Starch Retrogradation and Firming of Bread Containing Hydroxypropylated,Acetylated, and Phosphorylated Cross‐Linked Tapioca Starches for Wheat Flour

The present investigation aims at understanding the role of chemically modified starch on the firmness of fresh or stale bread. Bread was prepared from wheat flour or substituted wheat flour that contained 18% chemically modified tapioca starch and 2% vital gluten. Hydroxypropylated tapioca starch (HTS), acetylated tapioca starch (ATS), phosphorylated cross‐linked tapioca starch (PTS), and native tapioca starch (NTS) were tested. Bread prepared from the substituted flour with PTS showed a firmer texture on the day of baking compared with bread prepared from NTS, HTS, and ATS. PTS retained its granular structure in the gluten network after baking and seemed to play the role of filler particles in the gluten matrix, thereby increasing firmness of fresh bread crumb. Bread prepared from the substituted flour with HTS or ATS firmed at a lower rate and showed a lower endothermic melting enthalpy of amylopectin after three days of storage compared with NTS or PTS. These findings suggest that the staling of bread containing chemically modified tapioca starch involves recrystallization of amylopectin.     

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 Temperature on Sorption of Water by Wheat Gluten Determined Using Deuterium Nuclear Magnetic Resonance

The effects of lipids and residual starch components of wheat flour gluten on gluten hydration properties were investigated using nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) techniques. Whole or native, lipid-free, starch-free, and lipid- and starch-free gluten samples were prepared from wheat (Triticum aestivum) cv. Mercia. ²H NMR relaxation on gluten samples hydrated with deuterium oxide (D₂O) was measured over a 278–363 K temperature range. FTIR spectra were recorded in dry and fully hydrated material. Transverse relaxation (T₂) results indicated that all four gluten samples were hydrophilic in nature. There was little difference in relaxation behavior of whole and lipid-free gluten samples. T₂ values and populations of the relaxation components were very similar in each. The FTIR spectra of both samples showed an increase in extended β-sheet secondary structures on hydration. These results suggest that lipid binding in gluten, if it occurs, has little effect on wheat gluten properties. Adding starch to the gluten matrix results in an increase in water sorption on heating that may be attributed to the effects of starch gelation. However, the whole water uptake of the gluten cannot be accounted for by the contribution of the residual starch, as estimated by the effects of added starch. Extraction of residual starch required solubilization of the protein, including breaking of the disulfide bonds. This process altered the gluten structure and properties. Light microscope investigation showed that glutens with residual starch extracted were unable to form fibrillar strands on hydration. NMR and FTIR results showed greater water sorption in both samples with extracted starch than in the unextracted samples.     

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).     

Differential Scanning Calorimetric Study on the Effects of Frozen Storage on Gluten and Dough

Water transport from the gluten to the starch paste during frozen storage of a dough was studied by analysis of the differential scanning calorimetry (DSC) peak shape for gluten and dough. The results indicate that in gluten stored at ‐15°C, the water content in the gluten phase decreased by ≈1% over the first three weeks. An apparent steady state was attained over this period and the amount of ice did not increase further. Such changes were not observed for samples stored at ‐25°C. Qualitatively similar observations were made for dough stored at either ‐15 or ‐25°C. The greater sensitivity of dough to frozen storage is tentatively attributed to a slightly lower glass transition temperature in dough.     

Effect of Sucrose on Glass Transition,Gelatinization, and Retrogradation of Wheat Starch

