Effects of Temperature and Mechanical Input on Semisweet Biscuit (Cookie) Quality and Dough Characteristics

The effects of specific mechanical energy (SME) and dough temperature at the end of mixing (T_f) on semisweet biscuit dough characteristics and biscuit quality were studied using an experimental mixer fitted with monitoring devices. The fluid circulating in the double jacket of the mixing bowl was regulated at variable temperatures and mixed dough samples were prepared at T_f of 23, 30, and 37°C for three levels of SME input (20, 60 and 120 kJ/kg). Correlation analysis showed that semisweet biscuit length and thickness were independent quality parameters, influenced respectively by the T_f of dough and SME. Biscuit thickness and volume increased with SME input, but SME had no significant influence on the physicochemical characteristics of the dough. Biscuit length was related to the density and stickiness of the dough and to rheological behavior as assessed by fundamental and empirical measurements. A rise in dough temperature >35°C induced a dramatic increase in viscoelastic properties, leading to biscuit shrinkage. The increase of dough density with T_f seemed to be related to the melting of solid fat in the dough recipe. Melting of fat during mixing could also be a source of viscoelastic changes in the dough at T_f.     

Rheological Changes in Wheat Sourdough During Controlled and Spontaneous Fermentation

The changing rheological characteristics of wheat doughs during fermentation at 30°C for 72 hr were measured using a controlled stress rheometer. Dynamic oscillation tests were performed at frequencies ranging from 0.01 to 10 Hz. Wheat sourdoughs (dough yield 200) were prepared with a mixed starter culture containing typical hetero- and homofermentative sourdough lactic acid bacteria. Results from the controlled fermentation process were compared to results from spontaneous fermentation. Maximum phase angle values, especially at low frequencies, were closely related to total gas production in the doughs. Complex viscosity decreased during fermentation and reached lower final values for doughs without starter culture. Heating characteristics of doughs after various fermentation times were measured at temperatures ranging from 30 to 80°C. The highest values for complex viscosity were found at ≈65°C. When heated, fermented doughs produced weaker gels than fresh doughs. The temperatures at which these maxima occurred increased significantly with fermentation time for spontaneously fermented dough.     

Relationship Between Rheological Properties and Microstructural Characteristics of Nondeveloped,Partially Developed,and Developed Doughs

Farinography and mixography are two commonly used procedures for evaluating dough properties. These procedures, however, cannot separate hydration and energy input during dough development, both of which are critically important for understanding fundamental rheological properties of dough. A rheometer and laser scanning confocal microscopy (LSCM) were used to study the relationship between rheological properties and microstructural characteristics of developed (by farinograph with both shear and extensional deformations), of partially developed (by rheometer with either shear or extensional deformation), and of nondeveloped (no deformation) dough samples of wheat flours. Rheological data revealed that developed dough had the highest G* (most elastic or strong), followed by doughs partially developed with extensional deformation, and then shear deformation, and finally by nondeveloped dough. The LSCM z‐sectioning (scanning of different layers of the sample) and the analysis of amount of protein matrix showed that developed dough had the most protein matrix and nondeveloped dough had the least protein matrix. It also showed that the higher the G*, the greater the protein network. Moreover, the type of deformation appeared to contribute to the development of protein matrix and further increase the dough strength. In this study, a combination of shear and extensional deformations by farinograph produced the most protein matrix and the strongest dough, followed by extensional deformation, shear deformation, and then no deformation.     

Molecular and Gelatinization Properties of Rice Starches from IR24 and Sinandomeng Cultivars

The differences in pasting properties involving gelatinization and retrogradation of rice starches from IR24 and Sinandomeng cultivars during heating‐cooling processes were investigated using a Rapid Visco Analyser (RVA)and a dynamic rheometer. The results were discussed in relation to the molecular structure, actual amylose content (AC), and concentration of the starches. Generally, both starches possessed a comparable AC (≈11 wt%), amylose average chain length (CL), iodine absorption properties, and dynamic rheological parameters on heating to 95°C at 10 wt% and on cooling to 10°C at higher concentrations. In contrast to Sinandomeng, IR24 amylose had a greater proportion of high molecular weight species and number‐average degree of polymerization (DP_n). IR24 amylopectin possessed a lower DP_n and greater CL, exterior CL (ECL), and interior CL (ICL). Comparing the results of RVA analysis and dynamic rheology, the gelatinization properties and higher retrogradation tendencies of IR24 starch can be related to the structural properties and depend on starch concentration. In addition, the exponent n of starch concentration for storage moduli at 25°C (G′₂₅ ∝ Cⁿ) increased linearly with increasing AC.     

