INFLUENCE OF NATIVE LIPIDS ON THE RHEOLOGICAL PROPERTIES OF WHEAT FLOUR DOUGH AND GLUTEN

We report on the viscoelastic properties of dough and gluten (prepared by ultracentrifugation) after the flour lipids had been removed by solvents differing in polarity (chloroform, ethanol and diethylether). The extracted lipids were fractionated by thin layer chromatography. The flours differed in lipid composition after the extraction. Ethanol removed more polar lipids than the other solvents. Removal of lipids (0.6–0.9% on flour weight) altered the viscoelastic properties of dough significantly, whereas those of gluten were only marginally affected. The storage modulus (G′) of dough increased with used solvent polarity. The highest value of G′ was observed for the dough made with the flour where the lipids were removed by ethanol. This was consistent with a marked decrease in the frequency dependence of G′ of dough when the lipids were removed.     

EFFECT OF EMULSIFIERS AND FUNGAL α-AMYLASE ON RHEOLOGICAL CHARACTERISTICS OF WHEAT DOUGH AND QUALITY OF FLAT BREAD

Teftoon, a flat bread made of whole wheat flour, is prepared by hand sheeting of dough, followed by baking. Different emulsifiers, like lecithin, E471 (distilled monoglyceride) and E472 (diacetylated tartaric acid esters of mono- and digelycerid of fatty acids), were added to the flour at various levels ranging between 0.25 and 1.0% w/w, and it was observed that they improved the dough characteristics. Improvement in bread quality parameters, such as force to tear and sensory acceptability, were monitored. Fungal α -amylase was also incorporated into the flour at 5–20 g/100 kg flour basis alone and in combination with the emulsifier. The force required to tear the fresh bread was decreased with emulsifier and enzyme addition; however, E472 addition at 0.75% w/w of whole wheat flour gave the softest bread. The tear force of stored bread significantly increased with storage; however, bread containing E472 showed a less increase in tear force up to a period of 3 days. The sensory acceptability was found to be higher than that of the control bread for emulsifiers, and lower for enzyme at a concentration higher than 10 g/kg flour.

PRACTICAL APPLICATIONS

Flat bread is normally consumed fresh, but the staling phenomenon starts immediately after baking this kind of bread. Today, large-scale production and increased consumer demands for high-quality bread with long shelf life have created the need for functional food additives such as emulsifiers and α -amylase enzyme. Incorporation of emulsifiers and enzyme decreased the hardness of Taftoon bread. Emulsifiers and α -amylase enzyme enhanced the flat bread dough quality. The sensory acceptability also improved with the addition of emulsifiers. Optimizing the amount of emulsifiers and enzyme required for reduction of bread hardness is vital because the quality and price of the final product depend on this parameter.     

THE EFFECT OF PROTEIN FORTIFICATION ON THE ACCEPTABILITY AND RHEOLOGICAL PROPERTIES OF COOKIE DOUGH AND ITS FINAL PRODUCT1

All-purpose wheat flour and all-purpose wheat flour fortified with 6% soy flour; 2, 4 and 6% single cell protein (SCP) were used. Protein quantity was increased significantly in both flour and cookies. Sensory panel evaluations were conducted for flavor, texture and overall acceptability of cookies, and objective evaluation of rheological properties were made with the farinograph and shear-press on doughs, and shear-press on cookies. Fortification with SCP at all levels altered all the sensory parameters significantly, but fortification with soy flour altered only cookie texture. Fortification with both SCP and soy flour significantly decreased the “spread factor” quality. Correlations between panel texture scores and texture parameters from the farinograph or the shear-press were not significant. However “Consistency” and “Elasticity” obtained from farinograms were significantly increased due to the high level of fortification by SCP and soy flour, and the same results were found in “Viscoelasticity” obtained from the shear-press. Also, the determinations from both instruments showed that the tolerance to kneading was significantly reduced as a result of the fortification. Adhesive properties of dough as obtained from texturegrams were significantly increased due to the 5% SCP and soy flour fortifications. The variations of textural characteristics were highly predictable from texture parameters of doughs as obtained from both instruments. Thus the coefficient of determination (R²) of crispness and hardness as measured by the shear-press were 0.987 and 0.999 when farinogram parameters were used, and 0.999 and 0.997 when texturegram parameters were used as independent variables.     

