15N‐Labeling of Egg Proteins for Studying Protein Network Formation During Pound Cake Making

Proteins from wheat and egg are important for pound cake texture, but their exact role is insufficiently understood. A clear, analytical distinction between proteins from wheat flour, egg white, or egg yolk has been a main challenge. However, this can be addressed by using egg proteins carrying ¹⁵N. Therefore, egg white and yolk protein were enriched in ¹⁵N by mixing ¹⁵N‐labeled leucine into hen feed. Incorporation of egg and flour proteins in the protein network was monitored based on changes in their extractability during cake making. The relative contribution of different noncovalent and covalent bonds could be determined by using different extraction media. We for the first time distinguished between the contribution of egg white, egg yolk, and wheat protein in network formation during pound cake making. Our results show that during batter mixing hardly any intermolecular disulfide bonds are formed and that baking induces tremendous changes in protein extractability. A protein network based on both disulfide bonds and hydrophobic interactions is formed during baking. This covalent network includes almost all egg white protein and most of the yolk and wheat flour protein. The remaining protein fraction most probably lacks sulfhydryl groups and/or intramolecular disulfide bonds.     

Measurement of Contour and Volume Changes During Cake Baking

Volume is an important characteristic in the evaluation of cakes and cake quality, relating to the underlying structural development of the cake. A method for evaluation of changes in contour and volume during the cake baking process is proposed: the height profile method. Volumes of baked cakes were determined using two standard methods, rapeseed displacement and cross‐sectional tracings, and compared with height profile analysis to determine the accuracy of the new method for cake volume analysis. Height analysis values did not significantly differ from rapeseed and tracing results. The height profile method was used to analyze and calculate changes in volume during the baking process for cakes made with chlorine‐treated and nonchlorine‐treated flours. The method was also able to depict changes in contour of the baking cakes, showing definite differences in contour development between chlorine‐treated and nonchlorinetreated flours. The height profile method of volume determination is a nonintrusive method that can be employed in the study of volumetric and contour changes of cakes while they bake.     

Rheological Characterization of a New Oat Hydrocolloid and Its Application in Cake Baking

A new oat hydrocolloid containing 20% β‐glucan, called C‐trim20, was obtained from oat bran concentrate through steam jet‐cooking and fractionations. The rheological characterization of the C‐trim20 was conducted using steady and dynamic shear measurements. The C‐trim20 suspension exhibited a shear‐thinning behavior that was more pronounced at high shear rates and high concentrations. Its dynamic viscoelastic moduli increased with increasing concentration while the frequency at which G′ and G″ crossover decreased. The C‐trim20 suspension at various concentrations followed the Cox‐Merz rule. C‐trim20 was also evaluated for potential use in baked products, specifically cakes. The baking performance of C‐trim20 was tested by incorporating it into cake formulations. The inclusion of this hydrocolloid gave increased elastic properties to cake batters and produced cakes containing 1 g of β‐glucan per serving with volume and textural properties similar to those of the control cake.     

Significance of Starch Properties and Quantity on Sponge Cake Volume

We evaluated the qualitative and quantitative effects of wheat starch on sponge cake (SC) baking quality. Twenty wheat flours, including soft white and club wheat of normal, partial waxy, and waxy endosperm, as well as hard wheat, were tested for amylose content, pasting properties, and SC baking quality. Starches isolated from wheat flours of normal, single‐null partial waxy, double‐null partial waxy, and waxy endosperm were also tested for pasting properties and baked into SC. Double‐null partial waxy and waxy wheat flours produced SC with volume of 828–895 mL, whereas volume of SC baked from normal and single‐null partial waxy wheat flours ranged from 1,093 to 1,335 mL. The amylose content of soft white and club wheat flour was positively related to the volume of SC (r = 0.790, P < 0.001). Pasting temperature, peak viscosity, final viscosity, breakdown, and setback also showed significant relationships with SC volume. Normal and waxy starch blends having amylose contents of 25, 20, 15, and 10% produced SCs with volume of 1,570, 1,435, 1,385, and 1,185 mL, respectively. At least 70 g of starch or at least 75% starch in 100 g of starch–gluten blend in replacement of 100 g of wheat flour in the SC baking formula was needed to produce SC having the maximum volume potential. Starch properties including amylose content and pasting properties as well as proportion of starch evidently play significant roles in SC baking quality of wheat flour.     

