Effects of Glycerol and Moisture Redistribution on Mechanical Properties of White Bread

Effects of glycerol and moisture redistribution on mechanical properties of bread were investigated. Firmness increased in all bread crumb over storage time but firming rate was dependent on the initial moisture content, storage method (stored with and without crust), and the presence of glycerol. Faster firming was observed when bread crumb had low initial moisture content and high glycerol level, and was stored with crust. The effect of glycerol was more pronounced when stored with crust, suggesting a critical role of water loss. Firmness showed a good correlation (r² = 0.95) with the scale factor (C₁) from a mathematical model. Recoverable work rapidly decreased in first three days of storage and then remained relatively unchanged thereafter. Hardening of aged bread (but not fresh bread) by glycerol may be explained by local dehydration of bread polymer due to osmotic dehydration or competition for water, which in turn promote more rapid amorphous network formation but less amylopectin recrystallization.     

Water Self‐Diffusion Coefficient and Staling of White Bread as Affected by Glycerol

Water self‐diffusion coefficient (D) was investigated in bread crumb during storage to determine the effect of moisture loss and glycerol on the staling mechanism. D increased with added glycerol in breads of the same moisture content. D remained unchanged after storage without crust (with no moisture loss from crumb to crust). When stored with crust (with moisture loss), more mobile water was lost (probably from glycerol), resulting in a more rapid initial decrease in D in glycerol‐added bread. Competition of water may be a key influencing factor. Glycerol and loss of moisture (according to crumb‐crust moisture gradient) triggered a shift in moisture redistribution from starch and gluten to glycerol. This could have contributed to the increased structural rigidity and more rapid firming of the glycerol‐added bread. As a result, a greater firming rate was observed in glycerol‐added bread even with less amylopectin recrystallization as compared with the control.     

Breadmaking Use of Andean Crops Quinoa,Kañiwa,Kiwicha, and Tarwi

The effect of addition of flours from the highly nutritious Andean crops quinoa (Chenopodium quinoa), kañiwa (Chenopodium pallidicaule), kiwicha (Amaranthus caudatus), and tarwi (Lupinus mutabilis) has been investigated in wheat doughs and fresh bread quality. The thermomechanical profile of wheat doughs and bread quality has been explored by increasing substitution of wheat flour at 0–100% by Andean crop flours. Dough blends were evaluated using the Chopin Mixolab device, whereas bread quality assessment comprised sensory (overall acceptability) and physicochemical (moisture, specific volume, texture, color) determinations in composite breads. In general, no breads with aerated crumb structure could be obtained from 100% Andean crop flours, with the exception of quinoa breads that had overall sensory values about half a completely perfect score, and which were not significantly different from the breads made from a 50:50 blend of wheat and quinoa. Replacement of wheat flour by ≤12.5% (tarwi), 25% (kañiwa), and 50% (kiwicha), respectively, still produced breads with good sensory acceptability but variable color and doughs with acceptable thermomechanical patterns. Partial substitution of wheat flour by Andean crop flours constitutes a viable option to improve the nutritional value of the breads, with acceptable technological performance of dough blends and composite breads.     

Influences of Baking and Thawing Conditions on Quality of Par‐Baked French Bread

We examined the effects of baking time and temperature for the preparation of par‐baked French bread, and of thawing and second baking conditions on the characteristics of bread prepared from par‐baked bread. Par‐baked French bread with loaf volume and crumb structure comparable to fully baked bread (control) was obtained with ≥6 min baking at 218°C, which increased the crumb temperature to 97°C. Freezing, thawing, and second baking of par‐baked bread decreased loaf volume by ≥100 mL. The second baking time of par‐baked bread, which was adjusted to have the bread crumb subjected to 97°C for 14 min based on the crumb temperature profile, produced a darker crust of bread compared with the control. The par‐baked bread with 6 min of initial baking at 218°C and frozen at ‐30°C required 12 min of second baking after thawing for 180 min to ≈20°C to produce crust color, crumb moisture, and firmness comparable to that of the control. When thawing time of par‐baked bread was shortened from 180 to 0 min, the second baking time required to yield crust color similar to the control increased from 12 to 16 min. The crumb moisture content was higher in bread baked for 16 min without thawing par‐baked bread than those baked after thawing for 45 or 180 min. Lowering the initial baking temperature of par‐baked bread from 246 to 163°C with the adjustment of baking time from 4 to 12 min decreased crumb firmness of the re‐baked (218°C, 16 min) bread from 2.5 to 1.5 N at 2 hr after baking and from 9.8–10.3 to 6.2–6.3 N at 48 hr.     

