Prediction of Bread Crumb Density by Digital Image Analysis

The cellular structure of bread crumb (crumb grain) is an important factor that contributes to the textural properties of fresh bread. The accuracy of a digital image analysis (DIA) system for crumb grain measurement was evaluated based on its capability to predict bread crumb density from directly computed structural parameters. Bread was prepared from representative flour samples of two different wheat classes, Canada Western Red Spring (CWRS) and Canada Prairie Spring (CPS). Dough mixing and proofing conditions were varied to manipulate loaf volume and crumb density. Sliced bread was subjected to DIA immediately after physical density measurement. Experiments were repeated for the same bread samples after drying to three different moisture contents. Five computed crumb grain parameters were assessed: crumb brightness, cell wall thickness (CWT), void fraction (VF), mean cell area, and crumb fineness (measured as number of cells/cm²). Crumb density ranged from 0.088 to 0.252 g/cm³ depending on proofing and mixing treatments, and was predominantly affected by the former. With increasing crumb density, bread crumb became brighter in appearance, mean cell size and CWT decreased, crumb fineness increased, and the VF decreased. Approximately 80% of the variation in fresh or dried crumb density could be predicted using a linear regression model with two variables, CWT and VF. Results indicated that DIA of directly computed crumb grain could accurately predict bread crumb density after images had been correctly classified into cells and background.     

Effects of Flour Strength,Baking Absorption,and Processing Conditions on the Structure and Mechanical Properties of Bread Crumb

The objective of this study was to determine the effects of flour type, baking absorption, variation in sheeting, and dough proofing time on the density, crumb grain (visual texture), and mechanical properties (physical texture) of bread crumb. All response variables were measured on the same bread crumb specimens. Bread loaves were prepared by a short‐time bread‐making process using four spring wheat flours of varying strength. After crumb density measurement, digital image analysis (DIA) was used to determine crumb grain properties including crumb brightness, cell size, cell wall thickness, and crumb uniformity. Tensile tests were performed on bone‐shaped specimens cut from the same bread slices used for DIA to obtain values for Young's modulus, fracture stress, fracture strain, and fracture energy. Proof time had the most profound influence on the bread with substantial effects on loaf volume, crumb density, crumb brightness, and grain, as well as crumb mechanical properties. Increasing proof time resulted in higher loaf volume, lower crumb density and brightness, coarser crumb with fewer and larger cells with thicker cell walls, and weaker crumb tensile properties. Varying flour type also led to significant differences in most of the measured crumb parameters that appeared to correspond to differences in gluten strength among the flour samples. With increasing flour strength, there was a clear trend to increasing loaf volume, finer and more uniform crumb grain, and stronger and more extensible bread crumb. Increasing baking absorption had virtually no effect on crumb structure but significantly weakened crumb strength and increased fracture strain. In contrast, varying the number of sheeting passes had a minor effect on crumb cellular structure but no effect on mechanical properties. The experimental data were consistent with a cause‐effect relationship between flour strength and the tensile strength of bread crumb arising as a result of stronger flours exhibiting greater resistance to gas cell coalescence, thereby having fewer crumb defects.     

Effects of Oat Grain Hydrothermal Treatments on Wheat-Oat Flour Dough Properties and Breadbaking Quality

Hydrothermal treatments, which are routine in oat processing, have profound effects on oat flour dough rheological properties. The influence of roasting and steam treatments of oat grain on dough mixing and breadbaking properties was investigated when hydrothermally treated oat flour was blended with wheat flour. Roasting of oat grain (105°C, 2 hr) resulted in oat flours that were highly detrimental to wheat flour dough mixing properties and breadbaking quality. Steaming (105°C, 20 min) or a combination of roasting and steaming of oat grain significantly improved the breadbaking potential of the oat flours. The addition of oat flours increased water absorption and mixing requirements of the wheat flour dough and also decreased bread loaf volume. However, at the 10% substitution level, steamed oat flours exhibited only a gluten dilution effect on bread loaf volume when wheat starch was used as a reference. Oat flour in the breadbaking system decreased the retrogradation rate of bread crumb starch. The results indicate that adequate hydrothermal treatments of oat grain are necessary for oat flour breadbaking applications. Steamed oat flours used at a 10% level retarded bread staling without adversely affecting the loaf volume.     

