EFFECT OF GUM ARABIC ON THE RHEOLOGY OF CORN FLOUR DOUGHS AND FRIED PRODUCT QUALITY

Small deformation stress relaxation studies were performed on corn flour dough at 48–62%, wet basis moisture and 0–2% gum Arabic contents. Corn doughs were sensitive to moisture contents that were reflected by the values of the elastic and viscous components. The instrumental stickiness of the dough increased markedly when the moisture content was increased. The stress decay curves were modeled by using 3-element spring-dashpot models as evidenced by low values of root mean square error. Sensory assessment of the dough as well as fried products were conducted to relate the parameters obtained from stress relaxation studies.     

Rheological characterization of raw and roasted green gram pastes

Rheological properties of raw and roasted green gram pastes have been determined at different moisture contents (52–56 g/100 g) and temperatures (10–40 °C). These pastes exhibit shear-thinning behavior and possess yield stress. Cross model is suitable (0.986 ≤ r ≤ 0.999, p ≤ 0.01) to explain the flow characteristics of the pastes. The Cross model parameters such as zero-shear viscosity and relaxation time are sensitive to concentration of solids in the paste as well as temperature of measurement, and vary widely between raw and roasted samples. The effect of temperature on the apparent viscosity follows the Arrhenius type relationship (r ≥ 0.961, p ≤ 0.01). The viscoamylographic indices and trypsin inhibitor content are also different for raw and roasted samples. The roasted pastes show a smooth and cohesive microstructure. The optimized sample of roasted flour having a moisture content of 55 g/100 g is suitable as bread spread with appropriate stickiness and spreadability.     

Chemical composition and functional properties of raw and roasted Nigerian benniseed (Sesamum indicum) and bambara groundnut (Vigna subterranean)

Benniseed and bambara groundnut seeds were roasted at 80 and 120 °C for 10–60 min. For both flours, the effects of roasting temperature and time on selected functional properties and chemical composition were determined, as were the effects of pH on the emulsification capacity and nitrogen solubility. The chemical constituents of the raw flours were present at higher concentrations than those of the roasted flours except for fat and ash. Protein concentrates of both flours contained 80.5–81.5% crude protein as the major constituent. Nitrogen solubility was lowest at pH 4.0 for raw and roasted benniseed flour and pH 5.0 for raw and roasted bambara groundnut flour. Roasting generally lowered the nitrogen solubility and increased the water and oil absorption capacities while decreasing the foaming capacity and emulsification capacity of both flours.     

VISCOELASTICITY OF A SIMULATED POLYMER AND COMPARISON WITH CHICKPEA FLOUR DOUGHS

An integrated approach consisting of compression and stress relaxation is performed with a simulated model system of poly dimethyl siloxane (PDMS), a viscoelastic polymer material when the compressive strain, height of sample and crosshead speed were varied. The parameters derived are the forces at the end of compression and relaxation, energy for compression and the extent of elasticity of the sample based on the ratios of forces as well as the proposed energy values. The results were verified with food doughs undergoing large deformations that show a nonlinear behavior. The proposed extent of elasticity based on the ratios of energy stored and compression can be used as an index for the characterization of viscoelasticity. A nonlinear three‐parameter model had also been proposed to predict the stress decay characteristics as a function of time, which was found suitable for the PDMS system, and was better than the two‐parameter Peleg model as judged by lower variance values (0.0006–0.018 and 0.002–0.048, respectively). Further, an actual system of food doughs in the form of chickpea (Cicer arietinum L.) flour dough was used to verify the proposed model and viscoelastic index at different moisture contents (27–39%) subjected to compressive strains of 25–75%. The nonlinear relaxation characteristics of the food dough are sensitive to moisture content as well as to strain level.     