Differential Scanning Calorimetry Glass Transition Temperatures of White Bread and Mold Growth in the Putative Glassy State

Differential scanning calorimetry (DSC) was used to determine the onset and end temperatures of the glass transition (T_g) for white bread equilibrated between 53 and 84% rh. Calorimetric T_g end values were ≈20°C higher than onset values, indicating that it is probably more correct to refer to a “glass transition range” rather than a glass transition temperature. Slices of white bread inoculated with a mixture of xerophilic molds were equilibrated to 75% rh (equilibrium moisture content of 14.5 g of water/100 g of dry material) and stored at 26°C. In a parallel experiment, some of the equilibrated bread samples were stored without mold inoculation and subjected to spontaneous contamination from the immediate surroundings. As suggested by measured T_g, bread stored at 75% rh and 26°C appeared to be glassy. After storage, samples of bread (inoculated or not) were spoiled by xerophilic molds, suggesting that T_g, as measured by DSC, cannot be considered as an absolute threshold for mold growth inhibition.     

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.     

Innovative Traditional Italian Durum Wheat Breads: Influence of Yeast and Gluten on Performance of Sourdough Moddizzosu Breads

This research investigated the impact of semolina dough formulation (percentage of sourdough [SD] addition and presence of yeast [Y] or common wheat gluten [G]) added singly and in combination on the sensory and physicochemical profiles of fresh and stored sourdough‐started durum breads, particularly Moddizzosu type. Main distinctive features of breads were identified, and optimal amounts of SD addition in presence of either yeast or gluten were used to achieve high‐quality fresh and stored soured durum breads made with semolina and remilled semolina at a ratio of 80:20. Common features of durum breads included color parameters and crumb grain characteristics of either fresh or stored samples. Increasing SD significantly increased scores for overall acceptability. In yeasted costarted samples, a linear promotion of both aroma and taste intensity resulted from increasing amounts of SD, whereas the opposite trend was observed for unyeasted breads. Higher values for degree of acidification, specific volume, crumb cohesiveness, resilience, and springiness but lower pH, moisture content, crumb hardness, and chewiness in durum samples were achieved with increased SD. The presence of Y counteracted acidification, harmonized volume increase, hardness, cohesiveness, springiness, and resilience, minimizing the effects of the SD added. Y and G acting singly as crumb softeners when added together to soured durum breads started with SD at a dose >10% provided lower and slower crumb firming kinetics. Breads with especially slow retrogradation kinetics corresponded to yeasted started samples with or without added gluten, regardless the presence or absence of SD. In unyeasted soured breads, the dose of SD slightly decreased the rate and extent of amylopectin retrogradation, irrespective of gluten addition.     

Konjac Polysaccharides Affect the Quality,Cell Structure,and Moisture Balance of Baked Bread

The effect of addition of konjac glucomannan (KGM) and its derivative konjac superabsorbent polymer (KSAP) on fresh bread quality and its influence on bread staling were investigated. Both KGM and KSAP decreased the hardening rate of the bread crumb and retarded amylopectin retrogradation. Loaf quality of the KGM bread and KSAP bread were therefore improved, because collapse of gas cells during bread processing was prevented. Thermogravimetric analysis (TGA) showed that the presence of KGM and KSAP increased compartmentalized water and slowed release of the compartmentalized water. Deconvolution of TGA showed an alteration of the distribution of free and bound water and its interaction with starch and gluten. Additionally, by monitoring water‐binding strength and changes during storage by a_w measurements, it was found that water release from konjac polysaccharide‐enriched bread was extended over time compared with the release from control bread. The presence of KGM and KSAP significantly reduced the staling rate of bread.     

Effect of Different Enzymes on the Textural Stability of Shelf‐Stable Bread

Three enzyme systems (2 amylase‐based and 1 protease‐based) were tested in shelf‐stable bread to determine effectiveness in preserving texture during storage for eight weeks. Each enzyme was tested in formulations without glycerol or with 6% glycerol. Bread samples were analyzed to determine physical properties (crumb density, crust‐to‐crumb ratio, rate of moisture distribution from crumb to crust), mechanical properties (modulus, and a parameter [C1] describing resistance to high levels of deformation obtained by fitting stress‐strain data to a three‐parameter function), and thermal properties (thermal stability and enthalpy of transitions) as a function of storage time. Mechanical properties were further analyzed to predict asymptotic firmness. Bread firmness after storage as evaluated in terms of modulus and C1 were lower in all enzyme‐added systems, the effect of protease being the most significant. Enzymes had less effect on glycerol‐containing systems with no apparent trend. The breads had complex thermal behavior and exhibited multiple transitions. Both amylase preparations in the presence of glycerol reduced the amount of starch recrystallization.     

