Influence of Maillard reaction extent on acid induced gels of whey proteins and dextrans

Maillard reaction is a natural occurring reaction that takes place when proteins and saccharides are present. In this study, we have investigated the effect of Maillard reaction on some physicochemical properties of conjugates of whey proteins isolate (WPI) and dextrans (DX) of different molecular weight and their effects on the mechanical and microstructural properties of acid induced gels. The results indicated that the extent of Maillard reaction depended on DX concentration and DX molecular weight (MW). The higher the DX concentration and the lower the DX MW, the higher the extent of Maillard reaction. Conjugates with DX 6 kDa exhibited a decreased from 4.8 up to 4.4 in the isoelectric point, and a decreased in free sulfhydryl groups from 24.37 to 14.81 μmol SH/gprotein. In order to carried out the acid induced gel formation, all the systems were heated at 9% w/w (68.5 °C for 2 h) to form aggregates, which were confirmed by the increase in intrinsic viscosity values in all the systems. The acid gel formation was carried out by using glucono delta-lactone (GDL), which decreased the pH until the isoelectric point of the systems. WPI/DX conjugates of DX 40 kDa formed acid gels in most all DX concentrations, but the conjugation decreased the gel strength and the Young's modulus as compared with WPI gels. Gelation could not be carried out in systems with DX 6 kDa, indicating that Maillard reaction could change or even inhibit the acid gel formation, depending of its extent. After heating, all the systems increased the surface hydrophobicity (H0) as expected, except for WPI/DX6, which showed similar H0 values before and after heating, indicating that this might be the main reason for the inhibition of gel formation.