干法预糊化对苦荞面团流变学性质及芦丁降解酶活性的影响

为研究干法预糊化处理对苦荞面团流变学性质及芦丁降解酶活性的影响,采用单螺杆挤压设备处理苦荞粉得到预糊化粉,以未处理苦荞粉为对照,制作面团,通过粉质仪、TPA、应力松弛及扫描电镜对面团的结构进行测定、观察,并利用HPLC测定芦丁、槲皮素含量来表征芦丁降解酶的活性。结果表明,与全粉面团相比,干法预糊化面团的粉质特性得到改善,其硬度、黏聚性、残余应力、阻尼系数和松弛时间均增大,黏着性降低;SEM证明干法预糊化面团形成连续、均匀的网状结构。另一方面,干法预糊化处理使芦丁降解酶失活,从而降低苦味程度。     

UNIAXIAL COMPRESSIBILITY OF BLACKGRAM DOUGHS BLENDED WITH CEREAL FLOURS

The uniaxial compression characteristics of papad dough (moisture content 62%, dry basis), made from blackgram flour as well as after incorporation of different types of cereal (rice, sorghum and wheat) flours at different levels (20 and 40%), were determined. The stress-strain data can be interrelated by a power law type equation. The sensory attributes (stickiness, firmness, elasticity and ease of flattening/rolling) were correlated with the energy for compression, deformability modulus and apparent biaxial elongational viscosity. Inelastic doughs resulted from the blackgram dough; doughs with 20% rice or wheat blends were also inelastic but sorghum samples were elastic. The deformability modulus for sorghum doughs were extremely high. The blackgram dough as well as the wheat blended doughs were the easiest doughs to roll/flatten. Blended dough consisting of wheat flour (at 20 and 40% level) or rice flour up to 20% level was suitable for making cereal-blended papad doughs.     

The utilisation of barley middlings to add value and health benefits to white breads

The beneficial health effects of β-glucan, a major non-starch polysaccharide in barley, have become the focus of much attention in recent years, with the incorporation of barley fractions into baked products being a growing area in the development of healthier food products. In this study, flour formulations, doughs and breads were produced using the “middling” fraction (M) of wholegrain (WM) and pearled (PM) barley in different ratios (15%, 30%, 45% and 60% middlings with wheat flour). A 100% wheat formulation was used as a control. The protein content differed significantly (P < 0.01) between formulations (i.e. the amount of barley middlings substituted for flour) but did not differ significantly between WM and PM formulations of the same inclusion level. Starch pasting properties were significantly affected by the increased inclusion of barley middlings (BM) into the formulation. Fundamental dough rheology of the samples also showed significant differences between doughs made from different BM levels, with doughs containing BM having increased firmness, decreased resistance to extension and decreased elasticity. Bread quality was not significantly affected by the addition of up to 30% BM, the loaf volume and textural properties in particular of breads up to 30% BM inclusion were of a suitable standard when compared to the control. Both fibre and β-glucan content of the breads was increased significantly with the inclusion of BM; inclusion of BM at a 30% level increased the fibre and β-glucan contents, respectively.     

Rheology of Rice Flour Dough with Gum Arabic: Small and Large‐Deformation Studies,Sensory Assessment and Modeling

The absence of gluten protein makes the rice flour doughs difficult to handle when flattened/sheeted products are to be prepared. The rheological, sensory and microstructural changes in rice flour doughs having gum Arabic (0% to 5%, w/w) and moisture contents (44% to 50%) were studied for improving the dough handling characteristics. Rheological parameters like storage modulus (G′) and complex viscosity (η*) decreased with an increase in moisture content while loss angle (δ) increased. A power‐law type equation was suitable to relate angular frequency (ω) with G′, G″, and η* (0.814 ≤ r ≤ 0.999, P ≤ 0.01). An increase in gum and moisture contents increased δ from 6.9° to 15.5° but decreased the energy required for compression/flattening. The 6‐element spring‐dashpot model was suitable (r ≥ 0.991, P ≤ 0.01) for creep curves. The sensory panel had the opinion that dough with a low to moderate hardness between 3 and 4, and stickiness of ≤3.5 was suitable for the purpose of flattening in relation to the preparation of sheeted/flattened products; the appropriate condition for dough formulation was with the moisture and gum contents of 47.0% to 47.9% and 1.55% to 2.25%, respectively to offer the desirability index between 0.50 and 0.52. The microstructure of the rice flour dough in the absence of gum Arabic appeared to possess loosely bound flour particles. The presence of gum provided a coating on flour particles to yield dough having good cohesive microstructure.     

Quantitative Determination of Bound Water By NMR

SUMMARY— A Nuclear Magnetic Resonance (NMR) instrument was used to measure the amount of liquid water in a complex colloidal system over a broad temperature range. The bound water content, defined as that which remained liquid at 0°F (−18°C), was 0.29±0.01 g water per g dry solid in case of a wheat flour dough. This value was independent of total moisture content for doughs of the same flour with moisture contents greater than 24.6%. NMR signals indicated that most of this water remained liquid at −58°F (−50°C). This method gives a direct reading of bound water and is nondestructive of sample.     

