Further studies on acid phosphatase of leucocyte origin in normal and mastitic bovine milks

Abstract

The acid phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.2) of bovine milk occurs as a single isozyme in healthy animals and is the isozyme responsible for most of the significant acid phosphatase activity in cheese. The occurrence of mastitic infections [by Streptococcus agalactiae, S. dysgalactiae, S. uberis or Staphylococcus aureus] or the infusion of bacterial [Escherichia coli] endotoxin into the udder are accompanied by the invasion of polymorphonuclear leukocytes and blood plasma constituents into the milk. Total acid phosphatase activity in the milk is greatly elevated due to the influx of 2 isozymes of leukocyte origin. The possible presence in milk of hydrolytic lysosomal enzymes, i.e., acid phosphatase derived from leukocytes, raises the question of the importance of these enzymes to the stability of milk and milk products during processing and subsequent storage. The national [England] average of somatic cell counts in bulk herd milks is > 0.5 .times. 106/ml, with counts > 1.0 .times. 106/ml being not uncommon. The present paper extends the investigations of leukocyte acid phosphatases and attempts to correlate this activity with cell count and to assess the relative importance of these isozymes in a number of commerical milk samples.