Mechanisms of structure formation underlying the creaming reaction in a processed cheese model system as revealed by light and transmission electron microscopy

摘要

The “creaming reaction,” a general thickening of themolten cheese mass during the manufacture of processedcheese, which is often seen to occur in a stepwisefashion, affects the viscosity and texture of the finishedproduct. Thus, this phenomenon is of critical importancefor the processed cheese industry, yet mechanismsunderlying the structure formation in this surprisinglycomplex and dynamic food system are only poorly understood.Using a model system consisting of micellarcasein concentrate, vegetable oil, water, and a mixtureof melting salts, we followed the characteristic viscosityprofile with its primary and secondary increase overtime. A rheometer equipped with a custom-made cupgeometry was used, which served as a mini-reactionvessel to simulate the conditions during the manufactureof processed cheese. The mixture was subjected toconstant heat (90°C) and stirring (7.93 rpm), comparableto processed cheese cooking, for up to 410 min.At specific time points, samples were taken, and themicro- and ultrastructure was investigated with lightand transmission electron microscopy. Results from ourextensive study uncovered the following key steps: (1)a decrease in fat globule size with concomitant increasein the number of fat globules, which were also moreevenly distributed; (2) a progressive separation of thecasein matrix into fibrillogenic and nonfibrillogenicfractions; (3) formation of fibrils and their higher-orderstructuring followed by their partial degradation; and(4) increasing interactions of the fibrils with the fatglobule surface leading to a higher degree of emulsification.Of these different observations, results indicatethat after the caseins dissociated under the influence ofthe melting salts, protein–protein interactions were theprimary driver of the structure formation and thus contributedto the initial viscosity increase. Fat globuleswere involved in the structure formation at later timepoints. Therefore, fat–protein interactions in additionto continued protein–protein interactions were assumedto contribute to the secondary viscosity increase. Anupdated processed cheese creaming model is presented.The use of the term “texturization” instead of “creaming”is proposed.