Role of Starch Granules in Controlling Expansion of Dough During Baking

The role of starch granules in the expansion of doughs during baking was investigated using artificial flours made from dry vital wheat gluten and wheat starch, potato starch, or tapioca starch. The three starches were selected because of their diverse gelatinization properties. Baking tests on flour from tapioca starch gave the largest loaf volume and the most extensive postbaking shrinkage. Potato starch flour gave the smallest volume and the least shrinkage. Amylograph test data, dough expansion under decreased pressure, progress of expansion during baking, and scanning electron microscopy revealed the role starch granules play in ideal baking conditions. Starch granules should not gelatinize early in the baking cycle as potato starch does but should gelatinize later in the baking cycle as wheat starch does. This prevents early setting of the dough which inhibits expansion. Starch granules should not disrupt and fuse together during gelatinization as tapioca starch does, forming an impermeable gas membrane. Granules should gelatinize individually as wheat starch does, causing a disruption of cell membranes which prevents shrinkage of the loaf during cooling after baking.     

Detection of Proteins in Starch Granule Channels

Proteins were detected in channels of commercial starches of normal maize, waxy maize, sorghum, and wheat through labeling with a protein‐specific dye and examination using confocal laser scanning microscopy (CLSM). The dye, specifically 3‐(4‐carboxybenzoyl)quinoline‐2‐carboxaldehyde (CBQCA), fluoresces only after it reacts with primary amines in proteins, and CLSM detects fluorescence‐labeled protein distribution in an optical section of a starch granule while it is still in an intact state. Starch granules in thin sections of maize kernels also had channel proteins, indicating that proteins are native to the channels and not artifacts of isolation. Incubation of maize starch with protease (thermolysin) removed channel proteins, showing that channels are open to the external environment. SDS‐PAGE analysis of total protein from gelatinized commercial waxy maize starch revealed two major proteins of about M_r 38,000 and 40,000, both of which disappeared after thermolysin digestion of raw starch. Commercial waxy maize starch granule surface and channel proteins were extracted by SDS‐PAGE sample buffer without gelatinization of the granules. The major M_r 40,000 band was identified by MALDI‐TOF‐MS and N‐terminal sequence analysis as brittle‐1 (bt1) protein.     

小麦蛋白淀粉品质指标与面包品质关系的研究

选用近年来黄淮麦区大面积推广种植的小麦品种和新育成高代品系为材料,采用近红外(NIR)、面筋仪、粉质仪、快速粘度分析仪(RVA)和凝胶色谱(SE-HPLC)方法等对蛋白品质指标及淀粉糊化参数进行分析,分析各品质参数间的关系及其与面包烘焙品质的关系。结果表明,谷蛋白大聚体(GMP)、SDS(十二烷基硫酸钠)-沉降值、湿面筋指数、弱化度与多数蛋白品质指标间存在正向0.01或0.05水平相关,GMP、SDS-沉降值、湿面筋指数、干面筋含量、面粉蛋白含量、麦谷蛋白含量、形成时间、稳定时间均与面包烘焙品质间达0.01水平正相关,湿面筋含量与面包体积和评分间分别达0.01和0.05水平正相关;醇溶蛋白含量及弱化度与面包体积和评分间分别达0.05和0.01水平负相关。吸水率与糊化温度、最终粘度、回生值间达0.01水平负相关,形成时间与峰值粘度和稀澥值间达0.05水平正相关,GMP与糊化温度间达0.05水平负相关。各品质参数对面包体积的作用大小依次为湿面筋指数>弱化度>形成时间>湿面筋含量>糊化温度等,对面包评分的作用大小依次为麦谷蛋白>稳定时间>醇溶蛋白>面粉蛋白含量>吸水率等。小麦品质测试指标间有着广泛的相关性,湿面筋指数、弱化度和麦谷蛋白、稳定时间是反映面包烘焙品质的重要指标;早代可进行GMP或SDS-沉降值测定,中高代可进行面筋仪、粉质仪测定;在品质测试过程中应重视湿面筋指数、弱化度的重要性,小麦粉淀粉品质对面包品质的影响也应引起关注。     

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

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

Effect of Modified Oat Starch and Protein on Batter Properties and Quality of Cake

