Computational fluid dynamics (CFD) modeling of an electrical heating oven for bread-baking process

Radiation is the most dominant heat transfer mode in an electrical heating oven. A 3D CFD model for an electric heating baking oven was developed. Three different radiation models namely, discrete transfer radiation model (DTRM), surface to surface (S2S) and discrete ordinates (DO) were employed for the simulation of the electrical baking oven. All models predicted almost similar results, which tallied well with the experimental measurements. During the full heating cycle, the oven set-point temperature was reached after 360 s. Lower temperature zones occurred near oven wall due to lower air flow. Based on preliminary evaluation of applicability, the DO radiation model was selected for bread baking simulation and validated with the experimental measurement of bread temperature. Bread simulation was carried out to study the profiles of temperature and starch gelatinization of crust and crumb of the product. This study indicated the baking process to be complete at 1500 s when the temperature of bread-center reached 100 °C.     

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.     

Bread baking: Technological considerations based on process modelling and simulation

This paper presents a study of bread baking, mainly from a technological point of view, i.e. focused on transport phenomena and major quality changes occurring during the process. Such study was carried out by numerical simulation of a previously developed and validated mathematical model, which describes the simultaneous heat and mass transfer (with phase change in a moving boundary) taking place in bread during baking. Kinetic models for starch gelatinization and browning development were coupled to the transport model. Input variables to the model were oven temperature, heat transfer coefficient, and bread radius. A total of 105 operating conditions were simulated using the finite element method, and the end point of baking was established for three values of surface lightness. It is shown that an intense heating strategy can produce a browned but unbaked product, besides nutritional quality is negatively affected. Furthermore, minimization of baking time is restricted by internal resistance to heat transfer.     

Starch Gelatinization in Chemically Leavened Bread Baking

Differential scanning calorimetry was employed to assess the kinetics of the starch gelatinization in bread doughs. The process of gelatinization, which depended on the depth from the surface of the sample, followed the same first order kinetics in the baking treatment and in the calorimetric scan. Its progress was predictable when the local temperature could be suitably recorded. Accordingly, thorough temperature control allowed monitoring starch gelatinization and bread baking.     

Effect of Baking Conditions on Properties of Starch Isolated from Bread Crumbs: Pasting Properties,Iodine Complexing Ability,and X-ray Patterns

In order to understand starch changes induced by baking process at different locations of a slice of sandwich bread, namely the top, center, and bottom locations, starch was isolated from crumbs baked at two heating rates ( 6.31 and 4.67 °C/min) and evaluated for their pasting properties, gelatinization parameters, and iodine complexing ability. Results showed that starch isolated from the bottom and the center crumbs baked at higher heating rate presented the significant higher final viscosity and higher setback than that isolated from crumbs baked at lower heating rate. Thermal analysis showed that starch isolated from the center crumb of the bread slice presented the lower enthalpy value of gelatinization, confirming that these samples underwent higher heat-moisture treatment during the baking process. After equilibration at 0.97 a_w, the exposure to iodine vapor changed the X-ray diffraction intensity of starch samples. Polarized light microscopy showed that heating affects starch granule morphology due to the higher starch chain mobility and the higher granular swelling when breads were baked at lower heating rate.     

Physicochemical Properties of Partbaked Breads

In this current study eight partially-baked breads were studied and compared in terms of a number of physicochemical characteristics: moisture distribution, density, RVA patterns, starch gelatinization, and retrogradation, amylose lipid complex formation and X-ray diffraction patterns. The samples were different in terms of total moisture content (from 32 to 38%) and moisture distribution in the cross section of the samples, starch retrogradation level (from 0.9 to 4.5 (J/g)) and RVA patterns. DSC experiments were carried out to determine the level of starch gelatinisation. The results showed that all starch granules in the eight partbaked breads were fully gelatinized under the conditions used and there was no intact starch granules left in the systems. Therefore, the second phase of baking will not be of great importance in terms of setting the structure and texture of the crumb of a product made from partbakaed bread. The role of the second phase of baking will be to a large extent the generation of flavor, crust, and coloration in the bread.     

