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Reduction of Protease Activity in Milk by Continuous Flow High-Intensity Pulsed Electric Field Treatments

S. Bendicho^*, G. V. Barbosa-Cánovas and O. Martín^*

^* CeRTA-UTPV, Departament de Tecnologia d’Aliments, Universitat de Lleida, Av. Rovira Roure 191, 25198 Lleida, Spain
Department of Biological Systems Engineering, Center for Nonthermal Processing of Foods, Washington State University, Pullman 99164-6120

Corresponding author:
Olga Martín; e-mail:
omartin{at}tecal.udl.es.

High-intensity pulsed electric field (HIPEF) is a nonthermal food processing technology that is currently being investigated to inactivate microorganisms and certain enzymes, involving a limited increase of food temperature. Promising results have been obtained on the inactivation of microbial enzymes in milk when suspended in simulated milk ultrafiltrate.

The aim of this study was to evaluate the effectiveness of continuous HIPEF equipment on inactivating a protease from Bacillus subtilis inoculated in milk. Samples were subjected to HIPEF treatments of up to 866 µs of squared wave pulses at field strengths from 19.7 to 35.5 kV/cm, using a treatment chamber that consisted of eight colinear chambers connected in series. Moreover, the effects of different parameters such as pulse width (4 and 7 µs), pulse repetition rates (67, 89, and 111 Hz), and milk composition (skim and whole milk) were tested.

Protease activity decreased with increased treatment time or field strength and pulse repetition rate. Regarding pulse width, no differences were observed between 4 and 7 µs pulses when total treatment time was considered. On the other hand, it was observed that milk composition affected the results since higher inactivation levels were reached in skim than in whole milk. The maximum inactivation (81%) was attained in skim milk after an 866-µs treatment at 35.5 kV/cm and 111 Hz.

Key Words: high-intensity pulsed electric field • protease • enzyme • milk

Abbreviation key: HIPEF = high intensity pulsed electric fields, SM = skim milk, SMUF = simulated milk ultrafiltrate, WM = whole milk

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