Factors Controlling Gas Cell Failure in Bread Dough

Stress relaxation in the wall of a gas bubble, as measured by the alveograph, was used to study surface tension at the gas-dough interface of doughs from flours producing differing bread crumb grains. The surface tensions in the various wheat flour doughs were not different. Dough rheological properties, as measured by both dynamic oscillatory rheometry and lubricated uniaxial compression, were not different for doughs made from wheat flours that gave breads with different crumb grains. However, when the effect of starch granule size on gas cell wall stability was tested, the presence of a greater proportion of large starch granules in wheat flour dough was sufficient to result in gas cell coalescence and open crumb grain in the final baked product. This suggests that starch granule size is at least one of the factors that affects the crumb grain of bread.     

Influence of Bran Particle Size on Bread‐Baking Quality of Whole Grain Wheat Flour and Starch Retrogradation

The influence of bran particle size on bread‐baking quality of whole grain wheat flour (WWF) and starch retrogradation was studied. Higher water absorption of dough prepared from WWF with added gluten to attain 18% protein was observed for WWFs of fine bran than those of coarse bran, whereas no significant difference in dough mixing time was detected for WWFs of varying bran particle size. The effects of bran particle size on loaf volume of WWF bread and crumb firmness during storage were more evident in hard white wheat than in hard red wheat. A greater degree of starch retrogradation in bread crumb stored for seven days at 4°C was observed in WWFs of fine bran than those of coarse bran. The gels prepared from starch–fine bran blends were harder than those prepared from starch–unground bran blends when stored for one and seven days at 4°C. Furthermore, a greater degree of starch retrogradation was observed in gelatinized starch containing fine bran than that containing unground bran after storage for seven days at 4°C. It is probable that finely ground bran takes away more water from gelatinized starch than coarsely ground bran, increasing the extent of starch retrogradation in bread and gels during storage.     

Effects of Commercial Hydrolytic Enzyme Additives on Japanese‐Style Sponge and Dough Bread Properties and Processing Characteristics

The effects of increasing levels of eight commercial fungal enzymes enriched in four types of activity (α‐amylase, protease, xylanase, or cellulase) on Japanese‐style sponge and dough bread quality and processing characteristics have been studied using a Canadian red spring wheat straight‐grade flour. At optimum levels, the enriched α‐amylases, xylanases, and cellulases increased loaf volume and bread score and reduced crumb firmness, while the proteases only reduced crumb firmness. For α‐amylases, xylanases, and cellulases, optimum levels for crumb firmness were obtained at higher levels of addition than for loaf volume and bread score. At high levels of addition, all four enriched enzyme types reduced loaf volume and bread score and increased crumb firmness relative to optimum levels, with the proteases showing the most dramatic effects. α‐Amylases and cellulases had little impact on dough mixing requirements, while xylanases increased and proteases greatly reduced mixing requirements. All enzymes at optimum levels reduced sheeting work requirements, resulting in softer more pliable dough. Optimum bread properties for α‐amylases, xylanases, and cellulases were attained within a relatively narrow range of dough sheeting work values. This similarity in response suggests a dominant common nonspecific mechanism for their improver action, which is most likely related to water release and the resulting impact on physical dough properties.     

Quantitative Assessment of Gas Cell Development During the Proofing of Dough by Magnetic Resonance Imaging and Image Analysis

The structure of bread crumb is an important factor in consumer acceptance of bakery products. The noninvasive monitoring of the gas cell formation during the proofing of dough can aid in understanding the mechanisms governing the crumb appearance in the baked product. The development of gas cells during the proofing of dough was monitored in a noninvasive manner using magnetic resonance imaging (MRI) at 4.7‐T. The acquired MRI time series were analyzed quantitatively using image analysis (IA) techniques. The effects of both kneading temperature and mechanical damage by molding were studied. When additional rheological stress was introduced during molding, a more heterogeneous (coarse) gas cell size distribution was observed, and the dough had a smaller specific volume (as measured by MRI). These characteristics were preserved in the bread crumb structure after baking. The fast‐deformation during molding also resulted in an isotropic growth of the dough during proofing, whereas slow‐deformation during molding resulted in anisotropic growth. This can be related to a better conservation of stress in the dough under a moderate molding operation. A higher temperature during kneading also resulted in a coarser distribution of the gas cells and a smaller MRI specific dough volume. No effect of kneading temperature on the growth anisotropy could be detected, however. This indicates that temperature has a smaller effect on the conservation of stress in the dough than molding. The current work illustrates the capability of MRI/IA for understanding and predicting the influence of food processing parameters on consumer‐relevant features in a food product (bread).     

