Effect of ultra high pressure homogenization on alkaline phosphatase and lactoperoxidase activity in raw skim milk

摘要

High pressure homogenization (HPH) is an alternative food processing technique. As product heating is minimum, its characteristics are not affected in a large extend. At this work, the residual activity of milk native enzymes (alkaline phosphatese and lactoperoxidase) was measure in skin milk treated by HPH. Results showed that pressures up to 250 MPa promoted decrease on activity about 10-20% and pressures above 270 MPa resulted in total inactivation of the enzyme, probably indicating a process condition (pressure and temperature of homogenization) able to promote irreversible denaturation on the molecular structure of the protein. The results obtained for lactoperoxidase indicated that this enzyme is resistant to HPH as to heat treatment. At pressures between 100 and 250MPa it was observed an increase on enzymatic activity (around 20%) and just at 300MPa a reduction of around 30%, was detected. The increase of lactoperoxidase activity may be attributed to active sites exposure due to changes on tridimensional structure of the enzyme. The results indicate that residual activity of both enzymes can be used as indicative of pressure level applied in the milk during HPH process, considering the need of pressures above to 250 MPa to reaches enough microbial inactivation.