Volume change of bread and bread crumb during cooling,chilling and freezing,and the impact of baking

During baking, bread dough undergoes an expansion followed by a slight contraction at the end of baking. The contraction during baking has been evidenced by some authors. However, there is a limited amount of literature about the contraction of the crumb during the chilling phase and also during the freezing phase in the case of freezing. A study has been carried out to better understand the impact of the baking degree on the contraction of the crumb during chilling after baking and during freezing. The volume of the samples has been evaluated with a laser volumeter. Breads (70 g dough) were baked until reaching 75 °C, 85 °C, 95 °C, 98 °C and then 98 °C for 10 min. Results showed that a longer baking resulted in a lower contraction of the bread. The volume change was between 25% and 2.5% for baking at 75 °C—0 min dwell and 98 °C—10 min dwell, respectively. The contraction was compared to the contraction of degassed bread crumb samples, which was more important. SEM pictures showed that the degree of baking also corresponded to a very different structure of the crumb. For the longer baking, the starch granules were fully gelatinized and no ghosts of starch granules were visible. The magnitude of the contraction was thus associated with the degree of baking and with the degree of starch granule destructuration.     

Combining local pressure and temperature measurements during bread baking: insights into crust properties and alveolar structure of crumb

Improvements in both the miniaturisation and heat compensation of pressure transducers made it possible to measure pressures as low as 5 kPa inside bread dough during baking (ΔT = 80 °C). Additional calibration was found to be necessary to decrease it below 0.18 kPa according to the variations in temperature encountered during baking. Two probes with both a thermocouple and a miniature pressure transducer were used to reveal pressure gradients inside bread dough during baking and post-cooling. During baking, increase in pressure (up to 1.1 kPa) was mainly attributed to the mechanical restrictions exerted on the dough by the stiffened surface layers. Pressure build-up due to the stiffening of bubble walls could not be detected. Various effects of the rupture in the bubble walls are reported. Sudden falls in pressure observed up to 70 °C were attributed to the bubble coalescence phenomenon. Evidence of an open porous structure was provided by the balance in pressure through the dough before the end of baking and the almost simultaneous lowering of pressure (−0.15 kPa) throughout the crumb during cooling. The slight lowering of pressure during post-cooling was also evidence of lower permeability of the crust compared to the crumb.     

Effect of heat on rheology,surface hydrophobicity and molecular weight distribution of glutens extracted from flours with different bread-making quality

Gluten was extracted from flours of several different wheat varieties of varying baking quality. Creep compliance was measured at room temperature and tan δ was measured over a range of temperatures from 25 to 95 °C. The extracted glutens were heat-treated for 20 min at 25, 40, 50, 60, 70 and 90 °C in a water bath, freeze-dried and ground to a fine powder. Tests were carried out for extractability in sodium dodecyl sulphate, free sulphydryl (SH) groups using Ellman's method, surface hydrophobicity and molecular weight (MW) distribution (MWD) using field-flow fractionation and multi-angle laser light scattering. With increasing temperature, the glutens showed a decrease in extractability, with the most rapid decreases occurring between 70 and 90 °C, a major transition in tan δ at around 60 °C and a minor transition at 40 °C for most varieties, a decrease in free SH groups and surface hydrophobicity and a shift in the MWD towards higher MW. The poor bread-making variety Riband showed the highest values of tan δ and Newtonian compliance, the lowest content of free SH groups and the largest increase of HMW/LMW with increasing temperature. No significant correlations with baking volume were found between any of the measured parameters.     

Changes in gelatinization and rheological characteristics of japonica rice starch induced by pressure/heat combinations

Rice starch suspensions of 10% dry matter (DM) were treated by heat (0.1 MPa at 20–85 °C) or pressure/heat combinations (100–600 MPa at 20, 40 and 50 °C) for 15 min to investigate their gelatinization and rheological characteristics. The maximum swelling index of about 12 g water per gram of DM was obtained by thermal treatment at 85 °C, meanwhile, that of 7.0 g was observed by 600-MPa pressurization at 50 °C. The higher temperatures or pressures resulted in the higher degrees of gelatinization. Furthermore, treatments of 0.1 MPa at 85 °C, 500 MPa at 50 °C and 600 MPa at various temperatures caused complete gelatinization of rice starch. The consistency index (K) and storage modulus (G′) dramatically increased from 70 °C or 400 MPa. The G′ values were higher in pressure-treated samples than those in thermal-treated samples. Therefore, an application of pressure/heat combinations as a processing method to improve the quality of rice starch products would be possible.     