Iron-Enriched Bread with Karkade (Hibiscus sabdariffa) and Wheat Flour

Karkade (Hibiscus sabdariffa) was blended with wheat flour to make bread. When 0.5% Karkade was blended with wheat flour, maximum bread height and specific volume (cm³/g) were obtained (pH 4.8–5.0); these properties gradually deteriorated with increased Karkade. The pH of the bread crumb decreased with increased Karkade, reaching pH 3.35 when blended with 10% Karkade. The pH of Karkade alone was 2.5, which was adjusted to ≈5.0 by the addition of alkali just before blending with wheat flour and making bread. Control of the Karkade pH resulted in bread height and specific volume recovering to the original optimal levels. In addition, the deep reddish purple color (513 nm) of the bread crumb changed to a brownish color crumb. The Fe content was 0.14 mg of Fe/gram of dry crumb, or 6.22 mg of Fe/60 g of fresh bread when 5% Karkade was blended with wheat flour.     

Effects of (1→3)(1→4)-β-d-Glucans of Wheat Flour on Breadmaking

Water-soluble nonstarch polysaccharides were extracted from commercial hard red winter wheat flour and separated into three fractions by graded ethanol precipitation. The three fractions, F15, F40, and F60, varied in polysaccharide composition. Fraction F15 was rich in watersoluble (1→3)(1→4)-β-d -glucans, and fractions F40 and F60 were rich in arabinoxylans. Addition of individual fractions to a bread formula did not affect bread loaf volume. Addition of fraction F15 to the formula improved bread crumb grain. Treatment of (1→3)(1→4)-β-D -glucan-rich fraction F15 with lichenase before its addition to the bread formula resulted in bread with poor crumb grain. Treatment of the F15 fraction with β-xylanase before its addition to the bread formula resulted in bread with slightly improved crumb grain. Presumably, the (1→3)(1→4)-β-D -glucans in fraction F15 improved crumb grain by stabilizing air cells in the bread dough and preventing coalescence of the cells. Addition of pentosan-rich fractions F40 and F60 to the bread formula did not improve crumb grain and interfered with the improving effect of (1→3)(1→4)-β-D -glucan-rich fraction F15. Hydrolysis of the arabinoxylans in flour by adding β-xylanase to the bread formula resulted in improved crumb grain.     

Baking Performance of Durum and Soft Wheat Flour in a Sponge-Dough Breadmaking Procedure

Breadmaking properties were determined for formulations that included durum, soft, and spring wheat flour, using a pound-loaf sponge-dough baking procedure. Up to 60% durum or soft wheat flour plus 10% spring wheat flour could be incorporated at the sponge stage for optimum dough-handling properties. At remix, the dough stage required 30% spring wheat flour. Bread made with 100% spring wheat flour was used as a standard for comparison. Bread made with 60% durum flour exhibited internal crumb color that was slightly yellow. When storing pound bread loaves for 72 hr, crumb moisture content remained unchanged. Crumb firmness and enthalpy increased the most in bread made with 60% soft wheat flour. Crumb firmness increased the least in bread made with 100% spring wheat flour. Enthalpy changed the least in bread made with 60% durum flour. Crumb moisture content was significantly correlated with crumb firmness (r = -0.82) and enthalpy (r = -0.65). However, crumb moisture content was specific for each type of flour and a function of flour water absorption; therefore, these correlations should be interpreted with caution. Crumb firmness and enthalpy were significantly correlated (r = 0.65). Ball-milling flour resulted in an increase in water absorption of ≈2% and in crumb moisture content of ≈0.5% but had no effect on either crumb firmness or enthalpy.     

