Impact of composition and texture of protein-added yogurts on oral activity.

Understanding how oral processing is altered in response to changes in the composition and mechanical properties of food provides useful information to design food with improved satiating capacity which is largely influenced by oral exposure. In turn, this information deepens the knowledge about the physiology of texture perception. Six yogurts were formulated with different amounts of protein and protein sources and addition of apple cubes: control (C), extra skimmed milk powder-added (MP), whey protein isolate-added (WPI), and whey protein microgels-added (WPM). In addition, MP was also added with maltodextrin (MPMD) and with fresh apple cubes (MPF). Activities of masseter, anterior temporalis and anterior digastric muscles during oral processing of each sample were recorded (electromyography), and jaw movement amplitudes in three dimensions were determined (jaw tracking system). The jaw muscle activities were highly dependent on the type of yogurt. Addition of apple cubes (MPF) almost doubled the oral processing time, number of chews, and muscle activity of all samples. MP and MPMD required similar but lower values of oral processing than MPF attributed to their reinforced network of milk protein. The lowest values were found for WPI, C and WPM, indicating a weaker, more fluid material. These behavioral results, which clearly differentiate the samples, are discussed in connection to the rheological and sensory properties of the yogurts. This study suggests that adding apple cubes significantly alters the oral processing pattern, such that they may be a more effective way of increasing the oral processing time (time exposure) compared to more subtle changes in the protein amount or source. Nevertheless, changes in the protein amount and source also affected, although to a lesser extent, the behavioral, rheological, and sensory properties of yogurt.

Surface energy and viscoelasticity influence caramel adhesiveness.

Adhesion is an important textural attribute that directs consumer eating patterns and behaviors and can be a negative attribute during food processing. The objectives of this study were to modify caramel formulation and compare adhesion to different materials to quantify the influence of surface energetics and viscoelasticity on caramel adhesiveness. Mechanical adhesion was viewed in the context of pressure sensitive tack theory, where adhesion is controlled by viscoelasticity of the adhesive material and the surface energy relationship of material and probe. Caramel samples varied in total amount of fat and protein, and mechanical adhesion was measured using a series of materials with total surface energies of 39.7-53.2 mJ/m2 . Adhesiveness decreased as fat and protein content increased, with a significant effect of total surface energy. Viscoelasticity was modeled using creep recovery data fit to a four-element Burger mechanistic model. Burger model parameters representing retarded elasticity correlated strongly with adhesiveness. The results suggest two zones of adhesion based on formulation, one driven by both surface energy relationships-most notably dispersive and total surface energy-and viscoelasticity, and the other driven solely by viscoelasticity. PRACTICAL APPLICATIONS: Relationships between mechanical properties and adhesion have been explored but are still not well understood, and could aid in the design of food products with a controlled level of adhesion. The results of this study indicate the importance of considering material surface energy when measuring mechanical adhesion or texture profile analysis. Understanding the relationships between viscoelastic behavior and adhesion can be used to make inferences on perceived texture.

Modulation of physicochemical and conformational properties of kidney bean vicilin (phaseolin) by glycation with glucose: implications for structure-function relationships of legume vicilins.

