Quantification in starch microstructure as a function of baking time

The purpose of this study was the characterization of micro structural and thermal aspects of starch gelatinization in wheat dough/crumb during bread baking. The microstructure of starch granules was examined by confocal-laserscanning-microscopy (CLSM) and evaluated by an image analyzing tool. Supporting crystallinity changes in wheat dough/crumb were analyzed by differential-scanning-calorimetry (DSC) and calculated by the content of terminal extent of starch gelatinization (TEG). The micrograph of processed CLSM data showed starch structure changes during baking time. After gelatinization the starch fraction itself was inhomogeneous and consisted of swollen and interconnected starch granules. Image processing analyses showed an increment of mean granule area and perimeter of the starch granules. The results of DSC were examined to present an equation which provides a mean of predicting TEG values as a function of baking time. CLSM and DSC measurements present high significant linear correlation between mean starch granule area and TEG (r = 0.85). The possibility to combine CLSM with thermal physical analytical techniques like DSC in the same experiments is useful to obtain detailed structural information of complex food systems like wheat bread. Finally, it offers the option to enlarge the knowledge of microstructural starch changes during baking in combination with physicochemical transformation of starch components.     

Wheat starch granule protein: The isolation and characterisation of a salt-extractable protein from starch granules

A salt-extractable protein has been isolated and purified from large (A-type) wheat flour starch granules (Triticum aestivum cv. Maris Huntsman). This protein was the major species extractable with NaCl and because of its ease of extraction it was tentatively concluded that it was associated with the surface of the granules. It had a molecular weight of approximately 30 000 as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS-PAGE) and an isoelectric point (pI) in excess of 10 as judged by analytical isoelectric focusing in polyacrylamide gel. The amino acid composition of the protein was quite different from those of wheat gluten proteins. A protein with similar properties was present on small (B-type) Maris Huntsman starch granules and it could also be detected on A-type granules from another variety of hexaploid breadwheat (T. aestivum cv. Flinor) as well as on A-type granules from tetraploid durum wheat (T. durum). This protein was not present on starch granules prepared from germinated grains (Maris Huntsman). The protein had neither α-amylase activity nor inhibitory activity against either wheat or hog pancreatic α-amylases. Several other proteins could be extracted from A-type starch granules but only after gelatinisation of the starch granule in the presence of SDS. The electrophoretic behaviour of these proteins was quite different from that of the NaCl-extracted protein and the rigorous conditions required to separate the latter proteins from the starch granules suggested that they are internal components of the granules.     

Effects of L-Cysteine on some characteristics of wheat starch

In this study the effects of L-Cysteine as a food additive on wheat starch characteristics before and after gelatinization were studied. L-Cysteine (63 mg/kg, starch basis) was added to slurry of wheat starch in water (30%, w/w). One set of samples was prepared by mixing it at 40 °C for 45 min. Another set was gelatinized at 100 °C for 45 min. The scanning electro-micrographs of the samples prepared at 40 °C in the presence of L-Cysteine showed some spots on the granules. However, thermal properties, X-ray patterns and the degree of crystallinity of the samples did not obviously change (P > 0.05); while a reduction in intrinsic viscosity, peak and final viscosities of the samples was observed. After gelatinization, intrinsic, peak and final viscosities of the samples were reduced. Some of these changes may indicate degradation of starch molecules in the presence of L-Cysteine, particularly after gelatinization.     

Comparison of Endosperm Starch Granule Development and Physicochemical Properties of Starches from Waxy and Non-Waxy Wheat

Starch granule development and physicochemical properties of starches in waxy wheat and non-waxy wheat were investigated in this article. Starch granules in waxy wheat endosperm showed an early developmental process. Compared with non-waxy wheat starch granules (round-shaped), waxy wheat starch granules (ellipse-shaped) were larger and contained more B-type granules. According to the granule size, starch granules were divided into two groups in waxy wheat, but were divided into three groups in non-waxy wheat. Compared with non-waxy wheat starch, waxy wheat starch had higher swelling power, gelatinization temperatures (To, Tp, Tc), and relative degree of crystallinity. They showed similar ordered structures on external regions of starch granules. Additionally, waxy wheat starch had a higher proportion of double-helical components and a lower proportion of single-helical components than non-waxy wheat starch. Based on the previous results, it was concluded: (1) waxy wheat and non-waxy wheat not only differed in starch granule development, but also in physicochemical properties of starches; (2) waxy wheat had more potential value for producing traditional products than non-waxy wheat.     