干酪质地及流变学特性的研究进展

介绍了有关干酪的成分及工艺过程对质地和流变学特性影响的研究。在干酪成分中，蛋白质是影响产品流变学特性的主要因素，酪蛋白空间形成的网状结构构成了干酪流变学的基础。在加工过程中，pH、温度、钙浓度、蛋白水解等所有对干酪成分分子产生变化的因素都可能使干酪的流变学特性和质地发生变化。因此，干酪流变学特性的研究对更好地控制质地，生产出质优价廉的干酪，具有重要的意义。最后，研究状况进行了展望。     

EFFECTS OF EMULSIFIERS,SORBITOL, POLYDEXTROSE,AND CRYSTALLINE CELLULOSE ON THE TEXTURE OF REDUCED-CALORIE CAKES1

The textural and sensory qualities of reduced-calorie cakes prepared from non-shortening batters in which sucrose was partly replaced with sorbitol or poly-dextrose (with the addition of carboxymethylcellulose or microcrystalline cellulose to the latter) was studied. The batters were treated with different types and concentrations of emulsifier (Tandem 22H, Atlas A and MD-SSL). At the 30% replacement of sucrose with 1.5% or 3.5% (on flour weight) of Tandem 22H or Atlas A, the cakes were of an acceptable quality. Higher levels of emulsifier treatment further enhanced the aeration capacity of the batters, but impaired the overall quality of the final product. The emulsifier MD-SSL was found to be less suitable under the given conditions of cake baking because of the excessive aeration of batters. With cakes of acceptable quality, the calorie value reduction was in a 15 to 23% range compared with a standard full-calorie cake.     

EFFECT OF THE AMOUNT AND PARTICLE SIZE OF WHEAT FIBER ON TEXTURAL AND RHEOLOGICAL PROPERTIES OF RAW,DRIED AND COOKED NOODLES

ABSTRACT

Textural and rheological properties of raw, dried and cooked noodles enriched with wheat fibers were simultaneously evaluated by a texture analyzer. Increasing wheat fiber level led to an increase in the cutting force of raw and cooked noodles and a decrease in the breaking force of dried noodle as well as extensibility of raw and cooked noodles. Generally, raw, dried and cooked fiber‐enriched noodles with small fiber size had higher breaking force and extensibility and lower cutting force than that with large fiber size. The textural properties of raw noodle are good indicators to predict the strength and elasticity of dried and cooked noodles. Both three‐term Maxwell and Peleg–Normand models were found to fit well to the stress relaxation data of cooked fiber‐enriched noodle. Significant correlations were found between empirical textural properties and fundamental mechanical stress relaxation parameters.

PRACTICAL APPLICATIONS

Texture is one of the important factors affecting the quality of noodles. The increased consumption of noodles enriched with wheat bran or purified wheat fiber is proposed for health reasons. The textural properties of fiber‐enriched noodles are affected by the type, amount and size of wheat fiber. The cutting force, tensile strength and extensibility of raw noodle are good indicators to predict the strength and elasticity of dried and cooked noodles. Results of this study suggest that raw, dried and cooked fiber‐enriched noodles with good quality can be prepared by adding 4–8% fine wheat bran or 4% fine purified wheat fiber.     

EFFECTS OF SALT REDUCTION ON THE RHEOLOGICAL AND GELATION PROPERTIES OF WHITE AND DARK POULTRY MEAT BATTERS

The rheological and gelation properties of poultry dark and white meat batters prepared with average and reduced NaCl levels (2%, 1% and 0%) and with 0.5% hexametaphosphate (HMP) added to the 1% salt batters were studied. Lowering the salt content decreased the shear stress in both the white and dark meat at the same shear rates. HMP addition to the 1% NaCl treatments increased the shear stress in the dark meat but not in the white meat at the same shear rates using a concentric cylinder viscometer. The relationship between the rotor angular velocity and shear stress of the raw batters was nonlinear and resembled a pseudoplastic behaviour with yield stress in all cases. Plots of the modulus of rigidity (G) versus cooking temperature indicated that white meat always exhibited higher G than that of dark meat. The highest G was observed in the white meat with 2.0% NaCl and the lowest in the dark meat with no salt. The batters with no salt also exhibited gel formation, however with lower G values.     

THE RHEOLOGICAL BASIS OF DOUGH STICKINESS

Stickiness in wheat flour doughs was studied as a function of rheological and surface properties. Adhesion was measured using a modified peel test at various water additions, peel rates and peel layer thicknesses. Peeling energy gave a strong positive correlation with subjective bakery stickiness ratings. Peeling forces were highly rate dependent and showed transitions from sticky to nonsticky behvaiour with increasing rate of peeling. Dynamic storage modulus showed a negative correlation with stickiness ratings, suggesting stickiness is primarily a rheologically controlled process. Stress relaxation gradients were greater for sticky doughs and were very similar to peeling force vs. rate slopes, again indicating that adhesion is principally a function of the rheological properties of the dough. Surface tension measurements of sticky and nonsticky dough/liquor interfaces showed no significant differences and are typical of protein solutions. Calculated values of the interfacial surface energy between dough and interface were about 100 mJ/m², typical of secondary bonding interactions such as polar or van der Waals bonding.     

