Ultraviolet irradiation and pulsed electric fields (PEF) in a hurdle strategy for the preservation of fresh apple juice

The influence of ultraviolet irradiation (UV) and pulsed electric fields (PEF) on microbial inactivation, selected quality attributes (colour, pH, Brix, non-enzymatic browning index (NEBI) and antioxidant capacity) and enzymatic activity (polyphenol oxidase (PPO) and peroxidase (POD)) of fresh apple juice was investigated. The two technologies were applied as stand-alone treatments (T-UV or T-PEF) or in combination (TUV+PEF or TPEF+UV). T-UV was a batch process while T-PEF was continuous and consisted of 100 square-wave pulses (1 mu s, 15 Hz) at 40 kV/cm. Apple juice samples processed by a heat exchanger at 72 degrees C (T-H72) or 94 degrees C (T-H94) for 26 s were used as controls. T-UV and T-PEF resulted in a 2.2 and 5.4 log reduction respectively, while the respective reductions for T-H72 and T-H94 were 6.0 and 6.7 log cycles. TPEF+UV and TUV+PEF achieved similar reduction to T-H94 (6.2 and 7.1 log cycles, respectively) on an incubated sample (48 h at 37 degrees C), with TUV+PEF producing a greater microbial reduction than TPEF. Juice colour and level of phenolic compounds were less affected by the alternative treatments than by heat pasteurisation. Reduction of PPO and POD activity was greater (P < 0.001) in T-PEF, TUV+PEF or TPEF+UV than in T-H72. This experiment showed the potential of a combination of UV irradiation and PEF to obtain satisfactory total microbial inactivation and improved product quality compared to heat pasteurisation. (C) 2007 Elsevier Ltd. All rights reserved.