Effects of Germination of Wheat,Oats, and Pearl Millet on Alpha-Amylase Activity and Starch Degradation

Hard red winter wheat, oats, and pearl millet were germinated at 15°C for periods up to 14 days. Endosperm areas in kernels fractured with a razor blade and starches isolated from the malted flours were examined with a scanning electron microscope to determine the morphology of starch granules and the nature of α-amylolytic attack on granules. Free sugars content, damaged starch content, and α-amylase activity of the flours were determined to establish relationships between physical changes in the cereal grains and formation of α-amylase during germination. Starch granules in the three cereals were degraded during germination by α-amylase accompanied by production of free sugars and increases in the damaged starch of flours milled from the germinated grains. The cementing material embedding starch granules in endosperms of wheat and oats decreased and disappeared during germination; these changes were not obvious in germinated millet endosperm. Amorphous-appearing material seemed to cover starch granules in the endosperm of wheat and oats during later stages of germination, but were not observed in the isolated starch granules. Although wheat starch granules had the highest α-amylase activity, this enzymic degradation was less than expected. Enzymic attack was evidenced as channels or pits on the surfaces of wheat and millet starch granules. Compound oat starch granules were relatively resistant to enzymic attack and no evidence of erosion of the granule surface was observed; small granula were released from the compound granules during germination. The most extensive degradation was obtained with millet starch, appearing as discrete holes leading to the interior of the granule. Concentric shells were visible in the interior of wheat and millet starch granules, but were not observed in oat starch granules.     

Ghosts of B‐type Wheat Starch Granules in Concentrated KI/I2 Solution

When B‐type (2.0–8.0 µm) wheat starch granules containing various amounts (2.1–25%) of amylose were treated with 25% KI/10% I₂ solution, low‐amylose (below 10% amylose) B‐type wheat starch granules changed to the ghost form. It is known that A‐type (25–35 µm) wheat starch granules change to the ghost form and show a typical double structure (a black‐brown central portion and red‐brown surrounding portion), however, the B‐type wheat starch ghosts did not show the same double structure but rather a simple (red‐brown portion) sack form. The relative ghost areas in the B‐type wheat starch granules were highly correlated to the amylose content (%), which was similar to the results of A‐type starch granules. This suggests that the amylose molecule in B‐type starch contributes to the structural stability of the starch granule.     

Effects of sourdough and enzymes on staling of high-fibre wheat bread

The effects of sourdough and enzyme mixture (α-amylase, xylanase and lipase) on the specific volume, staling and microstructure of wheat pan bread supplemented with wheat bran were studied. Staling of bread was followed for 6 days by measuring the crumb firmness, changes in crystallization of amylopectin (DSC), increase in signal from the solid phase (NMR) and by light microscopy. The most effective treatment in improvement of quality was the combination of bran sourdough and enzyme mixture. During storage the rate of changes in crumb firmness, amylopectin crystallinity and rigidity of polymers were greatest for the white wheat bread. The most pronounced microstructural changes were swelling of starch granules and separation of amylose and amylopectin in the starch granules. Least changes in crumb firmness, amylopectin crystallinity and rigidity of polymers were observed in bran sourdough bread with enzymes. In contrast to white wheat bread, the starch granules were very much swollen in bran sourdough bread with enzyme mixture. This was hypothesized to be due to the higher water content of bran bread, and degradation of cell wall components leading to altered distribution of water among starch, gluten and bran particles during storage.     

