Pulsed electric field-assisted juice extraction of frozen/thawed blueberries

Pulsed electric field is an efficient method for cell membrane permeabilization of food tissues with most research being done on fresh plant cells. Freeze/thawing is also known to be capable of cell membrane permeabilization. In this work, frozen/thawed European blueberry (Vaccinium myrtillus L.) fruits were treated with pulsed electric field in order to further enhance the cell membrane permeabilization and, hence, the quality of blueberry juice during the subsequent pressing process. Blueberries tissues were exposed to 20 μs monopolar square wave pulses of different electric field strength (E = 1–3–5 kV cm-1) and total specific energy input (WT = 1–5–10 kJ kg-1), with their permeabilization being characterized by electrical impedance measurements and cell disintegration index (Zp). The juice, obtained after pressing (1.32 bar), was characterized for total polyphenols, anthocyanins content and antioxidant activity. The cell disintegration index (Zp) significantly (p < 0.05) increased from 0.2 up to 0.6 with increasing pulsed electric field treatment intensity (E and WT). As a results, in comparison with control, pulsed electric field treatment induced a slightly higher release of polyphenols (up to +8.0%) and anthocyanins (up to +8.3%), thus improving the antioxidant activity of the juice (up to +16.7%). In conclusion, frozen/thawed blueberries could be pulsed electric field treated in order to further increase juice quality.