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).     

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.     

Effect of water migration between arabinoxylans and gluten on baking quality of whole wheat bread detected by magnetic resonance imaging (MRI)

A new method, a magnetic resonance imaging (MRI) technique characterized by T(2) relaxation time, was developed to study the water migration mechanism between arabinoxylan (AX) gels and gluten matrix in a whole wheat dough (WWD) system prepared from whole wheat flour (WWF) of different particle sizes. The water sequestration of AX gels in wheat bran was verified by the bran fortification test. The evaluations of baking quality of whole wheat bread (WWB) made from WWF with different particle sizes were performed by using SEM, FT-IR, and RP-HPLC techniques. Results showed that the WWB made from WWF of average particle size of 96.99 μm had better baking quality than those of the breads made from WWF of two other particle sizes, 50.21 and 235.40 μm. T(2) relaxation time testing indicated that the decreased particle size of WWF increased the water absorption of AX gels, which led to water migration from the gluten network to the AX gels and resulted in inferior baking quality of WWB.     

Dough and Baking Properties of High‐Amylose and Waxy Wheat Flours

The dough properties and baking qualities of a novel high‐amylose wheat flour (HAWF) and a waxy wheat flour (WWF) (both Triticum aestivum L.) were investigated by comparing them with common wheat flours. HAWF and WWF had more dietary fiber than Chinese Spring flour (CSF), a nonwaxy wheat flour. Also, HAWF contained larger amounts of lipids and proteins than WWF and CSF. There were significant differences in the amylose and amylopectin contents among all samples tested. Farinograph data showed water absorptions of HAWF and WWF were significantly higher than that of CSF, and both flours showed poorer flour qualities than CSF. The dough of WWF was weaker and less stable than that of CSF, whereas HAWF produced a harder and more viscous dough than CSF. Differential scanning calorimetry data showed that starch in HAWF dough gelatinized at a lower temperature in the baking process than the starches in doughs of WWF and CSF. The starch in a WWF suspension had a larger enthalpy of gelatinization than those in HAWF and CSF suspensions. Amylograph data showed that the WWF starch gelatinized faster and had a higher viscosity than that in CSF. The loaves made from WWF and CSF were significantly larger than the loaves made from HAWF. However, the appearance of bread baked with WWF and HAWF was inferior to the appearance of bread baked with CSF. Bread made with WWF became softer than the bread made with CSF after storage, and reheating was more effective in refreshing WWF bread than CSF bread. Moreover, clear differences in dough and bread samples were revealed by scanning electron microscopy. These differences might have some effect on dough and baking qualities.     

Effect of Single‐Pass and Multipass Milling Systems on Whole Wheat Durum Flour and Whole Wheat Pasta Quality

Single‐pass and multipass milling systems were evaluated for the quality of whole wheat durum flour (WWF) and the subsequent whole wheat (WW) spaghetti they produced. The multipass system used a roller mill with two purifiers to produce semolina and bran/germ and shorts (bran fraction). The single‐pass system used an ultracentrifugal mill with two configurations (fine grind, 15,000 rpm with 250 μm mill screen aperture; and coarse grind, 12,000 rpm with 1,000 μm mill screen aperture) to direct grind durum wheat grain into WWF or to regrind the bran fraction, which was blended with semolina to produce a reconstituted WWF. Particle size, starch damage, and pasting properties were similar for direct finely ground WWF and multipass reconstituted durum flour/fine bran blend and for direct coarsely ground WWF and multipass reconstituted semolina/coarse bran blend. The semolina/fine bran blend had low starch damage and had desirable pasting properties for pasta cooking. WW spaghetti was better when made with WWF produced using the multipass than single‐pass milling system. Mechanical strength was greatest with spaghetti made from the semolina/fine bran or durum flour/fine bran blends. The semolina/fine bran and semolina/coarse bran blends made spaghetti with high cooked firmness and low cooking loss.     

Effects of Bran Prehydration on Functional Characteristics and Bread‐Baking Quality of Bran and Flour Blends

The effect of bran prehydration on the composition and bread‐baking quality was determined using bran and flour of two wheat varieties. Bran was hydrated in sodium acetate buffer (50mM, pH 5.3) to 50% moisture at 25 or 55°C for 1.5 or 12 h. The soluble sugar content in bran increased with prehydration. Decreases in phytate and soluble fiber were observed in prehydrated bran, but insoluble fiber was not affected by prehydration. Likewise, free phenolic content decreased, and there was little change in the content of bound phenolics in prehydrated bran. The compositional changes were greater in the bran prehydrated at 55 than at 25°C, and for 12 than for 1.5 h. Addition of prehydrated bran delayed dough development of bran and flour blends and slightly increased water absorption of dough. A higher loaf volume of fresh bread and lower crumb firmness of bread stored for 10 days were observed in bread containing bran prehydrated at 25°C than in bread containing nonhydrated bran or bran prehydrated at 55°C. The prehydration of bran at 25°C before being incorporated into refined flour for dough mixing improved bread quality by altering bran compositional properties, allowing enough water to be absorbed by fibrous materials in the bran and preventing water competition among dough constituents.     