Zein molecules in aqueous acetic acid solution: Self-assembling behaviors and formation mechanism of gluten-free doughs

The assembly behavior of biopolymers is affected by the type of solvent used. Previous investigations have focused on the self-assembly of zein molecules in aqueous ethanol. In this study, the self-assembly behavior of zein molecules in aqueous acetic acid solutions and their application in the development of zein-based gluten-free doughs was investigated. Zein molecules in low concentrations of acetic acid (30%–60%, v/v) assembled into irregular entities, in medium concentrations (70%, v/v) there was intermediate transition, and at high concentrations (80%–100%, v/v) they formed regular spheres. Interestingly, protein fibril formation was found to occur in 50% zein solutions in 50% and 60% acetic acid, as self-standing gels with solid-like properties resulted and the findings were verified using rheology. The 50% zein solutions in 70% acetic acid could form viscoelastic masses after anti-precipitation with the addition of excess water. Gluten-free dough with wheat-like properties was obtained by mixing the viscoelastic zein masses with wheat starch at room temperature. SEM observations showed that the formation mechanism for zein-based doughs involves the dispersion of starch granules in a three-dimensional zein network. These results will help to improve our understanding of zein assembly behavior regulation, and provide technical support for the development of zein in gluten-free food products.     

Ultrasound-treated starch: SEM and TEM imaging,and functional behaviour

Potato, wheat, corn and rice starch granules were suspended in water or ethanol and sonicated at frequency of 20 KHz and power 170 W for 30 min. The effect of ultrasonic treatment on starch structure was assessed on the basis of blue value (BV), A₆₈₀/A₅₄₅ ratio and λ_max determinations. The results showed that modification of starches in both solvents led to the reduction of all parameters connected with the starch–iodine complex. However, depolymerization of starch was higher when it was sonicated in water than in ethanol (e.g. BVs for potato starch: native and sonicated in water and ethanol were equal, respectively, 0.306, 0.275, and 0.279). Starch granules were also observed under scanning and transmission electron microscopes. The main effects of ultrasonic action were cracks and depressions on the surface of granules, which were especially well seen in the case of potato and wheat starches. Ultrasonic treatment, especially in water, influenced functional properties of starch causing an increase of fat and water absorption, least gelling concentration (except potato starch), solubility and swelling power, and a decrease of starch paste viscosity. Effect of ultrasounds on clarity of pastes was rather small, except potato starch for which its value increased from 70.3 to 82.5% after sonication in water.     

Study of Starch Granules Swelling by the Blue Dextran Method and by Microscopy

The evolution of corn and wheat starch granules swelling at different temperatures was determined by two techniques: the blue dextran method (which measures the swelling factor) and by optical (light) microscopy. The graphical results obtained using the blue dextran technique showed curves indicating the swelling of corn and wheat starch dispersions (at 64%, w/w, moisture content) characterized by an initial phase of slight swelling, a second phase of fast swelling and a final phase of maximum swelling. The concentrated solutions (42% and 47%, w/w, moisture content) showed a slight swelling with the increase in temperature. The effect of temperature on the shape of the granules was evaluated by the optical microscopy. The shape of the type A wheat starch granules was deformed at high temperatures. The corn and type B wheat granules had a spherical form. In the case of corn starch, a good correlation (r²= 0.929) was obtained between the results of optical microscopy and blue dextran techniques.     

面条、面包优质兼用小麦研究进展

小麦是我国重要的口粮作物,面条、面包优质兼用小麦更适合我国国情,淀粉理化特性改良是当前选育优质兼用小麦品种的关键.本文综述了选育优质兼用小麦的重要性、可行性以及淀粉理化特性对面条、面包品质的影响及其调控,以期为小麦品质遗传改良提供参考.兼用优质小麦蛋白和面团特性接近优质面包小麦,淀粉理化特性明显优于优质面包小麦,与优质...     

干热处理对藜麦淀粉结构和理化性质的影响

以高筋小麦粉为原料添加酵母制作面团,在温度28℃、湿度80%条件下发酵1～6 h,提取小麦淀粉。研究发酵时间对小麦直链淀粉含量、损伤淀粉含量、粒径、颗粒表面结构、糊化及消化特性的影响。结果表明：面团发酵1 h后直链淀粉含量和损伤淀粉含量均显著低于原淀粉(P<0.05)。快速黏度分析结果表明,发酵1 h的小麦淀粉峰值黏度、热浆黏度和冷浆黏度最低。发酵处理后淀粉的粒径均小于原淀粉,其中发酵5 h的平均粒径最小。扫描电镜结果表明,发酵6 h的小麦淀粉颗粒表面出现破裂现象。体外消化实验表明,发酵5 h和6 h小麦淀粉的消化速率最高,发酵后抗性淀粉含量低于原淀粉,而慢消化淀粉含量高于原淀粉(P<0.05)。     