Effect of extrusion conditions on resistant starch formation from pastry wheat flour

Pastry wheat flour was extruded under various conditions of feed moisture (20%, 40%, and 60%) and screw speed (150, 200, and 250 rpm), at constant barrel temperature profile (40, 60, 80, 100, and 120 °C, feed port to exit die). The extruded samples were stored at 4 °C for 0, 7, or 14 days, at which times resistant starch (RS) formation was analyzed. Thermal and pasting properties of extruded samples stored for 14 days were analyzed using a differential scanning calorimeter and rapid visco analyzer (RVA), respectively. The RS content increased after extrusion compared to non-extruded pastry wheat flour. High significant positive correlations of feed moisture (P < 0.01) and storage period (P < 0.05) with RS formation were observed. The RS derived from extrusion and storage showed higher thermal stability with decreasing feed moisture and screw speed. Statistically significant differences in pasting properties were observed with feed moisture or screw speed. In particular, the setback value from RVA of the sample was significantly increased with increasing feed moisture. These results indicate that feed moisture and storage time were both important factors for the formation of RS from pastry wheat flour during extrusion.     

Evaluation of l-ascorbic acid oxidation on SH concentration in soy-wheat composite dough during resting period

The effect of l-ascorbic acid (l-AA) on free sulfhydryl concentration (SH) was evaluated in soy-wheat composite dough from 100-500 (g/kg) soy flour substitution for wheat flour. Raw soy flour (RSF) and physically modified soy flours (PMSF1 and PMSF2) were used for the preparation of the composite dough with wheat flour. The two physically modified soy flours were prepared by steam flushing (PMSF2) and water boiling (PMSF1) of raw soy beans before flour preparation. Using a timer, dough blends were manually mixed (at approximately 60 rpm) to dough development time after which, dough was sampled for the estimation of free SH groups. l-AA (0.05% w/w) was mixed with the dough after dough development and the dough was sampled after 1 h of resting the dough. The results showed that l-AA (0.05% w/w) acted as a reducing agent by increasing SH levels in all soy-wheat dough blends (P<0.05). After 1 h of resting, soy-wheat composite dough without l-AA had lower concentrations of SH than that with l-AA. A positive correlation was shown between soy flour concentrations and SH concentration before and after dough resting. A negative correlation existed between l-AA consumption and SH concentration for RSF-wheat, PMSF1-wheat and PMSF2-wheat doughs. The results indicated that soy flour weakened wheat flour dough by increasing SH concentration and that l-AA could have a synergistic effect on the reduction of gluten proteins and thus weakening the dough.     

Water Binding of Wheat Flour Doughs and Breads as Studied by Deuteron Relaxation

Water mobility in wheat flour doughs and breads was investigated by deuteron relaxation using pulsed NMR. Water was replaced by deuterium oxide in dough and bread at different concentrations. Mixograms indicated that wheat flour associated more strongly with D₂O than it did with H₂O. Varying the D₂O:H₂O ratio of flour doughs had no effect on the longitudinal (T₁) or transverse (T₂) relaxation times of deuteron. Hard wheat and soft wheat flour doughs showed similar increases in T₁ and T₂ with increasing moisture content. Staling of bread crumb was accompanied by decreased T₁ and T₂, indicating an overall decrease in water mobility and increase in water binding. The decrease in water mobility of bread crumb with storage time was shown to be independent of reduction in moisture content.     

Physical and functional characteristics of selected dry bean (Phaseolus vulgaris L.) flours