Differential scanning calorimetry (DSC) was used to study the effect of sucrose on wheat starch glass transition, gelatinization, and retrogradation. As the ratio of sucrose to starch increased from 0.25:1 to 1:1, the glass transition temperature (T_g, T_g′) and ice melting enthalpy (ΔH_ice) of wheat starch‐sucrose mixtures (with total moistures of 40–60%) were decreased to a range of −7 to −20°C and increased to a range of 29.4 to 413.4 J/g of starch, respectively, in comparison with wheat starch with no sucrose. The T_g′ of the wheat starch‐sucrose mixtures was sensitive to the amount of added sucrose, and detection was possible only under conditions of excess total moisture of >40%. The peak temperature (T_m) and enthalpy value (ΔH_G) for gelatinization of starch‐sucrose systems within the total moisture range of 40–60% were increased with increasing sucrose and were greater at lower total moisture levels. The T_g′ of the starch‐sucrose system increased during storage. In particular, the significant shift in T_g′ ranged between 15 and 18°C for a 1:1 starch‐sucrose system (total moisture 50%) after one week of storage at various temperatures (4, 32, and 40°C). At 40% total moisture, samples with sucrose stored at 4, 32, and 40°C for four weeks had higher retrogradation enthalpy (ΔH) values than a sample with no sucrose. At 50 and 60% total moisture, there were small increases in ΔH values at storage temperature of 4°C, whereas recrystallization of samples with sucrose stored at 32 and 40°C decreased. The peak temperature (T_p), peak width (δT), and enthalpy (ΔH) for the retrogradation endotherm of wheat starch‐sucrose systems (1:0.25, 1:0.5, and 1:1) at the same total moisture and storage temperature showed notable differences with the ratio of added sucrose. In addition, T_p increased at the higher storage temperature, while δT increased at the lower storage temperature. This suggests that the recrystallization of the wheat starch‐sucrose system at various storage temperatures can be interpreted in terms of δT and T_p.     

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).     

Comparison of Oil,Shortening, and a Structured Shortening on Wheat Dough Rheology and Starch Pasting Properties

Monoacylglycerol‐stabilized oil in water emulsion (MAG gel) is an alternate shortening that is free of trans fatty acids, and low in saturated fatty acids. However, the behavior of MAG gels in comparison to other lipids has not been studied. This study investigated effects of structured MAG gel, a mixture of MAG gel unstructured components (Mixture), canola oil (Oil), or interesterified soy shortening (IE Soy) at different levels (6–24%) on hard or soft wheat dough properties. Doughs were prepared with different lipid types at equivalent lipid contents. Dough mixing and water absorption parameters were evaluated using a farinograph; gluten behavior was measured using a gluten peak tester (GPT); and pasting characteristics were measured using a micro‐viscoamylograph (MVAG). Water absorption values decreased with increasing lipid content. Dough development times were similar between the MAG gel and IE Soy, but farinogram curve characteristics during mixing were similar between MAG gel, Mixture, and Oil. The trend for peak max time in GPT was similar between MAG gel and IE Soy exhibiting delayed gluten aggregation; whereas Mixture and Oil exhibited earlier gluten aggregation. In MVAG, starch interaction with monoglyceride component of MAG gel and Mixture appeared to be the dominating factor resulting in increased pasting temperature and a second viscosity peak during cooling at higher levels of lipid addition.     

Effects of Transglutaminase on Rheology,Microstructure, and Baking Properties of Frozen Dough

The improving effects of transglutaminase (TGase) were investigated on the frozen dough system and its breadmaking quality. Rheological properties and microstructure of fresh and frozen doughs were measured using a Rapid Visco‐Analyser (RVA), dynamic rheometer, and scanning electron microscopy (SEM). The frozen doughs with three storage periods (1, 3, and 5 weeks at –18°C) were studied at three levels (0.5, 1.0, and 1.5%) of TGase. As the amount of TGase increased, hot pasting peak viscosity and final viscosity from the RVA decreased, but breakdown value increased. The TGase content showed a positive correlation with both storage modulus G′ (elastic modulus) and the loss modulus G″ (viscous modulus): G′ was higher than G″ at any given frequency. The SEM micrographs showed that TGase strengthened the gluten network of fresh, unfrozen dough. After five weeks of frozen storage at –18°C, the gluten structure in the control dough appeared less continuous, more disrupted, and separated from the starch granules, while the dough containing 0.5% TGase showed less fractured gluten network. Addition of TGase increased specific volume of bread significantly (P < 0.05) with softer bread texture. Even after the five weeks of frozen storage, bread volume from dough with 1.5% TGase was similar to that of the fresh control bread (P < 0.05). The improving effects of TGase on frozen dough were likely the result of the ability of TGase to polymerize proteins to stabilize the gluten structure embedded by starch granules in frozen doughs.     

