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.     

Stress relaxation/creep compliance behaviour of kashar cheese: Scanning electron microscopy observations

In this study, uniaxial and creep analyses were used to characterise stress relaxation and creep compliance behaviour of kashar cheese as a function of different compression (1.5, 3.0, 4.5, 6.0 and 7.5 mm) and stress (12.25, 24.50, 36.75, 49.00 and 61.25 kPa) levels. For this purpose, mechanical simulation models, namely generalised Maxwell, Nussinovitch, Peleg and Burger models were used to simulate the viscoelastic behaviour of kashar cheese as a function of different compression and stress levels. The results revealed that the compression levels could remarkably change internal structure and deformation properties of kashar cheese. Stress relaxation test demonstrated that kashar cheese showed more elastic behaviour, namely higher resistance to deformation at higher compression levels. Creep tests showed that rigidity of kashar cheese decreased as the stress level applied increased. Scanning electron microscopy (SEM) images showed that compression resulted in a less homogeneous protein matrix, an interrupted casein/fat network, and destroyed fat globules by forcing them to exude from the cheese surface. These results should be useful for dairy industry.     

Stress relaxation of reconstituted cassava dough

The viscoelastic characteristics of reconstituted cassava dough were evaluated using a stress-relaxation test. Cassava parenchyma (peeled root) processed under different cooking conditions and left at either −5 or −20 °C for 24 h was used to obtain flour, which was reconstituted into dough. Two stress-relaxation models (Maxwell two-termed and Peleg) were fitted to experimental data. Both models were valid for quantifying the relaxation behaviour; but the Maxwell model was better to predict experimental data. Most dough rheological attributes depend on the cooking method and the storage temperature. Dough samples made with flour from parenchyma boiled and left at −20 °C for 24 h had higher values of elasticity moduli, higher viscosity values and lower values of Peleg constants.     

Interpretation of viscoelastic behaviour of sweet cherries using rheological models

Viscoelastic behaviour of some commercial sweet cherry cultivars of Iran has been studied in current research. For this purpose, stress relaxation test was conducted on five cultivars of sweet cherry including Siah Mashhad, Abarde, Victoria, Dovom Ras and Tak Dane. Two common models (Generalised Maxwell model and Peleg model) were fitted to the experimental data. Both models could describe stress relaxation behaviour of cherries (R² = 0.99), but Generalised Maxwell model had lower root mean square error (RMSE) than Peleg model. Based on analysis of stress relaxation data using models constants, Tak Dane exhibited more solid properties, while Victoria showed less elastic behaviour than other cultivars. The results revealed that relaxation ratio (R%) and the area under the stress relaxation curve could be effective alternative to models with easier mathematical procedure.     

CREEP BEHAVIOUR OF TOMATO PERICARP TISSUE AS INFLUENCED BY AMBIENT TEMPERATURE RIPENING AND CHILLED STORAGE

The influence of normal ripening and chilling stress on viscoelastic properties of tomato pericarp tissue were investigated by measuring creep behaviour of tissue from fruit stored at 22C (nonchilled) or 5C (chilled) for 28 days, or at 5C for 16 days prior to transfer to 22C for an additional 12 days (prechilled). Creep compliance of tissue from all treatments subjected to a constant shear stress of 150 Pa for 5 min was best represented by a 6-element Burgers model containing two discrete Voigt-Kelvin units characterizing fast and slow rate viscoelastic properties. The magnitude of instantaneous elastic, viscoelastic and steady-state viscous compliances each increased steadily and contributed to the overall softening of nonchilled and prechilled tissues during ripening, but remained unchanged during chilling of tomato fruit. Increased fluidity of ripening tissues occurred at the expense of elasticity, consistent with a decrease in molecular weight-size distribution of structural elements contributing to respective viscoelastic properties. The physico-mechanical changes in prechilled tissue preceded those in nonchilled tissue by several days, and occurred at a faster rate. The 6-element Burgers model defining the creep behaviour of tomato pericarp tissue was interpreted with respect to general plant cell wall structure and biochemical changes known to occur during ripening of tomato fruits. Multiple mechanisms of softening were thereby consolidated into a single physico-mechanical model.     