Effects of Transglutaminase on Rheology,Microstructure, and Baking Properties of Frozen Dough

The improving effects of transglutaminase (TGase) were investigated on the frozen dough system and its breadmaking quality. Rheological properties and microstructure of fresh and frozen doughs were measured using a Rapid Visco‐Analyser (RVA), dynamic rheometer, and scanning electron microscopy (SEM). The frozen doughs with three storage periods (1, 3, and 5 weeks at –18°C) were studied at three levels (0.5, 1.0, and 1.5%) of TGase. As the amount of TGase increased, hot pasting peak viscosity and final viscosity from the RVA decreased, but breakdown value increased. The TGase content showed a positive correlation with both storage modulus G′ (elastic modulus) and the loss modulus G″ (viscous modulus): G′ was higher than G″ at any given frequency. The SEM micrographs showed that TGase strengthened the gluten network of fresh, unfrozen dough. After five weeks of frozen storage at –18°C, the gluten structure in the control dough appeared less continuous, more disrupted, and separated from the starch granules, while the dough containing 0.5% TGase showed less fractured gluten network. Addition of TGase increased specific volume of bread significantly (P < 0.05) with softer bread texture. Even after the five weeks of frozen storage, bread volume from dough with 1.5% TGase was similar to that of the fresh control bread (P < 0.05). The improving effects of TGase on frozen dough were likely the result of the ability of TGase to polymerize proteins to stabilize the gluten structure embedded by starch granules in frozen doughs.     

Comparison of Small and Large Deformation Measurements of Whole Meal Rye Doughs

The rheological properties of rye flour-water-salt doughs prepared from different flour types (different falling number and coarseness) at different water levels were studied after mixing and after 90 min of incubation (30°C and 80% rh). Both the effect of water and the coarseness of the flour had significant effects on storage modulus (G′) measured by oscillatory test in the linear viscoelastic region and on compressional force measured at large deformation. The results of the two rheological methods correlated very well with each other (correlation coefficients varied in the different doughs at r = 0.975–0.999). Dough rheological measurements suggested that falling number did not have a statistically significant effect on dough rheology after mixing or incubation. Although the two rheological methods correlated well, the responses for incubation were different. In the small deformation method, the storage modulus of all doughs, independent of the falling number, decreased during incubation, whereas in the large deformation method, only the hardness of doughs made from flours with lower falling number decreased during incubation. The rheological measurements of doughs after mixing and the viscosity measurements of flourwater suspension at 30 and 40°C did not correlate with each other. Total pentosans have great effect on viscosity measurements of flour-water suspensions, whereas flour particle size and soluble pentosans correlated more with rheological properties of doughs (r = 0.851 between G′ and soluble pentosans).     

Structural Modification of Gluten Proteins in Strong and Weak Wheat Dough as Affected by Mixing Temperature

The effects of temperature (≥25°C) on dough rheological properties and gluten functionality have been investigated for decades, but no study has addressed the effect of low temperature (<30°C) on gluten network attributes in flours with strong and weak dough characteristics. This study monitored changes in protein extractability in the presence and absence of reducing agents, the contents of readily accessible and SDS‐accessible thiols, and the secondary structural features of proteins in doughs from commercial hard wheat flour (HWF) and soft wheat flour (SWF) mixed at 4, 15, and 30°C. SWF mixed at 4 and 15°C showed similar mixing properties as HWF mixed at 30°C (which is the standard temperature). The effect of mixing temperature is different at the molecular level between the two flours studied. Protein features of HWF did not change as mixing temperature decreased, with the only exception being an increase in SDS‐accessible thiols. Decreasing mixing temperature for SWF caused an increase in SDS protein solubility and SDS‐accessible thiols as well as an increase in β‐turn structures at the expense of β‐sheet structures. Thus, noncovalent interactions appear to drive protein network at low temperatures (4 and 15°C), whereas covalent interactions dominate at standard mixing temperature (30°C) in doughs from both flours.     

