Qualitative and quantitative determination of proteolysis in mastitic milks

Abstract

SUMMARYProteolytic activity in mastitic skim-milk was often 5–10 fold higher than in normal milk, its level being related to somatic cell count but not precisely correlated with it. In milks with the highest levels of activity plasmin accounted for about one third of the total proteinase. A further third was sedimented with the micellar fraction together with the plasmin, but unlike plasmin, was not inhibited by addition of soyabean trypsin inhibitor (SBTI). The final third remained in the serum phase.Polyacrylamide gel electrophoresis (PAGE) showed that αsl- and β-caseins were degraded at about the same overall rate. The plasmin produced the usual readily identified fragments from β-casein, but incubation of mastitic milk also produced changes in patterns in the γ-casein region differing from plasmin-induced changes which were also apparent when the micellar fraction was incubated. As they were inhibited by SBTI, a second trypsin-like enzyme in addition to plasmin may also have been present. Other proteinase(s) not inhibited by SBTI was also associated with casein micelles and produced at least 3 characteristic protein fragments seen on PAGE. The serum phase proteinase(s) was likewise not inhibited by SBTI, and did not produce any well-defined electrophoretic bands, suggesting a rather non-specific breakdown of caseins. After separation of mastitic whole milk, a considerable proportion of the proteolytic activity was found in the cream phase. The proportion was enhanced by freezing and thawing, and the enzyme appeared to be identical to the SBTI-resistant micellar proteinase.Because of the considerable proteolysis likely to occur under the time and temperature conditions involved, our results may provide some explanation for the problems encountered in cheesemaking with mastitic milks (e.g. yield losses, poor curd strength and off-flavour development).

Effect of Recombinant Bovine Somatotropin on Milk Production and Composition of Cows with Streptococcus uberis Mastitis

“…The reduction in milk proteins might be due to a decreased absorption of amino acids in the gut and to a redirection of the use of amino acids toward immunoglobulins. Because of the increased proteolytic activity of the milk during mastitis (1,7,20,37), which is mainly due to increased plasmin activity, caseins are hydrolyzed. These changes in milk composition indicate serious damage to the blood-milk barrier with disruption of the tight junctions between mammary epithelial cells and paracellular leakage (43).…”

<i>Staphylococcus aureus</i> related mammary infection in cows: Correlation between somatic cell count and proteolysis during early and chronic phase of infection

“…Nevertheless, if the plasmin activity could reliably explain in part the variation of proteolysis, a significant measure of the proteolysis is attributed to the variation of SCC. This hypothesis was proposed more than 2 decades ago by De Rham and Andrews (1982) and confirmed recently by Moussaoui et al (2004).…”

Atividade de plasmina e plasminogênio no leite longa vida com alta e baixa contagem de células somáticas durante o armazenamento

“…No leite com baixa CCS, pode-se observar uma taxa normal de ativação do plasminogênio para plasmina. No entanto, uma taxa acentuadamente maior ocorre em leites com alta CCS (DE RHAM & ANDREWS, 1982). KENNEDY & KELLY (1997) demonstraram que a atividade da plasmina no leite cru com 800.000 células mL -1 foi aproximadamente duas vezes maior que no leite com CCS menor que 150.000 células mL -1 .…”