91E-19 |
Reduction of protease activity in simulated milk ultrafiltrate by high intensity pulsed electric fields |
S. BENDICHO1, G. V. Barbosa-Cánovas2, and O. Martín1. (1) Department of Food Technology, University of Lleida, Av. Rovira Roure 191, Lleida, 25198, Spain, (2) Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120 Bacillus subtilis is a gram-positive psichrotrophic bacteria that may be present in raw milk. This bacteria produces a protease that resists current thermal treatments and causes the development of a bitter flavour or even the coagulation of milk and dairy products. The aim of this work was to determine the effect of high intensity pulsed electric fields (HIPEF) on the activity of a protease from Bacillus subtilis suspended in simulated milk ultrafiltrate (SMUF) at different electrical conditions using a bench scale continuous flow mode equipment (model OSU-4F, Ohio State University) whose treatment chamber device consisted on 8 colinear chambers disposed in series. Samples of SMUF containing the enzyme were treated at field strengths from 19.7 to 35.5 kV/cm up to 896 µs using squared wave pulses of 4 or 7 µs. Frequencies from 66.66 to 111.11 Hz were tested. Protease activity was measured spectrophotometrically using azocasein as substrate. The reduction of protease activity depended of the treatment time, field strength, pulse frequency and pulse width. It was observed that enzyme activity lowered as the field strength, treatment time and frequency increased. Maximum inactivation of 70.2% was achieved after a process of 896 µs (7 µs-pulse width) at 35.5 kV/cm and 111.11 Hz; whereas, with a similar treatment but at 66.66 Hz, just 48% inactivation was observed. In relation to pulse width, if total treatment time was considered, no significant changes in enzyme inactivation were observed, although the wider the pulse width the lower the number of pulses required to reach the same inactivation levels. The activity of this heat-resistant microbial protease can be considerably reduced by HIPEF treatment. Inactivation depends on several factors such as treatment time, field strength, frequency and pulse width. However, further studies about the effect of HIPEF on enzyme activity are needed to know the effects on the milk itself and to scale up the technology for being used in the food industry.
Session 91E, Nonthermal Processing: Nonthermal processing of foods
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