The effect of exponential decay pulsed electric fields on peach (var. Miraflores) polyphenoloxidase (PPO) was evaluated. Electric field intensities ranged from 2.18 to 24.30 kV/cm. Pulses of 0.02 and 0.08 ms width were applied in mono-and bipolar mode. A 70% maximum reduction in enzymatic activity was achieved after 5 ms using 0.02 ms width pulses in bipolar mode at 24.30 kV/cm. Peach PPO activity decreased following an exponential decay kinetic model. Rate constants ranged from 9.0 to 138 ms -1 in monopolar mode, and from 8.7 to 235 ms -1 in bipolar mode. An exponential decay model may describe the relationship between residual PPO and input electric energy.
Milk and dairy products may contain microorganisms capable of secreting lipases that cause sensory defects and technological problems in the dairy industry. In this study, the effects of thermal and high-intensity pulsed electric field (HIPEF) treatments on an extracellular lipase from Pseudomonas fluorescens, suspended in a simulated skim milk ultrafiltrate (SMUF) have been evaluated. Heat treatments applied were up to 30 min from 50 to 90 degrees C. HIPEF treatments were carried out using pilot plant facilities in a batch or continuous flow mode, where treatment chambers consisted of parallel and coaxial configuration, respectively. Samples were subjected to up to 80 pulses at electric field intensities ranging from 16.4 to 37.3 kV/cm. This resulted in a lipase that was quite resistant to heat and also to HIPEF. High (75 degrees C-15 s) and low pasteurization treatments (63 degrees C-30 min) led to inactivations of 5 and 20%, respectively. Using the batch-mode HIPEF equipment, a 62.1% maximum activity depletion was achieved after 80 pulses at 27.4 kV/cm. However, when HIPEF treatments were applied in the continuous flow mode, an inactivation rate of just 13% was achieved, after applying 80 pulses at 37.3 kV/cm and 3.5 Hz. The results of both heat and HIPEF treatments on enzyme inactivation were adjusted with good agreement to a first-order kinetic model (R2 > 62.3%).
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