Effect of Glycerol and Sorbitol on the Properties of Dough and White Bread

Polyols could prolong shelf life and improve the quality of white bread. But the effect of high contents of polyols on dough properties and bread qualities is not yet clearly known. Thus, the properties of dough and white bread with different addition of polyols were evaluated by means of selected physicochemical properties. Rheology experiment results showed that both glycerol and sorbitol decreased the G′ and G″ of the dough. The results of thermogravimetric analysis revealed that polyols hindered the evaporation of water and that glycerol had a greater capacity for water retention than did sorbitol. In the bread, they caused more water to be absorbed on the surface of the gluten–starch system. They decreased the water activity and mass loss of the bread, but the specific volume of the bread also decreased. We found when glycerol and sorbitol addition was higher than 8%, it could slightly increase the viscidity of dough, enhance the moisture content of bread, and reduce the water activity of bread. But the gluten strength of dough decreased, and shaping and proofing of dough were difficult, which resulted in the deterioration the quality of white bread. We conclude that the addition of glycerol or sorbitol below 8% would be beneficial to the properties of dough and white bread and that sorbitol is a better option than glycerol.     

Influence of Added Starch on Mixing of Dough Made with Three Wheat Flours Differing in High Molecular Weight Subunit Composition: Rheological Behavior

The effect of mixing time (6 and 20 min) and starch content were studied on doughs prepared with three wheat flours differing in high molecular weight subunit composition. Rheological measurements were performed in dynamic oscillation: frequency and strain sweeps, stress relaxation, and in large deformation viscosity measurements. The flours were diluted with starch to cover flour protein contents of 10–15%. Water was added to keep the starch‐water ratio constant when doughs were prepared with different protein contents. By increasing the starch content of the doughs, the rheological properties approached those of a starch‐water mixture prepared with the same starch‐water ratio as in the dough. The effect of the starch granules was reinforced by prolonged mixing. This may explain the higher values of the storage modulus and relaxation times observed after 20 min of mixing. Qualities related to gluten properties, appeared more clearly in large deformation viscosity measurements.     

Qualitative Effect of Added Gluten on Dough Properties and Quality of Chinese Steamed Bread

Glutens isolated from 15 soft red winter (SRW) wheat flours were added into a SRW wheat flour to obtain protein levels of 9.6 and 11.3% for determination of the qualitative effect of added gluten on the dough properties and quality of northern‐style Chinese steamed bread (CSB). Sodium dodecyl sulfate sedimentation (SDSS) volume of the gluten source flour exhibited positive relationships with mixograph absorption, midline peak time (MPT), and midline peak value (MPV) of the gluten‐added flours and with surface smoothness, crumb structure, and total score of CSB prepared from the gluten‐added flours regardless of protein content. Positive correlations were also observed between SDSS volume of the gluten source flour and specific volume and stress relaxation score of CSB prepared from the gluten‐added flours of 11.3% protein. The increase in protein content from 9.6 to 11.3% by gluten addition raised mixograph absorption, MPT, and MPV but had no apparent effect on resistance breakdown, dough maximum force for extension, and extensibility, and it increased CSB specific volume and crumb structure score without affecting surface smoothness, stress relaxation, and total score. Mixograph parameters exhibited significant relationships with CSB total score, indicating that they could be effective predictors of the CSB‐making quality of flours.     

