High intensity pulsed electric fields and heat treatments applied to a protease from Bacillus subtilis. A comparison study of multiple systems

The effects of several thermal treatments and high intensity pulsed electric fields (HIPEF) processing on a protease from Bacillus subtilis, suspended in simulated milk ultrafiltrate (SMUF) or milk, were evaluated. This protease did not show high resistance to conventional thermal treatments since, in milk, a high reduction of protease activity was achieved with both LTLT (low temperature long time; 63 °C-30 min) and HTST (high temperature short time, 75 °C-15 s) pasteurization treatments. The enzyme was more heat resistant suspended in SMUF than in milk. HIPEF affected the activity of the studied protease in different ways when treatments up to 500 kJ/l were applied using several types of equipment. Only when HIPEF treatment was applied with a continuous flow device and coaxial electrodes did the enzyme activity vary, changing from a slight inactivation when suspended in SMUF to some enhancement of activity when suspended in milk.