Physicochemical characterization and in-vitro digestibility of extruded rice noodles with different amylose contents based on rheological approaches

The physicochemical properties and in-vitro digestibility of extruded rice noodles with different amylose contents were characterized from a rheological point of view. Thermo-mechanical measurements showed that the rice flour with higher amylose contents exhibited greater stability to dual-mixing and higher degrees of starch gelatinization and retrogradation. In addition, greater elastic properties were clearly observed in the high amylose rice samples. The use of high amylose rice flour produced noodles with a harder texture, consequently contributing to reduced cooking loss. Furthermore, the rheological changes of extruded rice noodles were monitored in real time during the in-vitro starch digestion. The rice noodle digesta with higher amylose contents exhibited greater viscosities throughout the simulated oral-gastric-intestinal digestion steps. The flow behaviors of the rice noodle digesta consisted of the Power-law region and infinite shear plateau that were satisfactorily characterized by the Sisko model (R² > 0.99).     

Thermal and rheological properties of brown flour from Indica rice

The thermal, paste and rheological properties of brown flours from four Indica rice subspecies with different amylose content were examined using Differential scanning calorimetry (DSC), Brabender Viscometer and rheometer. Peak, final and setback viscosities (p < 0.05) increased with increasing amylose content from Brabender micro Visco-Amylo-Graph (MVA), but the phase transition temperatures of brown rice flour from DSC (p < 0.05) decreased with increasing amylose content. Rheological properties were determined by steady shear, small amplitude oscillatory shear (SAOS) and thixotropic experiments. SAOS results showed a gel-like viscoelastic behavior with G′ higher than G″. Steady-shear results showed that the brown rice flour exhibited a non-Newtonian shear-thinning behavior and the flow curves can be well described by the Herschel-Bulkley model. The upward-downward rheograms showed that brown rice flour gel, except IR-1, had a hysteresis loop, indicating a strong thixotropic behavior.     

苜蓿食用叶蛋白的提取及其在曲奇中的应用研究

[目的]为了研究苜蓿食用叶蛋白的提取及其在曲奇中的应用。[方法]以压块苜蓿为原料,采用酸度法和离心法相结合提取苜蓿食用叶蛋白质。[结果]随着苜蓿蛋白添加比例的增加,面粉的吸水率增加,面团的形成时间、稳定时间缩短,弱化度增加,评价值降低,面团的最大拉伸阻力、拉伸能量减少,拉伸长度先增加后减小。随着苜蓿蛋白添加量的增加,曲奇面团的弹性降低,曲奇的黏着性、硬度、弹性、胶着性、咀嚼度、回复性减小,而它的酥脆性增大。添加2%的苜蓿蛋白的曲奇评价值最高。[结论]苜蓿蛋白对曲奇而言,是良好的营养强化剂和面团改良剂(弱筋剂),添加的最佳比例是2%。     

Statistical comparison of a new rheological method for defining changes in mash consistency during mashing with the established Rapid Visco Analyser

The determination of mash consistency proved to be difficult but is of great importance particularly with regard to process and quality control. Therefore, the aim of this study was to develop a new rheological method for precisely determining changes in mash consistency occurring during the mashing process. For that purpose, five mashes with various levels of unmalted oats (0–40%) have been analyzed using a Physica MCR rheometer equipped with a paddle-shaped rotor enabling mash particles to be kept in suspension throughout the rheological measurement. For validating this new method, a statistical comparison with the established Rapid Visco Analyser (RVA) has been carried out. For this purpose, the mash consistency curves have been described by regression functions with the aim to determine characteristic curve points mathematically correct. As a result, the start and end point of starch gelatinization/liquefaction have been well-defined. By calculating the coefficients of determination, good to very good linear correlations between respective curve values and adjunct levels have been found for both methods (MCR and RVA). By calculating the repeatability, however, it has been revealed that the precision of the MCR method is significantly better than that of the RVA method.     

Effect of quinoa flour on gluten-free bread batter rheology and bread quality

A new gluten-free bread formulations composed of quinoa, buckwheat, rice flour and potato starch were developed in the present study. Rheological characteristics of the bread batter with increasing amount of quinoa were determined; storage (G′) and loss modulus (G″) values were also measured for investigation of viscoelastic properties. To evaluate the quality of breads; technological and physical (bake loss %, specific volume, texture, microstructure, color), chemical (protein, moisture, ash) and sensory properties were determined. All batter formulations independent of the quinoa amount exhibited pseudoplastic behavior, and G′ values were found to be higher than G″ values in expressing the solid like characteristics of the batter. Amount of quinoa flour addition did not present significant difference on bake loss%, specific volume and protein content (p>0.05); however, 25% quinoa flour bread displayed better results with its higher sensory scores and softer texture. Quinoa and buckwheat flour mixture therefore will be a good alternative for conventional gluten-free bread formulations.     