Effects of Baking Temperature on Crumb-Staling Kinetics

This study evaluated the effects of bread baking temperature on the staling kinetics of crumb. Bread dough was leavened and baked in sealed molds. Cooking trials were performed at various temperatures ranging from 90 to 110°C. The crumb samples were then stored at 20°C at constant moisture, and staling was evaluated by measuring crumb elastic modulus (using an Instron dynamometer) and starch retrogradation degree (using differential scanning calorimetry). Results show that the cooking temperature greatly influences bread staling. The lower the cooking temperature, the lower the staling rate, both in terms of crumb hardening and of starch retrogradation. Starch and protein solubility was evaluated on crumb cooked at 90 and 110°C. An increase in cooking temperature resulted in an increase in protein insolubilization and starch granule disruption.     

Model approach to starch functionality in bread making

We used modified wheat starches in gluten-starch flour models to study the role of starch in bread making. Incorporation of hydroxypropylated starch in the recipe reduced loaf volume and initial crumb firmness and increased crumb gas cell size. Firming rate and firmness after storage increased for loaves containing the least hydroxypropylated starch. Inclusion of cross-linked starch had little effect on loaf volume or crumb structure but increased crumb firmness. The firming rate was mostly similar to that of control samples. Presumably, the moment and extent of starch gelatinization and the concomitant water migration influence the structure formation during baking. Initial bread firmness seems determined by the rigidity of the gelatinized granules and leached amylose. Amylopectin retrogradation and strengthening of a long-range network by intensifying the inter- and intramolecular starch-starch and possibly also starch-gluten interactions (presumably because of water incorporation in retrograded amylopectin crystallites) play an important role in firming.     

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.     

Partial Characterization of Buckwheat (Fagopyrum esculentum) Starch

Laboratory-isolated buckwheat (Fagopyrum esculentum) starch was compared to commercial corn and wheat starches. Buckwheat starch granules (2.9–9.3 μm) were round and polygonal with some holes and pits on the surface. Buckwheat starch had higher amylose content, waterbinding capacity, and peak viscosity, and it had lower intrinsic viscosity when compared with corn and wheat starches. Buckwheat starch also showed restricted swelling power at 85–95°C and lower solubility in water at 55–95°C and was more susceptible to acid and enzymatic attack. Gelatinization temperatures, determined by differential scanning calorimetry, were 61.1–80.1°C for buckwheat starch compared to 64.7–79.2°C and 57.1–73.5°C for corn and wheat starches, respectively. A second endotherm observed at 84.5°C was an amylose-lipid complex attributed to the internal lipids in buckwheat starch, as evidenced by selective extraction. The retrogradation of buckwheat, corn, and wheat starch gels was examined after storage at 25, 4, and -12°C for 1–15 days. In general, buckwheat starch retrogradation was slower than that of corn and wheat starch, but it increased as storage time increased, as did that of the other starch pastes. When the values of the three storage temperatures were averaged for each storage period analyzed, buckwheat starch gels showed a lower percentage of retrogradation than did corn and wheat starch gels. Buckwheat starch also had a lower percentage of water syneresis when stored at 4°C for 3–10 days and had better stability to syneresis after three freeze-thaw cycles at -12 and 25°C.     

Fortification of Bread with Hulls and Cotyledon Fibers Isolated from Peas,Lentils, and Chickpeas