变性淀粉及谷朊粉对面团特性的影响研究

研究淀粉及变性淀粉、谷朊粉对面团特性的影响。结果显示：在面粉中，按4％的比例添加马铃薯变性淀粉，对面团的稳定时间、弱化度及抗张强度等均有显著的影响（P〈0．01）；添加6％木薯变性淀粉，面团抗张力增加26、6％；添加3％的谷朊粉，面团形成时间及稳定时间均有较大增加。木薯原淀粉及其变性淀粉等对面团的特性影响不大。     

THE EFFECT OF HEAT AND SHEAR ON THE VISCOELASTIC PROPERTIES OF SOY FLOUR DOUGH

This paper is concerned with the effect of heat and shear on the rheological properties of defatted soy dispersions and doughs of 30 to 60% flour by weight. Capillary and rotary rheometers (Rheometrics Mechanical Spectrometer) were used to heat doughs up to 75° C and shear them simultaneously. In one series of experiments using a modified Instron capillary rheometer the doughs were heated to several different temperatures and then sheared. The linear viscoelastic properties of the dough which were determined by means of a plate-plate rheometer were then compared to the fresh dough and those of a heated but nonsheared dough. In another experiment a cone-and-plate rheometer was used to heat and shear the dough. The linear viscoelastic response of the dough was used to monitor any changes as it was heated and sheared. It was observed that only in the higher moisture dispersions (i.e., moisture contents greater than 50%) were there any signs of an increase in rheological properties which might be associated with “cooking”. It was concluded that cooking of soy flour doughs most likely does not involve the formation of a permanent network formed by covalent chemical bonds. Hence, in extrusion cooking processes involving soy flour doughs, it may not be necessary to treat the rheological properties of the dough as a thermosetting system.     

CHEMICAL MODIFICATION EFFECTS ON TEXTURE AND GELATION PROPERTIES OF FINELY COMMINUTED BEEF

The effects of various chemical modifications on gelation and texture of finely comminuted lean beef mixes were investigated. Urea, which disrupts non-covalent bonds, significantly increased (at 95% level) the modulus of rigidity (G) and hardness values compared to the control (no additive). Oxidation of free sulphdryl groups by H₂O₂ resulted in lower G but similar hardness values of the control. The β-mercaptoethanol (ME) treatment was similar to the control in G values but higher in hardness, gumminess and chewiness. Ethylenediamine tetraacetic acid (EDTA) addition resulted in excessive cooking losses, the lowest G value and the hardest texture. Polyoxyethylene sorbitan monooleate did not have any significant effect on the textural characteristics of the finely comminuted mixes but resulted in lower G compared to the control.     

USE OF NONLINEAR DIFFERENTIAL VISCOELASTIC MODELS TO PREDICT THE RHEOLOGICAL PROPERTIES OF GLUTEN DOUGH

Nonlinear viscoelastic models of the differential type, such as the Phan Thien Tanner model, White‐Metzner model and Giesekus model were used to predict the steady shear, oscillatory shear and transient shear properties of gluten dough. The predictions were compared with new data and the experimental results of Wang and Kokini (1995b). The Phan‐Thien Tanner model and the Giesekus model were used in eight modes to fit the relaxation modulus accurately. The White‐Metzner model gave the best prediction for the steady shear properties as it used a Bird‐Carreau dependence for the shear viscosity. The Phan‐Thien Tanner model and the Giesekus model predicted the transient shear viscosity and the transient first normal stress coefficient better than the White‐Metzner model. A consistent prediction of all the experimental data could not be obtained using a single model.     

A COMPARISON OF THE FARINOGRAPH AND A MODIFIED SHEAR-PRESS FOR MEASURING THE RHEOLOGICAL PROPERTIES OF DOUGH AND ITS FINISHED PRODUCTS1

The development of a single texture testing instrument for determining the complicated properties of dough and the textural characteristics of the final product of dough will eliminate the need for a series of specialized instruments. The farinograph and a modified shear-press were used to determine the rheological properties of doughs made from 15 mixtures of all purpose wheat flour, hard wheat flour and 6% soy fortified wheat flour adjusted with 54.7, 58.0, 61.1, 64.6 and 67.9% water absorptions. The shear-press was also used to determine the textural characteristics of the finished products. The shear-press was found to be equal to the farinograph in providing information on certain rheological properties of dough, and high correlations were obtained between these ‘texturegrams’ and farinogram parameters. For instance, the correlation between “viscoelasticity” per texturegram and “maximum consistency” per farinogram was 0.982; between “viscoelasticity” per texturegram and “elasticity” per farinogram was 0.969; and the correlation between “stability of viscoelasticity” per texturegram and “twenty minute drop” per farinogram was 0.941. The adhesive and cohesive properties of dough obtained from shear-press texturegrams explained 88.4% of the variance of the hardness of the end-products. The consistency and elasticity of dough obtained from farinograms explained 90.6% of the variance of the hardness of the end-products. If the method of water absorption and mixing of flour could be standardized, the shear-press could be utilized both for predicting rheological properties of bakery products from determinations on doughs as well as direct evaluations of the finished products.