The Combination of Rhizopus chinensis Lipase and Transglutaminase Affects the Rheology and Glutenin Macropolymer Properties of Frozen Dough

The combination of Rhizopus chinensis lipase (RCL) and transglutaminase (TG) was previously reported to improve the quality of frozen dough bread. In this study, the effects of RCL, TG, and their combination on the modification of glutenin macropolymer (GMP) and rheological properties of dough during frozen storage were investigated. Frozen storage changed both GMP and rheology properties of dough. TG treatment significantly decreased the ratio of high‐molecular‐weight glutenin subunits to low‐molecular‐weight glutenin subunits and GMP content in fresh dough, and GMP particle size increased. The effect of RCL on GMP properties was not significant, but its combination with TG dramatically increased the proportion of the larger particles and weighted average volume (D_4.3) in GMP. The treatment with the enzyme combination could have inhibited the depolymerization of GMP, which slowed down the decrease rate of some parameters such as GMP content, proportion of larger particles, D_4.3, and release of free amino and thiol groups during frozen storage. The modification of GMP properties by enzyme treatment weakened the effect of the freezing process on rheological properties of dough, especially TG treatment and its combination with RCL. Correlation between GMP particle size and dough properties (dough tensile force and elastic modulus) after freezing and enzyme treatment were confirmed.     

Effects of Micronization on Protein and Rheological Properties of Spring Wheat

This research investigated the effects of micronization, at different moisture levels, on the chemical and rheological properties of wheat. A set of tests designed to analyze protein fraction characteristics and rheological behaviors were conducted on samples from four wheat cultivars (AC Karma, AC Barrie, Glenlea, and Kanata). After being subjected to infrared radiation at three moisture levels (as‐is, 16%, and 22%), the seeds were milled to produce straight‐grade flour. The protein fractionation test revealed significant decreases (P ≤ 0.01) in both monomeric proteins (from 54% of total protein in the control to 37% in the tempered micronized sample) and soluble glutenins (9.4–2.5%). There was a strong negative correlation (r = ‐0.98) between the percentages of monomeric proteins and insoluble glutenins. Total extractable proteins of micronized samples tempered to 22% moisture decreased 43.5% when compared with nonmicronized control samples using size‐exclusion HPLC (SE‐HPLC). Micronization had a significant effect on gluten properties, as seen from a decrease in water absorption (P ≤ 0.01) and dough development time (P ≤ 0.01). Results showed that micronization at 100 ± 5°C had detrimental effects on wheat flour gluten functionality, including a decrease in protein solubility and impairment of rheological properties. These phenomena could be due to the formation of both hydrophobic and disulfide bonds in wheat during micronization.     

Centrifuged Liquid and Breadmaking Properties of Frozen‐and‐Thawed Bread Dough

Breadmaking properties (bread height, mm, and specific volume, cm³/g ) showed marked deterioration when bread dough was frozen and stored at ‐20°C for one day. However, these properties of bread dough baked after storage for three to six days were not further deteriorated as compared with that baked after one day of storage. A large amount of liquid was oozed from the frozen‐and‐thawed bread dough. The liquid was separated from the bread dough by centrifugation (38,900 × g for 120 min at 4°C), and collected by tilting the centrifuge tube at an angle of 45° for 30 min. There was a strong correlation between the amount of centrifuged liquid and breadmaking properties (bread height and specific volume). The mechanism responsible for the oozing of liquid in frozen‐and‐ thawed bread dough was studied. The presence of yeast and salt in bread dough was suggested to be closely related to the amount of centrifuged liquid, and fermented products particularly had a large effect on the amount of centrifuged liquid.     