Bread was prepared from wheat flour and wheat flour fortified with either 3, 5, and 7% legume hulls or insoluble cotyledon fibers, or with 1, 3, and 5% soluble cotyledon fibers isolated from pea, lentil, and chickpea flours. Incorporation of hulls or insoluble fibers resulted in increases in dough water absorption by 2–16% and increases in mixing time of dough by 22–147 sec. Addition of soluble fiber resulted in decreases in water absorption as the substitution rate increased and similar mixing times to the control dough. Loaf weights of breads containing hulls or insoluble fibers were generally higher than that of control bread at 149.4–166.5 g. However, the loaf volume of breads fortified with legume hulls and fibers (685–1,010 mL) was lower than that of the control bread (1,021 mL). Breads containing soluble fibers were more attractive in terms of crumb uniformity and color than breads containing either hulls or insoluble fibers. Breads fortified with legume hulls and fibers were higher in moisture content than control bread regardless of the type, source, or fortification rate. Bread fortified with up to 7% hulls or insoluble cotyledon fibers or up to 3% soluble cotyledon fibers, with the exception of 7% insoluble pea fiber, exhibited similar firmness after seven days of storage compared with the control bread, despite their smaller loaf volume. Breads containing hull fibers exhibited the lowest starch transition enthalpies as determined by DSC after seven days of storage, while the starch transition enthalpies of breads containing added soluble or insoluble fiber were not significantly different from the control bread.     

Effects of Rice Flour Blends on Bread Texture and Staling

The effects of blending rice flour with wheat flour on bread texture and staling were investigated with three rice varieties with different amylose contents. For the texture analysis of bread crumb, the compression test, puncture test, and tensile test were performed. A flour blend containing rice flour suppressed the recovery of the crumb after compression. For the puncture test, blends with rice flour increased the distance to penetrate the crumb. The rupture strain measured with the puncture test decreased with staling of the bread crumb for all samples tested. The fresh bread crumb sample containing waxy rice flour had much greater extensibility in the tensile test than the other samples tested, but it was dramatically decreased after one day of storage. Endothermic enthalpies corresponding to retrograded amylopectin, which is part of the staling process, were also measured. The enthalpy of bread crumb from the blended flour was lower than that of wheat flour bread up to three days but was higher on day 4. A blend of rice flour thus reduced amylopectin retrogradation during early storage, but it was accelerated later. Bread blended with waxy rice flour showed the lowest enthalpy during storage.     

Impact of Wheat Fiber on Frozen Dough Shelf Life and Bread Quality

Freezing and prolonged frozen storage of dough results in constant deterioration in the overall quality of the final product. In this study the effect of wheat bran and wheat aleurone as sources of arabinoxylan (AX) on the quality of bread baked from yeasted frozen dough was investigated. Wheat fiber sources were milled to pass through a 0.5 mm screen, prehydrated for 15 min, and incorporated into refined wheat flour at 15% replacement level. Dough products were prepared from refined flour (control A), whole wheat flour (control B), aleurone composite flour (composite flour A), and bran composite flour (composite flour B) and stored at –18°C for 28 weeks. Dough samples were evaluated for breadmaking quality at zero time, 14 weeks, and 28 weeks of storage. Quality parameters evaluated were loaf weight, loaf specific volume, and crumb firmness. Composite flour bread samples showed the most resistance to freeze damage (less reduction in the overall product quality), indicating a possible role of some fiber components (e.g., AX) in minimizing water redistribution in the dough system and therefore lessening adverse modifications to the gluten structure. The data suggest that the shelf life of frozen dough and quality of obtained bread can be improved with the addition of an AX source.     

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.     

Staling Effects When Adding Low Amounts of Normal and Heat‐Treated Barley Flour to a Wheat Bread

The properties of a white wheat bread could be changed by adding normal or heat‐treated barley flour in small amounts (2 and 4%) to a white wheat bread recipe. Differences regarding gelatinization as well as retrogradation properties were found when analyzing the two flours in model systems. The heat‐treated flour was fully gelatinized due to prior time, temperature, and pressure treatment and could therefore absorb larger amounts of water than the other flours. In gelatinized model systems with 40% flour (dwb), the heat‐treated barley flour contained less retrograded amylopectin as compared with normal barley flour after storage for up to 14 days, whereas no differences were found with 20% flour (dwb). However, stored breads showed an increased retrogradation of amylopectin (as measured by differential scanning calorimetry [DSC]) when 2% pretreated barley flour was added as compared with addition of 2% normal barley flour. On the other hand, there were no significant differences at the 4% level. Addition of either of the barley flours resulted in less firm breads during storage as compared with the control breads. Increased water absorption in barley flour and thus increased water content in the breads or different water‐binding capacities of the flour blends could explain these results. The present study indicated that water had a stronger influence on bread firmness than the retrogradation of amylopectin. This conclusion was based on breads with pretreated barley flour being less firm than breads with normal barley flour, although the retrogradation, as determined by DSC, was higher.     

