Improving the extraction yield of juice and valuable compounds from sweet cherry and their by-products by Pulsed Electric Fields

Pulsed Electric Fields (PEF) treatment has recently gained interest as a milder and efficient alternative to conventional cell disintegration techniques of plant cell. In this work the influence of PEF pre-treatment on the extraction yield and antioxidant properties of juice obtained after pressing of sweet cherry (Prunus Avium) fruits of "Duroni Nero" variety and on the recovery of bioactive compounds from cherry by-products (pressed cakes) were investigated and compared to both untreated and freeze-thawed samples. The cellular disintegration index (Zp) of fruit tissue increased progressively with PEF treatment at field strengths of 0.5, 1 and 3 kV/cm and at a fixed total specific energy input of 10 kJ/kg, up to a maximum value of 0.76. PEF (0.5, 1, and 3 kV/cm at 10 kJ/kg) assisted mechanical pressing (1.64 bar for 5 mM) led to significant increase in juice yield (1-40%) with respect to the control, showing similar results than freeze-thawed sample. The juice obtained from PEF pre-treated cherries (E = 1 kV/cm) contained significantly higher amounts of anthocyanins (+85%) and antioxidant power (+28%) with respect to untreated samples, while freeze thawed samples showed the highest value only for the anthocyanins. Further increases of the electric field strength (E = 3 kV/cm) did not lead to additional advantages in quali-quantitative characteristics of the juice. Extracts from electroporated pressed cakes led to the highest increase in anthocyanins (+40%) and antioxidant power ( 40%) for the lowest electric field strength investigated (E = 0,5 kV/cm). The extractability of bioactive compounds from cherries press cake was not significantly increased by further increasing the field strength applied (1 - 3 kV/cm). The results obtained from this study demonstrate the possibility to implement a PEF system into a cherry juice production line to increase yield and quality of juice as well as to valorize the cherry by-product.