Textural Comparisons of Gluten‐Free and Wheat‐Based Doughs,Batters, and Breads

Studies were conducted with two newly developed gluten‐free bread recipes. One was based on corn starch (relative amount 54), brown rice (25), soya (12.5), and buckwheat flour (8.5), while the other contained brown rice flour (50), skim milk powder (37.5), whole egg (30), potato (25), and corn starch (12.5), and soya flour (12.5). The hydrocolloids used were xanthan gum (1.25) and xanthan (0.9) plus konjac gum (1.5), respectively. Wheat bread and gluten‐free bread made from commercial flour mix were included for comparison. Baking tests showed that wheat and the bread made from the commercial flour mix yielded significantly higher loaf volumes (P < 0.01). All the gluten‐free breads were brittle after two days of storage, detectable by the occurrence of fracture, and the decrease in springiness (P < 0.01), cohesiveness (P < 0.01), and resilience (P < 0.01) derived from texture profile analysis. However, these changes were generally less pronounced for the dairy‐based gluten‐free bread, indicating a better keeping quality. Confocal laser‐scanning microscopy showed that the dairy‐based gluten‐free bread crumb contained network‐like structures resembling the gluten network in wheat bread crumb. It was concluded that the formation of a continuous protein phase is critical for an improved keeping quality of gluten‐free bread.     

沙蒿籽粉和谷朊粉对燕麦全粉食品加工品质的影响

为了探讨全燕麦粉面包、馒头加工品质及燕麦粉冷冻面团品质特性,以燕麦全粉为原料,研究了添加沙蒿籽和谷朊粉对燕麦全粉食品(含冷冻面团食品)加工品质改良效果。试验结果表明,谷朊粉对面包制作影响较大;沙蒿籽粉对馒头制作影响较大;沙蒿籽粉和谷朊粉共同使用的效果优于两者单独使用;加入2.5%沙蒿籽粉和8%谷朊粉对燕麦全粉面包和馒头品质改善效果最好。对冷冻面团加工而言,随着冷冻时间的延长面团品质不断下降,冻藏4 d后燕麦全粉冷冻面团面包、馒头品质显著降低。     

Effect of starch on the molecular mobility of amorphous sucrose

Molecular mobility in amorphous solid biomaterials is modulated by the composition and environment (primarily temperature). Phosphorescence of the triplet probe erythrosin B was used to generate a mobility map within amorphous sucrose films doped with starch ranging from 0.001 to 0.1 g starch/g sucrose. Data on the emission energy and lifetime of erythrosin B in sucrose and sucrose-starch films over the temperature range from 5 to 100 °C indicates that starch influences the molecular mobility as well as dynamic site heterogeneity of amorphous sucrose in a dose-dependent manner. At a starch/sucrose weight (wt) ratio below 0.005, both emission energy and lifetime decreased, and both the dipolar relaxation rate and nonradiative quenching rate k(TS0) increased, indicating that starch increased the matrix molecular mobility. At a ratio above 0.005, both emission energy and lifetime increased, and the dipolar relaxation rate and nonradiative quenching rate decreased, indicating that starch decreased the matrix mobility both in the glass and in the melt. The mobility showed a minimum value at a ratio of 0.01. The interactions existing in the sucrose-starch matrix are considered as the determining factor to influence the molecular mobility of sucrose-starch mixtures. Changes in the distribution of emission energies (emission bandwidth) and lifetimes indicated that starch increased the spectral heterogeneity at high contents while showing insignificant change or a slight decrease in the heterogeneity at low starch contents. These data illustrate the complex effects of a polymer with mainly linear structure and flexible conformation on the mobility of an amorphous, hydrogen bonded sugar matrix.     

Effects of Varying Weight Ratios of Large and Small Wheat Starch Granules on Experimental Straight‐Dough Bread

One commercial bread wheat flour with medium strength (11.3% protein content, 14% mb) was fractionated into starch, gluten, and water solubles by hand‐washing. The starch fraction was separated further into large and small granules by repeated sedimentation. Large (10–40 μm diameter) and small (1–15 μm diameter) starch fractions were examined. Flour fractions were reconstituted to original levels in the flour using composites of varying weight percentages of starch granules: 0% small granules (100% large granules), 30, 60, and 100% (0% large granules). A modified straight‐dough method was used in an experimental baking test. Crumb grain and texture were significantly affected. The bread made from the reconstituted flour with 30% small granules and 70% large granules starch had the highest crumb grain score (4.0, subjective method), the highest peak fineness value (1,029), and the second‐highest elongation ratio (1.55). Inferior crumb grain scores and low fineness and elongation ratios were observed in breads made from flours with starch fractions with 100% small granules or 100% large granules. As the proportion of small granules increased in the reconstituted flour, it yielded bread with softer texture that was better maintained than the bread made from the reconstituted reference flour during storage.     