Biodegradable foam tray from cassava starch blended with natural fiber and chitosan

This work developed biodegradable foam trays from cassava starch blended with the natural polymers of fiber and chitosan. The kraft fiber at 0, 10, 20, 30 and 40% (w/w of starch) was mixed with cassava starch solution. Chitosan solution at 0, 2, 4 and 6% (w/v) was added into starch/fiber batter with 1:1. Hot mold baking was used to develop the cassava starch-based foam by using an oven machine with controlled temperature at 250 °C for 5 min. Results showed that foam produced from cassava starch with 30% kraft fiber and 4% chitosan had properties similar to polystyrene foam. Color as L^*, a^* and b^* value of starch foam tray was slightly increased. Density, tensile strength and elongation of the starch-based foam were 0.14 g/cm³, 944.40 kPa and 2.43%, respectively, but water absorption index (WAI) and water solubility index (WSI) were greater than the polystyrene foam.     

Impact of different baking processes on bread firmness and starch properties in breadcrumb

The influence the quality and shelf life of baked product has previously been reported to be effected by the time and temperature of the baking process. In this study, dough was baked at 219 °C by using different ovens (conventional, impingement or hybrid) or with doughs of different sizes (large or small) for varying times. During baking the temperature profile at the dough center was recorded. Texture, thermal properties and pasting characteristics of baked product with reference to baking conditions were investigated. Small breads baked in the hybrid oven had the highest heating rate (25.1 °C/min) while large breads baked in conventional oven had the lowest heating rate (6.0 °C/min). When the data are viewed as a function of heating rate in this study, the enthalpy of amylopectin recrystallization, rate of bread firmness and the amount of soluble amylose were all-lower at the slower heating rate. The differences observed in product firmness following storage are potentially a consequence of the extent of starch granule hydration, swelling, dispersion and extent of reassociation; all of which are affected by the heating rate during baking.     

Crystallinity changes in wheat starch during the bread-making process: Starch crystallinity in the bread crust

The crystallinity of starch in crispy bread crust was quantified using several different techniques. Confocal scanning laser microscopy (CSLM) demonstrated the presence of granular starch in the crust and remnants of granules when moving towards the crumb. Differential scanning calorimetry (DSC) showed an endothermic transition at 70 °C associated with the melting of crystalline amylopectin. The relative starch crystallinity, as determined by X-ray and DSC, from different types of breads was found to lie between 36% and 41% (X-ray) and between 32% and 43% (DSC) for fresh bread crust. Storage of breads in a closed box (22 °C) for up to 20 days showed an increase in crust crystallinity due to amylopectin retrogradation both by X-ray and DSC. However, DSC thermograms of 1-day old bread crust showed no amylopectin retrogradation and after 2 days storage, amylopectin retrogradation in the crust was hardly detectable. ¹³C CP MAS NMR was used to characterize the physical state of starch in flour and bread crumb and crust. The intensity of the peaks showed a dependence on the degree of starch gelatinization.     

Contribution of Major Ingredients during Baking of Biscuit Dough Systems

Nineteen dough systems were made of a combination of two to nine of the following ingredients: flour, water, fats (coconut and/or palm oils), sugars (sucrose, invert) and chemical leaveners (ammonium bicarbonate, sodium bicarbonate, citric acid and sodium acid pyrophosphate). Their thermal behaviour was studied over a large temperature scale (20 °C to 160 °C). Thermal analysis of baking by three different methods (DSC, DMTA and TGA) at the same heating rate (3 °C/min) provided information about phase transitions, volume and mass changes of doughs during heating. Temperature ranges over which all ingredients reacted were identified. Melting transitions of fats occurred between 10 °C and 50 °C. Sugars increase temperatures of starch transitions. Chemical leaveners decrease rise temperature, whereas fats and sugars have a delaying effect on their action. The texture of biscuits results from interactions between ingredients; complete dough cannot thus be considered as merely a simple addition of all components.     

