Identification of the initial reactive sites of micellar and non-micellar casein exposed to microbial transglutaminase

Abstract To investigate the influence of internal micellar structure on course enzymatic cross-linking especially in initial phase reaction, casein micelles isolated from raw milk via ultracentrifugation were incubated with microbial transglutaminase (mTG) comparison non-micellar sodium caseinate. Reactive lysine and glutamine residues identified using a label-free approach, based identification isopeptides within tryptic hydrolysates by targeted HRMS as well manual monitoring fragmentation spectra. Identified reactive sites furthermore weighted tracking formation over an incubation time 15, 30, 45 60 min, respectively. Fifteen formed early stage mTG caseins further specified concerning position involved reaction. The results revealed K176 Q175 β-casein most residues, which might be located highly flexible region molecule different possible reaction partners this study. Except for isopeptide α s1 K34–α s2 Q101 caseinate (SC), all detected casein, indicating that is not affected aggregation caseins. Graphical abstract