Unaided efficient transglutaminase cross-linking of whey proteins strongly impacts the formation and structure of protein alginate particles

Mikkel Madsen; Sanaullah Khan; Sonja Kunstmann; Finn L Aachmann; Richard Ipsen; Peter Westh; Cecilia Emanuelsson; Birte Svensson

doi:10.1016/j.fochms.2022.100137

Unaided efficient transglutaminase cross-linking of whey proteins strongly impacts the formation and structure of protein alginate particles

Food Chem (Oxf). 2022 Sep 19:5:100137. doi: 10.1016/j.fochms.2022.100137. eCollection 2022 Dec 30.

Authors

Mikkel Madsen¹, Sanaullah Khan¹, Sonja Kunstmann¹, Finn L Aachmann², Richard Ipsen³, Peter Westh¹, Cecilia Emanuelsson⁴, Birte Svensson¹

Affiliations

¹ Department of Biotechnology and Biomedicine, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
² Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
³ Department of Food Science, University of Copenhagen, DK-1958 Frederiksberg, Denmark.
⁴ Department of Biochemistry, Lund University, 223 62 Lund, Sweden.

Abstract

There is a dogma within whey protein modification, which dictates the necessity of pretreatment to enzymatic cross-linking of β-lactoglobulin (β-Lg). Here microbial transglutaminase (MTG) cross-linked whey proteins and β-Lg effectively in 50 mM NaHCO₃, pH 8.5, without pretreatment. Cross-linked β-Lg spanned 18 to >240 kDa, where 6 of 9 glutamines reacted with 8 of 15 lysines. The initial isopeptide bond formation caused loss of β-Lg native structure with t_1/2 = 3 h, while the polymerization occurred with t_1/2 = 10 h. Further, cross-linking effects on protein carbohydrate interaction have been overlooked, leaving a gap in understanding of these complex food matrices. Complexation with alginate showed that β-Lg cross-linking decreased onset of particle formation, hydrodynamic diameter, stoichiometry (β-Lg/alginate) and dissociation constant. The complexation was favored at higher temperatures (40 °C), suggesting that hydrophobic interactions were important. Thus, β-Lg was cross-linked without pretreatment and the resulting polymers gave rise to altered complexation with alginate.

Keywords: Dynamic light scattering; Far- and near-UV CD; Intrinsic and ANS fluorescence spectra; LC-MS/MS cross-link identification; Molecular dynamics inter-residue distance analysis; Size exclusion chromatography.