Factors That Influence the Microwave Expansion of Glassy Amylopectin Extrudates

The microwave expansion of glassy, unexpanded amylopectin pellets was studied. Amylopectin was extruded at three levels of specific mechanical energy (483, 809, and 846 kJ/kg), and 35–40% moisture content, without expansion at the die. Glassy pellets were obtained by drying and equilibrating the extrudates at five water activities (a_w 0, 0.11, 0.33, 0.67, and 0.75). The pellets were characterized by measuring volume, porosity, and moisture content. The pellets were then expanded in a constant power microwave oven to determine the degree of expansion. When subjected to microwave heating, regardless of extrusion condition and initial a_w, the pellets expanded from the center where the highest temperature was recorded and then expansion advanced in the whole volume. Maximum expansion was reached after 30 sec of heating, after which samples started to burn from the center. Samples simultaneously expanded and lost moisture, both processes being faster and more intense for pellets of higher initial a_w. No expansion was observed for the pellets stored at a_w 0, while collapse was observed for pellets stored at a_w 0.73. A linear correlation between pellet expansion temperature and glass transition temperature was obtained. A hypothesis for the microwave expansion of glassy extrudates was formulated and represented on a state diagram.     

Solid-State 13C CP/MAS NMR studies on aging of starch in white bread

The effects of storage methods and glycerol on the aging of breadcrumbs were studied using solid-state (13)C CP/MAS NMR. After baking, a shift in C(1) peaks from triplet (A-type) to singlet (V-type) was observed. Addition of glycerol reduced the carbon peak intensities of fresh and aged breads, which correlated well with the DSC amylopectin "melting" enthalpy (r(2) = 0.91). Upon storage of bread with crust in hermetically sealed containers (when moisture migrated from the crumbs to the crust), the (13)C CP/MAS NMR peak intensity increased more rapidly during aging than when the bread was stored without crust. Although addition of glycerol retarded the starch retrogradation, as observed by (13)C CP/MAS NMR and DSC, it accelerated the firming rate. Therefore, bread firming in this case was controlled not only by starch retrogradation but also by other events (such as local dehydration of the matrix or gluten network stiffening).     

Influence of Amylose Content on Properties of Wheat Starch and Breadmaking Quality of Starch and Gluten Blends

The effects of amylose content on thermal properties of starches, dough rheology, and bread staling were investigated using starch of waxy and regular wheat genotypes. As the amylose content of starch blends decreased from 24 to 0%, the gelatinization enthalpy increased from 10.5 to 15.3 J/g and retrogradation enthalpy after 96 hr of storage at 4°C decreased from 2.2 to 0 J/g. Mixograph water absorption of starch and gluten blends increased as the amylose content decreased. Generally, lower rheofermentometer dough height, higher gas production, and a lower gas retention coefficient were observed in starch and gluten blends with 12 or 18% amylose content compared with the regular starch and gluten blend. Bread baked from starch and gluten blends exhibited a more porous crumb structure with increased loaf volume as amylose content in the starch decreased. Bread from starch and gluten blends with amylose content of 19.2–21.6% exhibited similar crumb structure to that of bread with regular wheat starch which contained 24% amylose. Crumb moisture content was similar at 5 hr after baking but higher in bread with waxy starch than in bread without waxy starch after seven days of storage at 4°C. Bread with 10% waxy wheat starch exhibited lower crumb hardness values compared with bread without waxy wheat starch. Higher retrogradation enthalpy values were observed in breads containing waxy wheat starch (4.56 J/g at 18% amylose and 5.43 J/g at 12% amylose) compared with breads containing regular wheat starch (3.82 J/g at 24% amylose).     

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.     

Effect of Isomaltooligosaccharide Syrup on Quality Characteristics of Sponge Cake

Sponge cakes were formulated using isomaltooligosaccharide (IMO) syrup as a sweetener to replace 0, 25, 50, 75, and 100% sucrose. The qualities of cakes were evaluated by physicochemical, microbiological, and sensory evaluation analyses. The viscosity in cake batter, cake volume, crumb Hunter a value, and IMO contents of baked cakes increased with increasing IMO syrup level, whereas the specific gravity in cake batter, crust L a b, and crumb L and b values, and hardness of baked cakes showed a reverse trend. The crust and crumb of cakes became darker and less yellow and had a better tender and less sweet texture as IMO syrup level increased and sucrose decreased. The degree of overall liking of cakes increased with increasing IMO syrup level. Total plate counts exceeded 10⁵ CFU/g for cakes stored at 25°C for three days and <10³ CFU/g for the samples stored at 5°C for seven days. The changes in the moisture content, water activity, L a b values, and IMO contents of samples did not differ during storage. Overall, sucrose in the formulation of sponge cakes could be partially or fully replaced with IMO syrup.     