Impact of the baking kinetics on staling rate and mechanical properties of bread crumb and degassed bread crumb

This paper presents a study on the impact of baking conditions on crumb staling. Breads were baked at 220 °C, 200 °C and 180 °C corresponding to 6, 8 and 10 min to rise the temperature to 98 °C in the crumb (heating rates 13, 9.8 and 7.8 °C/min respectively with an initial temperature of 20 °C). A new protocol has been developed, consisting in baking a slab of degassed dough in a miniaturized oven to mimic the baking conditions of conventional bread making. Texture tests were done during staling on degassed crumb and on conventional crumb. Calorimetry tests showed that during storage, amylopectin recrystallisation occurred before crumb stiffening. A first order kinetics model was used to fit the evolution of the crumb texture (Young's modulus) and of the recrystallisation of amylopectin. The results showed that the hardening of the crumb during staling occurred after retrogradation of amylopectin. In addition, the staling rate was faster for faster baking kinetics. A mechanical model showed that the relative Young modulus is proportional to the square of the relative density of the crumb.     

Comparison of predictions of baking volume using large deformation rheological properties

Three large deformation rheological tests, the Kieffer dough extensibility system, the D/R dough inflation system and the 2 g mixograph test, were carried out on doughs made from a large number of winter wheat lines and cultivars grown in Poland. These lines and cultivars represented a broad spread in baking performance in order to assess their suitability as predictors of baking volume. The parameters most closely associated with baking volume were strain hardening index, bubble failure strain, and mixograph bandwidth at 10 min. Simple correlations with baking volume indicate that bubble failure strain and strain hardening index give the highest correlations, whilst the use of best subsets regression, which selects the best combination of parameters, gave increased correlations with R²=0.865 for dough inflation parameters, R²=0.842 for Kieffer parameters and R²=0.760 for mixograph parameters.     

Effects of glycerol on water properties and steaming performance of prefermented frozen dough

The amount of ice in both unfrozen steamed bread dough (UFD) and prefermented frozen steamed bread dough (PFD) with and without glycerol was investigated by differential scanning calorimetry (DSC). The quality of unfrozen steamed bread (UFB)/prefermented frozen dough steamed bread (PFB) was also evaluated. Frozen stability and steaming performance of prefermented frozen dough were negatively correlated with ice crystal growth. Glycerol effectively prevented the formation of ice crystals during freezing and frozen storage, maintaining the quality of steamed bread from prefermented frozen dough even over a period of 30 days. The best steamed bread performance was observed with the dough containing 2% of glycerol (flour weight basis) addition. Prefermenting conditions significantly affected the quality of UFB/PFB. The highest quality scores of steamed bread from prefermented frozen dough were obtained from 32 °C and 85% rh for 40 min.     

Improvement to baking quality of frozen bread dough by novel zein-based ice nucleation films

Freezing deteriorates the baking quality of frozen bread dough. This study revealed the protective effects of zein-based ice nucleation films (INFs) on the baking quality of frozen dough. INFs were prepared by immobilizing biogenic ice nucleators on the surface of zein films, which consequently revealed ice nucleation activity and increased the ice nucleation temperature of water from −15 °C to −6.7 °C. By using these films to wrap frozen dough during five freeze/thaw cycles, the specific volume of bread was increased by up to 25% compared to the bread from control frozen dough. The reason was attributed to 40% more viable yeast cells preserved by INFs. In addition, zein-based INFs also reduced the water loss by frozen dough resulting in higher water content in bread crumb. Combining the protective effects on both specific volume and water content from zein-based INFs, the obtained bread showed 68% lower firmness and fracturability and 2.4 times higher resilience compared to the control. The INFs were also superior in that for zein-based INFs, biogenic ice nucleators showed desirable affinity with the surface to sustain at least fifteen repetitive uses on freezing water.     

