Viscoelastic properties of reconstituted cassava dough

The influence of water (60–70%) and salt (1–2%) content on the viscoelastic properties of cassava dough, reconstituted from cooked flour, was studied using a controlled strain rheometer. Reconstituted cassava dough behaved as a solid-like material with the storage modulus (G') predominant over the loss modulus (G"). As the water content was increased, G' decreased and G" increased; but tan δ was practically independent of the water content. This behaviour suggested that water had plasticising effects, but probably did not change dough structure. The effect of salt content on the dynamic rheological properties of cassava dough was not significant, except for G" values at water contents close to 60%.     

Rheological and textural properties of sorghum-based formulations modified with variable amounts of native or pregelatinised cassava starch

Sorghum bread was made from native or pregelatinised cassava starch and sorghum flour in the ratio 10:90, 20:80, 30:70, 40:60 and 50:50. The other ingredients, measured on flour-weight-basis, were water (100%), sugar (6.7%), egg white (6%), fat (2%), salt (1.7%) and yeast (1.5%). The dynamic oscillatory behaviours of the batters were affected by the amount and type of starch. In the amplitude sweep measurements, increasing concentration of native starch decreased storage modulus, whereas increasing concentration of pregelatinised starch increased the linear viscoelastic range of the batters. In the frequency sweep measurements, the loss factor of batters treated with native starch declined with increasing frequency. Batters treated with 10 or 20% pregelatinised starch showed declining loss factors, whereas batters treated with 40 or 50% pregelatinised starch showed increasing loss factors with increasing frequency. Sorghum-based batters containing native starch gave bread with better crumb properties than batters containing pregelatinised starch. Crumb firmness and chewiness declined with increasing native or pregelatinised starch concentration. Crumb adhesiveness of breads containing pregelatinised starch increased with increasing starch content but was not affected by native starch. Cohesiveness, springiness and resilience increased with increasing native starch content, but were minimally affected by increasing pregelatinised starch content.     

Chemical,functional and physicochemical properties of flour from cassava stored under freezing

Cassava root spoils rapidly after harvest but can be well preserved by storing under freezing. This study investigated the functional, chemical and physicochemical properties of flour produced from frozen cassava roots. Freezing period did not significantly (p < 0.05) alter the moisture, ash, fat and fibre, but had slight effect on the carbohydrate and protein contents of the flour. Lightness, yellowness index and bulk densities of the flour samples reduced with freezing period. While freezing did not significantly (p < 0.05) change the ability of the flour samples to absorb oil, a slight but significant increase in the water absorption capacity was observed. Potassium (1.29–3.46 mg/kg), sodium (1.24–1.28 mg/kg), and calcium (0.94–1.34 mg/kg) were the major minerals in the cassava flour samples. The cyanide content (10.80–22.95 mg/kg) reduced as freezing days increased but peak, setback, breakdown and final viscosities did not follow a particular pattern. The information from this study is important to further determine the industrial potentials of flour from stored cassava roots.     

Physicochemical characteristics of starches and flours from cassava varieties having different cooked root textures

Starches and flours from 12 cassava varieties having differences in cooked root texture - mealy, firm and mealy & firm - were investigated, with a particular focus on aspects of physicochemical characteristics. It was found that chemical composition (protein, lipid, fiber, ash), pasting properties, firmness of gel, thermal properties, morphology and granular size distribution and crystalline pattern of starches from the 12 varieties were not significantly different. On the contrary, cassava flours which consisted of both starch and non-starch components exhibited wider variations in these properties, especially pasting properties and firmness of gel, than the starches. All flour samples had lower paste viscosities than their corresponding starches. Pasting temperatures of flours were in a range of 70-74 ^°C, which was higher than those of starches (67-70 ^°C). Fluctuation in the values of pasting parameters of flours among the varieties was associated with the variations in the chemical composition and α-amylase activity, i.e. paste viscosity and setback were positively correlated to starch content and negatively correlated to α-amylase activity, while protein, lipid and fiber did not show correlation with pasting parameters. Cassava starches from all varieties, except the F-18 variety, had higher firmness of gels than their corresponding flours. Firmness values (except the F-18 variety) of starches were in a range of 149-207 g, whereas those of flours were 75-163 g. Firmness of flour gels was negatively correlated to lipid and fiber content, while strong positive correlation was found with the amylase activity.     