豆渣-玉米粉挤压膨化分散体系流变特性

为提高豆渣的利用率、拓宽豆渣在食品工业中的应用范围,研究了豆渣-玉米粉挤压膨化加工后所得分散体系的流变特性。分别考察了加工温度、喂料含水率和豆渣添加量对挤压产品分散体系流变特性的影响,并从频率扫描试验和蠕变及蠕变回复试验对豆渣-玉米糊进行了动态流变特性研究。频率扫描试验得到豆渣-玉米糊的流变特性符合幂律模型,蠕变及蠕变回复试验表明其蠕变特性符合伯格斯模型,且均拟合较好。     

Molecular aspects of cereal β-glucan functionality: Physical properties,technological applications and physiological effects

Cereals β-glucans are linear homopolysaccharides of consecutively linked (1→4)-β-d-glucosyl residues (i.e. oligomeric cellulose segments) that are separated by single (1→3)-linkages. β-Glucans display all the functional properties of viscous and gel forming food hydrocolloids combined with all the physiological properties of dietary fibres. This review focuses on the relationships between the molecular–structural characteristics of β-glucans and their physicochemical properties in aqueous dispersions and in food systems as well as their physiological functions in the gastro-intestinal tract. The physical properties of β-glucans, such as solubility and rheological behaviour in the solution and gel states, are controlled by their molecular features, such as their distribution of cellulosic oligomers, their linkage pattern and their molecular weight as well as by temperature and concentration. The technological and nutritional functionality of β-glucans is often related to their rheological behaviour. Incorporation of β-glucans into various products (bread, muffins, pasta, noodles, salad dressings, beverages, soups, reduced-fat dairy and meat products) showed that attributes, such as breadmaking performance, water binding and emulsion stabilising capacity, thickening ability, texture, and appearance appear to be related to the concentration, molecular weight and structure of the polysaccharide. The health benefits of β-glucans, such as reducing blood serum cholesterol and regulating blood glucose levels, are also correlated with the amount and molecular weight of the solubilised β-glucans in the gastro-intestinal tract.     

Rheology of concentrated xanthan gum solutions: Steady shear flow behavior

Using a strain-controlled rheometer, the steady shear flow properties of aqueous xanthan gum solutions of different concentrations were measured over a wide range of shear rates. In this article, both the shear rate and concentration dependencies of steady shear flow behavior are reported from the experimentally obtained data. The viscous behavior is quantitatively discussed using a well-known power law type flow equation with a special emphasis on its importance in industrial processing and actual usage. In addition, several inelastic-viscoplastic flow models including a yield stress parameter are employed to make a quantitative evaluation of the steady shear flow behavior, and then the applicability of these models is also examined in detail. Finally, the elastic nature is explained with a brief comment on its practical significance. Main results obtained from this study can be summarized as follows: (1) Concentrated xanthan gum solutions exhibit a finite magnitude of yield stress. This may come from the fact that a large number of hydrogen bonds in the helix structure result in a stable configuration that can show a resistance to flow. (2) Concentrated xanthan gum solutions show a marked non-Newtonian shear-thinning behavior which is well described by a power law flow equation and may be interpreted in terms of the conformational status of the polymer molecules under the influence of shear flow. This rheological feature enhances sensory qualities in food, pharmaceutical, and cosmetic products and guarantees a high degree of mixability, pumpability, and pourability during their processing and/or actual use. (3) The Herschel-Bulkley, Mizrahi-Berk, and Heinz-Casson models are all applicable and have equivalent ability to describe the steady shear flow behavior of concentrated xanthan gum solutions, whereas both the Bingham and Casson models do not give a good applicability. (4) Concentrated xanthan gum solutions exhibit a quite important elastic flow behavior which acts as a significant factor for many industrial applications such as food, pharmaceutical, and cosmetic manufacturing processes.     

Rheological characterization of refrigerated and frozen non-fermented gluten-free dough: Effect of hydrocolloids and lipid phase

This work intended to study the rheological and textural behavior of gluten-free dough for “empanadas” and pie-crusts production. Traditionally, these products are made with non-fermented wheat-based dough. They are highly consumed in Latin America, but unsuitable for celiac people. Gluten matrix is a major determinant of the properties of dough, thus it must be replaced with other network forming components, such as hydrocolloids. Different hydocolloids were tested: hydroxypropylmethylcellulose (HPMC) and mixtures of xanthan/guar, and xathan/HPMC gums. Three different kinds of lipid phase were also studied; i.e. sunflower oil and low and high solid content margarine at two different levels (20–30%). Changes in rheological and textural properties during refrigerated storage were evaluated by dynamic oscillatory measurements and puncture and elongation tests on the unbaked dough. Best results were obtained using either of the hydrocolloid mixtures. Besides, the textural characteristics of cooked empanadas were also studied. Freezing before baking did not alter the quality of the crust in the products. ESEM micrographs revealed a continuous matrix formed by hydrocolloid entanglements. Starch granules were homogenously distributed in the dough and acted as inactive fillers. An untrained panel accepted the xanthan/HPMC dough with a 74/90 score and it was significantly preferred over a commercial gluten-free dough.     

Texture,processing and organoleptic properties of chickpea-fortified spaghetti with insights to the underlying mechanisms of traditional durum pasta quality

Nutritionally enhanced spaghetti was prepared from durum semolina fortified with 0–30% desi chickpea ‘besan’ flour. This study examined the dough rheology, processing ease and quality attributes of the fortified spaghetti including protein, starch, texture (firmness, resilience and stickiness), colour, cooking loss, and organoleptic acceptability. Chickpea-fortified spaghetti was acceptable to consumers, had reasonable pasta quality, including lower cooking loss and less stickiness than the control spaghetti and retained firmness better than durum after refrigeration. This study suggests that chickpea-fortified spaghetti may be suited to uses such as fresh pasta, in soups, canning, and microwave re-heating. In addition, this study has added to the understanding of the underlying mechanisms of pasta quality. The main findings were: (1) gluten content/composition appears to be more important than protein content for pasta firmness; (2) the protein–polysaccharide matrix appears to be more important than the starch composition for cooking loss; (3) increased protein and amylose contents were associated with decreased pasta stickiness; (4) cooking loss and stickiness were not necessarily as strongly related as commonly believed. Further research into these theories is necessary to fully understand the underlying mechanisms of pasta quality.