Effects of Salt,Polyethylene Glycol,and Water Content on Dough Rheology for Two Red Spring Wheat Varieties

In this research, the relationship between dough rheology and water behavior was investigated in response to two osmotic regulators, salt (NaCl) and polyethylene glycol (PEG), using two Canadian Western Red Spring (CWRS) wheat varieties (Harvest and Pembina). The effects of NaCl (0.5, 1.0, and 1.5 g/100 g of flour) and PEG 400 (2.5, 5.0, and 7.5 g/100 g of flour) on dough rheology (oscillatory and creep) were estimated by using a central composite design. Variation of NaCl showed a significant effect on the phase angle δ, indicating that increasing the NaCl resulted in a more elastic dough. The opposite trend was observed with the addition of PEG. PEG 400 exerted a softening effect owing to plasticization, so that a more compliant liquid‐like dough was produced. The effects of water content (±10% of farinograph absorption) and PEG molar mass on dough rheology and freezable water content were estimated by using a full factorial design. PEGs with different molar mass (400, ≈1,600, and 3,350 g/mol) were added at a concentration of 1 g/100 g of flour. The water content significantly affected all dough rheological attributes, whereas PEG molar mass had no effect. The complex shear modulus (G* ) decreased with increasing water content, and dough creep compliance (J _max) increased. The elastic response of dough, determined as the relative elastic part (J _el) decreased with increasing water content. A high correlation was found between the freezable water content and dough rheological attributes.     

Evaluation of the Displacement Value as a Method to Detect Reduced Corn Wet-Milling Quality

A procedure based on the resistance and capacitance (RC) properties of corn to calculate a displacement value (DV) was evaluated for detection of corn that had reduced wet-milling quality. In 1991 and 1992, three hybrids were dried at air temperatures between ambient and 115°C in batch dryers. Additional samples, obtained from commercial elevators in 1992, had been dried with air temperatures ranging from 52 to 136°C. A baseline reference relationship was developed between log₁₀-resistance and capacitance with data from ambient-dried samples. A DV was defined as the horizontal distance along the capacitance axis from a sample RC data point to the baseline reference. RC properties of samples dried at air temperatures >50°C were compared to the baseline and the DV determined. Selected drying treatments were wet-milled by a laboratory-scale procedure to verify milling quality and correlation with DV. The effects attributed to hybrid and harvest moisture content on the RC properties of ambient-dried samples were small, allowing the baseline reference to be applied to a wide range of corn samples. In 1992, the baseline shifted upward from the 1991 baseline by 0.5 units on the log₁₀-resistance axis. DV increased significantly at drying air temperatures >50°C for batchdried samples. While DV correlated with drying temperature in batchdried samples (r = 0.66), it did not correlate with starch yield or recovery of commercial samples (r ≤0.10). Although the specific causes could not be determined, the shift in the baseline indicates the method would be difficult to implement on a practical scale. Although not indicated by DV, starch recovery decreased significantly for samples batch-dried at air temperatures ≥70°C. All samples dried at 115–136° had significantly lower starch recoveries.     

Use of Ultrasound to Investigate Glucose Oxidase and Storage Effects on the Rheological Properties of Cooked Asian Noodles

This is the first use of a longitudinal ultrasonic technique to address the rheological properties of cooked noodles. Ultrasound (11 MHz) was utilized to investigate the influence of glucose oxidase (GOx) at the 1.5 U/g of flour level on the rheological properties of cooked alkaline noodles before and after 72 h of storage at 4°C. Cooked noodle dough samples were studied by simultaneously conducting stress relaxation and transmission ultrasonic measurements, yielding Peleg's K₁ and K₂ parameters (initial rate of relaxation and extent of relaxation, respectively) and ultrasonic information on noodle texture properties. Ultrasonic phase velocities and attenuation coefficients did not show significant differences between control and GOx noodles either before or after 72 h of refrigeration. However, refrigerated storage of control and GOx noodles did result in a significant increase in wave velocity and storage modulus (M′) as well as a decrease in attenuation and tanδ_L (ratio of longitudinal loss modulus to longitudinal storage modulus), indicating increased firmness of noodle structure with storage time. Stress relaxation results on fresh unrefrigerated noodles showed an increase in Peleg's K₁ and K₂ parameters with GOx addition but did not resolve any significant changes in these parameters after 72 h of storage. This small amount of GOx did not improve cooked noodle texture, although noodle matrix changes during storage were clearly revealed by the noninvasive ultrasonic data.     

