Rheological Properties of Acidified and UV‐Irradiated Starches

This study evaluated the effect of added lactic acid and/or UV irradiation on the depolymerization and rheological properties of cassava and corn starches. Combination of lactic acid addition and UV irradiation decreased the intrinsic viscosity of corn and cassava starches. Lactic acid addition alone also decreased paste viscosity in both starches. The paste viscosity of cassava (but not corn) starch was also reduced after UV irradiation. Acidification and UV irradiation increased expansion volume during the baking of cassava (but not corn) starch dough. The baking expansion of cassava starch may be due to its high swelling capacity and solubility resulting from molecular degradation after acidification and irradiation. For corn starch, its high gelatinization temperature and internal lipids content could interfere in starch leaching and thus delay the decrease in viscosity and inhibit dough expansion.     

DEVELOPMENT OF DYNAMIC MODULUS AND CELL OPENING OF DOUGH DURING BAKING

The dynamic shear modulus (elastic and viscous modulus) development of dough during baking was studied. Flooded parallel plate geometry was used to monitor the rheological changes of commercially available canned doughs (bread dough, bun dough and biscuit dough). The normal force exerted on the upper plate by the expanding dough was measured to study the cell‐opening event. The dough‐baking process was simulated in a rheometer oven. The morphology of baked dough was studied using a scanning electron microscope to elucidate the effect of ingredients and process parameters on the properties of the final baked product. Three stages of modulus development were observed during the baking process: bubble growth and packing, rapid expansion/starch gelatinization and final curing. The cell opening coincided with the sudden rise in modulus caused by starch gelatinization. The rate at which starch gelatinization takes place controls the temperature of the cell opening. The type and concentration of various ingredients have a greater effect on the modulus and on the cell opening than the heating rates. Frequency dependence was observed during baking, but the effect on modulus development diminished at higher frequencies.     

Expansion Properties of Sour Cassava Starch (Polvilho Azedo): Variables Related to its Practical Application in Bakery

Sour cassava starch (polvilho azedo) is a chemically and enzymatically modified starch with the specific property of expansion in bakery products without the use of any chemical or biological leavening agents. In this work, the cumulative knowledge about sour cassava starch is presented in relation to its physicochemical characteristics, with the purpose of establishing a relation between the application properties and some structural and chemical characteristics in order to design a model of the modified structure of starch and the most important technical variables. Such approach will help to provide some quality standards for future adequate valorization of sour cassava starch, especially with respect to potential use in gluten‐free products. This work showed that a good sour cassava starch is significantly different from low expansion cassava starches with respect to pH, acid factor, swelling power, specific volume, and polymerization degree (intrinsic viscosity). These variables could be related to the maximization of sour cassava starch expansion for a future predictive decision analysis about a high quality sour cassava starch to the baking use.     

Effect of pre-dehydration treatment on the in vitro digestibility of starch in cookie

In order to understand the effect of pre-dehydration on the in vitro digestibility of cookie starch, cookie dough samples were dehydrated by vacuum treatment, and melting temperature (T(m)) of the crystalline amylopectin in the dough, internal temperature and water content of the dough during baking, and non-hydrolysed starch content of the obtained cookies were investigated. The T(m) of crystalline amylopectin increased with decreased water content of the dough, and the result was described as a T(m)-curve. The internal temperature of non-dehydrated dough surpassed the T(m)-curve during baking. Pre-dehydrated dough, on the other hand, always indicated a lower internal temperature than the T(m)-curve. The non-hydrolysed starch content obtained under a given condition increased significantly with a decrease in the initial water content of cookies. This will be because the melting of crystalline amylopectin was prevented, at least partially, during baking.     