Viscoelastic behavior of persimmons dried at constant air temperature

The viscoelastic behavior of dried persimmons at different air-drying temperatures and velocities was evaluated. Air temperatures and velocities were varied according to a second-order central composite design, with temperature ranging from 40°C to 70°C and air velocity from 0.8 to 2.0 m/s. After drying, persimmons were equilibrated at four different water activities: 0.432, 0.576, 0.625 and 0.751. The rheological behavior of dried and conditioned persimmons was studied under uniaxial compression–relaxation tests. Three different rheological models were fitted to the experimental relaxation curves: Maxwell, Generalized Maxwell and Peleg and Normand. Based on the root mean square of residuals, the Generalized Maxwell model showed the best fit and a regression analysis was applied to obtain response surfaces for the model parameters. The dependence of the rheological properties on water activity was also analysed. Results showed that only the linear effect of air temperature was significant at a 5% level on the equilibrium stress and relaxation times. In a general way, these parameters increased with increasing air temperature and decreasing water activity.     

Phenomenological viscoelasticity of some rice starch gels

The applicability of a powerful but still easy to use technique, based on a phenomenological theory of viscoelasticity, for processing and analyzing dynamic mechanical data of some rice gels was investigated. Based on this theory a continuous relaxation spectra was generated by application of Tikhonov regularization procedure on continuous Maxwell model. Interpretation of relaxation spectra in terms of number of peaks, its peak intensity H(λ) and appearance of its main distribution peak and magnitude of equilibrium elasticity modulus (G_e) of continuous Maxwell model was found to appropriately reflect main peculiarities of the viscoelastic behavior of rice starch gels. An increase in number of peaks in the relaxation spectra was observed for starch gels having higher amylose content indicating the creation of more heterogeneous structure. H(λ) and G_e values also increased with increase in amylose content demonstrating a transition of the system to more stable state like a gel.     

Chemical composition,sensory and cooking quality evaluation of durum wheat spaghetti enriched with pea flour

The goal of the study was to obtain spaghetti enriched with pea flour with sensory properties close to conventional pasta. To this aim, the study has been organised in two subsequent trials. In the first, the pea flour amount added to the spaghetti was continuously increased until the overall sensory quality reached its threshold value (pea flour concentration = 15%). In fact, the spaghetti samples supplemented with 15% pea flour (15%S‐P) showed less elasticity, unpleasant colour and higher firmness compared to the control sample (CTRL). The second step was aimed to improve the overall sensory quality of the 15%S‐P spaghetti by means of guar gum (GUAR). The sample with GUAR (15%S‐P/GUAR) showed a pleasant colour, odour and taste. Furthermore, the 15%S‐P/GUAR sample recorded a low starch digestibility value (i.e. 54) and a higher soluble fibre content with respect to the 15%S‐P sample.     

Prediction of viscoelastic properties of peanut-based 3D printable food ink

Viscoelastic properties of 3D printable peanut-based food ink were investigated using frequency sweep and relaxation test. The incorporation of xanthan gum (XG) improved the shear thinning behavior (n value ranging from 0.139 to 0.261) and lowered the η*, G′, and G′′ values, thus making food ink 3D printable. The addition of XG also caused a downward shift in the relaxation curve. This study evaluates the possibility of an artificial neural network (ANN) approach as a substitute for the Maxwell three-element and Peleg model for predicting the viscoelastic behavior of food ink. The results revealed that all three models accurately predicted the decay forces. The inclusion of XG decreased the hardness and enhanced the cohesiveness, so enabling the 3D printing of food ink. The hardness was highly positively correlated with Maxwell model parameters F_e, F₁, F₂, F_3, and Peleg constant k₂ (0.57) and negatively correlated with k₁ (−0.76).     

Influence of Drying Temperature and Rehydration on Selected Textural Properties of Carrots

Cubes of carrots dried at 60, 70, 80, and 90°C were rehydrated up to 180 min at 20°C and up to 10 min at 95°C. Kinetics of cutting strength were determined for the samples soaked at 95°C. Compression stress relaxation behavior of the samples was studied on carrots rehydrated at 20 and 95°C. Kinetics of cutting strength were satisfactorily described by means of a first-order kinetic model. The compression stress relaxation of carrots was analyzed using five element Maxwell and empirical Peleg models. Both of the models were found to be appropriate for characterizing viscoelastic properties of dried and rehydrated carrot cubes. The results indicated that the use of low drying temperatures was suitable for preserving the quality attributes of carrots after rehydration, and drying air temperature of 60°C was chosen as the most appropriate for hot air processing of carrots.     