Soaking of Maize Determines the Quality of Aflata for Kenkey Production

Aflata is a gelatinised maize paste, serving as intermediate in the manufacture of kenkey, a traditional cooked fermented maize product of Ghana. The effect of water uptake during soaking of whole or dry-milled maize, the extent of starch damage, dough pH, fermentation time, and of endogenous and added enzymes on pasting and set-back viscosities of aflata dough were studied. Water uptake by coarsely dry-milled maize (grits) reached 0·63 mL/g dry matter in just 1 h, compared with 0·50 mL/gin 3 days for whole grain. High endogenous activity of proteases and carbohydrases were recorded in both grits and whole maize when soaked at 4 °C or 25 °C. These were significantly reduced after soaking at 60 °C. Soaking of grits at 60 °C with a heat-stable protease, or wet fine-milling of fermented grits resulted in significant (P<0·05) increases in pasting viscosities. Peak viscosities increased with fermentation time up to 24 h. Pasting viscosities decreased with repeated wet milling of fermented dough.     

Predicting wheat quality – consequences of the ascorbic acid improver effect

Genotype and environment sets of wheat cultivars and breeding lines were tested for bread making, dough mixing, dough rheology, protein composition and thiol/disulphide composition to find methods that could identify wheat with high baking quality (high-BQ) and moderate work input (moderate-WI) requirement using the mechanical dough development system. Wheat with these properties generally had a high baking response to ascorbic acid (AA) and a GluD1a (HMW-GS 2 + 12) allelic composition. Strong wheat with high WI and high-BQ generally had low baking response to AA and a GluD1d (HMW-GS 5 + 10) allelic composition. Using protein composition data to identify wheat of high-BQ (with AA) and moderate-WI, it was best to select wheat with as high as possible percent of SDS-unextractable polymeric protein (%UPP) in flour and as low as possible %UPP in total polymeric protein. Using a dough extension test for identifying wheat of high-BQ (with AA) and moderate-WI, it was best to select wheat with intermediate values for maximum resistance to extension (Rmax) and for values of extension at Rmax as high as possible within the intermediate Rmax range. Cysteine content of protein fractions and glutathione content of flour gave mostly poor to weak correlations with all baking and mixing properties.     

Glucose and pyranose oxidase improve bread dough stability

When used in bread dough systems, glucose oxidase (GO) and pyranose oxidase (P₂O) generate H₂O₂ from O₂. We here studied their potential to improve dough and bread characteristics. Neither GO nor P₂O significantly affected the volume of straight dough bread produced with fermentation and proofing times of respectively 90 and 36 min at dosages up to 0.50 nkat/g flour. Supplementation with 1.00 nkat/g flour of GO or P₂O significantly decreased bread loaf volume. The resistance of dough (fermented for 20 min and proofed for 56 min) to an applied shock was substantially improved by inclusion of 0.08, 0.25, 0.50 or 1.00 nkat/g flour of GO or P₂O in the dough recipe. Thus, the proofed doughs showed significantly less collapse and the resultant breads had higher loaf volumes than did the reference breads. Yeast probably exerts an oxidizing effect on dough, which, depending on the exact breadmaking protocol used, might veil the positive oxidizing effect of the enzymes on dough properties during prolonged fermentation.     

Effect of the drying rate on the complex viscosity of wheat flour dough transforming into crust and crumb during baking

This study aimed at characterizing the effect of hydrothermal dynamics on the dough rheology, in order to develop a complete dough viscosity model valid at different locations during baking. The dough rheology was characterised using dynamic mechanical thermal analysis (DMTA). Temperature and water content (WC) were monitored during DMTA. At high heating rates (15–30°C/min), relevant to the top crust, viscosity behaved as if WC was kept constant, in spite of dehydration (37%); such similarity was valid up to 80°C (stage A). Beyond, the viscosity decrease observed in the samples at constant WC was replaced by a long-lasting plateau (stage B, 3–4 × 10⁶ Pa.s), attributed to WC reduction below ∼37%. Above the boiling water temperature, the logarithm of viscosity increased linearly with decreasing WC (stage C). At lower heating rates (5°C/min), relevant to the bottom crust, viscosity was two-fold higher than that at higher heating rates, suggesting lower oven-rise. The viscosity decrease, observed at high temperatures (>80°C) for samples at constant WC, was not observed if drying occurred late (case of crumb beneath the crust); instead, viscosity increased up to levels close to that of the top crust (2–3 × 10⁷ Pa.s at WC∼20%). Despite these deviations, viscosity as a WC function was modelled with a unique equation set.     