Role of dough viscoelastic properties and rice variety in the thermal expansion and the quality of unconventional rice-based bread: case of steamed-cooked ‘Ablo’

Ablo is a rice-based bread consumed in Southern Benin. We investigated the impact of pre-cooking conditions and starch characteristics on dough and Ablo physical properties. The solid-like behaviour of doughs measured by rheological sweep tests appears significantly negatively correlated to Ablo quality; above a starch gelatinisation level (7%–8%), the solid-like behaviour of the doughs increased sharply and the fluidity decreased, leading to Ablo of poor quality. A comparison between three rice cultivars tends to show that rice with low amylose content and/or gelatinisation temperature gives dough with higher fluidity and Ablo with lower density. In addition, a specific rheological test for measuring simultaneously dough expansion and rheological properties during heating has been developed. It shows that whatever the rice variety, thermal expansion of proofed dough begins and is followed by a dough/crumb transition. This innovative rheological test could be used for studying dough/crumb transition for other types of breads.     

Dynamic rheological properties of dough as affected by amylases from various sources

The effect of alpha-amylases from cereal, fungal, and bacterial sources on dough dynamic rheological properties was investigated. Dynamic rheological study of flour-and-water doughs during resting period showed significant changes in dough rheological properties as a function of alpha-amylases. Addition of alpha-amylases caused a time-dependent decrease in G', storage modulus. The enzyme action on starch during baking increased viscous flow properties. These changes were temperature-dependent. The thermal inactivation temperature of alpha-amylase plays an important role in modification of starch. Rheological changes in dough will alter the machinability of the dough and the quality of end products.     

Effects of Fat and Sugar on Dough and Biscuit Behaviours and their Relationship to Proton Mobility Characterized by TD-NMR

This study aimed to analyse the effect of large variations in fat and sucrose contents of biscuit formulation on dough rheology, biscuit quality and proton mobility. Control dough (full fat and sucrose) and 25 and 50% fat and sucrose-reduced doughs were elaborated. Rheological properties of dough were determined. Dough cooking behaviour and biscuit quality were evaluated. Fat reduction produced an increase in the consistency and elastic properties of the dough. The decrease in sucrose content affected to a lesser extent the rheological properties at room temperature, although it produced significant changes during dough baking. The biscuit quality decreased with fat and sucrose reductions. The reduction of fat or sucrose produced gluten hydration and extra interactions and subsequent cross-linking during baking, and a reduction of sucrose led to the swelling and partial gelatinization of starch during baking. A dipolar reversed eco NMR sequence was applied to determine changes in the amount and mobility of solid and mobile components both in dough and biscuits. TD-NMR results allowed corroborating the proposed hypotheses about the effects on dough and biscuit characteristics as a consequence of reduction of main ingredients, as fat and sucrose. The redistribution of water after baking can be correlated with biscuit factor and breaking force.     

Overall and Local Bread Expansion,Mechanical Properties,and Molecular Structure During Bread Baking: Effect of Emulsifying Starches

In order to determine the relationship between molecular structure of wheat bread dough, its mechanical properties, total and local bread expansion during baking and final bread quality, different methods (rheological, nuclear magnetic resonance, magnetic resonance imaging and general bread characterisation) were employed. The study was extended on wheat dough with starch modified by octenyl succinic anhydride (OSA) in order to generalise the results. The interest of investigating multi-scale changes occurring in dough at different phases of baking process by considering overall results was demonstrated. It was found that OSA starch improved the baking performance during the first phase of baking. This feature was due to a higher absorption of water by OSA starch granules occurring at temperatures below that of starch gelatinization, as confirmed by NMR, and consecutive higher resistance to deformation for OSA dough in this temperature range (20–60 °C). This was explained by a delayed collapse of cell walls in the bottom of the OSA dough. In the second phase of baking (60–80 °C), the mechanism of shrinkage reduced the volume gained by OSA dough during the first phase of baking due to higher rigidity of OSA dough and its higher resistance to deformation. MRI monitoring of the inflation during baking made it possible to distinguish the qualities and defaults coming from the addition of OSA starch as well as to suggest the possible mechanisms at the origin of such dough behaviour.     

