Improvement of polyphenol extraction from grape skin by pulse electric field

Effects of a treatment of grape peels with pulsed discharges under water at applied voltage from 30 to 60 kV on the evolution of total polyphenols in Kyoho grape processing was investigated using a six-stage Blumlein-line pulsed power generator. The grape peels were sunk in diluted water and the pulse voltage was applied to five needle electrodes set into the water. The experimental results showed that the permeabilization of the grape peels by application of the pulsed discharges at room temperature caused an increase of total polyphenols with respect to the control during the process. The total polyphenols increased from 2.5 to 4.78 μmM gallic acid eq. /100g with increasing applied voltage from 30 to 60 kV at 5 pps (pulses per second). The increase rates of the total polyphenols by applying pulse voltage were obtained to be 16.7% at 30 kV, and 84.2% at 60 kV applied voltage. A microscopic measurement clearly showed that red color pigments were extracted from anthocyanoplasts into the cells through an electroporation process.