Rheological/textural properties of starch and crude hsian‐tsao leaf gum mixed systems

The Effects of hsian‐tsao leaf gum (HG) on the rheological/textural properties of non‐waxy starches were studied. Pronounced interactions between starch and HG were observed. The rheological properties, including pseudo‐gel viscosity in the rapid visco‐analyser test, storage and loss moduli in the dynamic rheological test, as well as firmness in the texture analyser test, of the mixed gels generally improved with increasing gum concentration to a certain level, then deteriorated with further increase in gum concentration. The critical gum concentration for the development of optimal rheological properties depended on the starch type and concentration. Within the concentration range studied, mixed systems with wheat starch could generally reach the highest pseudo‐gel viscosity, firmness, and storage modulus if the starch/HG ratio was appropriate, followed by those with corn and tapioca starch. Copyright © 2003 Society of Chemical Industry     

超声波处理对豌豆淀粉糊化、流变及质构特性的影响

以豌豆淀粉为原料,分别用0,150,300,450 W的超声波进行处理,考察超声波处理对豌豆淀粉糊化、流变及质构特性的影响。结果表明:超声波处理对豌豆淀粉的糊化、流变及质构特性都有较大影响。随着超声波功率的增加,豌豆淀粉糊峰值黏度、终值黏度、崩解值及回升值都显著下降,使豌豆淀粉冷稳定性及热稳定性得到提升;稠度系数k减小,流体指数n增大,触变性减小,流动性增加,使豌豆淀粉流变稳定性提高;G′与G″减小,tanδ增大,使豌豆淀粉黏弹性降低。此外,超声作用使豌豆淀粉凝胶的硬度、弹性、内聚性、胶着性及咀嚼性都呈下降趋势,其中硬度与胶着性下降最显著。扫描电镜表明,超声波对豌豆淀粉产生破坏作用,使淀粉颗粒表面出现坑洞及皱褶,部分颗粒结构变得不完整。     

Wheat noodles enriched with A-type and/or B-type wheat starch: physical,thermal and textural properties of dough sheet and noodle samples from different noodle-making process

This study explored the effects of adding A-type starch (AS), B-type wheat starch (BS) on the physicochemical or edible quality of dough sheet and noodle samples at different stages of the noodle-making process, which included 1-mixing, 2-kneading, 3-resting, 4-sheeting and cutting and 5-drying. The swelling power and pasting viscosities of samples in noodle-making process were decreased compared with mixed flour, indicating gluten network during noodle-making inhibits these properties of starch. Adding 20% BS enhanced the formation and aggregation of gluten network during kneading and drying compared by adding AS. The drying process increased cooking yield and cooking loss and decreased hardness and springiness, and the effect was weakened when adding BS. The correlation results show the increased solubility and decreased setback during drying are the main reason for the changes of cooking and texture quality of noodles. The increase of swelling power resulted in the increased cooking yield.     

Rheological and textural properties of gluten-free doughs made from Andean grains

The objective of this research was to evaluate the rheological and textural properties of gluten-free doughs based on potato starch, which was partially substituted by different proportions of quinoa (10%, 30% and 50%), kiwicha (10%, 30% and 50%) or tarwi flour (10%, 20% and 30%). The influence of the substitution on the kinetics of the leavening process was studied as well. The back-extrusion technique was used to determine rheological and textural properties of the dough, and the leavening kinetics were modelled using the Gompertz equation. The results showed that textural properties such as firmness, consistency, cohesiveness and viscosity index, as well as the consistency index of the doughs increased as the level of substitution of the Andean grain flour in the formulation increased. It was determined that the formulations with an addition of 10% and 20% for quinoa or kiwicha flour, and 10% for tarwi flour would be most suitable for developing gluten-free breads.     

