The effect of Pulsed Electric Field as a pre-treatment step in Ultrasound Assisted Extraction of phenolic compounds from fresh rosemary and thyme by-products

Emerging extraction techniques, including pulsed electric field (PEF) and ultrasound (US), are attracting considerable interest in the recovery of bioactives. Though, limited work has focused on PEF application as pre-treatment for US assisted extraction to enhance the release of phenolics from herbs. Hence, the present study investigated the use of an optimized PEF pre-treatment to enhance the recovery of phenolics from fresh rosemary and thyme by-products in a subsequent US assisted extraction step. Total phenolic content (TPC), 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and ferric reducing antioxidant power (FRAP) were assessed as an index of extraction efficacy. Qualitative and quantitative analyses were performed through liquid chromatography-mass spectrometry analyses to evaluate the influence of the methods on individual phenolic compounds and the formation of potential derivatives. The results indicated that in a number of cases PEF pre-treatment enhanced (p < 0.05) the recovery of phenolic compounds and antioxidant capacity compared to US individually.