醋酸酯变性淀粉对低筋面团热机械学特性的影响

将荞麦粉与小麦粉以6:4比例混合,制成低筋粉,再将马铃薯醋酸酯淀粉及木薯醋酸酯淀粉按不同比例分别添加到低筋粉中,利用Mixolab混合仪研究两种醋酸酯变性淀粉对低筋粉形成的面团流变及糊化特性的影响。结果表明:两种醋酸酯淀粉都可显著的增强面团的强度及蒸煮稳定性(p<0.05),木薯醋酸酯淀粉可延长面团的形成和稳定时间、减小机械弱化值,而马铃薯醋酸酯淀粉会降低面团的吸水率及热弱化值。      

Effect of acid treatments and drying processes on physico-chemical and functional properties of cassava starch

The effects of acid treatments (HCl or organic acids) and drying processes (oven or sun) on the physico-chemical and functional properties of cassava starch have been studied. The objective was to obtain modified starches with expansion properties similar to those of sun dried fermented cassava starch (polvilho azedo) as produced by an empirical process. Expansion was evaluated using a baking test. Independent of the drying method, organic acid-hydrolysed cassava starch presented the same X-ray diffraction patterns (changes from C to A) and similar intrinsic viscosity values. SEM observations showed no differences between granule surfaces of sun dried and oven dried samples. However sun dried organic acid-hydrolysed starches presented lower paste consistency values at 30°C when compared with oven dried ones. HCl-modified cassava starches were oven or sun dried, giving biscuits with low specific volumes (2·5–3·1 ml g⁻¹). Similar behaviour was obtained using oven dried organic acid modified cassava starches. When submitted to sun drying, organic acid modified starches showed great improvements in biscuit expansion (5–10 ml g⁻¹). The highest average specific volumes were obtained using lactic acid modified starches. © 1998 SCI.     

不同变性淀粉对冷冻面团热力学特性的影响

采用差示扫描量热法(DSC)研究4种不同种类变性淀粉对冷冻面团热力学特性(玻璃化转变温度、冰晶融化特性和可冻结水含量)的影响。结果表明,冷冻面团的玻璃化转变温度在-30℃左右,不同变性淀粉对冷冻面团玻璃化转变基本无明显影响;添加5%马铃薯羟丙基淀粉、木薯羟丙基淀粉和木薯醋酸酯淀粉可以显著降低冷冻面团冰晶融化范围,面团中形成的冰晶大小更加均匀;冷冻面团可冻结水含量随着马铃薯醋酸酯淀粉和马铃薯羟丙基淀粉添加量的增加呈降低趋势,添加10%木薯羟丙基淀粉时,面团可冻结水含量显著低于空白组,而木薯醋酸酯淀粉对面团可冻结水含量无显著影响。     

The role of corn starch,amaranth flour,pea isolate,and Psyllium flour on the rheological properties and the ultrastructure of gluten-free doughs

The removal of gluten from bakery products, in order to produce foods (mainly based on gluten-free cereal flours and starch) for people with celiac disease, impairs dough’s capacity to properly develop during leavening and baking. The main aim of this research was to produce and evaluate some experimental gluten-free (GF) doughs containing different levels of corn starch, amaranth flour (to enhance the nutritional benefits), pea isolate (to increase the protein content) and Psyllium fiber (as thickening agent and fiber source) in order to study the influence of the different ingredients on the rheological properties and on the ultrastructure of the doughs. Psyllium fiber generally enhanced the physical properties of the doughs, due to the film-like structure that it was able to form, and the most complex among the experimental formulations looked promising in terms of final bread technological and nutritional quality even when compared to two different commercial GF mixtures.     

流态起酥油对冷冻面团烘焙特性的影响研究

使用冷冻面团生产面包具有经济、方便、快捷,产品质量稳定的特点,冷冻面团的主要缺点是:面团的醒发时间随着冷冻储存时间的延长而延长,且面包比容小.起酥油系统是提高冷冻面包面团储存稳定性的关键因素之一,流态起酥油具有良好的功能性和流动性,可以满足食品工业自动化生产的要求.研究了一种流态起酥油对冷冻面团烘焙特性的影响,结果表明在冷冻面团研究开发中使用流态起酥油可以很好地改善冷冻面团面包的烘焙特性,使得用冷冻面团制得的面包与新鲜面包在制作参数和口感上相比没有很大的区别,冷冻面团在冷冻储存期间烘焙品质的下降可以用一种专用于冷冻面团的起酥油系统来弥补.     

