PEF-assisted juice extraction from different grape varieties

PEF treatments of different intensities (Electric field ranging from 0.5 to 5 kV/cm and total specific Energy from 1 to 20 kJ/kg) were applied during the pressing process to enhance the expression of grape juice of Aglianico and Piedirosso varieties. Preliminary measurements of electrical impedance were used to define the optimal PEF treatment conditions to obtain maximum tissue permeabilization: at the pressure of 1.3 bar, sufficient to obtain a satisfactory juice expression from both varieties, the specific energy for complete tissue permeabilization was 12 kJ/kg for Aglianico grapes, but only 3 kJ/kg for Piedirosso. Juice extraction experiments showed that PEF treatment increased the yield of juice of about 15% for Aglianico in comparison with control, while for Piedirosso a higher increase was observed (+20%), which was comparable to the effect of freeze-thawing. PEF treatment did not affect the content of polyphenols in Aglianico juices, while it increased the content of more than 30% in juice obtained from Piedirosso. Remarkably, the antioxidant activity, measured by DPPH method, on PEF-treated samples was always significantly higher (up to 6-folds higher) than in untreated samples for both Aglianico and Piedirosso juices.