ENZYME ACTIVITY AND COLOUR CHANGES IN APPLE JUICE PASTEURISED THERMALLY AND BY PULSED ELECTRIC FIELDS

Pasteurisation of apple juice by a high temperature-short time treatment (HTST) at 90 degrees C for 30 s was compared with a high-voltage pulsed electric field treatment (PEF). The PEF treatment was carried out using a laboratory unit set with a bipolar pulse (4 mu s wide), an intensity of 35 kV cm(-1), and a frequency of 1200 pulses per second (pps). Enzyme inactivation and colour changes of the treated juices were compared, using a non-treated sample as control. Enzyme residual activities of pectinmethylesterase (PME) and polyphenoloxidase (PPO), as well as the chroma index for colour, showed statistical difference between treatments. No statistical significant difference was observed for the hue colour index. PEF could be considered a feasible alternative for producing pasteurised and stable apple juice.