Cereal Chem. 79(4):567-571Measurements of creep-recovery of flour-water doughs were made using a dynamic mechanical analyzer (DMA) in a compression mode with an applied probe force of 50 mN. A series of wheat flour and blend samples with various breadmaking potentials were tested at a fixed water absorption of 54% and farinograph optimum water absorption, respectively. The flour-water doughs exhibited a typical creep-recovery behavior of a noncross-linked viscoelastic material varying in some parameters with flour properties. The maximum recovery strain of doughs with a fixed water absorption of 54% was highly correlated (r = 0.939) to bread loaf volume. Wheat flours with a large bread volume exhibited greater dough recovery strain. However, there was no correlation (r = 0.122) between maximum creep strain and baking volume. The maximum recovery strain of flour-water doughs also was correlated to some of the parameters provided by mixograph, farinograph, and TA-XT2 extension.The main ingredients of bread doughs are wheat flour and water. Flour dough belongs to a group of viscoelastic materials in which a high degree of plasticity or viscosity is combined with considerable elasticity (Schofield and Scott Blair 1932). Variations in baking quality among wheat cultivars exist and the reasons are not fully understood (Schofield 1985). Rheology has been a useful physical approach to study the relationships between wheat flour doughs and bread quality (Faubion and Hoseney 1990) because rheological properties of dough are important for breadmaking performance (Bloksma and Bushuk 1988). However, scientists often have difficulty relating basic rheological parameters of wheat flour dough to its baking behavior because of the use of empirical instruments (Szczesniak 1988).7he farinograph, mixograph, and extensigraph are the most common empirical instruments used for physical dough tests. They have provided much practical and useful information for the milling and baking industries and are still important in characterizing properties of wheat flour doughs. However, they do not provide enough information to interpret the fundamental behavior of dough rheology and its baking quality (Szczesniak 1988). The predictive correlation between physical dough test results, such as water absorption and mixing development time, and baking quality is not high (Oliver and Allen 1992), which means the usual physical dough tests do not appear to measure properties that are directly important for breadmaking performance (Bloksma 1990a,b). Therefore, dough technologists have become more interested in fundamental rheological measurements.Dynamic oscillatory measurements in the synthetic polymer industry have been applied to dough systems (Faubion and Hoseney 1990). However, there is no consensus as to the practical advantages over established empirical methods (Amemiya and Menjivar 1992; Edwards et al 1999). Neither dynamic modulus nor tand value of wheat flour doughs shows a clear relationship with bread quality (Janssen et al 1996), which is p...

Cereal Chem. 77(4):478-483Pioneer 8500, a red hard sorghum hybrid, was steeped batchwise using three steeping solutions at 50°C: SO 2 solution; SO 2 solution containing 1.25% (w/w) of a commercial multiple-enzyme preparation (Novo SP249); and SO 2 solution with the addition of 0.5% (w/w) lactic acid. Novo SP249 contained pectolytic, cellulolytic, hemicellulolytic, and proteolytic activities and small amounts of saccharolytic activities. Three SO 2 concentrations (0.1, 0.2, and 0.3% w/v) prepared by dissolving sodium bisulfite in distilled water and three steeping times (24, 36, and 48 hr) were used. Incorporation of multiple enzymes into the SO 2 resulted in an increase in starch yield with reduced protein content compared with the SO 2 solution alone. The best wet-milling performance for sorghum resulted from the SO 2 solution containing 0.5% lactic acid; it produced the whitest starch with the highest yield and the lowest protein content. Both higher SO 2 concentration of the steeping solution and longer steeping time led to higher starch yield, lower protein content in starch, and whiter starch. However, no significant differences in starch yield, protein content in starch, and starch color occurred between SO 2 concentrations of 0.2 and 0.3% for all three steeping solutions. The optimum steeping process for wet milling of sorghum was using a 0.2% SO 2 solution with 0.5% lactic acid for 36 hr at 50°C. Under these conditions, the starch yield, protein content in starch, and L value of starch color were 60.2% (db), 0.49% (db), and 92.7, respectively, which were not significantly different from the best values from the 48-hr steeping using the solution with 0.3% SO 2 and 0.5% lactic acid.Publication no. C-2000-0606-01R.

Cereal Chem. 79(1):108-114The viscoelastic behavior of bread crumb was studied using dynamic mechanical analysis (DMA) in the compression mode with the frequency sweep. The dynamic storage modulus (E′), loss modulus (E″), and tanδ (E″/E′) were measured for bread crumb aged up to three days at ambient temperature. The viscoelastic properties of bread crumb showed a characteristic frequency dependence similar to that of a soft rubberlike solid. Typical behavior of bread crumb involved a transition from rubberlike to glasslike consistency with increasing frequency. At a low frequency region, the E′ and E″ values were relatively small and nearly constant, showing characteristics of the rubbery plateau. Then, they increased rapidly with increasing frequencies and approached a glasslike state. Tanδ was low and almost constant at low frequencies before the transition, then went through a prominent peak with increasing frequency. The frequency at which the tanδ of bread crumb started to rapidly increase was defined as the onset frequency (f o ) of the transition. The f o values increased with the aging of bread crumb samples, which correlated highly to bread staling (r = 0.942). Both dynamic moduli E′ and E″at f o also increased with the aging of bread, which correlated highly to firmness obtained using a texture analyzer in a static compression mode (r = 0.941 and 0.943, respectively). DMA measurements could be helpful in characterizing bread staling.

Cereal Chem. 76(1):87-91Thermal expansion of a wheat flour-water dough was measured with a dynamic mechanical analyzer (DMA) at a temperature scan range of 25 to 160°C, in 5°C/min increments. Dough water-absorption levels were increased from 50 to 70% (14% mb) in 4% increments. A standard breadbaking method was used, and loaf volume was measured for regression analysis. The thermal expansion pattern of flour-water dough during heating included four stages with changes in the thermal expansion coefficient: gas thermal expansion (GTE) (25-60°C), starch gelatinization-gluten matrix formation (GMF) (60-100°C), vapor pressure expansion (VPE) (100-120°C), and structure fixation-crust formation (SCF) (>120°C). The onset temperature (T o ) between each stage and the thermal expansion coefficient (C e ) of each stage were affected significantly by dough water content. The onset temperature (To 1-2 ) from GTE to GMF (the starting temperature of gelatinization of starch in dough) decreased from 68 to 55°C as water absorption increased from 50 to 70%. The thermal expansion coefficient (Ce 2 ) of flour-water dough during GMF was highly correlated (r 2 = 0.886) to bread loaf volume. The ratio (Ce 2 /Ce 1 ) of thermal expansion coefficient during the GMF stage to the coefficient during the GTE stage also was significantly correlated (r 2 = 0.882) to baking volume. Thus, DMA measurement of dough thermal expansion has the potential to be a powerful method of predicting baking quality in cultivar screenings, baking simulations, and scale-up studies.Publication no. C-1999-0106-04R.