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.     

Computational Fluid Dynamics (CFD) Modeling for Bread Baking Process—A Review

Computational fluid dynamics (CFD) modeling of entire bread baking process is very complicated due to involvement of simultaneous physiochemical and biological transformations. Bread baking is a fickle process where composition, structure, and physical properties of bread change during the process. CFD finds its application in modeling of such complex processes. This paper provides the basics of CFD modeling, different radiation models used for modeling of heating in electrical heating ovens, modeling of bread baking process along with the predictions of bread temperature, starch gelatinization, and browning index. In addition, some recent approaches in numerical modeling of bread baking process are highlighted. Moreover, current limitations, recent developments, and future applications in CFD modeling of bread baking process are discussed in detail.     

Quantification in starch microstructure as a function of baking time

The purpose of this study was the characterization of micro structural and thermal aspects of starch gelatinization in wheat dough/crumb during bread baking. The microstructure of starch granules was examined by confocal-laserscanning-microscopy (CLSM) and evaluated by an image analyzing tool. Supporting crystallinity changes in wheat dough/crumb were analyzed by differential-scanning-calorimetry (DSC) and calculated by the content of terminal extent of starch gelatinization (TEG). The micrograph of processed CLSM data showed starch structure changes during baking time. After gelatinization the starch fraction itself was inhomogeneous and consisted of swollen and interconnected starch granules. Image processing analyses showed an increment of mean granule area and perimeter of the starch granules. The results of DSC were examined to present an equation which provides a mean of predicting TEG values as a function of baking time. CLSM and DSC measurements present high significant linear correlation between mean starch granule area and TEG (r = 0.85). The possibility to combine CLSM with thermal physical analytical techniques like DSC in the same experiments is useful to obtain detailed structural information of complex food systems like wheat bread. Finally, it offers the option to enlarge the knowledge of microstructural starch changes during baking in combination with physicochemical transformation of starch components.     

Two-dimensional CFD modeling and simulation of crustless bread baking process

A special type of baking oven was developed where crustless bread was made by gently baking the dough at controlled temperature by spraying water at prefixed intervals on the surface of the dough. In this study, a two-dimensional (2D) CFD model for crustless bread during baking has been developed to facilitate a better understanding of the baking process. Simultaneous heat and mass transfer from the bread during baking was successfully simulated. It was found that core temperature of the bread reached at 95 °C at the end of baking where as moisture of the bread satisfies the normal bread quality. The model can be successively applied to study the unsteady heat and mass transfer from the crustless bread during baking.     

A Study on Degree of Starch Gelatinization in Cakes Baked in Three Different Ovens

The main objective of the study was to determine the effects of different baking ovens and different cake formulations on the degree of starch gelatinization during cake baking. Baking was performed in microwave, infrared–microwave combination, and conventional ovens. Starch gelatinization levels of fat free, 25% fat, and 25% Simplesse™-containing cake samples were examined using differential scanning calorimeter (DSC) and rapid visco analyzer (RVA). Both DSC and RVA results showed that increasing baking time increased gelatinization level for all baking types significantly. It was also found that the effect of fat content on starch gelatinization was different depending on the type of baking. Addition of fat reduced the degree of starch gelatinization in conventional baking. However, fat enhanced the gelatinization in microwave and infrared–microwave combination ovens. Usage of Simplesse™ as a fat replacer decreased the starch gelatinization in all types of baking significantly. There was insufficient starch gelatinization in microwave-baked cakes in which the degree of gelatinization ranged from 55% to 78% depending on formulation. On the other hand, it ranged from 85% to 93% in conventionally baked cakes. Combining infrared with microwaves increased degree of starch gelatinization (70–90%).     

A quality comparison of breads baked by conventional versus nonconventional ovens: A review

Undesirable qualities of breads baked in nonconventional ovens have been observed by most researchers. The altered heat and mass transfer patterns and much shorter baking times associated with microwave radiation resulted in a crustless product with tougher, coarser, but less firm texture. Insufficient starch gelatinization, microwave-induced gluten changes, and rapidly generated gas and steam caused by the heating mode could be reasons for quality changes in the microwave-baked breads. Although breads baked in an electrical resistance oven did not brown, their interior characteristics and shelf-life were superior to those of products baked in a conventional oven. Bread with a superior keeping quality was obtained using an air impingement convection oven. The determination and explanation of the physical and biochemical changes that occur in products during baking in conventional versus nonconventional ovens are fruitful areas for future research.     

