W.K. Solomon

Effect of drying methods and blending ratios on dough rheological properties, physical and sensory properties of wheat-taro flour composite bread

Abstract The study was conducted to evaluate the effect of taro drying methods and blending ratios on the physical quality attributes and sensory quality of wheat–taro bread and rheological properties of the blend dough. Farinographic properties like water absorption capacity, dough development time, dough stability time, time to break down, mixing tolerance index, and farinographic quality number were significantly (p < .05) affected by drying methods and blending ratio and their interaction. Increased taro flour (10–20 g) per 100 g of wheat flour resulted in an increased water absorption capacity (57.38%–58.23%) and mixing tolerance index (67.33–70.21 FU). The sensory analysis had revealed that as taro flour blending ratio increased the acceptability of blended breads were reduced. With respect to physical and sensory properties, the control bread had better acceptability than that of 10, 15, and 20 g taro flour‐mixed bread. The study revealed that there is possibility of incorporating taro flour up to 15 g per 100 g of wheat flour with acceptable sensory attributes of the composite bread.

Hydration kinetics of direct expanded tef flour breakfast cereals in water and milk.

Hydration kinetics of tef flour breakfast cereals extruded at barrel temperatures of 110, 130, and 150°C was investigated by hydrating them in water and whole milk at 25°C (±1°C). The normalized Weibull model described the rehydration characteristics of the extrudates in water and milk adequately (R2 = 0.98–0.99). Water absorption rate was significantly (P < 0.05) influenced by barrel temperature where extrudates processed at 150°C barrel temperature exhibited high water absorption rate followed by those extruded at 130 and 100°C, respectively. Hydration rate and equilibrium moisture content were higher for samples hydrated in water than those in milk. In view of the values of the shape parameter β, the hydration process is predominantly controlled by diffusion (β = 0.40–0.51) for samples extruded at 110°C whereas external resistance to mass transfer dominated (β = 0.60–0.73) those extruded using 150 and 130°C. Extrudates processed at 130 and 150°C exhibited better hydration characteristics. Thus, these temperature ranges could be used to produce extruded products from tef.

Comparison of Axial and Radial Compression Tests for Determining Elasticity Modulus of Potatoes

The effect of sample size, loading rate, and compression level on the determination of tangent modulus of elasticity of potatoes in axial (Ea) and radial (Er) compression tests was studied. Cylindrical potato samples of 10, 15, and 20 mm diameter with length-to-diameter (L/D) ratio 1, 1.5, and 2 and loading rates of 50, 100, 200, 300, and 400 mm/min were used. A third-degree polynomial best described the force-deformation (F-D) plot of the test specimens (R2 = 0.98 to 0.99) in both tests. In view of the non-linearity of the F-D plot, Ea and Er were calculated corresponding to 10, 20, and 30% compression. The values of Ea and Er obtained for various combinations of sample size and compression level had coefficient of variation (CV) of about 24 and 8%, respectively, indicating relatively greater influence of experimental conditions in axial than radial compression testing. Apparently, Ea increased with an increase in compression level and loading rate whereas Er exhibited inconsistent trend. The combined effects of sample size and compression level accounted for about 93 and 20% of the changes in Ea and Er, respectively signifying the minimal effects of these parameters in radial compression testing. Similarly, the loading rate and compression level accounted for about 96 and 28% of the changes in Ea and Er, respectively. The results of this article revealed that determination of modulus of elasticity of potatoes in axial compression testing was significantly influenced by testing conditions and sample size, whereas radial compression testing appeared to be independent of testing conditions and sample size.

Application of Peleg's Equation to Describe Creep Responses of Potatoes Under Constant and Variable Storage Onditions

The application of Pelegs equation to characterize creep behavior of potatoes during storage was investigated. Potatoes were stored at 25, 15, 5C, and variable (fluctuating) temperature for 16 or 26 weeks. The Peleg equation adequately described the creep response of potatoes during storage at all storage conditions (R2  = .97to .99). Peleg constant k1 exhibited a significant (p < .05) decreasing trend with storage time (ts ) for samples stored under the experimental conditions whereas the constant k2 appeared to be unaffected much by ts except for samples stored at 25C. Under constant temperature storage, k1 was found to be a linear function of ts (R2  = .87 to .97). Also, the rate of change of k1 appeared to be temperature dependent described by a linear relationship between the degradation rate constant for k1 (α) and storage temperature (T). For the variable storage condition, a bulk mean temperature (Tbm ) was calculated to account for a series combination of storage time and temperature which the potatoes were subjected to. It was possible to describe the changes in k1 due to variable storage temperature in terms of Tbm and ts using stepwise multiple regression (R2  = . 94). PRACTICAL APPLICATIONS Precise description of the changes in the rheological properties of raw potatoes during storage could help predict the associated effect on the texture of cooked potatoes. Easy and simple methods of describing creep responses during storage or processing will be potentially helpful to better understand the phenomenon. The model parameters from such model could be used to relate rheological properties of raw and cooked potatoes. Moreover, the model parameters could be used to establish relationship between instrumental and sensory attributes which will help in the prediction of sensory attributes from instrumental data.