Effect of oxidative enzymes on bulk rheological properties of wheat flour doughs

The use of enzymes such as peroxidases or glucose oxidase instead of chemical oxidants is a very interesting option for improving breadmaking performance of doughs. In this study the effect of such enzymes on bulk rheological properties of dough was quantified and their influence on the polymer network in dough deduced. Small deformation oscillation and relaxation tests (strain 0.001) are not suitable for discriminating between doughs prepared in the presence of the different enzymes. Flow relaxation tests at high deformation and long relaxation times showed a clear distinction between the effect of peroxidase and glucose oxidase. Peroxidase increases only the number or lifetime of transient bonds, whereas glucose oxidase additionally produced cross-links that were permanent on time scales up to 3 h. Peroxidase probably introduced a second, more transient structure (arabinoxylan network) through the gluten network, whereas glucose oxidase may also have strengthened the gluten network. A higher water addition could not compensate for the effect of peroxidase; on longer time scales the stress remained at a higher level. Similar results were obtained in large deformation biaxial and uniaxial extension tests. Peroxidases only increased stress levels. The addition of glucose oxidase resulted in a higher stress and more intense strain hardening. Only in biaxial extension was an influence of pH observed. An increase in stress level was accompanied by a decrease in fracture strain, making predictions of the effects on bread structure complicated. © 2002 Published by Elsevier Science Ltd

Foams and surface rheological properties of b-casein, gliadin and glycinin

Interfacial rheological properties and their suitability for foam production and stability of two vegetable proteins were studied and compared to ß-casein. Proteins used ranged from flexible to rigid/globular in the order of ß-casein, gliadin and soy glycinin. Experiments were performed at pH 6.7. Network forming properties were characterised by the surface dilational modulus (determined with the ring trough) and the critical falling film length (Lstill) at which a stagnant protein film will break. Gliadin had the highest dilational modulus, followed by glycinin and ß-casein, whereas glycinin formed the strongest film against fracture in the overflowing cylinder. The rate of decrease in the surface tension was studied at the air–water (Wilhelmy plate method) and the oil–water interface (bursting membrane) and the dynamic surface tension during compression and expansion in the caterpillar. Gliadin had the lowest equilibrium interfacial tensions and ß-casein the lowest dynamic surface tension during expansion. Hardly any foam could be formed at a concentration of 0.1 g/l by shaking. At a concentration of 1.4 g/l most foam was formed by ß-casein, followed by gliadin and glycinin. It seems that in the first place the rate of adsorption is important for foam formation. For the vegetable proteins, adsorption was slow. This resulted in lower foamability, especially for glycinin

Effect of Oxidative Enzymes on Bulk Rheological Properties of Wheat Flour Doughs

The use of enzymes such as peroxidases or glucose oxidase instead of chemical oxidants is a very interesting option for improving breadmaking performance of doughs. In this study the effect of such enzymes on bulk rheological properties of dough was quantified and their influence on the polymer network in dough deduced. Small deformation oscillation and relaxation tests (strain 0·001) are not suitable for discriminating between doughs prepared in the presence of the different enzymes. Flow relaxation tests at high deformation and long relaxation times showed a clear distinction between the effect of peroxidase and glucose oxidase. Peroxidase increases only the number or lifetime of transient bonds, whereas glucose oxidase additionally produced cross-links that were permanent on time scales up to 3 h. Peroxidase probably introduced a second, more transient structure (arabinoxylan network) through the gluten network, whereas glucose oxidase may also have strengthened the gluten network. A higher water addition could not compensate for the effect of peroxidase; on longer time scales the stress remained at a higher level. Similar results were obtained in large deformation biaxial and uniaxial extension tests. Peroxidases only increased stress levels. The addition of glucose oxidase resulted in a higher stress and more intense strain hardening. Only in biaxial extension was an influence of pH observed. An increase in stress level was accompanied by a decrease in fracture strain, making predictions of the effects on bread structure complicated. Author Keywords: dough rheology, relaxation, peroxidase, glucose oxidas

The Kieffer dough and gluten extensibility rig - An experimental evaluation

Load-extension tests on flour dough are widely used by plant breeders, millers and bakers. The 'Kieffer dough and gluten extensibility rig' is a small-scale version of the Brabender extensograph, in which test pieces of about 0.4 g are extended. With the Kieffer rig, lower strain rates can be applied than in the Brabender extensograph and the experimental data can be expressed in terms of stress and strain. In this paper the performance of the Kieffer rig is illustrated by measurements on a weak and a strong dough. Formulas are given for the calculation of fundamental rheological parameters from the results of measure­ments with the Kieffer rig. Sagging and bending of the test pieces before measurements could be started, caused difficulties in the determination of the exact starting point of extension. The deformation was not purely uniaxial extension, because a shear component was also observed. The amount of dough that is extended did not increase throughout the test. This is probably due to the occurrence of a shear component fracture which occurred mainly near the hook. A relatively large variation in stress and strain at fracture was observed. The maximum in stress represents the strain at which the sample fractures macro­scopically better than the maximum in force. Variation in deformation history and volume of the test pieces have a negative effect on the reproducibility

Relative importance of cohesion and adhesion for sensory stickiness of semisolid foods

Sensory stickiness (sticky mouthfeel) was hypothesized to result from the viscoelastic and adhesive properties of a foodstuff. The objective of the present study was to investigate the relative importance of these two properties. Measurements consisted of compression decompression cycles on a texture analyzer, with product, type of surface, the presence or absence of saliva and compression regime as variables. Products included commercial mayonnaises, custard desserts and warm sauces, varying in apparent viscosity (at shear rate of 10 s1) between 0.3 and 18.3 Pa.s. Fairly good models were obtained, predicting sensory stickiness with R2 = 0.850.92. The predictive value of the mathematical models did not increase when the surface characteristics approached those of the human tongue (use of porcine lingual mucosa). Different surfaces or the use of saliva resulted in differences in the absolute values of the parameters, but their relative values when comparing different products did not change. The parameters appearing in the predictive models represented product characteristics only. The type of surface was not an important factor in determining differences in sensory stickiness between these samples. For the products used in this study, adhesion was large enough to prevent detachment of the sample from the surfaces, i.e., adhesion was not limiting. Variations in perceived stickiness could be explained with R2 = 0.86, based on only two product characteristics: consistency and 'long behavior' (the extent to which necking occurs during decompression). This was better than the correlation between sensory stickiness and apparent viscosity (R2 = 0.77), confirming the relevance of 'long behavior' for sensory stickiness