The structure-function relationships of plant oligomeric globulins are still not fully recognized. The present work investigated the influence of glycation with glucose (at 1:50 and 1:100 protein/sugar molar ratios; incubation periods of 2.5, 5.0, and 10.0 h) on the physicochemical and conformational properties of kidney bean vicilin (phaseolin), with the aim of understanding the structure-function relationships of legume vicilins. Protein solubility (PS), surface charge (isoelectric point) and hydrophobicity (H0), and secondary, tertiary, and/or quaternary conformations, as well as the emulsifying activities (emulsifying activity and emulsion stability indices, EAI and ESI) were evaluated. The 2.5 h incubation period of glycation led to least PS and highest H0, and after that, the PS and H0, on the contrary, gradually changed with increasing incubation period. The glycation increased the α-helix content and highly ordered secondary structures (α-helix+ß-strand), as evidenced by far-UV circular dichroism (CD) spectroscopy. Combined analyses of differential scanning calorimetry, intrinsic emission fluorescence, and near-UV CD spectroscopy indicated that phaseolin underwent a tertiary conformation unfolding and subsequent rearrangement process (to form a new tertiary conformation), whereas the quaternary conformational flexibility progressively increased upon increasing degree of glycation. The conformation rearrangement was more distinct at the 1:100 molar ratio than at the 1:50 counterpart. The glycation at 5.0 and 10.0 h periods considerably increased the EAI, but only at the 1:50 molar ratio was the ESI progressively increased with the incubation period. These results confirmed that besides surface properties (e.g., PS and H0), the flexibility in tertiary and/or quaternary conformations played a major role in the emulsifying properties of glycated vicilins. The findings would have important implications for understanding the structure-function relationships of legume oligomeric globulins, thus providing a direction to further improve the surface-related functional properties of these proteins.

How micro-phase separation alters the heating rate effects on globular protein gelation.

UNLABELLED: This study was conducted to determine how the combination of heating rate and pH can be used to alter viscoelastic properties and microstructure of egg white protein and whey protein isolate gels. Protein solutions (1% to 7% w/v protein, pH 3.0 to 8.5) were heated using a range of heating rates (0.2 to 60 °C/min) to achieve a final temperature of 80 °C. The gelation process and viscoelastic properties of formed gels were evaluated using small strain rheology. Single phase or micro-phase separated solution conditions were determined by confocal laser scanning microscopy. In the single phase region, gels prepared by the faster heating rates had the lowest rigidity at 80 °C; however, a common G' was achieved after holding for 4 h at 80 °C . On the other hand, under micro-phase separation conditions, faster heating rates allowed phase separated particles to be frozen in the network prior to precipitation. Thus, gels produced by slower heating rates had lower rigidities than gels produced by faster heating rates. The effect of heating rate appears to depend on if the solution is under single phase or micro-phase separated conditions. PRACTICAL APPLICATION: The effect of heating rate and/or time on protein gel firmness can be explained based on protein charge. When proteins have a high net negative charge and form soluble aggregates, there is no heating rate effect and gels with equal firmness will be formed if given enough time. In contrast, when electrostatic repulsion is low, there is a competition between protein precipitation and gel formation; thus, a faster heating rate produces a firmer gel.

Mechanical and water-holding properties and microstructures of soy protein isolate emulsion gels induced by CaCl2, glucono-δ-lactone (GDL), and transglutaminase: influence of thermal treatments before and/or after emulsification.

The mechanical properties, water-holding capacities (WHC), and microstructures of emulsion gels, induced by glucono-δ-lactone (GDL), CaCl(2), and microbial transglutaminase (MTGase) from unheated and heated soy protein isolate (SPI)-stabilized emulsions (at protein concentration 5%, w/v; oil volume fraction, 20%, w/v), were investigated and compared. The influence of thermal pretreatments (at 90 °C for 5 min) before and/or after emulsification was evaluated. Considerable differences in mechanical, water-holding, and microstructural properties were observed among various emulsion gels. The thermal pretreatment after emulsification increased the strength of the emulsion gels induced by GDL and CaCl(2), whereas in the case of MTGase, thermal pretreatments before and/or after emulsification on the contrary greatly inhibited gel network formation. The application of the enzyme coagulant exhibited much higher potential to form SPI-stabilized emulsion gels with higher mechanical strength than that of the other two coagulants. The WHC of the emulsion gels seemed to be not directly related to their gel network strength. Confocal laser scanning microscope analyses indicated that the network microstructure of the formed emulsion gels, mainly composed of aggregated protein-stabilized oil droplets and protein aggregate clumps, varied with the type of applied coagulants and emulsions. The differences in microstructure were basically consistent with the differences in mechanical properties of the gels. These results could provide valuable information for the formation of cold-set soy protein-stabilized emulsion gels.