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Combined effects of trisodium citrate (TSC), transglutaminase (Tgase) and heating were studied with relation to the mechanical properties of acid milk gels. Acidification of skimmed microfiltered milk samples was performed at 30 °C by addition of glucono – δ lactone to achieve final pH of 4.6 in 4 h. Increasing levels of TSC (0, 10 and 20 mM) were added to the samples, followed by addition of a constant level of Tgase (3 U/g of protein), and subsequent heating to 85 °C for 30 min. Prior to acidification, suspensions were analyzed in terms of amount of sedimentable material, hydration, hydrodynamic diameter (Dh) and ζ-potential (ζ) of the particles. Acid-induced gelation was studied using small deformation rheology followed by large deformation test. The water holding capacity of the gels (WHC) was performed at pH 4.6. Gels microstructure were investigated by confocal laser scanning microscopy at pH 4.6 and determination of mean pore size was performed by 2D-correlation analysis. Results showed that combined Tgase and TSC treatments had significant effect on rheological properties, WHC and gel microstructure. Higher stiffness of the gels was observed with Tgase and TSC at 10 mM, whereas a homogenous network distribution with smaller pore size was observed in the presence of Tgase and TSC at 20 mM.

The forces behind supramolecular structures (SS) formation need to be deeply understood, to allow identifying conditions under which their production can be optimized. In this study, a multi-spectroscopic approach was used to study SS formation upon ovalbumin (OVA) and chitosan (CHS) interaction in HCl solution, at pH 4.0 (both biomacromolecules positively charged) or 6.0 (biomacromolecules oppositely charged). UV-Vis and fluorescence spectroscopies showed that the biomacromolecules interacted and formed complexes without suggesting major modifications in the protein’s structure. The increase in CHS concentration progressively augmented the UV-vis absorption of OVA-CHS structures at 278 nm, whereas reduced the fluorescence emission of OVA, at both pH values, without promoting obvious shift of the maximum fluorescence wavelength, with an estimated center of spectral mass of = 341.41 ± 0.31 nm (at pH 4.0) and = 342.30 ± 0.40nm (at pH 6.0). Additionally, a conjoint analysis of CD and FT-IR spectroscopies revealed that the presence of CHS promoted alterations on the secondary structure of OVA. Indeed, CHS may have affected the hydrogen bonding network that stabilized the structure in the native protein, increasing the stability of α-helix and random coil structures, which was reflected in the loss of β-sheet. Results suggested that the OVA-CHS interaction, at pH 6.0, are driven mainly by electrostatic forces (attractive) and H-bonds. At pH 4.0, these macromolecules are more likely to interact through a balance of electrostatic forces (repulsive), hydrophobic interactions and H-bonds.