title: Plasmin activity in UHT milk: relationship between proteolysis, age gelation, and bitterness.
abstract: Plasmin, the major indigenous protease in milk, is linked to quality defects in dairy products. The specificity of plasmin on caseins has previously been studied using purified caseins and in the indigenous peptide profile of milk. We investigated the specificity and proteolytic pathway of plasmin in directly heated UHT milk (>150 °C for <0.2 s) during 14 weeks of storage at 20 °C in relation to age gelation and bitter peptides. Sixty-six peptides from αS- and β-caseins could be attributed to plasmin activity during the storage period, of which 23 were potentially bitter. Plasmin exhibited the highest affinity for the hydrophilic regions in the caseins that most probably were exposed to the serum phase and the least affinity for hydrophobic or phosphorylated regions. The proteolytic pattern observed suggests that plasmin destabilizes the casein micelle by hydrolyzing casein-casein and casein-calcium phosphate interaction sites, which may subsequently cause age gelation in UHT milk.
authors: Arla Foods Strategic Innovation Centre , Rørdrumvej 2, DK-8220 Brabrand, Denmark.
authors: Valentin M
authors: VM
authors: Rauh
authors: Lene B
authors: LB
authors: Johansen
authors: Richard
authors: R
authors: Ipsen
authors: Marie
authors: M
authors: Paulsson
authors: Lotte B
authors: LB
authors: Larsen
authors: Marianne
authors: M
authors: Hammershøj
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D005341:Fibrinolysin / Q000378:metabolism*; D005519:Food Preservation; D005782:Gels / Q000378:metabolism*; D006358:Hot Temperature; D008823:Micelles; D008892:Milk / Q000737:chemistry / Q000201:enzymology*; D008969:Molecular Sequence Data; D010455:Peptides / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D059748:Proteolysis; D013379:Substrate Specificity; D013649:Taste
chemical_list: D002364:Caseins; D005782:Gels; D008823:Micelles; D010455:Peptides; D005341:Fibrinolysin