Many varieties of dry beans (Phaseolus vulgaris L.) are available with entirely different physico-chemical and sensory characteristics. Selected dry bean varieties (red kidney, small red kidney, cranberry and black) were processed into flour and analyzed for the physico-chemical and functional characteristics. The bulk density of the beans flours varied significantly (p < 0.05) from 0.515 g/ml for black bean flour to 0.556 g/ml for red kidney bean flour. The small red kidney bean flour had the highest water absorption capacity (2.65 g/g flour) while black bean flour showed the lowest at 2.23 g/g flour. Significant differences were observed for oil absorption capacities of bean flours, which ranged from 1.23 g/g for small red kidney bean flour to 1.52 g/g for red kidney bean flour. The bean flours emulsion capacity and stability and foaming capacity and stability also varied significantly and was variety-dependent. The highest apparent viscosity, 0.462 Pa.s, was recorded for small red kidney bean flour whereas black bean flour exhibited the lowest value of 0.073 Pa.s at 30 g/100 ml water content in the flour dispersions. The force-deformation curves for doughs from different bean flours showed that black bean flour had the highest peak force or hardness value of 90.7 N followed by doughs from cranberry, small red kidney and red kidney bean flours. The results of this study offer useful data on bean flours' potential uses in different food products.     

RHEOLOGICAL MODELING of POTATO FLOUR DURING EXTRUSION COOKING

A generalized model for predicting the effects of shear rate, temperature, moisture content, time-temperature history and strain history on viscosity has been evaluated for extruded potato flour doughs. an Instron Capillary Rheometer and a 50 mm Baker Perkins co-rotating twin screw extruder were used to evaluate all effects incorporated in the model, except strain history. the power law model was used to describe shear rate effects in the range 10–10000 s^?1. the generalized model fit observed data for temperatures of 25–95°C and moisture contents ranging from 22 to 50%, wet basis. Since potato flour by its manufacturing process is pregelatinized, it was unnecessary to evaluate the effects of time-temperature history. Strain history was found to have an insignificant influence on the viscosity.     

Effects of cold extrusion process on thiamine and riboflavin contents of fortified corn extrudates

In this study, corn extrudates were produced from fortified corn flour by conventional and cold extrusion techniques at different barrel temperatures of 80, 110, 130 and 80 °C, respectively, and feed moisture contents. Thiamine and riboflavin contents of extrudates were determined by HPLC. Thiamine contents of the samples produced at feed moisture contents 20% and 25% decreased as temperature increased. There was no significant difference between riboflavin contents of conventional extrudates produced at both feed moistures at 80 and 110 °C barrel temperatures. However, riboflavin content of extrudates produced at 20% feed moisture was higher than the one produced at 25% feed moisture at 130 °C. In cold extrusion, there was no significant difference between riboflavin contents of samples. The samples produced by CO₂ injection had the lowest expansion index and uniform air cells. However, the samples produced by conventional extrusion had higher expansion index and size distributions of air cells were not uniform.     

The effect of genotype and roasting on the fatty acid composition of peanuts

The impact of two factors, genotype (G) and treatment (raw or roasted peanut) (T), on the chemical composition of peanuts was studied using a chemometric method and Tukey's test. The peanut genotypes evaluated were cultivar cavalo vermelho (CCV), cultivar cavalo rosa (CCR) and cultivar tatu (CTA), in both raw and roasted states. The total lipid contents in the CTA and CCR peanuts were 40 and 45%, respectively. These values did not vary significantly (P < 0.05) after roasting. CCV had the greatest total lipid content, but it decreased significantly after roasting (from 50% to 45%). The variation in the percentage of lipids in the CCV and CCR genotypes was not significant, in contrast to the CTA genotype. The fatty acid (FA) 18:1n−9 predominated in the CCR and CCV samples (50%), without any difference between their raw genotypes. The values for FA 18:1n−9 were lower in the CTA peanut (40%). The second most abundant FA was 18:2n−6 (CCV = 28%, CTA = 38% and CCR = 25%), followed by 16:0 (CCV and CCR = 16% and CTA = 11%). The other FAs found in the peanuts were 18:0, 20:0, 22:0, 24:0, 20:1n−9 and 18:3n−3. The contents of FAs 18:1n−9, 16:0, 20:0, and 20:1n−9 suffered significant reduction after roasting in all genotypes. ANOVA analysis of the influence of the main factors indicated that the contribution of the T variable for the majority of responses was low, being between 0.2 and 13%, except for FAs 16:0 and 18:3n−3 and for the saturated FA summations, which were 38, 60 and 22%, respectively. There was a significant contribution from the G factor for all responses, with values between 17 and 99%. The contribution of the interaction between the T and G factors was greater for the responses n6/n3 (56.6%) and for the FA 16:0 (23%). The other responses had values between 0.02 and 14%.     