Impact of baking conditions and storage temperature on staling of fully and part-baked Sangak bread

Bread staling involves a combination of physico-chemical phenomena that leads to a reduction of quality. This study aims at evaluating the impact of baking conditions (280 °C, 8 min; 310 °C, 5.5 min; 340 °C, 4 min), baking type (of fully baked (FB) and part-baked (PB)) and storage temperature (−18, 4 and 20 °C) on the staling of Sangak bread. Results showed that lower baking temperature with longer baking time produced drier bread with higher firmness. In FB Sangak breads, amylopectin retrogradation, amount of unfreezable water and firmness (measured by compression test) increased during storage at positive temperatures but hardness (determined by Kramer shear test) decreased significantly during first day of storage. The recrystallized amylopectin traps the free water resulting in crumb hardening. Water is also absorbed by the dry crust resulting in changes of rheological properties in the crust and crumb, and finally in staling. Storage at 4 °C resulted in increasing melting enthalpy of amylopectin crystallite in comparison with storage at 20 °C. Also it was found that firmness of PB breads due to rebaking was significantly lower than FB breads. There were no significant changes in staling parameters of FB and PB stored at −18 °C.     

Effect of fat level,mixing pressure and temperature on dough expansion capacity during proving

In this work the effect of fat content on dough aeration during proving was investigated using dynamic dough density measurements. Doughs of three different fat levels (0%, 0.04% and 0.2% flour basis) were mixed under various pressures using a Tweedy mixer and proved at five different temperatures (30, 35, 40, 45 and 50 °C) in the dynamic dough density system. The dough expansion capacity and the time of the gas loss of each dough sample were measured and related to fat level, mixing pressure and proving temperature.     

Assessment of amyloglucosidase activity during production and storage of laminated pie dough. Impact on raw dough properties and sweetness after baking

Amyloglucosidase (AMG) is an enzyme that hydrolyzes starch into glucose units. AMG activity was tested in a model pie dough during the dough-making process (after mixing and sheeting) and during storage for 4 weeks at 4 °C. The activity was quantified by measuring the glucose content of dough and baked products using HPLC. The consequences of AMG activity on the sweet taste of the baked products (sensory ranking test) and on the rheological properties of the dough were studied and compared with a control dough formulated with sucrose. The results showed a significant production of glucose during the dough-making process and during baking when AMG was used. During the dough-making process, AMG activity was limited by the substrate. During baking, the substrate was no longer a limiting factor and the amount of glucose released was directly proportional to the amount of AMG used. The mixing time was increased and the elastic properties of the dough decreased when AMG was added. However, these impacts of AMG on dough properties were not as significant as those of sucrose addition. Addition of 0.75% AMG (flour basis) developed a sweet taste equivalent to that obtained by addition of 17% sucrose (flour basis).     

The influence of temperature extremes on some quality and starch characteristics in bread,biscuit and durum wheat

Environmental conditions during grain-fill can affect the duration of protein accumulation and starch deposition, and thus play an important role in grain yield and flour quality of wheat. Two bread-, one durum- and one biscuit wheat were exposed to extreme low (−5.5 °C for 3 h) and high (32 °C/15 °C day/night for three days) temperatures during grain filling under controlled conditions for two consecutive seasons. Flour protein content was increased significantly in one bread wheat, Kariega, under heat stress. Cold stress significantly reduced SDS sedimentation in both bread wheats. Kernel weight and diameter were significantly decreased at both stress treatments for the two bread wheats. Kernel characteristics of the biscuit wheat were thermo stable. Kernel hardness was reduced in the durum wheat for the heat treatment. Durum wheat had consistently low SDS sedimentation values and the bread wheat high values. Across the two seasons, the starch content in one bread wheat was significantly reduced by both high and low temperatures, as is reflected in the reduction of weight and diameter of these kernels. In the durum wheat, only heat caused a significant reduction in starch content, which is again reflected in the reduction of kernel weight and diameter.