Size Distribution and Properties of Wheat Starch Granules in Relation to Crumb Grain Score of Pup‐Loaf Bread

Twelve hard winter wheat flours with protein contents of 11.8–13.6% (14% mb) were selected to investigate starch properties associated with the crumb grain score of experimentally baked pup‐loaf bread. The 12 flours were classified in four groups depending on the crumb grain scores, which ranged from 1 (questionable‐unsatisfactory) to 4 (satisfactory). Flours in groups 1, 2, 3, and 4 produced breads with pup‐loaf volumes of 910–1,035, 1,000–1,005, 950–1,025, and 955–1,010 cm³, respectively. Starches were isolated by a dough handwashing method and purified by washing to give 75–79% combined yield (dry flour basis) of prime (62–71%) and tailing (7–16%) starches. The prime starch was fractionated further into large A‐granules and small B‐granules by repeated sedimentation in aqueous slurry. All starches were assayed for weight percentage of B‐granules, swelling power (92.5°C), amylose content, and granular size distribution by quantitative digital image analysis. A positive linear correlation was found between the crumb grain scores and the A‐granule sizes (r = 0.65, P < 0.05), and a polynomial relationship (R² = 0.45, P < 0.05) occurred between the score and the weight percentage of B‐granule starch. The best crumb grain score was obtained when a flour had a weight percentage of B‐granules of 19.8–22.5%, shown by varietal effects.     

Bran Characteristics and Bread‐Baking Quality of Whole Grain Wheat Flour

Variations in physical and compositional bran characteristics among different sources and classes of wheat and their association with bread‐baking quality of whole grain wheat flour (WWF) were investigated with bran obtained from Quadrumat milling of 12 U.S. wheat varieties and Bühler milling of six Korean wheat varieties. Bran was characterized for composition including protein, fat, ash, dietary fiber, phenolics, and phytate. U.S. soft and club wheat brans were lower in insoluble dietary fiber (IDF) and phytate content (40.7–44.7% and 10.3–17.1 mg of phytate/g of bran, respectively) compared with U.S. hard wheat bran (46.0–51.3% and 16.5–22.2 mg of phytate/g of bran, respectively). Bran of various wheat varieties was blended with a hard red spring wheat flour at a ratio of 1:4 to prepare WWFs for determination of dough properties and bread‐baking quality. WWFs with U.S. hard wheat bran generally exhibited higher dough water absorption and longer dough mixing time, and they produced smaller loaf volume of bread than WWFs of U.S. soft and club wheat bran. WWFs of two U.S. hard wheat varieties (ID3735 and Scarlet) produced much smaller loaves of bread (<573 mL) than those of other U.S. hard wheat varieties (>625 mL). IDF content, phytate content, and water retention capacity of bran exhibited significant relationships with loaf volume of WWF bread, whereas no relationship was observed between protein content of bran and loaf volume of bread. It appears that U.S. soft and club wheat bran, probably owing to relatively low IDF and phytate contents, has smaller negative effects on mixing properties of WWF dough and loaf volume of bread than U.S. hard wheat bran.     

Factors Influencing Yeast Fermentation and the Effect of LMW Sugars and Yeast Fermentation on Hearth Bread Quality

The purpose of this study was to investigate how wheat cultivar, growth location, type of mill, LMW sugar composition of wheat flours, mixing time, and type of mixer affected yeast fermentation. Also studied was the effect of yeast fermentation and LMW sugar composition on hearth bread quality. To achieve this, 36 different flours were produced from two different mills using six different wheat cultivars grown at three locations. Yeast fermentation in doughs, measured as gas production, was determined using realtime pressure measurements and GasSmart software. A short mixograph mixing or spatula mixing was not efficient enough to rehydrate instant dry yeast. Compressed yeast and a short mixing time were enough to reach maximum fermentation rate. Maximum pressure after 210 min of fermentation was higher for instant dry yeast than for compressed yeast. Wheat cultivar and growth location had a significant effect on LMW sugar composition. Wheat cultivar, growth location, and type of mill used significantly affected pressure curve parameters. Oligosaccharides and damaged starch were positively correlated, and ash content and flour yield were negatively correlated with pressure curve parameters. Hearth bread characteristic crumb structure was positively correlated with all pressure curve characteristics except fast fermentation rate. Increased levels of mono‐ and disaccharides in wheat flour gave hearth breads with a more round shape.     