Bread Quality of Spelt Wheat and Its Starch

Flours from five spelt cultivars grown over three years were evaluated as to their breadbaking quality and isolated starch properties. The starch properties included amylose contents, gelatinization temperatures (differential scanning calorimetry), granule size distributions, and pasting properties. Milled flour showed highly variable protein content and was higher than hard winter wheat, with short dough‐mix times indicating weak gluten. High protein cultivars gave good crumb scores, some of which surpassed the HRW baking control. Loaf volume was correlated to protein and all spelt cultivars were at least 9–51% lower than the HRW control. Isolated starch properties revealed an increase in amylose in the spelt starches of 2–21% over the hard red winter wheat (HRW) control. Negative correlations were observed for the large A‐type granules to bread crumb score, amylose level, and final pasting viscosity for cultivars grown in year 1999 and to pasting temperature in 1998 samples. Positive correlations were found for the small B‐ and C‐type granules relative to crumb score, loaf volume, amylose, and RVA final pasting viscosity for cultivars grown in 1999, and to RVA pasting temperature for samples grown in 1998. The environmental impact on spelt properties seemed to have a greater effect than genetic control.     

Starch Hydrolyzing Enzymes for Retarding the Staling of Rice Bread

Previous attempts have been made to obtain gluten‐free bread of acceptable quality for bread specific volume and crumb texture. Rice bread is a good alternative to celiac patients, but it has a very rapid staling during storage. Rice starch is more prone to retrograde during storage than wheat starch, and the special hydrophobic nature of the rice proteins requires specific enzymes to be used in the rice bread process. To retard rice bread staling, two different starch hydrolyzing enzymes (α‐amylase of intermediate thermostability and cyclodextrin glycoxyl transferase [CGTase]) have been tested and their effect on fresh bread quality and staling during storage has been evaluated. The addition of α‐amylase improved bread specific volume and crumb firmness but very sticky textures were obtained. The addition of CGTase produced even higher specific volume and similar crumb firmness with better texture. Both enzymes decreased the ability of amylopectin to retrograde during storage. The firming kinetic was lowered by the α‐amylase but not the limiting firmness, while the rice crumb from CGTase firmed quickly with a very short range of firmness increase. Results revealed that the starch hydrolysis brought about by the α‐amylase was not sufficient to retard staling. CGTase was considered a better antistaling agent because of its starch hydrolyzing and cyclizing activity.     

Formation of Oligosaccharides and Polysaccharides by Lactobacillus reuteri LTH5448 and Weissella cibaria 10M in Sorghum Sourdoughs

Gluten‐free breads, which are composed of gluten‐free flours, starch, and hydrocolloids, differ from wheat and rye breads in relation to texture, volume, and crumb structure. Moreover, the dietary fiber content is lower compared with wheat or rye breads. Cereal isolates of lactic acid bacteria frequently produce oligo‐ and homopolysaccharides from sucrose, which can improve the nutritional and technological properties of gluten‐free breads as prebiotic carbohydrates and hydrocolloids, respectively. Sorghum sourdough was fermented with Lactobacillus reuteri LTH5448 or Weissella cibaria 10M, which synthesize fructooligosaccharides (FOS) and levan, and isomaltooligosaccharides and dextran, respectively. The gluten‐free bread was produced with 14% sourdough addition. L. reuteri LTH5448 formed FOS and 1.5 g of levan/kg DM in quinoa sourdoughs. FOS were digested by the baker's yeast during proofing, and the levan could be qualitatively detected in the bread. W. cibaria 10M produced >60 g of isomaltooligosaccharides/kg DM and 0.6 g of dextran/kg DM, which could still be detected in the bread. Breads prepared with W. cibaria 10M were less firm compared with breads prepared with L. reuteri LTH5448 or a FOS and levan‐negative mutant of L. reuteri LTH5448. The addition of sourdoughs fermented with oligo‐ and polysaccharide forming starter cultures can increase the content of prebiotic oligosaccharides in gluten‐free breads.