Determination of a representative volume element based on the variability of mechanical properties with sample size in bread

Quantitative analysis of food structure is commonly obtained by image analysis of a small portion of the material that may not be the representative of the whole sample. In order to quantify structural parameters (air cells) of 2 types of bread (bread and bagel) the concept of representative volume element (RVE) was employed. The RVE for bread, bagel, and gelatin-gel (used as control) was obtained from the relationship between sample size and the coefficient of variation, calculated from the apparent Young's modulus measured on 25 replicates. The RVE was obtained when the coefficient of variation for different sample sizes converged to a constant value. In the 2 types of bread tested, the tendency of the coefficient of variation was to decrease as the sample size increased, while in the homogeneous gelatin-gel, it remained always constant around 2.3% to 2.4%. The RVE resulted to be cubes with sides of 45 mm for bread, 20 mm for bagels, and 10 mm for gelatin-gel (smallest sample tested). The quantitative image analysis as well as visual observation demonstrated that bread presented the largest dispersion of air-cell sizes. Moreover, both the ratio of maximum air-cell area/image area and maximum air-cell height/image height were greater for bread (values of 0.05 and 0.30, respectively) than for bagels (0.03 and 0.20, respectively). Therefore, the size and the size variation of air cells present in the structure determined the size of the RVE. It was concluded that RVE is highly dependent on the heterogeneity of the structure of the types of baked products.     

Fractal texture analysis of bread crumb digital images

A fractal texture analysis technique was applied to bread crumb digital images. Fractal dimensions obtained from several methods (fractional Brownian motion, frequency domain, relative differential box-counting, morphological fractal, mass fractal and random walks methods) were investigated in order to determine their capability to accurately describe the surface roughness of bread crumb images or the visual appearance of bread crumb in meaningful terms. A total of 500 bread crumb images of different porosity and grain quality were analysed. It was found that bread crumb appearance could be effectively quantified by the fractal dimension of its digital image. Correlations of fractal dimensions with mean cell area, standard deviation of cell area and void fraction were variable for the fractal methods. While the mass fractal method measured better crumb heterogeneity, other methods quantified coarseness, cell–cell wall ruggedness and cell wall tortuosity. A vector comprising fractal dimensions would objectively depict crumb grain and would allow comparisons between different bread crumb images.     

Evaluation of Image Analysis Tools for Characterization of Sweet Bread Crumb Structure

Many approaches to evaluate bread crumb features by applying free or at least not too expensive image analysis (IA) software have been published; however, the described procedures showed noticeable differences. The aim of this work was to compare different image scanning resolutions and thresholding techniques to quantify sweet bread crumb features (cell density, mean cell area, shape factor) and their relation with fractal dimension. Two sets of experiments were carried out, one to determine the effect of scanning resolution and thersholding method and the other to validate the previous results by evaluating breads with different crumb structures. Nine different scanning resolutions (75, 100, 150, 200, 300, 355, 435, 515, 555 dpi) and two segmentation procedures (Otsu and Manual) were tested. Three different types of commercial sweet breads and a yeasted sweet bread added with different concentrations (six, 12%) of Chia flour (Salvia hispanica) were evaluated. Results showed that the percentage of particles with areas between 0.1 and 4.0 mm² remained almost constant when using 350 dpi or larger resolution values, while the smallest particles (<0.1 mm²) increased their proportion up to 87% at the highest scanning resolution for both thresholding methods. IA was useful to detect crumb structure differences among commercial breads and breads added with Chia flour as obtained from cell density (154 ± 4.6–246 ± 2.5) and mean cell area (0.81 ± 0.02–0.7 ± 0.03) results. However, the number of selected objects to calculate these parameters produced different results. The addition of 6% of Chia flour did not affect the bread crumb features, while at the largest proportion more and smaller pores were obtained. Fractal texture was useful to evaluate bread crumb structure, as it not depends on the number of particles detected.     