Functional and dynamic rheological properties of acetylated starches from two cultivars of cassava

The starches derived from two different cultivars of cassava were modified with acetic anhydride. The increase in swelling power and solubility of the cassava starch (CS) pastes treated with different acetic anhydride concentration could be attributed to easier hydration, resulting from reduction of interaction between starch chains due to the substitution. The transition temperatures (T_o, T_p and T_c) and enthalpy of gelatinisation (ΔH) of acetylated CS, were determined. The values were lower than those of native starches. Rheological properties of CS pastes (5% w/w) as a function of the degree of substitution were evaluated in dynamic shear force measurements. Magnitude of storage modulus (G′), loss modulus (G′′) and complex viscosity (Eta*) of acetylated CS pastes were determined also. Dynamic moduli (G′, G′′ and Eta*) values of acetylated sweet cultivar pastes were generally higher than those of native starch whereas the acetylated samples of the bitter cultivar were lower than those of native starch. The magnitudes of G′ were greater than those of G′′ and Eta* at all frequencies (ω). The fact that all the tan δ (ratio G′′/G′) values (0.7–0.48 and 0.25–0.44) were less than one is an indication that the samples are more elastic than viscous. The acetylated starches could find promising industrial uses in food products like Lemon curd and Mayonnaise and other non‐food applications.     

Understanding the structural characteristics,pasting and rheological behaviours of pregelatinised cassava starch

The structural characteristics, pasting and rheological behaviours of cassava starch before and after pregelatinisation were determined by various modern analysis techniques. Pregelatinisation, especially in an ultrasonic environment, can disrupt the granule structure, crystalline structure and short‐range ordered molecular structure of cassava starch. Compared with native starch, pregelatinisation had significantly decreased viscosities and weakened gel structures of starch pastes. Not only did native and pregelatinised starch pastes exhibit shear‐thinning behaviours but also the pregelatinised treatment resulted in the formation of weak gel structures. This study enabled us to acquire the desired pasting and rheological properties of pregelatinised starch by modulating its hierarchical structural changes.     

Low-moisture part-skim mozzarella cheese made from blends of camel and bovine milk: Gross composition,proteolysis, functionality,microstructure, and rheological properties

Camel (CM) milk is used in variety of ways; however, it has inferior gelling properties compared with bovine milk (BM). In this study, we aimed to investigate the physicochemical, functional, microstructural, and rheological properties of low-moisture part-skim (LMPS) mozzarella cheese, made from BM, or BM mixed with 15% CM (CM15%) or 30% CM (CM30%), at various time points (up to 60 d) of storage at 4°C after manufacture. Low-moisture part-skim mozzarella cheeses using CM15% and CM30% had high moisture and total Ca contents, but lower soluble Ca content. Compared with BM cheese, CM15% and CM30% LMPS mozzarella cheese exhibited higher proteolysis rates during storage. Adding CM affected the color properties of LMPS mozzarella cheese manufactured from mixed milk. Scanning electron microscopy images showed that the microstructure of CM15% and CM30% cheeses had smooth surfaces, whereas the BM cheese microstructures were rough with granulated surfaces. Low-moisture part-skim mozzarella cheeses using CM15% and CM30% showed significantly lower hardness and chewiness, but higher stringiness than BM cheese. Compared with BM cheese, CM15% and CM30% cheeses showed lower tan δ levels during temperature surges, suggesting that the addition of CM increased the meltability of LMPS mozzarella cheese during temperature increases. Camel milk addition affected the physicochemical, microstructural, and rheological properties of LMPS mozzarella cheese.     

Physicochemical,textural and viscoelastic properties of palm diacylglycerol bakery shortening during storage

BACKGROUND: Diacylglycerol (DAG), which has health‐enhancing properties, is sometimes added to bakery shortening to produce baked products with enhanced physical functionality. Nevertheless, the quantity present is often too little to exert any positive healthful effects. This research aimed to produce bakery shortenings containing significant amounts of palm diacyglycerol (PDG). Physicochemical, textural and viscoelastic properties of the PDG bakery shortenings during 3 months storage were evaluated and compared with those of commercial bakery shortening (CS). RESULTS: PDG bakery shortenings (DS55, DS64 and DS73) had less significant increments in slip melting point (SMP), solid fat content (SFC) and hardness during storage as compared to CS. Unlike CS, melting behaviour and viscoelastic properties of PDG bakery shortenings remained unchanged during storage. As for polymorphic transformation, CS contained only β crystals after 8 weeks of storage. PDG bakery shortenings managed to retard polymorphic transformation for up to 10 weeks of storage in DS55 and 12 weeks of storage in DS64 and DS73. CONCLUSION: PDG bakery shortenings had similar if not better storage stability as compared to CS. This is mainly due to the ability of DAG to retard polymorphic transformation from β′ to β crystals. Thus, incorporation of DAG improved physical functionality of bakery shortening. Copyright © 2010 Society of Chemical Industry     

Rheological,mechanical and moisture sorption characteristics of cassava starch‐konjac glucomannan blend films