Starch and protein separated from oat were chemically modified using cross‐linking and acetylation protocols for starch, and deamidation and succinylation for protein isolate. Cross‐linking decreased swelling power of starch, whereas syneresis increased, but cross‐linking does not have a significant effect on gelatinization temperature. Acetylation increased swelling power, but gelatinization temperature and syneresis diminished. Deamidation and succinylation increased nitrogen solubility index, emulsion activity, foaming capacity, and water and oil binding capacity. Emulsion stability did not change with deamidation and it diminished with succinylation, while foaming stability decreased with both treatments. Acetylated starch and two types of modified proteins were substituted for 5, 10, 15, and 20% of oat flour to bake cake samples and then physical properties of the cakes were measured. Acetylated starch increased batter viscosity, cake volume, and whiteness of cake crust. Increased level of deamidated protein produced cakes with lower batter viscosity, higher volume, and darker color (increase in redness). Application of higher levels of succinylated protein led to higher batter viscosity and lightness, and lower cake volume. Therefore, substitution of deamidated protein and acetylated starch can improve cake properties.     

Influence of Milk,Corn Starch,and Baking Conditions on the Starch Digestibility,Gelatinization, and Fracture Stress of Biscuits

Dough for nontraditional semisweet biscuits—prepared with wheat flour or replacing part of the wheat flour with corn starch, with or without skim milk—was baked at two oven temperatures, 120 or 170°C, until reaching moisture content and water activity lower than 6% and 0.5, respectively. Assays of fracture stress, differential scanning calorimetry, X‐ray diffraction, and starch digestibility were performed. Results showed that biscuits containing milk had the highest fracture stress, and biscuits baked at low temperature were harder than biscuits baked at high temperature. The degree of starch gelatinization during baking was higher when dough was baked at 170°C, compared with dough baked at 120°C. The decrease in gelatinization coincides with the decrease in the height and surface of peaks at 15 and 23° in the X‐ray diffraction patterns. Milk and corn starch did not affect the starch digestibility of biscuits, but biscuits baked at 170°C presented lower fracture stress and higher starch digestibility than biscuits baked at 120°C.     

Association of Starch Granule Proteins with Starch Ghosts and Remnants Revealed by Confocal Laser Scanning Microscopy

Starch suspensions (0.25%) were gelatinized to 70 and 100°C, and starch ghosts (defined as gelatinized starch granule envelopes after the majority of internal starch polymers have been released) and remnants were collected by centrifugation and washed with water. Protein was revealed in isolated gelatinized normal starch ghosts using confocal laser scanning microscopy and a protein‐specific dye that fluoresces only after reaction with primary amines in protein. This technique eliminates background interference from residual dye. Observation of fluorescent‐labeled protein in the starch ghosts at different optical depths of field revealed that protein was concentrated in the envelopes of swollen, gelatinized potato, maize, and wheat starch ghosts. Only traces of protein were found in gelatinized starch granule remnants of waxy maize and amylose‐free potato starches after they were heated to 100°C, indicating that the proteins observed in gelatinized normal maize starch were largely granule‐bound starch synthase (GBSS). Moreover, fragility of the gelatinized waxy and amylose‐free starch granule remnants might be caused in part by the lack of GBSS. Gel electrophoresis of proteins in starch ghosts confirmed that GBSS in potato and maize was tightly associated with the starch ghosts. The study provides a structural explanation for a role of granule‐associated proteins in maintaining the integrity of starch ghosts and remnant structures, and their consequent effect on paste rheology.     

Effects of Prolonged Storage at Freezing Temperatures on Starch and Baking Quality of Frozen Doughs

The effects of prolonged frozen storage on the starch, rheological, and baking properties of doughs were investigated. Four hard red spring (HRS) wheat cultivars exhibiting consistently different gluten characteristics were used. Gelatinization properties of starches isolated from fresh and thawed frozen doughs over 16 weeks of frozen storage were examined using differential scanning calorimetry (DSC). Significance of results varied with cultivar, but all cultivars showed a significant increase in ΔH with increased frozen storage time, indicating water migration and ice crystallization. The amount of freezable water in frozen doughs increased for all cultivars with frozen storage, but the rate of increase varied. Glupro showed a consistent increase in freezable water during frozen storage (41.6%), which may be associated with its high protein content and strong gluten characteristics. Rheological strength of the frozen doughs which was determined by decreases in extensigraph resistance and storage modulus (G′), declined throughout frozen dough storage. Proofing time increased from 45 min for fresh doughs to an average of 342 min for frozen doughs stored 16 weeks. Concomitantly, loaf volumes decreased from an average of 912 cm³ for fresh doughs to an average of 738 cm³ for the frozen doughs. Longer proof times and greater loaf volume loss were obtained for the cultivars exhibiting greater gluten strength characteristics.     