Interrelationship between image,dough and Barbari bread characteristics; use of image analysis to predict rheology,quality and shelf life

Cellular materials are often anisotropic, i.e. their properties depend on the direction in which they are measured. The aim of this work was to examine the effect of liquid improver components on image features (colour difference, average size, area fraction, cell wall thickness, fractal dimension, solidity, and circularity) of Barbari flat bread in both cross and longitudinal sections. Glycerol, sodium stearoyl‐2‐lactylate and enzyme active soy flour were evaluated as improver constituents. Image characteristics were furthermore correlated with dough rheology, quality, and shelf life in both sections of bread. Results from statistical analysis suggest that the parameters describing anisotropy or the favourite orientation of cell structure are crucial in understanding more than 50% of differences observed in crumb architecture. The coefficients of determination of all the response variables were higher than 0.81. Among image features, colour difference and average size gave the most correlations from ?0.857 to 0.896 and ?0.784 to 0.698 with other properties, respectively.     

Optimization of Gluten-Free Formulations for French-Style Breads

ABSTRACT:  The formulation of gluten-free bread, which will be suitable for patients with coeliac disease, was optimized to provide bread similar to French bread. The effects of the presence of hydrocolloids and the substitution of the flour basis by flour or proteins from different sources were studied. The added ingredients were (1) hydrocolloids (carboxymethylcellulose [CMC], guar gum, hydroxypropylmethylcellulose [HPMC], and xanthan gum), and (2) substitutes (buckwheat flour, whole egg powder, and whey proteins). The bread quality parameters measured were specific volume, dry matter of bread, crust color, crumb hardness, and gas cell size distribution. Specific volume was increased by guar gum and HPMC. Breads with guar gum had color characteristics similar to French bread. Hardness decreased with the addition of hydrocolloids, especially HPMC and guar. Breads with guar gum had the most heterogeneous cell size distribution, and guar gum was therefore selected for further formulations. Bread prepared with buckwheat flour had improved quality: an increased specific volume, a softer texture, color characteristics, and gas-cell size distribution similar to French bread. Bread with 1.9% guar gum (w/w, total flour basis) and 5% buckwheat flour (of all flours and substitutes) mimicked French bread quality attributes.     

Digital bread crumb: Creation and application

Bread is a foam and the softness of breads is an important quality attribute. For many non-food foams, digital environments have been implemented which can be used to characterize the structure to optimize products for specific functionalities. For breads, structure based models that incorporate pore structure, which is comprised of the pore distribution and overall porosity, with solid matrix properties are lacking. For the first time, such structure based models have been stochastically, or randomly, generated for a range of breads using previously published X-ray microtomography data (Wang et al., 2011). The Weibull probability distribution has been used to characterize closed pore distributions, stochastic probability theory has been used to obtain representative porosities, and digital bread crumb models which incorporate pore structure have been created. Digital bread crumbs have been compared against real world samples via visual texture and small strain compression experiments. Digital bread crumbs exhibited similarities to real products in terms of cell wall thicknesses as seen from surface appearance. Results from digital compression experiments using finite element analysis showed differences in Young’s moduli between breads can be attributed to both differences in pore distribution as well as porosity.     

Flour quality tests for selected wheat cultivars and their relationship to Arabic bread quality

Analytical and rheological parameters were established for flours from nine selected wheat cultivars, each covering a range of protein contents. Arabic and pan breads were baked from these flours and baking quality was determined. Wheat cultivars were found to differ in their suitability for Arabic bread production. Within cultivars the relationship between protein content and Arabic bread score was best described by a quadratic equation. Traditional flour quality tests do not adequately describe the flour quality requirements for Arabic bread as clearly as for pan bread. Ranges and optimum values for a number of parameters can be set to describe flours most likely to be suited to the production of Arabic bread. However, for reliable evaluation of baking quality for Arabic bread, flours fitting the prescribed range must be test baked.     

利用图像分析仪评价馒头品质的研究

以我国小麦主产区的222份小麦制成的馒头为研究对象,进行了感官评价和图像分析仪C-Cell测试。以此为基础进行C-Cell参数聚类分析,将C-Cell的34个特征参数聚为4类,筛选出了11个代表性特征参数。初步探索了馒头仪器评价和感官评价之间的关系,结果表明：C-Cell特征参数与感官评价指标存在一定的相关性,切片面积、周长和切片亮度与内部结构、感官总分的相关性较好,都呈极显著正相关;而气孔对比度、气孔密度、粗糙气孔体积及粗细气孔比都与馒头感官总分呈显著或极显著负相关。回归分析得到了以C-Cell特征参数为自变量的馒头感官评分的回归方程,为客观评价馒头品质提供了参考。     

