Self-association of casein studied using enzymatic cross-linking at different temperatures

Size Modulation of Enzymatically Cross-Linked Sodium Caseinate Nanoparticles via Ionic Strength Variation Affects the Properties of Acid-Induced Gels

“…Figure 3 depicts the maximum storage modulus (G' max ) and the corresponding tan δ of acid-induced gels from the different casein systems as a function of mTGase incubation time. In line with previous results [29,31,39], G' max of NaCn gels without added salts increased continuously with increasing incubation time. The presence of 0.1 M NaCl or 0.005 M CaCl 2 barely affected pH development during acidification with GDL, although slight differences could be noticed at the beginning of the acidification (see inserts to Figure 3).…”

“…The different casein types co-eluted in this peak following the order β-casein < αS-caseins < κcasein [36]. Therefore, the shift of the monomer peak to higher VE with ongoing incubation indicates increasing cross-linking velocities of the different casein types in the order βcasein > αS-caseins > κ-casein, which is in agreement with previous observations using gel electrophoresis [29,35,37]. During incubation with mTGase, monomeric caseins were covalently cross-linked and could not be dissociated by denaturing agents anymore.…”

“…A variation of the incubation temperature (10-40 • C), however, did not affect particle size and gelation properties of NaCn [29], and a change in incubation pH (5.9-7.3) affected the proteolytic activity of indigenous plasmin [30]. On the other hand, an increase in the ionic strength or the presence of bivalent Ca 2+ ions resulted in larger cross-linked casein particles, as was shown by size exclusion chromatography (SEC) [31].…”

“…Based on multi-angle light scattering results, these research groups concluded that the last eluting fraction corresponded to small casein aggregates as well as some monomeric caseins at the end of the peak. Due to the low light scattering intensity provided by casein monomers, their molar mass is easily overestimated, especially at low concentrations [29]. The similar V E in denaturing and non-denaturing SEC therefore suggests that this fraction might rather be composed of mainly monomeric casein.…”

“…Incubation was carried out at 40 • C for 1-48 h or at 30 • C for 3 h-14 days (see Table 1). In the latter case, mTGase concentration was adjusted to compensate for the different enzyme activity at 30 • C (41.1 U/g [29]). After specific incubation times, the samples were heated for 15 min at 85 • C min for enzyme inactivation and subsequently cooled in ice water.…”