Journal Article


Alan L. Kelly
William J Meaney
Bernadette O'Brien
Joanne M Somers



chemistry milk proteins female cell count cattle enzymology electrophoresis polyacrylamide gel cysteine endopeptidases animals metabolism cathepsin d cytology regression analysis endopeptidases hydrogen ion concentration fibrinolysin milk food preservation

Heterogeneity of proteolytic enzyme activities in milk samples of different somatic cell count. (2003)

Abstract 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 degrees 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.
Collections Ireland -> University College Cork -> PubMed

Full list of authors on original publication

Alan L. Kelly, William J Meaney, Bernadette O'Brien, Joanne M Somers

Experts in our system

Alan L. Kelly
Total Publications: 63
Bernadette O'Brien
Total Publications: 48