Effects of Additives and Storage Temperature on Staling Properties of Bagels

The effects of xanthan gum, Novamyl (a type II α‐amylase), Instant Tender‐Jel C starch (a modified starch), and GMS‐90‐SSK (a hydrated monoglyceride) on the staling properties of bagels stored at 4 and 22°C from 0–7 days were studied. Texture analysis and moisture determination were conducted on the bagels before lyophilization. Analysis of percent soluble starch, crumb pasting (Rapid Visco Analyser) and degree of amylopectin recrystallization (differential scanning calorimeter) were conducted on lyophilized bagel crumb. Novamyl‐treated bagels appeared to be the most resistant to staling over time at both storage temperatures in relation to the enthalpy of gelatinization (ΔH). Bagels containing xanthan gum, Instant Tender‐Jel C starch, and GMS‐90‐SSK showed some improvements over the control bagels, although the effects of the additives on the characteristics of the bagels varied. Bagels made with xanthan gum or monoglyceride retained slightly higher crumb moisture percentages over most days of storage. The monoglyceride‐treated bagels had higher enthalpy values, lower percentages of soluble starch, and a higher pasting profile but had the softest texture. The apparent onset of increased staling of the monoglyceride‐ treated bagels was attributed to complexes formed with the starch fractions.     

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.     

Application of Response Surface Methodology in the Development of Gluten‐Free Bread

The formulation of gluten‐free (GF) bread of high quality presents a formidable challenge as it is the gluten fraction of flour that is responsible for an extensible dough with good gas‐holding properties and baked bread with good crumb structure. As the use of wheat starch in GF formulations remains a controversial issue, naturally GF ingredients were utilized in this study. Response surface methodology was used to optimize a GF bread formulation primarily based on rice flour, potato starch, and skim milk powder. Hydroxypropylmethylcellulose (HPMC) and water were the predictor variables. Analyses of the treatments from the design were made 24 hr after baking. Specific volume and loaf height increased as water addition increased (P < 0.01). Crumb firmness decreased as water levels increased (P < 0.01). Significant interactions (P < 0.01) between HPMC and water were found for the number of cells/cm². The number of large cells (>4 mm²) decreased with increasing levels of HPMC and water. Optimal ingredient levels were determined from the data obtained. The optimized formulation contained 2.2% HPMC and 79% water flour/starch base (fsb) and measured responses compared favorably to predicted values. Shelf‐life analysis of the optimized formulation over seven days revealed that, as crumb firmness increased, crust firmness and crumb moisture decreased.     

Volatiles in Selected Commercial Breads

Selected types of commercial breads obtained from local markets, including white sandwich, Irish oatmeal, soft rye, hearty rye, sour dough, home-like white, and onion-basil, were analyzed for volatiles. Using a purge and trap instrument, volatiles were purged directly from fresh crumb and crust samples of each bread type, collected on a trap (Tenax-TA), and transferred to a gas chromatograph. Separated components were detected and identified using mass and infrared spectroscopic detectors. Many components were present in all of the bread samples, with relative amounts varying among bread types and crust and crumb samples of a given bread type. Alcohols were generally the most abundant, followed in approximate order by aldehydes, esters, ketones, acids, various aromatics, terpenes, and hydrocarbons. Flavor additives, such as limonene, carvone, and other related compounds, were found mostly in rye and onion-basil breads. Composition of volatiles from sour dough bread differed greatly from the other breads, especially in increased levels of aldehydes, acids, and certain esters. Unsaturated aldehydes, such as 2-hexenal and 2-heptenal, were most abundant in sour dough bread.     

Effect of Freeze‐Thaw Cycles on the Gluten Fibrils and Crumb Grain Structures of Breads Made from Frozen Doughs

The effects of freeze damage on the crumb grain and on the underlying gluten fibrils of baked breads were studied using scanning electron microscopy (SEM) and magnetic resonance imaging (MRI). Sweet and white bread doughs were stored at ‐20°C and subjected to freeze‐thaw cycles. SEM images of grain pore walls that were washed with distilled water (20°C) clearly showed that gluten fibrils forming the skeletal framework of pore walls were cut and became coarse and nonuniform strings and that many knots were generated on gluten fibrils from freeze damage. An increase in the number of freeze‐thaw cycles increased both the coarseness of the gluten fibrils and the size of the knots, although the apparent damage was not clearly detected on the crumb grain with MRI.