Rheological characterization of fresh and cooked potato tissues (cv.?Monalisa)

 The rheological properties of fresh and cooked (15 min in boiling water) potato tissue which had been deformed to a lessor or greater extent by uniaxial compression, shear, uniaxial tension, successive cycles of stress relaxation, creep compliance and texture profile analysis were evaluated. Structural failure of fresh tissue under compression always occurred along a single plane of maximum shear stress, while fresh tensile specimens failed under tension. Tensile tests proved better methods by which to determine the failure parameters of cooked specimens since it was possible to observe two differents modes of failure with this technique. Equivalent modes of failure (causing damage to the cell wall or cell separation) and changes in structural components caused by cooking proved easier to idetify with tensile tests. The six element Burger's model incorporating two discrete Voigt-Kelvin units was the most suitable for defining tissue creep behaviour. The instantaneous elastic modulus could be related to the internal cell pressure, and gelatinization of starch and viscoelastic units appeared to reflect the viscoelastic properties of pectic sustances and hemicelluloses, respectively. Received: 1 December 1997     

Viscoelastic characterization of solid foods from creep compliance data: application to potato tissues

 Two software systems were developed to simplify acquisition and analysis of data describing creep behavior of viscoelastic solid foods and to determine the magnitude of instantaneous elastic compliance, viscoelastic compliances and viscosity associated with Newtonian flow. The first of these systems was used to store information on the experiment, to collect the data generated during the experiment, to present these in real time and to create files containing the experimental data for subsequent analysis. The second system was used to fit data to discrete Kelvin-Voigt models with four, six or eight constants. The systems were tested in the calculation of rheological properties of fresh and cooked potato tissues. A six-element Burgers model containing two discrete Voigt units proved the most suitable for defining tissue creep behavior, suggesting that different structural components could be related to each unit. The instantaneous elastic modulus could be associated with internal cell pressure. Gelatinization of starch and viscoelastic units appeared to reflect the viscoelastic properties of pectic substances and hemicelluloses, respectively. Received: 5 March 1998     

The viscoelastic properties of soybean curd (tofu) as affected by soymilk concentration and type of coagulant

The viscoelastic properties of different types of tofu were investigated. Soymilk concentrations were 5, 6, 7, 8 and 9%. Coagulants used were 30 mm CaSO₄ or 30 mm glucono‐delta‐lactone (GDL). As the concentration of soymilk was increased viscosity and handling difficulties increased. A high concentration of soymilk in tofu gave a high break stress and produced hard tofu. The four‐element Burgers model fitted the creep behaviour and both viscous and elastic parameters could be acquired from model analysis, reflecting changes in elasticity and viscosity of tofu. The constant viscous parameter in the model increased with increasing soymilk concentration. The viscous parameters of viscoelastic materials like tofu gel, obtained from small deformation tests, seemed to correlate, to some extent, with the break stress obtained from large deformation tests. For hard tofu production increasing the soymilk concentration within a certain range and the partial replacement of calcium sulphate coagulant by GDL could be effective options.     

Effect of insoluble dietary fibre addition on technological,sensory, and structural properties of durum wheat spaghetti

Insoluble fibres are important in human health and disease prevention and can be incorporated into food. High fibre pasta prepared with bran is typically inferior quality compared to durum pasta. This study compared spaghetti prepared from durum semolina substituted with various amounts of either durum bran or germ (pollard) dried at high temperature. Pasta was evaluated for cooking properties, texture, sensory, fibre content, antioxidant status (AO) and in vitro starch digestibility to determine the dose producing acceptable quality. Pollard at 10% substitution had minimal impact on quality with higher AO and fibre. Above 30%, pasta had undesirable colour, sensory properties and higher starch digestion. Although bran substituted pasta had undesirable sensory and technological properties, especially at 30% incorporation, it does provide more dietary fibre and antioxidants than regular pasta and does not affect starch digestibility. Interestingly, a significant amount of AO was retained in the cooked pasta. The study illustrates the value of structural analysis to explain observed technological properties of the product with fibre inclusion.     

The Effect of Cooking Water Composition on Textural and Cooking Properties of Spaghetti

The effect of cooking water on both textural and cooking properties of spaghetti was investigated for spaghetti samples, which differ in protein content. The samples were analysed after cooking in deionised, laboratory tap water, deionised water with 2.5% salt and deionised water with 5.0% salt. Brands A, B, and C were usual durum wheat spaghetti and brand D was spaghetti enriched with bran. Regardless of the cooking water used, brand D had higher hardness and lower adhesiveness than other spaghetti samples and required longer cooking time to achieve optimum cooking. It was found that samples cooked deionised water had lower hardness and adhesiveness values as compared to samples cooked in salty water. It can be concluded that a certain amount of salt in the cooking water improves textural characteristics of cooked pasta.     

