Modelling of methylcellulose thermogelation as a function of polymer concentration, pH and ionic strength

Food industries are continuously searching for new non-conventional products interesting for people having specific dietary preferences or restrictions. Generally, structure and texture are crucial aspects in developing these products, because the performances of traditional foods are hard to be achieved when some basic ingredients are substituted. To make up for the lack of conventional structuring ingredients (e.g. gluten proteins, sucrose, fats), hydrocolloids, such as methylcellulose, are usually added to control or minimize possible defects. Despite the large number of factors that can influence hydrocolloid properties, only a limited basic research has been performed on this topic. Thus, the aim of this work was to methodically study the thermogelation process of methylcellulose in aqueous systems, as a function of three experimental factors: polymer concentration (1-3%), pH (4-10) and ionic strength (50-150 mM) of the dispersing medium. To simultaneously evaluate the effects of the different factors and of their interactions, a Box Behnken Design of Experiment was applied. The thermogelation process was evaluated by means of fundamental (strain sweep, frequency sweep, and temperature sweep) and empirical (penetration tests) rheological methods. Significant response surface models able to describe the methylcellulose structuring properties as a function of the three considered experimental factors were calculated. In particular, pH and ionic strength seemed to mainly influence the fundamental rheological behaviour of the methylcellulose systems, whereas variables evaluated at higher strains were especially affected by the polymer concentration. The obtained models describing methylcellulose thermogelation represent a first step for a deeper knowledge of molecular interactions in food systems and they could be exploited in the development of new foods, making easier the modulation of the structural and textural features of products as a function of recipes, technological processes, and consumer requirements.