Effect of water stress at different stages of grain development on the characteristics of starch and protein of different wheat varieties

The effect of water stress (WS) at 8 and 15 days post anthesis (DPA) on the characteristics of starch and protein separated from C-306, HD-2329, PBW-175, PBW-343 and NI-5439 wheat varieties was studied. WS-induced changes in A-, B- and C-type granules distribution were variety- and stage-dependent. A-type granules increased in response to WS at both stages in all varieties, the extent of increase being greater at 15 DPA. The proportion of B-type granules decreased in all the varieties, except C-306, in response to WS at 15 DPA. C-type granules also decreased in response to 15 DPA in all varieties, except HD-2329. The starch from wheat exposed to WS at 15 DPA showed lower amylose content, lipids content and pasting temperature, and higher peak viscosity, final viscosity and setback. DSC analysis of starches showed two endotherms (associated with the melting of crystallites and amylose–lipid [AML] complexes) during heating, and an exotherm (associated with reforming of AML) during cooling. Transition temperatures (T_o, T_p and T_c) of AML dissociation and association were lower for starch from wheat exposed to WS, the effect being more at 15 DPA. The changes in pasting and thermal properties of starch caused by WS were observed to be related to lipids, amylose content and distribution of granules. The effect of WS on accumulation of different dimethyl formamide-soluble and insoluble proteins was significant and variety dependent.     

Microstructural changes of starch in cooked wheat grains as affected by cooking temperatures and times

The changes of starch microstructure in soft and hard wheat grains after cooking in a pressure cooker were investigated using a scanning electron microscope (SEM) and a light microscope (LM) in conjunction with image analysis. The conditions studied included variation of the cooking times (20-120 min) at the constant temperature (120 °C) and with variable temperatures (110-140 °C) for constant time (40 min). SEM images showed that steam induced changes in the intact starch granules of cooked wheat grains, with the microstructure becoming more in mud-like structure, with increased cooking time or temperature. The swelling and gelatinization of starch granules could contribute to this change. Suspensions of cooked wheat flour were selectively stained with iodine, for observation using the LM. The image analysis software was used for quantitative analysis of the images captured from the LM, providing both the number and area of the starch granules (determined from the dark-blue spots) per fixed image size. With increased cooking time or temperature, the number of starch granules decreased and the area increased as a result from the swelling and melting of starch granules. This study demonstrated the use of SEM and LM for the investigation of starch granules in cooked wheat grains without prior starch isolation.     

Starch Granule Size Distribution in Grains at Different Positions on the Spike of Wheat (Triticum aestivum L.)

The present study was carried out to characterize the effects of soil water status, cultivar and grain position on starch granule size distribution. The starch granule size distribution and protein and starch content were determined from three wheat cultivars with reference to the position of the grain on the spike. The results showed that the contents of A‐, B‐ and C‐type starch granules were affected by soil water, genotype and soil water×genotype interaction. Grain position was significant for A‐ and C‐type starch granules. Genotype×grain position and soil water×genotype×grain position interactions only affected C‐type starch granules. Both basal and distal grains on middle spikelets contained three types of starch granules: smaller C‐type granules with diameters <2.0 μm, medium B‐type granules with diameters 2.0–9.8 μm and large A‐type granules with diameters >9.8 μm at maturity. Both percent volume and percent surface area distribution of starch granules in basal grains showed the typical three populations, and those in distal grains exhibited a two‐peak curve. The volume and surface area percentage of C‐type granules and protein content in basal grains were higher than that in distal grains, but those of A, B‐type granules in basal grains were lower than that in distal grains. Compared with irrigation, the percent volume and surface area of B, C‐type starch granules and protein content in basal and distal grains were significantly increased, and those of A‐type were evidently decreased in rainfed condition.     