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 Extrusion and Starch Removal Pretreatment on Zein Proteins Extracted from Corn Gluten Meal

In this study, the structure and selected properties of zeins extracted from corn gluten meal (CGM) pretreated by extrusion and removal of starch were investigated. The structure and properties of the zeins from pretreated CGM changed significantly. Pretreatments can decrease the extraction yields of zeins and change the granule shape and size of zein aggregates. The studies indicated that extrusion and removal of starch can significantly decrease the thermal enthalpy (ΔH₁ and ΔH₂) of zein from 1.94 ± 0.20 to 0.19 ± 0.10 and from 107.20 ± 0.80 to 78.62 ± 2.30 and J/g, respectively. The SDS‐PAGE results confirmed that the molecular weight of zeins from CGM was 24,000 and 27,000, and the molecular weight of zeins did not change with the pretreatment. On the other hand, the circular dichroism spectroscopy results showed that the processing of extrusion and removal of starch can change the secondary structure content of β‐sheets and β‐turns; these results indicated that extrusion and removal of starch can significantly break the secondary structure of zeins. Furthermore, extrusion and removal of starch can change the sulfhydryl content of zeins. The obtained results provided some fundamental information that is useful for further modification of CGM to improve its functional properties and industrial applications.     

Mixing Properties,Baking Potential,and Functionality Changes in Storage Proteins During Dough Development of Triticale‐Wheat Flour Blends

Flours from advanced lines or cultivars of six triticales and two prime hard wheats, along with triticale‐wheat blends, were investigated for mixing, extension (excluding blends), and baking properties using microscale testing. Percentage total polymeric protein (PPP) and percentage unextractable polymeric protein (UPP) of flours and doughs, including blends, mixed to optimal dough development were estimated using size‐exclusion HPLC to determine the changes in protein solubility and association with blend composition (BC), mixing properties, and loaf height. Each triticale was blended with flours of each of the two wheat cultivars (Hartog and Sunco) at 0, 30, 40, 50, 60, 70, and 100% of wheat flour. Nonlinear relationships between BC and mixograph parameters (mixing time [MT], bandwidth at peak resistance [BWPR], and resistance breakdown [RBD]) were observed. A linear relationship between BC and peak resistance (PR) was predominant. PPP of triticale flours was mostly higher than PPP of wheat cultivars. UPP of all triticales was significantly lower than wheat cultivars. PPP of freeze‐dried doughs was mostly nonsignificant across the blends and showed a curvilinear relationship with BC. The deviations from linearity of MT and PPP were higher in triticale‐Sunco blends than in triticale‐Hartog blends. UPP of blends was closer to or lower than the lower component in the blend. The deviations from linearity for MT and UPP were greater in triticale‐Hartog blends than triticale‐Sunco blends. A highly significant correlation (P < 0.001) was observed between BWPR and loaf height. This suggested that BWPR in triticale‐wheat flour blends could be successfully used for the prediction of loaf height. Triticale flour could be substituted for wheat flour up to 50% in the blend without drastically affecting bread quality. Dough properties of triticale‐wheat flour blends were highly cultivar specific and dependent on blend composition. This strongly suggested that any flour blend must be tested at the desired blend composition.     

Effects of Ice Structuring Proteins on Freeze‐Thaw Stability of Corn and Wheat Starch Gels

The effect of ice structuring proteins (ISP, 0.5%, starch weight basis) on the freeze‐thaw stability of corn and wheat starch gels (CS and WS, respectively) was studied. Syneresis measurement, hardness, thermal properties using differential scanning calorimetry (DSC), X‐ray diffractions, and scanning electron microscopy (SEM) were determined with starch gels (SG) subjected up to nine freeze‐thaw cycles (FTC). The gelatinized SG were stored at –20°C for 22 hr and thawed at 30°C for 2 hr. As the number of FTC increased, syneresis was increased; however, ISP significantly (P < 0.05) reduced the syneresis for all FTC except at FTC 1. Hardness was increased up to FTC 4, then decreased for both SG. ISP significantly lowered the hardness of both SG. The ice melting enthalpy (ΔH_{ice sample}) of SG increased as FTC increased but SG with ISP had significantly lower enthalpy. The retrogradation ratio (RR) from DSC was significantly increased as the number of FTC increased. ISP reduced RR but most of RR was not significantly different for the corresponding FTC. The X‐ray diffraction patterns showed less recrystallization of WS with addition of ISP. The microstructures from SEM showed that the addition of ISP reduced the size of ice cell cavities.     