Structural Changes in the Dough During the Pre-baking and Re-baking of French Bread Made with Whole Wheat Flour

This study investigates the changes occurring in the dough after the pre-baking and re-baking steps in the preparation of frozen bread (French rolls) made with whole wheat flour. At the end of each step, the different parts of the rolls (inner crumb, outer crumb, and crust) were characterized and compared with the dough. The temperature profile obtained showed that the opening of the cut height occurred when the inner crumb temperature was close to 40 °C. The moisture content of the inner and outer crumbs remained high even after the two baking steps, overcoming problems cited in literature such as weight loss and drying out of the re-baked bread. The color of these parts was not affected by the re-baking step. Using RVA, infrared spectrometry, and scanning electron microscopy analyses, it was found that right after pre-baking, the starch granules in the crumb and crust were not completely gelatinized and gelatinization continued during the re-baking process. After pre-baking, a few isolated intact starch granules remained in the inner and outer crumbs, and a greater amount was found in the crust, as observed by polarized light microscopy. This behavior was also observed after the re-baking step. The DSC and X-ray diffraction results indicated that the amylose–lipid complex present or formed in the dough was still present in all parts of the rolls after the pre-baking and re-baking steps.     

Effect of different baking modes on the physico-chemical and sensory characteristics of tandoori roti

Studies were carried out to determine the effect of baking, in different types of oven such as an earthen tendoor, a gas tandoor, an electric oven and a heated plate, on the physico-chemical and quality characteristics of tandoori roti. The studies indicated that the extent of gelatinization of starch varied depending on the type of oven used and was found to be 74.6, 78.4, 90.7 and 88.4% in roties baked in an earthen tandoor, a gas tandoor, an electric oven and a heated plate respectively. The pasting characteristics of starch, separated from the tandoori roti sample and measured using a Rapid Visco Analyzer, indicated the highest peak viscosity (36 SNU) for tandoori roti baked in an earthen tandoor and the lowest (25 SNU) for that baked in an electric oven. The concentration of high molecular weight proteins was lower in roti baked in an earthen tandoor and a gas tandoor, indicating greater dissociation of high molecular weight proteins during baking in such ovens. The sensory texture, taste and flavour of roti baked in an earthern tandoor was found to be superior to those baked in other types of ovens.     

基于模糊数学综合感官评价的甘薯淀粉面包的工艺优化

为了提高面包营养价值,改善滋味,降低面包老化速度,延长保质期,将甘薯淀粉添加到面包当中,采用单因素和正交实验,考察配方(甘薯淀粉、黄油、干酵母的添加量)及加工工艺(一次醒发时间、醒发温度和烘焙时间)对面包感官性状和质构的影响。基于模糊数学的评价方法评价甘薯淀粉面包的品质,对甘薯淀粉面包的形状、色泽、松软度、香味、滋味进行感官性质的分析。结果表明:最佳配方为混合粉(小麦粉+甘薯淀粉)150 g,甘薯淀粉的含量为15 g、黄油15 g、干酵母5.5 g;最优加工工艺为一次醒发时间为60 min、醒发温度为25 ℃、烘焙时间为9 min;最优条件下其硬度为27.95 N,弹性为15.18 mm,咀嚼性为228.30 mJ,胶粘性为15.05 N。按此条件制作的甘薯淀粉面包色泽金黄,外形饱满,柔软适口具有甘薯淀粉面包特有的风味,为甘薯淀粉面包工业化生产提供理论指导,同时丰富面包种类,拓宽甘薯淀粉用途。     

Effect of green plantain flour addition to gluten‐free bread on functional bread properties and resistant starch content