Characteristics of French Bread Baked from Wheat Flours of Reduced Starch Amylose Content

Wheat genotypes of wild type, partial waxy, and waxy starch were used to determine the influence of starch amylose content on French bread making quality of wheat flour. Starch amylose content and protein content of flours were 25.0–25.4% and 14.3–16.9% for wild type; 21.2 and 14.9% for single null partial waxy; 15.4–17.1% and 13.2–17.6% for double null partial waxy; and 1.8 and 19.3% for waxy starch, respectively. Wheat flours of double null partial waxy starch produced smaller or comparable loaf volume of bread than wheat flours of wild type and single null partial waxy starch. Waxy wheat flour, despite its high protein content, generally produced smaller volume of bread with highly porous, glutinous, and weak crumb than wheat flours of wild type and partial waxy starch. French bread baked from a flour of double null partial waxy starch using the sponge-and-dough method maintained greater crumb moisture content for 24 hr and softer crumb texture for 48 hr of storage compared with bread baked from a flour of wild type starch. In French bread baked using the straight-dough method, double null partial waxy wheat flours with protein content >14.3% exhibited comparable or greater moisture content of bread crumb during 48 hr of storage than wheat flours of wild type starch. While the crumb firmness of bread stored for 48 hr was >11.4 N in wheat flours of wild type starch, it was <10.6 N in single or double null partial waxy flours. Wheat flours of reduced starch amylose content could be desirable for production of French bread with better retained crumb moisture and softness during storage.     

Improvement of Sponge Cake Baking Test Procedure for Simple and Reliable Estimation of Soft White Wheat Quality

The sponge cake baking test is accepted and routinely used as a standard quality evaluation tool of soft white wheat for Asian markets, but its lengthy and laborious procedure makes it unsuitable for the routine evaluation of a large number of wheat breeding lines. We simplified the sponge cake baking procedure in the egg‐whipping step and improved its consistency by replacement of the hand mixing of cake batter with mechanical mixing, using a wire whisk or a BeaterBlade paddle. Egg whipping and mechanical batter mixing conditions were optimized by comparing foam density, sponge cake volume, and crumb grain to those obtained by the conventional procedure. Foam density, sponge cake volume, and crumb grain comparable to the conventional 100 g flour procedure were obtained with modifications, including extension of whipping time without heat input using a 5 L KitchenAid mixer, one‐time water addition at 3 min before the completion of egg whipping instead of twice, as in the conventional procedure, and cake batter mixing with a KitchenAid wire whisk or a BeaterBlade paddle. For baking a 50 g flour cake, egg foam of appropriate density was obtained with increased whipping speed and shortened egg‐whipping time (8 min). The modified sponge cake baking procedure yielded egg‐foam density, cake volume, and crumb grain similar to the conventional procedure and effectively differentiated soft wheat flours of different quality. Sponge cake volume of 14 soft white wheat flours ranged from 1,134 to 1,426 mL with the conventional procedure, from 1,113 to 1,333 mL with the modified procedure of batter mixing with a wire whisk, from 1,108 to 1,360 mL with the modified procedure of batter mixing with a BeaterBlade paddle, and from 577 to 719 mL with the modified method of 50 g of flour and batter mixing with a wire whisk. The modified methods with the BeaterBlade paddle and wire whisk exhibited significant correlation in cake volume with a conventional procedure (r = 0.931, P < 0.001 and r = 0.925, P < 0.001, respectively).     

Production of Two Types of Pocket‐Forming Flat Bread by the Sponge and Dough Method

Two types of flat bread (thin and thick) were produced from straight‐grade flour by the traditional straight dough (SD) and sponge and dough (SPD) methods using 50 and 60% sponges. Quality of the resulting bread was evaluated with respect to specific volume, crumb distribution between layers, moisture content, overall sensory quality, and rate of staling. The results showed that the method of production has a significant effect (P < 0.05) on the specific volume of the crumb‐rich thick flat bread but not on the almost crumb‐free thin type. The study showed that breads produced with the SPD method were superior to those produced by the SD method with respect to their overall quality and resistance to staling, and that using 50% sponge gave bread with superior overall sensory quality to that obtained using 60% sponge. The results indicate that the Structograph can be used to follow the staling of these breads. Nonetheless, using the SPD method has some drawbacks, mainly longer fermentation time, and more space, mixing, and labor requirements that are expected to limit its use in commercial production of flat bread types.     

