Continuous pulsed electric field treatment of French cider apple and juice expression on the pilot scale belt press

Abstract

Pulsed electric field (PEF) treatment (E = 1000 V/cm, f = 200 Hz and tp = 100 μs) was applied to French cider apple mash pumped into a collinear treatment chamber at the flow rate of 280 kg/h. Juices were recovered continuously using a single belt press. PEF treatment of the mash (32 ms and 46 kJ/kg) increased the juice yield by 4.1%. The content of total native polyphenols decreased by 17.8% in the treated juice due to oxidation by polyphenoloxidase. Meanwhile, the activity of this enzyme in PEF-treated juices was also decreased by 18.3%. It was suggested that PEF treatment enhanced the oxidation of native polyphenol compounds in cells because of electroporation of the inner cell membrane. The loss of PPO activity was related to the inhibition of the enzyme by the oxidised phenolic compounds. For this reason, one of the oxidation markers (molecular ion [M-H]− of chlorogenic acid dimer m/z = 705) was monitored in the juices and electric treatment was observed to increase the content of this compound by 6.8% in the treated samples. A significant difference in the colour (DE = 6) in the L*a*b* space was detected between the control and treated juices. The colour of the treated juice was the most appreciated attribute among the sensorial panel when compared to the control. The overall chemical composition of the treated juices was not different when compared with the respective controls. The mechanical expression of fruit juices assisted by pulsed electric fields (PEF) has received considerable attention over the past few years and will most likely be scaled up for industrial applications. Consequently for the legal approval of such a process the in-depth characterisation of the treated product is required. Through this study, a high potential of PEF treatment for the sensorial improvement of juices was found and limited differences in the nutritional quality characteristics between untreated and PEF-treated apple juices were observed. However, more work regarding the mechanisms of changes during PEF treatment is required on both the pilot and industrial scales.