Heterogeneity of proteolytic enzyme activities in milk samples of different somatic cell count

Milk contains the alkaline proteinase plasmin and lysosomal proteinases; the significance of the latter is ill-defined. The objective of this study was to investigate composition and activities of several different proteolytic enzymes in milk samples of varying somatic cell count (SCC). Increasing m...

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Bibliographic Details
Published in:Journal of dairy research 2003-02, Vol.70 (1), p.45-50
Main Authors: Somers, Joanne M, O'Brien, Bernadette, Meaney, William J, Kelly, Alan L
Format: Article
Language:English
Subjects:
Animal productions
Animals
Biological and medical sciences
cathepsin
Cathepsin D - metabolism
Cattle
Cell Count
Cysteine Endopeptidases - metabolism
Electrophoresis, Polyacrylamide Gel
Endopeptidases - metabolism
Female
Fibrinolysin - metabolism
Food industries
Food Preservation
Fundamental and applied biological sciences. Psychology
Hydrogen-Ion Concentration
milk
Milk - chemistry
Milk - cytology
Milk - enzymology
Milk and cheese industries. Ice creams
Milk Proteins - analysis
Plasmin
proteolysis
Regression Analysis
somatic cell count
Terrestrial animal productions
Vertebrates
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Summary:Milk contains the alkaline proteinase plasmin and lysosomal proteinases; the significance of the latter is ill-defined. The objective of this study was to investigate composition and activities of several different proteolytic enzymes in milk samples of varying somatic cell count (SCC). Increasing milk SCC was correlated with increased plasmin, cathepsin D and cysteine protease activities, with concomitant increases in proteolysis in milk. Addition of plasmin inhibitors confirmed the heterogeneity of proteinase activities in milk, as urea-PAGE analysis of milk samples showed casein hydrolysis in milk after 7 d storage even in samples with inhibitors added; extent and heterogeneity of proteolysis was correlated with milk SCC. Rennet coagulation properties were not significantly correlated with SCC, or activities of measured enzymes. Milk of increasing SCC also exhibited decreased physical stability during incubation of milk at 37 °C. Pasteurized milk was more stable than raw milk, suggesting that the enzyme(s) or mechanisms leading to such instability are impaired by pasteurization. Overall, milk has a very heterogeneous proteolytic enzyme population, with a higher significance of non-plasmin enzymes, such as cathepsin D and cysteine proteinases, than perhaps previously recognised.
ISSN:0022-0299
1469-7629
DOI:10.1017/S0022029902005988