GMC-fuzzy control of pH during enzymatic hydrolysis of cheese whey proteins

Abstract

The pH control of the enzymatic hydrolysis of cheese whey in a continuous-flow, perfectly mixed tank reactor, carried out by alcalase immobilized on agarose gel, was studied here. The partial, tailor-made hydrolysis of whey proteins is a good alternative for adding commercial value to this effluent of the dairy industry. Whey hydrolysis may either change or evidence functional properties of the resulting peptides, increasing their applications. A relevant point in this process is the pH control of the enzymatic reactor. Proteolytic reactions change the pH of the medium, affecting the activity of the enzyme(s). An attractive alternative to the conventional automatic control methods, usually PI or on-off schemes, is the Generic Model Control (GMC) algorithm. However, the control performance of model-based algorithms is known to be vulnerable to biases, inconsistencies, or lack of fitness of the model. This feature is especially evident in systems with non-linear dynamics like pH titration. To circumvent this problem, a hybrid GMC-fuzzy algorithm is proposed. Tuning of the GMC parameters was accomplished successfully according to Ziegler and Nichols’ method. A fuzzy algorithm was coupled to the GMC architecture, taking into account process/model mismatches. Simulations and experimental assays showed that the hybrid system presented a good performance in both regulatory and servo problems.