Bread Crumb Grain Development During Baking

Scanning electron microscopy was used to study gas cell size, shape, and distribution throughout the breadmaking process. Flours that produced bread with a relatively good grain and a relatively poor grain were used. Micrographs of the dough samples were taken at mixing; before and after each of two punches; before and after panning; after proofing; and after 12, 18, and 24 min (complete) of baking. No differences were found between the two flours at any dough stage. However, after 12 min of baking, the cell distributions were different between the doughs. These results suggest that the crumb grain differentiates during the early stages of baking. The changes documented during this time, i.e., cells becoming larger and the cell walls thicker, indicate that some gas cells coalesce during the early stages of baking and that this is reflected in the crumb grain of the bread.     

Physicochemical Properties of Oat Varieties and Their Potential for Breadmaking

The breadmaking potential of six oat varieties was compared with and related to their physicochemical properties. The most significant differences in the bread characteristics were found in the crumb structure. The varieties Buggy, Energie, and Zorro resulted in good bread quality with an even gas‐cell distribution characterized by a high number of relatively small pores. In contrast, Typhon, Ivory, and Nord 08/311 each had a large hole in the center of the crumb and accordingly poor quality. Breads differed little in specific volume, bake loss, and density. Rheological analysis revealed positive effects of low batter resistance to deformation on oat bread quality. On the basis of the physicochemical characterization, protein and fat contents were identified as key factors responsible for differences observed in bread quality, provided that starch damage and water‐hydration capacity were low. Additionally, high setback and final viscosity, as determined by Rapid Visco Analyser (RVA) analysis, positively affected oat bread quality. High α‐amylase activity was found to influence negatively the breadmaking performance of oats. Overall, protein, fat, dietary fiber content, starch pasting properties, and α‐amylase activity were responsible for the breadmaking properties of oat varieties.     

Effects of Bran Fermentation on Quality and Microstructure of High‐Fiber Wheat Bread

We compared the effects of spontaneous fermentation of the bran fraction and fermentation with added yeast or added yeast and lactic acid bacteria (Lactobacillus brevis) on the quality of wheat bread supplemented with bran. Prefermentation of wheat bran with yeast or with yeast and lactic acid bacteria improved the loaf volume, crumb structure, and shelf life of bread supplemented with bran. The bread also had added flavor and good and homogenous crumb structure. Elasticity of the crumb was excellent. Spontaneous fermentation of the bran fraction did not have the same positive effects on bread quality. The microstructure of the breads was characterized by light microscopy. The positive effect of fermentation of bran on bread quality was evident when comparing the well‐developed protein network structure of the breads baked with fermented bran with the control bread. Prefermentation of the bran with yeast and lactic acid bacteria had the greatest effect on the structure of starch. The starch granules were more swollen and gelatinized in the breads made with prefermented bran. The pretreatments of the bran fraction had no detectable effect on the microstructure of the cell wall particles in the test breads.     

End-Use Quality of Flour from Rhyzopertha dominica Infested Wheat

The objective of this study was to evaluate how Rhyzopertha dominica infestation of stored wheat grain affects the rheological and baking properties of bread made with the milled flour. Wheat samples were infested with R. dominica and stored for up to 180 days at room temperature. Every 45 days, samples of wheat were collected and evaluated for insect population and flour yield. Flour milled from these wheat samples was evaluated for color reflectance, pH, fat acidity, and rheological properties which were measured by a farinograph. Loaves of bread were baked using a straight-dough procedure. Volume, height, and weight of the loaves were evaluated. None of the analyses performed on the control wheat flours showed any changes during the storage period, and they were similar to the initial wheat. The insect population increased during storage of the wheat up to 90 days, and the flour yield decreased with the storage up to 180 days. Flours from insect-infested wheat absorbed more water than did flours from control wheat. Dough stability and dough development times of infested flours decreased. Bread volume showed a progressive decline throughout the storage experiment. In conclusion, flour from insect-infested wheat exhibited changes in rheological properties such as dough stability, dough development times, water absorption, and mixing stability; bread had an offensive odor; and volume and loaf characteristics were negatively affected.