Performance of biochar derived from Cymbopogon winterianus waste at two temperatures on soil properties and growth of Bacopa monneri

ABSTRACT

The present study aimed to evaluate the effect of biochar derived from the distilled waste of Cymbopogon winterianus at two different pyrolysis temperatures (450°C and 850°C) on the chemical and biological properties of sandy loamy soil (SLS) and its subsequent impact on plant growth. Pot experiments utilizing Bacopa monnieri were performed in a greenhouse with four different application rates of biochar (2%, 4%, 6%, and 8% (w/w)) for 120 days. Biochar induced alterations in soil properties (nutrients, enzymes, and microbes) and plant responses (yield, biocide and antioxidant content) to biochar addition were measured. Biochar application, notably improved the soil carbon, cation exchange capacity, and the availability of NH₄ ⁺ and phosphorus. Initially, biochar produced at the lower temperature had more effect on the available nitrogen, phosphorus, soil enzymatic properties, and plant biomass growth. After 120 days, the pyrolysis temperature had only a marginal influence on biochar-induced effects on soil pH, WHC, and soil enzymatic activities. Our results suggest that C. winterianus derived biochar amendment leads to an overall amelioration of soil fertility and plant growth improvement. In specific biochar produced at lower temperatures (450°C) was more effective for improvement of plant biomass and soil characteristics.     

Thermal Expansion of Flour-Water Dough Measured with a Dynamic Mechanical Analyzer

Thermal 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 () 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 () of flour-water dough during GMF was highly correlated (r² = 0.886) to bread loaf volume. The ratio () of thermal expansion coefficient during the GMF stage to the coefficient during the GTE stage also was significantly correlated (r² = 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.     

Dynamic Viscoelastic Behavior of High-Pressure-Treated Wheat Gluten

The effects on the viscoelastic behavior of hydrated wheat gluten after treatment at different pressures (200–800 MPa), temperatures (20, 40, and 60°C), and holding times (20 and 50 min) were investigated by controlled stress rheometry. Because of the wide range of properties, four different torque amplitudes were used (0.5, 1.00, 3.00, and 6.00 mNm). Significant effects on rheological properties were observed, except when samples were analyzed at 0.5 mNm (limited heat and pressure treatments). Both storage modulus (G′) and loss modulus (G″) were more affected by temperature than pressure. The holding time had substantial effect on the slopes of both moduli at mild treatments; for the more severe treatments, the intercepts of the storage moduli in particular were extensively affected.     

1H Nuclear Magnetic Resonance (NMR) and Differential Scanning Calorimetry (DSC) Studies of Water Mobility in Dough Systems Containing Barley Flour

This study used ¹H nuclear magnetic resonance (NMR) spin‐spin relaxation time (T₂) and differential scanning calorimetric (DSC) measurements of unfreezable water content (UFW), to assess water behavior in freshly prepared (25°C), refrigerator‐stored (4°C, one day), or freezer‐stored (–35°C, one day) doughs containing 5, 10, or 30% whole grain, air‐classified β‐glucan‐diminished, and air‐classified β‐glucan‐enriched (BGB‐E) barley flours. Three populations of water were detected by NMR, depending on moisture content of dough, namely, tightly (T₂₁, 2–5 msec), less tightly (T₂₂, 20–50 msec), and weakly (T₂₃, 100–200 msec) bound water. T₂₂ peak was always detectable, and T₂₂ peak time linearly correlated to moisture content of dough in a range of 0.7–2.0 g/g db (r = 0.99, P < 0.05). Freezer storage showed less effect on water mobility in dough compared with refrigerator storage, whereas cooking and cool storage of cooked dough significantly decreased the water mobility (P < 0.05). Adding barley flour steadily decreased the water mobility in dough, and the reduction was more significant with adding BGB‐E (P < 0.05). Immobile water content was calculated by extrapolating T₂₂ peak time versus total moisture content in dough and significantly correlated to the UFW content measured by DSC (r = 0.72, P < 0.05).     

