.86 min for total phenolics. However, an extraction temperature of 41.60 ̊C, power of 44.88 % and time of 27.49 min was optimal for free radical scavenging activity (judged by from DPPH reduction). Further, the UAE processes were significantly better than solvent extractions without ultrasound. By electron microscopy it was concluded that ultrasonic processing caused damage in cells for all treated samples (pumpkin, peach). However, the FTIR spectra did not show any significant changes in chemical structures caused by either ultrasonic processing or solvent extraction.
Altemimi, Ammar, Watson, Dennis G., Choudhary, Ruplal, Dasari, Malika R. and Lightfoot, David A. "Ultrasound Assisted Extraction of Phenolic Compounds from Peaches and Pumpkins." PLOS One 11, No. 2 (Feb 2016). doi:10.1371/journal.pone.0148758.