Starch from Hull‐less Barley: Ultrastructure and Distribution of Granule‐Bound Proteins

Starch granules isolated from waxy, normal, and high‐amylose hullless barley grains were examined by transmission electron microscopy with cytochemical techniques. The micrographs showed two distinct regions of different sizes: 1) densely packed granule growth rings (which varied in size and number depending on the genotype), and 2) a loose filamentous network located in the central region of the granule. The granule ring width decreased with increasing amylose content. In all three genotypes, the growth rings closer to the granule surface were narrower in width than those within the granule interior. The waxy starch had wider intercrystalline amorphous growth rings, semicrystalline growth rings, and more open crystalline lamellae than normal and high‐amylose starches. Granule bound proteins (mainly integral proteins) were located in the central and peripheral (growth ring) regions of the granule.     

Physicochemical and Thermal Characteristics of Starch Isolated from a Waxy Wheat Genotype Exhibiting Partial Expression of Wx Proteins

A unique wheat genotype carrying waxy‐type allelic composition at the Wx loci, Gunji‐1, was developed, and its starch properties were evaluated in comparison to parental waxy and wild‐type wheat varieties. Gunji‐1 was null in all three of the Wx genes but exhibited a lower level of Wx proteins than the wild‐type. Starch amylose content and cold water retention capacity were 10.1 and 70.5% for Gunji‐1, 4.2 and 76.6% for waxy, and 27.9 and 65.0% for wild‐type, respectively. No significant differences were observed in microstructure, granule size distribution, and X‐ray diffractograms of the starch granules isolated from Gunji‐1 compared with those of waxy and wild‐type wheat varieties. Starch pasting peak, breakdown, and setback viscosities and peak temperature of Gunji‐1 were intermediate between waxy and wild‐type wheat. In starch gel hardness, Gunji‐1 (1.1 N) was more similar to waxy wheat (0.5 N) than to the wild‐type variety (17.6 N). Swelling power, swelling volume, paste transmittance during storage, and gelatinization enthalpy of Gunji‐1 were lower than those of waxy wheat but greater than those of wild‐type wheat. Retrogradation of starch stored for one week at 4°C expressed with DSC endothermic enthalpy was absent in the waxy wheat variety, whereas Gunji‐1 exhibited both retrogradation of amylopectin and amylose‐lipid complex melting similar to the wild‐type parent, even though enthalpies of Gunji‐1 were much smaller than the wild‐type parent.     

Composition,Functional Properties,Starch Digestibility,and Cookie‐Baking Performance of Dry Bean Powders from 25 Michigan‐Grown Varieties

The chemical composition, functional properties, starch digestibility, and cookie‐baking performance of bean powders from 25 edible dry bean varieties grown in Michigan were evaluated. The beans were ground into coarse (particle size ≤1.0 mm) or fine (≤0.5 mm) powders. Starch and protein contents of the bean powders varied between 34.4 and 44.5% and between 19.1 and 26.6% (dry basis [db]), respectively. Thermal properties, pasting properties, and water‐holding and oil‐binding capacities of the bean powders differed and were affected by particle size. After blending the bean powders with corn starch (bean/starch = 7:3, db), the blends were used for cookie baking following a standard method ( 1 Approved Method 10‐54.01). Generally, the cookies baked from the fine bean powders had smaller diameters, greater thicknesses, and greater hardness values than those from the coarse counterparts. Differences in the cookie‐baking performances of the bean powders were observed among the 25 varieties. Larger proportions of resistant starch (RS) were retained in the bean‐based cookies (54.7–126.7%) than in the wheat‐flour‐based cookies (10.4–19.7%) after baking. With higher contents of RS and protein, the bean‐based cookies had more desirable nutritional profiles than those baked from wheat flour alone.