Gelation on slow acidification by hydrolysis of D-glucono--lactone (GDL) has been studied for guluronate-rich sodium alginate from Laminaria hyperborea.
Network formation by alginate–GDL mixtures during holding at 25°C was monitored by low-amplitude oscillatory measurements of storage modulus (G') and loss modulus (G") at 1 rad s^-1 and 0.5 % strain.  For samples in which the final pH was held constant (at 3.0) and alginate concentration (c) was varied, the slope of log G' versus log c decreased progressively with increasing concentration towards a limiting value of 2 (c²-dependence), as seen
for other gelling biopolymers. A numerical analysis is reported which demonstrates that the concentration of GDL required to achieve a constant value of final pH increases in direct proportion to the concentration of alginate used. Thermal annealing (heating to 85°C and cooling back to 25°C ) of samples acidified to pH 3.0 caused a large (~10-fold) increase in G' at low concentration (0.5 wt % alginate), attributed to a co-operative disorder–order transition during cooling by chain segments freed by disaggregation during heating. Increase in modulus on cooling became progressively smaller as the concentration of alginate was increased to 1.0 wt %, and at 1.5 wt % was replaced by a sharp decrease, attributed to excessive aggregation (incipient precipitation) of the acidified polymer.