Effects of Four Essential Oils on Wheat Dough Structural Transformations Assessed by Extended Mixolab Evaluation, Variance Components Analysis, and Adapted Principal Components Method

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The conventional interpretation of Mixolab curves describing wheat dough behavior under simultaneous mechanical and thermal stress was substantially extended by introducing a series of novel kinetic and geometrical descriptors. In addition to the standard Mixolab parameters, new indexes of Mechanical Weakening of Proteins (MWP), Thermo-Mechanical Weakening of Proteins (TMW), several traits aiming at stability of dough consistency (STAC1 rel, C12/STAC1), Structural Recovery Index (C5/C1), micro-scaled torque change rates (ΔmCij) and physical angular descriptors (slopes omega°, delta°) were developed to characterize individual phases of viscoelastic dough transformation to the solidified bread crumb-like material. The approach was applied to investigate the effects of four chemically distinct essential oils (EOs), namely cinnamon, oregano, lemongrass, and thyme ones, incorporated into wheat flour at five concentration levels (5–80 mg · 100 g–1 flour). Besides those all innovations, selected standard Mixolab torque-parameters were informatively recalculated to the Brabender units—to be easily compared to the Farinograph proof results, because this rheological test represents the standard in the cereal chemistry and technology branch. Adaptation of the Principal Components Analysis lies in: i) using of the Variance Components Analysis in a role of the input data filter and ii) unfolding of the 3D-space to 2D-surfaces pair of plots along the shared PC2 coordinate. Conventional Mixolab parameters revealed that cinnamon and oregano oils significantly weakened the gluten network, reducing dough stability and lowering the minimum protein-related torque C2, whereas lemongrass oil preserved the protein stability at levels comparable to the control flour. Oregano and thyme oils significantly increased the final torque C5, indicating enhanced starch retrogradation and formation of a firmer structure of the cooled gel. The innovative descriptors provided substantially deeper insight into these transformations. Cinnamon oil generated the highest MWP values (up to 18.5 %), indicating pronounced mechanically induced gluten weakening. In contrast, lemongrass oil maintained MWP values close to the control while accelerating starch gelatinization and hot-gel breakdown, reflected by elevated beta° values and steepened gamma° slopes. Oregano and thyme oils reduced the gelatinization kinetics but markedly supported the retrogradation-related parameters, including C54, slope delta°, and the C5/C1 ratio, indicating enhanced structural recovery during cooling. Correlation analysis confirmed that the innovative descriptors captured complementary information and exhibited substantially lower redundancy than conventional Mixolab variables. Before Principal Components Analysis from 34 variables in total, Variance Components Analysis identified 17 representative parameters with the highest distinguishing power; Principal Component Analysis demonstrated two-component model of PC1 and PC2 explained 72% of total experimental variability and reduced data noise to only 6 % (per contra to 61% and 14%, respectively, in the case of the standard Mixolab parameters). The multivariate models clearly differentiated essential oils according to their chemical composition and dose-dependent rheological effects on water-dough behavior. The results demonstrated chemically distinct essential oils influence on wheat dough rheology through different mechanisms affecting protein weakening, starch gelatinization, hot-gel stability, and starch retrogradation. The proposed kinetic and geometrical descriptors substantially enhance the interpretive capacity of Mixolab analysis and provide a valuable tool for mechanistic–kinetic investigation of functional ingredients in cereal-based systems.

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