Effects of flour from different barley varieties on barley sour dough bread

Twenty flours from 16 different barley varieties cultivated in 1990 and 1992, and a Swedish reference flour, were fermented by Lactobacillus plantarum A1 to sour doughs. Barley breads (40% barley/60% wheat flour) from each flour type were baked with and without an admixture of barley sour dough in order to investigate how the sour dough admixture would affect the baking properties. A trained panel carried out sensory evaluation by conventional profiling on breads made from three of the barley varieties and the Swedish reference flour, made with and without sour dough admixture.

The barley varieties influenced both the sour dough properties and the properties of the barley bread. The pH of bread with sour dough ranged from 4.6 to 4.8 as compared to 5.4 to 5.6 in bread without sour dough. The acidity of the breads with sour dough ranged from 4.1 to 5.0 ml NaOH/ 10 g bread crumb as compared to 2.4 to 3.6 in breads without sour dough. In 14 of the twenty bread types an addition of sour dough lowered the bread volume. Breads with a sour dough admixture scored higher for total taste and acidulous taste than breads without sour dough. The β-glucan content of the flours had no significant influence on the sour dough or the sensory characteristics of the bread, except for the breadcrumb colour.     

Influence of Natural Fermentation and Drying Conditions on the Physicochemical Characteristics of Cassava Starch

The physicochemical characteristics of cassava starches sampled at a pilot plant in Colombia during fermentation and drying processes were determined in relation to their ability for making specific bread-like products that inflate during baking. Nitrogen compounds and non-starch polysaccharides are minor components which were unlikely to be involved in the baking expansion property of fermented cassava starch. Thirty percent of the lactic acid synthesised during the fermentation step was not recovered after sun-drying whereas it remained constant when oven-dried. The crystalline structure of starch was not changed by the fermentation and drying processes whereas the behaviour of starch polysaccharides in water was dramatically modified. This behaviour seemed to be related to the baking expansion potential of cassava starches; the lower the intrinsic viscosity, the hot paste viscosities and the hydrodynamic volumes of the starchy components, the higher the baking expansion ability. These results suggest the occurrence of an oxidative modification of starch molecules, such as depolymerisation, due to the joint action of fermentation and sun-drying. © 1997 SCI.     

Significance of lipid binding on the functional and nutritional profiles of single and multigrain matrices

Lipid fractions and starch- and protein-lipid binding of single and blended oat, rye, buckwheat and wheat flour, dough and bread matrices were investigated, and results correlated with the functional and nutritional properties of the grain matrices during mixing and baking. Non-starch lipid was the most prominent fraction in terms of absolute content and as a percentage of total lipids. Free lipids, starch lipids and bound lipids were, respectively, the major, intermediate and minor lipid fractions in flours, doughs and breads. Great differences in total lipid content due to sampling result in divergences amongst lipid fraction content and distribution, especially for starch and bound lipid fractions. Lipids bound to proteins during dough mixing are translocated and bound to starch during baking. In blended samples, the higher fibre content seems to provoke a reduction of the lipid–protein and lipid–starch linkages due to interactions between fibres and endogenous biopolymers. Starch lipid showed the most significant correlations with parameters related to dough and bread performance during breadmaking, especially over the mixing step. Valuable fresh bread functional characteristics, such as high specific volume and high sensory score for softness and overall acceptability, correspond to a starch lipid’s increase due to mixing. The higher the free and starch lipids decrease by reason of temperature treatment—baking—the larger the starch hydrolysis and the higher β-glucans and total dietary fibre contents.     

