Apple juice pasteurization using ultrafiltration and pulsed electric fields

Apple juice was treated by means of non-thermal processing methods as a way of verifying whether a microbial stable and quality-acceptable product could be obtained. Ultrafiltration and high electric voltage pulsed electric fields were the techniques used. For ultrafiltration, the factors under study were membrane pore (10,000 and 50,000 daltons), trans-membrane pressure (103, 120.5, 138 and 155 kPa) and recovery percentage (0, 25, 50 and 75% for the 10,000 daltons membrane, as well as 0, 10, 20, 30, 40, 50 and 60% for the 50,000 daltons membrane). In terms of the pulsed electric fields experiments, electric field strength (50, 58 and 66 kV cm(-1)) and number of pulses (2, 4, 8 and 16) were the factors investigated. The responses to these factors were evaluated for microbial determinations, namely: aerobic plate count, yeasts and moulds, aciduric bacteria, and quality attributes such as pH,acidity, soluble solids and colour. Appropriate statistical comparisons were made between types of membrane and techniques. Multiple linear regression models were fitted by means of a stepwise technique. Both membrane treatments and pulsed electric fields technique showed that microbial inactivation is possible and efficient. Except for colour, quality attributes were kept unaltered. Significant relative colour changes were observed for both techniques such as browning for the ultrafiltered juice and fading for pulsed electric field treatment.