Enhanced extraction of phenolic compounds from onion by pulsed electric field (PEF)

The extraction of water-soluble phenolic compounds from onion assisted by pulsed electric field treatment (PEF) was investigated as well as the antioxidant activity of the extracts. Results indicated that the yield of water-soluble phenolic compounds (PC) and flavonoid compounds (FC) from onion was significantly increased after treated by PEF treatment following water extraction. Meanwhile, the antioxidant activity of extracts increased with the increase in electric field intensity and treatment time. Box-Behnken design was employed to optimize the extraction process. The optimal conditions were 2.5 kV/cm, 90 pulses and 45 degrees C for both of PC and FC. Under those conditions, the content of PC and FC in extracts was 102.86 mg GAE 100 g(-1) FW and 37.58 mg QE 100 g(-1) FW, increased by 2.2 and 2.7 times, respectively, in comparison to control (Non-PEF treatment) (PC is 32.13 GAE 100 g(-1) FW,FC is 10.22 mg QE 100 g(-1) FW). Although the extraction yields of PC and FC for PEF-assisted aqueous extraction was just 1/3 and 1/2 of soxhlet extraction, compared to conventional extraction methods with toxic, organic solvent, PEF-assisted aqueous extraction method is a selective, environmental friend process to recover water-soluble PC and FC from onion. Practical application Onion is abundant of phenolic compounds, particularly flavonols which are considered to be a reduced risk of many diseases by inhibition of lipid peroxidation. PEF processing as a non-thermal technology for preservation of liquid foods has been investigated extensively during the last decades without destroying original sensorial and nutritional properties of food. In this study, it demonstrated that as efficient cell wall disruption technique, the aqueous extraction of phenolic compounds (PC) and flavonoid compounds (FC) from onion was facilitated significantly by PEF treatment. Therefore, PEF-assisted aqueous extraction method has great potential as a selective, environmental friend process to recover water-soluble PC and FC from onion.