Comparison of the expansion ability of fermented maize flour and cassava starch during baking

The modifications occurring during the fermentation (at 20 or 35 °C) and drying (under the sun or in an oven at 40 °C) of maize flour (ogi) and cassava starch along with their expansion ability during baking were characterised and compared. A high temperature accelerated the fermentation but favoured lactic acid synthesis for maize ogi and butyric acid for cassava starch. The increase in acidity was higher for maize, but dried maize ogi did not evidence any expansion ability whatever the experimental conditions. Cassava starch that had been fermented at 20 °C then sun‐dried presented the highest expansion ability. It was associated with low paste viscosities and high swelling and solubilisation values. When the fermentation was carried out at 35 °C, an annealing of cassava starch occurred that delayed starch gelatinisation and which could be involved in its lower baking expansion ability. © 2000 Society of Chemical Industry     

Effect of freezing and frozen storage on the gelatinization and retrogradation of amylopectin in dough baked in a differential scanning calorimeter

Frozen and non-frozen dough were baked in a differential scanning calorimeter (DSC) pan (heated in the calorimeter at temperatures similar to those of the center of the crumb during baking) and were aged at different temperatures. Gelatinized dough (DSC-baked dough) was heated again in the DSC. This methodology permitted us to study the effects of dough freezing and frozen storage on gelatinization and retrogradation of starch. During storage of frozen doughs at −18 °C an increase in the gelatinization enthalpy after 150 day of storage was observed. At 230 days of frozen storage a decrease in the onset temperature and an increase in the gelatinization temperature range was also detected. An increase of starch retrogradation with time of storage in frozen conditions was observed. During the aging of dough baked in DSC, a higher retrogradation temperature range was detected together with a faster retrogradation of starch at low temperature of aging.     

Ultrasonic Investigation of the Effect of Vegetable Shortening and Mixing Time on the Mechanical Properties of Bread Dough

ABSTRACT:  Mixing is a critical stage in breadmaking since it controls gluten development and nucleation of gas bubbles in the dough. Bubbles affect the rheology of the dough and largely govern the quality of the final product. This study used ultrasound (at a frequency where it is sensitive to the presence of bubbles) to nondestructively examine dough properties as a function of mixing time in doughs prepared from strong red spring wheat flour with various amounts of shortening (0%, 2%, 4%, 8% flour weight basis). The doughs were mixed for various times at atmospheric pressure or under vacuum (to minimize bubble nucleation). Ultrasonic velocity and attenuation (nominally at 50 kHz) were measured in the dough, and dough density was measured independently from specific gravity determinations. Ultrasonic velocity decreased substantially as mixing time increased (and more bubbles were entrained) for all doughs mixed in air; for example, in doughs made without shortening, velocity decreased from 165 to 105 ms⁻¹, although superimposed on this overall decrease was a peak in velocity at optimum mixing time. Changes in attenuation coefficient due to the addition of shortening were evident in both air-mixed and vacuum-mixed doughs, suggesting that ultrasound was sensitive to changes in the properties of the dough matrix during dough development and to plasticization of the gluten polymers by the shortening. Due to its ability to probe the effect of mixing times and ingredients on dough properties, ultrasound has the potential to be deployed as an online quality control tool in the baking industry.     

Physical aspects of the improvement of dough by fat

Shortening containing a fraction which is solid at dough temperatures is an essential ingredient in rapid breadmaking processes, but optional in long fermentation processes. Hypotheses concerning the action of fat are reviewed, and it is concluded that physical mechanisms, rather than those involving lipid oxidation, account for the increased loaf volume on the addition of shortening to the dough. Recent work using ‘model’ fats has shown that increased loaf volume results when sufficient of the solid component remains ‘free’ in the dough, and work with stored flour confirmed the importance of the free lipid fraction. A study of carbon dioxide release from doughs during baking showed that fat increases gas retention in the initial stage of rapid expansion. It is suggested that the solid components of the fat facilitate the production of orientated structures in dough, which can persist even when the temperature exceeds the melting point of the fat, and that these structures favour gas retention in the earliest stages of baking.