Green plantain flour (GPF) was used as a functional ingredient to produce gluten‐free (GF) bread based on a flour blend of rice flour and GF wheat starch (50:50) to improve their functional properties and to increase their resistant starch (RS) content. In pretrials, an addition of up to 30% GPF provided acceptable bread quality with maximum RS content. Based on these trials, two 2³ factorial screening experimental designs were applied, where water content, baking temperature and baking time of GF bread containing 30% GPF addition were optimised. The best baking conditions to achieve satisfying GF bread quality – higher loaf volume, softer crumb firmness and regular porosity structure at the highest RS content could be defined to a maximum addition of water at 160%, baking temperature of 180 °C and baking time of 90 min. The incorporation of GPF showed good potential to improve the quality of GF bread.     

冲泡即食豌豆粉的研究

利用快速黏度仪(RVA)和差式扫描量热仪(DSC)比较了不同烘烤温度和时间对豌豆粉热力学特性、糊化特性及透明度的影响,结果表明,在130℃温度下,烘烤50min所制得豌豆粉品质较佳,其糊化度大、冷热糊稳定性好、透明度适中。进一步比较藕粉和绿豆粉与豌豆粉复配后产品的色泽、气味、口感与黏性,发现添加20%的藕粉或10%的绿豆粉与豌豆粉复配后,在色、香、味上最易被人们接受。     

Cake Baking in Conventional, Impingement and Hybrid Ovens

White layer cakes were baked in three types of air impingement ovens, a hybrid (microwave/air impingement) oven, and a reel oven. Cakes were evaluated based on volume, crust color, and texture. Oven heat transfer rates were measured directly, and ranged from 22.8 to 84.8 J/s m²C° for top and from 17.4 to 110.9 for bottom surfaces, exposed in the different ovens, with the conventional reel oven having the lowest values. An RSM design was used to establish optimum baking conditions for each oven. For air impingement ovens, baking time was reduced by almost half but produced cakes very similar to those from the control (reel) oven. Incorporating microwaves enabled a further reduction in baking time, to one fourth. Cakes baked with microwaves had similar color, but had 15% less volumes and firmer textures than control cakes.     

Effect of baking method on some characteristics of starch in pound cake crumbs

BACKGROUND: The effect of the baking process (microwave versus conventional oven) on some starch characteristics of pound cake was evaluated. Proximal chemical analysis, total resistant starch (RS), retrograded resistant starch (RS3), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD) were evaluated. Pound cake, one of the major products of Mexico's bread industry, was selected for analysis because the high moisture and fat content in the beaten dough might reduce the quality defects often associated with microwave baking. RESULTS: Crumbs from microwave‐baked pound cakes contained lower moisture than crumbs from conventionally baked pound cake. Lower RS was observed in fresh microwave‐baked than conventionally baked pound cake. RS3 increased significantly in conventionally baked products stored for 8 days at room temperature, whereas slightly lower changes in RS3 were observed in the microwaved product. DSC revealed less gelatinisation in microwaved pound cake which is related to limited water availability during the microwave heating process. The crystallinity peaks present in conventionally baked pound cake might be associated with RS3 content; the resistant retrograded starch formed during storage, is reflected in the XRD pattern. CONCLUSION: Microwave‐baked pound cake crumbs showed less gelatinisation than conventionally baked pound cake crumbs. Copyright © 2007 Society of Chemical Industry     

Effect of the amount of steam during baking on bread crust features and water diffusion

Surface mechanical properties in fresh bread and during storage are greatly affected by the water plasticizing effect. However, the incidence of steaming during baking on the crust mechanical properties remains still unclear. The impact of the amount of steam (100, 200 and 400 ml) during baking on the crust features and water diffusivity was investigated. The amount of steam significantly (p < 0.05) affected the crust colour, glossiness and mechanical properties. An increase in the amount of steam led to reduced colour, failure force and failure firmness, whereas increased glossiness. Water vapour transfer rate and water vapour permeability of the bread crust significantly decreased when increasing the amount of steam applied during baking. Crust microstructure studies carried out by scanning electron microscopy and X-ray microtomography confirmed that the amount of steam greatly affected the surface starch gelatinization and also the protein-starch network.