Measurement and Comparison of Glass Transition and Sticky Point Temperatures of Distillers Dried Grains with Solubles (DDGS) with Varying Condensed Distillers Solubles (CDS) and Drying Temperature Levels

Distillers dried grains with solubles (DDGS) is the main coproduct of the U.S. fuel ethanol industry and has significantly impacted the livestock feed markets in recent years. Particle agglomeration and subsequent flowability problems during storage and transport are often a hindrance, a nuisance, and expensive. This paper aims at characterizing the glass transition (T_g) and sticky point (T_s) temperatures of DDGS samples prepared with varying condensed distillers solubles (CDS) levels (10, 15, and 20%, wb), drying temperatures (100, 200, and 300°C), and moisture contents (0, 10, and 20%, db), and it discusses implications on DDGS flowability behavior. Distillers wet grains were combined with specified levels of CDS and dried in a convection‐style laboratory oven to produce DDGS. Subsequently, predetermined amounts of water were added to the DDGS to achieve desired moisture content levels. To determine T_g (°C), a differential scanning calorimeter was used, whereas T_s (°C) was determined through a novel technique with a rheometer. Results indicated high correlations between observed T_s and observed T_g (R² = 0.87) data for DDGS samples. Also, the empirical model for predicted T_g = f (drying temperature, CDS level, and moisture content) based on the Gordon–Taylor model showed favorable R² (0.74). Stickiness of DDGS increased with an increase in moisture content, indicating flow problems resulting from moisture. It was found that drying temperatures and CDS levels each had significant effects on T_g and T_s as well.     

Effect of Single Strain and Traditional Mixed Strain Starter Cultures on Rheological Properties of Wheat Dough and on Bread Quality

Investigations were made to test the effect of two different sourdough starter culture types on wheat dough and bread quality. Two single‐strain starter cultures consisting of well‐defined strains of lactic acid bacteria (Lactobacillus plantarum, L. brevis) and a traditional mixed‐strain sourdough culture (containing L. crispatus, L. pontis, and Saccharomyces cerevisiae) were evaluated for their effects on the rheological characteristics of wheat dough using both fundamental rheological and standard baking tests. Two other doughs were also evaluated, one which was chemically acidified to a comparable pH value by the addition of lactic acid, and a control which was not acidified. Dynamic oscillation tests were performed using a controlled stress rheometer. The phase angle and the absolute value of the complex dynamic modulus were measured for all doughs at frequencies of 0.1–10 Hz. The addition of sourdough prepared using single‐strain or mixed‐strain cultures significantly increased the phase angle and reduced the complex modulus of the doughs at all frequencies (P < 0.05). Significant differences were found between the dough which was chemically acidified and those doughs which were biologically acidified. The addition of sourdough effected an increase in loaf specific volume relative to both the chemically acidified and the nonacidified doughs.     

Effect of Added Fat on the Rheological Properties of Wheat Flour Doughs

The effect of added fat content on the rheological properties of wheat flour doughs was determined for three different added fat contents (2.5, 5.0, and 7.5%) at 25°C using dynamic mechanical analysis (DMA) and stress relaxation (SR) tests. Frequency sweeps indicated that added fat had a plasticizing effect on G′ and G″ in the rubbery region. SR results were parameterized using a Maxwell model and a Williams-Watts (WW) model. The WW model indicated that each dough could be characterized by just two major relaxation modes, while four elements were needed for the Maxwell model. The average relaxation time for the shorter process was <1 sec and was not affected by added fat. However, the average relaxation time for the longer WW process actually increased from 107 to 261 sec with added fat up to 5%, and then decreased again. Taken together, these results suggest that added fat actually delayed the onset of viscous flow, while simultaneously attenuating the short-time elastic properties of the gluten fraction of the dough. Furthermore, rheological testing over a wide time (frequency) scale was needed to observe the effect of added fat on both the short-time elastic and longer-time viscous behavior of these doughs.