Effect of gel structure on the dissolution of heat-induced β-lactoglobulin gels in alkali

The dissolution of heat-induced β-lactoglobulin (βLg) gels in alkaline solution plays an important role in the cleaning-in-place of fouled dairy and other food plants. The dissolution behavior is strongly influenced by the conditions under which the gel is formed. At low alkaline pH values (<13), the dissolution rate constant k_g′ decreases with longer gelation time and higher temperature. An inverse relationship is observed between the k_g′ value and the amount of covalently cross-linked proteins in the gel, which is mainly due to disulfide bonds. β-Elimination kinetics of intramolecular cystines in βLg have been used to estimate the amount of intermolecular disulfide bonds that are cleaved during dissolution. The results call into question current dissolution models for these systems based on external mass transfer through the fluid next to the swollen gel. At low temperatures, the amount of disulfide cleavage is estimated to be small, indicating that dissolution is likely to involve the (slow) disengagement of large protein clusters, analogous to the dissolution of synthetic polymers.