ELISA to detect proteolysis of ultrahigh-temperature milk upon storage.
Casein proteolysis can occur in milk during storage leading to its gelation. The two main proteolytic systems suspected to be involved are the plasmin and the proteases produced by psychrotrophic bacteria. The latter have been shown to cleave kappa-casein at the Phe105-Met106 bond. Although several techniques allow the determination of plasmin in milk, few rapid and easy-to-perform analytical techniques are available to check for bacterial proteolytic activity. This study presents the development of an inhibition ELISA allowing for the quantification of the kappa-casein intact at the Phe105-Met106 bond. It uses a monoclonal antibody specifically directed against this peptide bond that binds to the protein as long as the molecule's cleavage site is intact but not when it is cleaved. This simple technique allows for the rapid analysis of more than 20 samples within 3 h. Applied to commercial milks, this assay allowed for the detection of unstable milk.
Dupont
Didier
D
L'Institut National de la Recherche Agronomique (INRA), Unité de Recherches en Technologie et Analyses Laitières, Place du Champ de Foire, F-39800 Poligny, France. dupont@poligny.inra.fr
Lugand
Damien
D
Rolet-Repecaud
Odile
O
Degelaen
Jacques
J
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D002364:Caseins / Q000032:analysis* / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005341:Fibrinolysin / Q000378:metabolism; D005519:Food Preservation; D006358:Hot Temperature; D008892:Milk / Q000737:chemistry* / Q000382:microbiology*; D010447:Peptide Hydrolases / Q000378:metabolism*; D011551:Pseudomonas fluorescens / Q000201:enzymology
D000911:Antibodies, Monoclonal; D002364:Caseins; D010447:Peptide Hydrolases; D005341:Fibrinolysin