Dielectric properties of chestnut flour relevant to drying with radio-frequency and microwave energy

Dielectric properties of compressed chestnut flour samples with 11.6–48.0% w.b. moisture content were determined with a network analyzer and an open-ended coaxial-line probe over a frequency range from 10 to 4500 MHz and a temperature range from 20 to 60 °C. The results showed that the permittivities of chestnut flour were a function of frequency, moisture content and temperature. Both dielectric constant and loss factor decreased with increasing frequency but increased with increasing moisture content and temperature. The relationship between permittivities and moisture content and temperature at 27, 40, 915 and 2450 MHz could be described by second- or third-degree polynomial models, with the coefficients of determination higher than 0.993. The analysis of variance showed that moisture content and temperature had strong significant effects on permittivity values. The penetration depth decreased with increasing frequency, moisture content and temperature. Large penetration depth at radio frequencies below 100 MHz may provide practical large-scale dielectric drying of chestnut.     

THE COMPUTATION OF VISCOSITY AND RELAXATION TIME OF DOUGHS FROM BIAXIAL EXTENSION DATA 1

Stress (T) versus time (t) data were obtained for wheat flour doughs in lubricated, constant crosshead speed, uniaxial compression experiments. These data were then analyzed by using the Upper Convected Maxwell (UCM) Model with two parameters, a relaxation time (Λ) and a shear viscosity (η). The numerical solutions to the differential equation governing the behavior of the UCM model in this experiment can be very sensitive to the initial slope of the stress/time plots. This region of the curve, near t = 0, is most sensitive to experimental error. Best-fit values of Λ and η were thus computed for a given curve at a series of initial starting points, t_i, which were sequentially taken up the stress/time plots. There was considerable fluctuation in the best-fit parameters but, nevertheless, values of relaxation time and shear viscosity could be obtained that gave good agreement between computed and experimental stress/strain curves.     

Characterisation of phenolic components present in raw and roasted wattle (Acacia victoriae Bentham) seeds

The effect of roasting on the phenolic components of Australian wattle (Acacia victoriae Bentham) seed was investigated. Wattle seeds were roasted at 200 °C for 5–30 min and ground to flour, which were then extracted with 70% acetone. The total phenolic and flavonoid contents of the extracts were determined, and the phenolic components were analysed by reverse phase-high performance liquid chromatography (RP-HPLC) coupled with an on-line post-column reaction system to determine the active antioxidant peaks. The major peaks were then purified by preparative HPLC and identified by gas chromatography–mass spectrometry (GC–MS) analysis. Roasting of wattle seeds resulted in significant increases in its soluble phenolic content. The concentration of total phenolics and flavonoids in the seeds roasted for 30 min was more than nine and four times higher, respectively, than that in the raw seeds. The major phenolic acids present in wattle seeds were found to be succinic and gallic acids, the concentration of which increased by up to 10-fold as a result of roasting.     

Reducing cracking and breakage of soybean grains under combined near-infrared radiation and fluidized-bed drying

Near-infrared radiation was combined with fluidized-bed drying to reduce the cracking and breakage of soybean grains because of its advantages such as a decrease in the moisture gradient and the stresses development within the grain kernel, leading to high quality of product. Physical qualities, i.e. cracking, breakage and colour, were investigated together with microstructure of soybean grains. Protein solubility and urease activity were also determined. The parameters studied were near-infrared radiation powers of 4, 6 and 8 kW, air velocity of 4.5 m/s, air temperature of 40 °C and grain bed depth of 6 cm. Results showed that the drying rate was increased with the increase of near-infrared radiation power. The moisture content was reduced from an initial moisture content of 20% d.b. to the final moisture contents of 13.5% d.b. (4 kW), 12.8% d.b. (6 kW) and 12.5% d.b. (8 kW). The cracking and breakage of soybean grains occurred negligible, which was lower than 4.4% and 5.3% for cracking and breakage, respectively. At near-infrared radiation powers of 4 and 6 kW was accepted for both soybean grains trade and animal feed industries in Thailand. The total colour difference changes (ΔE) were varied in the range of to 2.9-4.2. The protein solubility of final product was in an acceptable range (77-82%) for feed meal. The reduction of residual urease was varied in the range of to 39-70%. This study has demonstrated that the soybean grains under combined near-infrared radiation and fluidized-bed drying was properly treated.