Influence of ageing time on sodium caseinate gelation induced by glucono-δ-lactone at different temperatures

The aim of this work was to study the influence of a wide range of incubation temperatures (4 to 40 degrees C) and sodium caseinate concentrations (2 to 6% (w/w)) on acid-gel properties during and after long ageing times, formed under different acidification rates promoted by gradual hydrolysis of glucono-delta-lactone (GDL) into gluconic acid. The kinetics of acidification and gelation were followed from pH 6.7 to a final pH value around 4.6 by evaluation of the pH and mechanical properties using uniaxial compression measurements (stress and strain at rupture). As a general trend, faster acidification rates led to faster gel network formation, and lower incubation temperatures led to a higher final pH, while increasing caseinate concentration promoted a small increase in the pH value. Stress at rupture of gels induced by fast acidification rates did not exhibit a weaker gel network, showing the contribution of rearrangements of the network gel at final pH to the electrostatic balance, besides the fact that the hydrophobic interactions and hydrogen bonds were important forces involved in microstructure stabilization. Rearrangement of the gel network was mainly observed at pH values close to 4.6 and was more pronounced at longer ageing times of incubation. The stronger gels were obtained at incubation temperatures of 10 degrees C followed by 25, 4 and 40 degrees C, which was an indication of the behavior of the gel network microstructure, since at the highest temperature the pores were larger and syneresis more pronounced. The results of this study suggest that the incubation temperature, protein concentration and rearrangement at final pH have a great influence on the balance between the attractive and repulsive forces between protein and water, contributing to development of optimized texture and water-holding capacity of acid-gels of sodium caseinate.