title: Plasmin digestion of photooxidized milk proteins.
abstract: Plasmin-mediated hydrolysis of 6 different milk protein preparations [alpha(S)-casein (alpha(S1) + alpha(S2)), beta-casein, kappa-casein, alpha-lactalbumin, beta-lactoglobulin, and lactoferrin] was found to be very dependent on photooxidation of the said proteins. Changes in plasmin proteolysis were investigated in a peptide-mapping study applying liquid chromatography-mass spectrometry. The changes were seen in the formation of peptides formed by plasmin-mediated hydrolysis after photooxidation, which was initiated with the naturally occurring photosensitizer riboflavin in all the milk protein preparations studied. The changes in the plasmin-mediated hydrolysis of photooxidized proteins are discussed in relation to changes introduced in the protein structure upon photooxidation. Plasmin-mediated hydrolysis of alpha(S)-casein, consisting of a mixture of alpha(S1)- and alpha(S2)-casein and a preparation of beta-casein, was most highly affected by photooxidation, which is in agreement with the fact that those 2 proteins have been found to be most labile toward photooxidation. Changes in the formation of potential angiotensin-I-converting enzyme-inhibitory peptides as well as peptides proposed to have antibactericidal activities by plasmin were observed by oxidation of milk proteins before plasmin-mediated hydrolysis.
authors.affiliation: Department of Food Science, University of Aarhus, Faculty of Agricultural Sciences, PO Box 50, DK-8830 Tjele, Denmark.
authors.forename: T K
authors.initials: TK
authors.lastname: Dalsgaard
authors.forename: C W
authors.initials: CW
authors.lastname: Heegaard
authors.forename: L B
authors.initials: LB
authors.lastname: Larsen
mesh_terms: D000327:Adsorption; D002364:Caseins / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004063:Digestion; D005341:Fibrinolysin / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007781:Lactoferrin / Q000737:chemistry; D007782:Lactoglobulins / Q000737:chemistry; D008027:Light; D008894:Milk Proteins / Q000737:chemistry*; D010084:Oxidation-Reduction; D010777:Photochemistry
chemical_list: D002364:Caseins; D007782:Lactoglobulins; D008894:Milk Proteins; D007781:Lactoferrin; D005341:Fibrinolysin