Relationship between Rice Flour Particle Sizes and Expansion Ratio of Pure Rice Bread

We examined a method to produce bread from crystalline rice flour without using thickening agents such as gluten, polysaccharide thickening, and amorphous rice flour. Rice grains were pulverized by a jet mill to produce flour. Samples of rice flours of various particle size distributions were prepared by using a size shifter. The degree of starch damage and the dynamic viscoelasticity of rice batter were measured in this work. We also baked bread of the flour of each size distribution to study processability for making bread. The batter made by the pulverized flour of rice particle size ranging from 75 to 106 μm had the highest expansion ratio and a good processability for baking breads compared to other particle size batters. The rice bread with high expansion ratio was produced by controlling particle size of crystalline rice flour without using thickening agents.     

Cell Size Distributions of Puffed Corn Extrudates

The cell size distributions of various experimental puffed corn extrudates were determined by image analysis, applied to longitudinal and transversal cross sections. Individual cell cross-sectional area was used as the size measure. All the cell size distributions, regardless of specimen orientation, composition and extrusion conditions, were described mathematically by both the log-normal and Rosin-Rammler distribution functions. The distributions mean size, degree of skew-ness or the corresponding distribution functions constants, were characteristic of the extrudate type and its particular cellular structure.     

GUAR AND LOCUST BEAN GUMS AS PARTIAL REPLACERS OF ALL-PURPOSE FLOUR IN BREAD: AN OBJECTIVE AND SENSORY EVALUATION

All purpose flour was partially replaced with locust bean (LBG) and guar gums at 0% (control), 2% and 4% replacement levels in a bread product. All bread treatments were evaluated objectively and subjectively. Two percent LBG replacement significantly increased standing height. Firmness of bread was significantly firmer. Crumb color was not significantly different for any of the 5 bread treatments. Crust color was not significantly different for any of the 5 bread treatments. Crust color, however, was significantly lighter for the control in comparison with the 2% and 4% guar and 4% LBG breads. Two percent guar produced a more even cell size distribution throughout the bread crumb. For all 5 bread formulations moistures were not significantly different. Sensory evaluation revealed a significant difference between the control and 4% LBG. Neither the control nor 4% LBG breads were not significantly preferred. Both gums were found to retard bread staling; 2% LBG was the most effective.     

Dough and crumb grain changes during mixing and fermentation and their relation with extension properties and bread quality of yeasted sweet dough

Dough and crumb grain evolution of yeasted sweet dough, as affected by the combined effect of mixing (dough development) and fermentation times, and their relation to rheological properties and bread quality was studied. Structural changes of under or optimum developed dough, without fermentation, were related mainly to increments in extensibility (P > 95%), without a noticeable change in pH. At all mixing stages, fermentation duration increased R_m, whereas extensibility and pH decreased. When plotting R_m with bread specific volume, cell area, total cell area fraction or yellow crumb colour parameter (b*) simple mathematical models, with determination coefficients larger than 0.85 were obtained. Bread crumb image analysis showed that crumb cell size was not affected by mixing time, while fermentation duration had a direct influence on this parameter, increasing the proportion of the smallest and the largest crumb cells, without changing cell density, possibly as a result of Ostwald ripening, coalescence and separation‐redistribution mechanisms.     

Evaluation of viscoelastic properties and air-bubble structure of bread containing gelatinized rice

The impact of addition of gelatinized rice porridge to bread has been investigated on loaf volume, viscoelastic properties and air-bubble structure. We prepared four variety of bread: bread containing rice porridge (rice porridge bread), bread containing gelatinized rice flour (gelatinized rice flour bread), and wheat flour and rice flour breads for references. Instrumental analyses the bread samples were carried out by volume measurement of loaf samples, creep test and digital image analysis of crumb samples. Rice porridge bread showed the maximum specific volume of 4.51 cm³/g, and even gelatinized rice flour bread showed 4.30 cm³/g, which was larger than the reference bread samples (wheat and rice flour breads). The values of viscoelastic moduli of gelatinized rice flour bread and rice porridge bread were significantly smaller (p < 0.05) than those of wheat flour and rice flour breads, which indicates addition of gelatinized rice flour or rice porridge to bread dough encouraged breads softer. Bubble parameters such as mean air- bubble area, number of air-bubble, air-bubble area ratio (ratio of bubble area to whole area) were not significantly different among the bread crumb samples. Therefore, the bubble structures of the bread samples seemed to similar, which implied that difference of viscoelasticity was attributed to air-bubble wall (solid phase of bread crumb) rather than air-bubble. This study showed that addition of gelatinized rice to bread dough makes the bread with larger loaf volume and soft texture without additional agents such as gluten.     