CHANGES IN COOKING AND TEXTURAL PROPERTIES OF SPAGHETTI COOKED WITH DIFFERENT LEVELS OF SALT IN THE COOKING WATER

The effect of cooking water on textural and cooking properties of spaghetti was examined using four different salt concentrations 0, 1, 2, 3 and 4% in the cooking water and two types of spaghetti. Brand A was normal durum wheat spaghetti and brand B was spaghetti enriched with bran. Regardless of the cooking water used, brand B was harder, less sticky than brand A and it absorbed less water. Brand A required less cooking time. As salt concentration increased cooking time and hardness scores increased. Adhesiveness values were highest at the early stages of cooking and declined as cooking time increased.     

Non-linear creep-recovery measurements as a tool for evaluating the viscoelastic properties of wheat flour dough

Creep-recovery measurements were used to analyze the non-linear viscoelastic properties of wheat flour. First the effect of creep time, recovery time and shear stress was investigated on the non-linear viscoelastic properties of Bussard dough. The Burgers model was fitted to the creep and recovery curves. A linear increase of maximum creep compliance was observed with increasing creep time. On the other hand, maximum recovery compliance remained constant but an increase of the retardation time was observed which indicates a slower recovery. A recovery time of 10 min seemed to be sufficient to obtain most of the recovery. Maximum creep compliance increased proportionally with increasing shear stress until a plateau was reached. Maximum recovery was constant between 100 and 500 Pa but the speed of the recovery increased as shear stress increased. Finally, the optimised creep-recovery methodology was used to analyze the non-linear viscoelastic properties of 17 pure wheat cultivars. By applying principal component analysis, it was possible to identify three groups of wheat cultivars with similar rheological properties and bread volumes.     

Mechanical strength and rheological behaviour of barley kernels

Basic mechanical and rheological properties (stress relaxation behaviour) of single barley kernels under uni-axial compression were studied. The mechanical properties studied were the modulus of elasticity, yield and ultimate compressive strength, and the modulus of toughness as influenced by the moisture content. The stress relaxation experiments also included the effect of deformation rates and strain levels.
Results indicated that with an increase in moisture content, the strength of the barley kernels decreased while the energy required to cause rupture in the kernel increased initially and then decreased. The stress relaxation behaviour of barley kernels was described by a threeterm Maxwell model with a Maximum Relative Difference (MRD) ≤5%, when compared with one- and two-term Maxwell models. The elastic component (E¹) and relaxation time constant (τ¹) of the first term of the three-term Maxwell model decreased linearly with increase in moisture content. Of the different variables studied, moisture content had a significant influence on both of these parameters.     

Study of woven fabric shear behaviour

The paper presents the shear frame test with a new method of gripping the fabric sample to describe the shear behaviour of fabrics used in the garment industry under high shear strain conditions (maximum shear angles of 20°). This shear frame test was also used to compare between hysteresis curves given by the Kawabata evaluation system (KES) test, the bias extension test and the shear frame test for 10 woven fabrics. The linear viscoelastic theory was used to analyse the shear relaxation behaviour of the woven fabrics. In addition, in this study, the kernel function of the generalised Maxwell model has been used to describe the viscoelastic properties of the fabrics.     

添加改性麸皮对含麸皮面包结构及消化特性的影响

采用酶解-高压湿热处理对小麦麸皮进行改良,将改良后的小麦麸皮回添至高筋粉中获得不同麸皮含量的面粉,制作含麸皮面包,研究改良麸皮添加量对含麸皮面包的结构及消化特性的影响规律。结果表明：改良后的小麦麸皮中脂肪酶残余酶活降至0,不溶性膳食纤维含量从37.38%降低至15.64%,持水力升高了41.26%。与改良前的含麸皮面包相比,改良后的含麸皮面包香气浓郁,比容、硬度、弹性都得到了明显的改善。随着改良麸皮添加量增加,面包的老化程度降低、比容降低、硬度增加、弹性降低、感官品质降低。添加改良麦麸的含麸皮面包抗性淀粉含量增加,淀粉水解率降低。此外,改良麦麸显著降低了面包血糖生成指数。