Cassava starch (ST)‐konjac glucomannan (KGM) blend films were prepared and their thermal, rheological, mechanical, moisture sorption properties and water vapour transmission rate were determined. Response surface methodology was employed for the preparation of films using different levels of ST, KGM and glycerol. All the filmogenic solutions exhibited shear thinning behaviour. Apparent viscosity and the dynamic rheological properties of filmogenic solutions varied considerably with KGM content. Rheological analysis revealed that the blend films are more appropriate than neat ST film for controlled drug release studies and for food coating. The melting temperature and enthalpy of fusion of the blend films were lower than that of neat ST film. When compared to neat starch film, the blend films showed broader peaks in DSC patterns, which suggests that incorporation of KGM decreased the crystallinity of ST. Mechanical properties, elongation at break and tensile strength of blend films were significantly higher (112.8% and 22.5 MPa, respectively) than those of neat ST film. Due to the more hydrophilic nature of KGM when compared to ST, the WVTR and moisture absorption of blend films were greater than that of neat ST film. Though KGM is more hydrophillic in nature, blend films with higher amount of KGM (0.643g) showed comparably lower values for both WVTR and moisture absorption than other blends. The solubility of the blend films was lower than that of neat starch film which also confirmed the strong intramolecular attraction between ST and KGM.     

Effect of enzymatic crosslinking on the handling properties of dough as a function of NaCl levels for CWRS varieties,Pembina and Harvest

The effects of transglutaminase (TG) and glucose oxidase (GO) on the handling properties of model bread dough were examined at both normal (2% wt. by flour) and reduced (1% wt.) sodium chloride (NaCl) levels using two Canada Western Red Spring (CWRS) cultivars; Pembina and Harvest. The reduction of NaCl level had negative effects on dough rheology and stickiness, however, the inclusion of GO (0.001 and 0.01% by flour weight) or TG (only at the 0.5% by flour weight inclusion) was able to improve dough strength and reduce stickiness. GO appeared to be more effective than TG (at 0.01%) at equivalent concentrations for improving dough‐handling properties. Flour cultivar had significant effects; Harvest flour (weaker) was more impacted by salt reduction and enzyme inclusion compared to Pembina flour (stronger). Crosslinking assays showed significant differences in glutenin macropolymer (GMP) content in dough prepared with GO, and dough prepared with different flours. Additionally, significantly fewer free thiol groups were found in dough produced with GO compared to dough without any enzymes and those with TG. GO appears to have potential for use as a bread improver to reduce stickiness and improve the strength of bread dough produced at lower salt concentrations, especially for dough prepared with weaker flour cultivars.     

Thermal, microstructural and textural characterisation of gelatinised corn, cassava and yam starch blends

The functional properties of mixtures of maize, cassava and yam starches and their relationships with microstructural characteristics were investigated. Experiments were performed following the simplex‐centroid design with internal points and restrictions (upper limit) for yam starch proportion. The statistical model used (Scheffé canonical equation) was a powerful tool to predict the pastes behaviour within the limits of the experimental area. Polynomials with second level interactions were applied to obtain the surface response. Viscoelastic attributes of mixtures differed from those of individual starches. As shown by differential scanning calorimetry and microscopical observations, physical properties of the mixtures depended on the type of networks obtained. These networks varied upon yam, corn and cassava starch proportions as each one has a particular characteristic: gelatinisation temperature, granule size, swelling capacity and amylose/amylopectin ratio among others.     

改良剂对燕麦面团流变特性及其挂面品质的影响

使用混合试验仪研究了谷朊粉、海藻酸钠、谷氨酰胺转氨酶（TG酶）、硬脂酰乳酸钠（SSL）、对燕麦‐小麦混合粉面团粉质特性、糊化特性,以及对燕麦挂面的蒸煮特性和感官评价的影响。研究结果表明：四种改良剂均使混合粉面团的稳定时间、形成时间延长,蛋白质弱化度下降,回生值降低;谷朊粉使面团的最低黏度值变大;SSL使面团的糊化峰值黏度值、最低黏度值均变大,使面团的黏度和糊化热稳定性增强;燕麦挂面中加入改良剂后,挂面的吸水率、蛋白质损失率均呈降低趋势,挂面的感官评分基本呈上升趋势,其中SSL和TG酶的改良效果较优,感官评价分值较高。