Physical assessment of bread destructuration during chewing

This work consisted in characterizing the physical properties of bread bolus by its rheological behavior, moisture content and particle size. Two breads of different texture were chewed for different durations by a healthy subject, until swallowing. An apparent viscosity of the bolus was determined by capillary rheometry, whereas its viscoelastic behavior was determined by an oscillatory test on a rheometer equipped with a vane geometry. An imaging method was set up in order to determine the distribution of bread particle size after chewing. For both breads, the apparent viscosity of bread boluses followed a power law with a consistency index decreasing with chewing time; this consistency index reached similar values for the two breads before deglutition, about 10 times lower than bread initial consistency; same trend was obtained for viscoelastic moduli. Meanwhile, the moisture content increased significantly, and mastication reduced the bread into an increasing number of small particles. The results suggested that plasticization of bread by water from saliva had more effect on the rheological behavior of the bolus than its fragmentation.     

Quality and mold control of enriched white bread by combined radio frequency and hot air treatment

This study explored the application of radio frequency (RF) energy in conjunction with conventional hot air treatment to provide uniform heating for control of mold in pre-packaged bread loaf. A 6 kW, 27.12 MHz RF system was used to develop treatment protocols. The treatment parameters were selected based on minimum time-temperature conditions that were required for 4-log reduction of Penicillium citrinum spores while yielding acceptable bread quality. During combined RF and hot air treatments, the core and periphery of the bread loaf were heated together with almost the same heating rate. The maximum temperature difference within one bread slice was less than 5 °C. The moisture contents and water activities of RF treated samples first increased and then decreased compared to those of untreated samples, while firmness increased during the storage for both heat treated and untreated samples, yet the overall differences in sample qualities between RF treated bread samples and control were not significant. Because of better heating uniformity, much lower mean product temperature and shorter holding time were used for control of P. citrinum spores with combined RF and hot air treatment as compared to conventional heating alone. Heating bread to 58 °C or higher resulted in 4-log reduction of P. citrinum spores isolated from moldy bread. The storage life at room temperature (23 °C) was extended by 28 ± 2 days for the treated white bread.     

Granulometry of bread crumb grain: Contributions of 2D and 3D image analysis at different scale

Six bread crumbs were prepared from three different recipes and three baking procedures. Images of crumb were acquired in 2D at a macroscopic scale by using a flat bed scanner (resolution 85 μm) and in 3D at a local scale by X-ray tomography (resolution 10 μm). The cellular structure was assessed by mathematical morphology. 2D image analysis was completed by principal component analysis. The first principal component was found to reflect crumb fineness, in agreement with the mean cell size determined in 3D at a local scale. 3D mean cell wall size were about 220 μm and were not significantly different. The second principal component was linked to the 2D macroscopic heterogeneity of the crumb and to the macroscopic cell wall thickness. 2D images can be applied to the rapid control of crumb grain and could be used to quantify the cellular structure for the calculation of mechanical properties.     

添加麦芽粉和抗坏血酸对面包烘焙品质的影响

研究添加麦芽粉和抗坏血酸对面包烘焙品质的影响。以河南和山东2个小麦主要生产省的29个代表性品种样品为材料,用布勒实验磨制粉后,在面包基础配方上设置添加组和未添加组,研究添加麦芽粉和抗坏血酸后面包感官评分、质构及C-Cell图像分析变化。结果表明,添加麦芽粉和抗坏血酸后,可明显提高面包体积、体积评分、外观评分和最终综合评分,使面包冠变大,颈变明显;对面包芯色泽、质地和纹理的改善作用不明显。质构分析中面包的硬度和韧性均明显减小,衰减比例无明显变化。C-Cell指标中的面包切片面积、切片周长、气孔数量、平均气孔密度值均明显增大,切片亮度和气孔直径明显降低。仪器评价指标与面包感观评价中部分参数存在相关关系。