Water dynamics and retrogradation of ultrahigh pressurized wheat starch

The water dynamics and retrogradation kinetics behavior of gelatinized wheat starch by either ultrahigh pressure (UHP) processing or heat are investigated. Wheat starch completely gelatinized in the condition of 90, 000 psi at 25 degrees C for 30 min (pressurized gel) or 100 degrees C for 30 min (heated gel). The physical properties of the wheat starches were characterized in terms of proton relaxation times (T2 times) measured using time-domain nuclear magnetic resonance spectroscopy and evaluated using commercially available continuous distribution modeling software. Different T2 distributions in both micro- and millisecond ranges between pressurized and heated wheat starch gels suggest distinctively different water dynamics between pressurized and heated wheat starch gels. Smaller water self-diffusion coefficients were observed for pressurized wheat starch gels and are indicative of more restricted translational proton mobility than is observed with heated wheat starch gels. The physical characteristics associated with changes taking place during retrogradation were evaluated using melting curves obtained with differential scanning calorimetry. Less retrogradation was observed in pressurized wheat starch, and it may be related to a smaller quantity of freezable water in pressurized wheat starch. Starches comprise a major constituent of many foods proposed for commercial potential using UHP, and the present results furnish insight into the effect of UHP on starch gelatinization and the mechanism of retrogradation during storage.     

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.     

Gelatinization and Retrogradation Kinetics of High‐Fiber Wheat Flour Blends: A Calorimetric Approach

The impact of dietary fiber (DF) mixtures on dough thermal properties needs to be investigated when designing high‐fiber wheat bread. Effects of flour replacement at different levels (6–34%) by soluble (inuline [FN]), partially soluble (sugar beet [FX], pea cell wall [SW]), and insoluble (pea hull [EX]) DF on wheat dough thermal profiles have been investigated by simulating baking, cooling, and storage in differential scanning calorimetry (DSC) pans. In general, DF incorporation into water‐flour systems delayed endothermic transition temperatures for both gelatinization and retrogradation phenomena except for the peak temperature (T_p) of retrogradation. With some exception, the pattern of the enthalpy of amylopectin retrogradation was lower and slower (lower constant of proportion, k) over 10 days of storage in gelatinized hydrated flour‐fiber blends when compared with control without DF. FX, a partially soluble fiber, provided major effects on gelatinization (T_p decrease and ΔH increase) and retrogradation kinetics (the Avrami exponent, n, increase). Single presence of EX allowed a significant reduction in the Avrami exponent n leading to slower kinetics for amylopectin retrogradation when included in the blends.     

Retrogradation of Maize Starch After Thermal Treatment Within and Above the Gelatinization Temperature Range

Studies of starch retrogradation have not considered the initial thermal treatment. In this article, we explore the effect of heating to temperatures within and above the gelatinization range on maize starch retrogradation. In the first experiment, 30% suspensions of waxy (wx) starch were initially heated to final temperatures ranging from 54 to 72°C and held for 20 min. On reheating in the differential scanning calorimeter immediately after cooling, the residual gelatinization endotherm peak temperature increased, the endotherm narrowed, and enthalpy decreased. Samples stored for seven days at 4°C showed additional amylopectin retrogradation endotherms. Retrogradation increased dramatically as initial holding temperature increased from 60 to 72°C. In a second experiment, wx starch was initially heated to final temperatures from 54 to 180°C and rapidly cooled, followed by immediate reheating or storage at 4°C. Maximum amylopectin retrogradation enthalpy after storage was observed for initial heating to 82°C. Above 82°C, retrogradation enthalpy decreased as initial heating temperature increased. A similar effect for ae wx starch was observed, except that retrogradation occurred more rapidly than for wx starch. These experiments show that heating to various temperatures above the range of gelatinization may profoundly affect amylopectin retrogradation, perhaps due to varying extents of residual molecular order in starch materials that are commonly presumed to be fully gelatinized. This article shows that studies of starch retrogradation should take into account the thermal history of the samples even for temperatures above the gelatinization temperature range.     

Effect of freezing and frozen storage of doughs on bread quality

The effects of freezing and storage in frozen conditions on bread quality, crumb properties, and aggregative behavior of glutenins were analyzed. The effect of different additives on bread quality was also studied. The results obtained showed that freezing and storage at -18 degrees C decreased the bread quality. Samples stored in frozen conditions supplemented with diacetyl-tartaric acid ester of monoglycerides, gluten, and guar gum produced breads of greater volume and more open crumb structure than those prepared with the base formulation (without additives). All additives analyzed increased the proof time. Crumb firmness increased with dough frozen storage and bread aging time at 4 degrees C. A decrease in the amount of glutenin subunits of high molecular mass was observed by electrophoresis analysis of the SDS-soluble proteins aggregates extracted from the frozen dough. This result suggested that the protein matrix of bread underwent depolymerization during storage in frozen conditions.