Scanning electron microscopic observations of dough and bread supplemented with Gastrodia elata Blume powder

Dough and bread prepared from wheat flour containing varying amounts of added Gastrodia elata Blume (GEB) rhizome powder [0, 0.5, 1.0, 1.5, and 2.0% (w/w)] were examined by scanning electron microscopy (SEM) during fermentation and baking. The structure of the doughs containing added GEB was found to be related to the protein matrix. Further, it was found that large starch granules and strings of small starch granules play an important role in dough structure. The control dough (no added GEB) had a membrane-like structure, and doughs with 0.5–1.0% added GEB had membrane-like structures that were more developed than those of the control, resulting in increased bread volumes. At 1.5–2.0% GEB levels, however, the doughs tended to have mesh-like structures and result in decreased bread volumes. The dough samples with 0.5 and 1.0% added GEB powder had well-developed gluten matrices with evenly dispersed starch granules. These samples resulted in breads with numerous gas bubble eruptions on their surfaces and consequently in larger loaf volumes than were obtained at other levels of GEB. After the second fermentation, many expanded starch granules were observed and these starch granules were dispersed more evenly than after the first fermentation. In 0.5–1.0% GEB bread, many of the large starch granules had expanded after fermentation, but small starch granules had not. The data obtained in this study suggest that bread baked with 0.5–1.0% GEB exhibits a better loaf volume due to the more complete development of a gluten matrix.     

Optimization of hydroxypropylmethylcellulose,yeast β-glucan,and whey protein levels based on physical properties of gluten-free rice bread using response surface methodology

Response surface methodology (RSM) was used to analyze effects of hydroxypropylmethylcellulose (HPMC), yeast β-glucan, and whey protein isolate (WPI) on physical properties of gluten-free bread baked from formulas based on rice starch. A Box–Behnken design with three independent variables (HPMC, yeast β-glucan, and WPI) and three levels was used to develop models for the different responses (physical properties). Individual contour plots of the different responses produced from the models were compared to the corresponding reference wheat bread data and were superimposed to locate gluten-free bread formulations that met the wheat bread standards for spread ratio, specific volume, hardness, cohesiveness, chewiness, and crumb color L∗ value. The optimal formulation, determined from the data, contained 4.35 g/100 g HPMC, 1 g/100 g β-glucan, and 0.37 g/100 g WPI, rice starch basis. Predicted values of the optimized bread were experimentally tested and compared with the experimental wheat bread data. A good agreement among these data was observed. Moreover, the optimized rice starch bread was found to be acceptable according to the results of sensory analysis.     

The Effect of pH on the Zeta Potential of Wheat and Potato Starch

The facility with which starch is dispersed in aqueous media and the interactions of starch with other components are functions of the surface properties of starch granules. The zeta potentials of wheat and potato starch granules have been measured in the pH range 2 – 10 by microelectrophoresis. Removal of components from the surface of granules using appropriate reagents has enabled us to identify the contributions of the charged groups present on te surface of the granules. Results obtained from micropotentiometric titration of starch suspensions support the conclusions obtained from zeta potential measurements. At their isoelectric points, starch preparations flocculated, indicating that starch suspensions are charge-stabilized.     

Characteristics of Canaryseed (Phalaris canariensis L.) Starch

Canaryseed starches from three locations were isolated by an alkali steeping process and evaluated for their chemical, pasting and structural properties by amylograph, scanning electron microscope (SEM), differential scanning calorimeter, X-ray diffractometer and image analysis, in comparison with isolated wheat starch. The average yield of canaryseed starch was 50 ± 2.9g starch per 100g of groat with a mean extraction efficiency of 77%. The starch isolates contained from 93 to 97% starch with amylose contents ranging from 16 to 22%. Canaryseed starch was uniform in appearance, being small polygonal granules having an average diameter of 2.0 μm. The granules were stable when subjected to shear and heat effects as indicated by visco/amylograph response and SEM-photomicrographs. The transition temperatures (peak and conclusion) and enthalpy of gelatinization of canaryseed starch were higher than those of wheat starch. Canaryseed starch showed major peaks around d-spacings of 5.9, 5.2, 4.8 and 3.8 Å similar to wheat starch which are characteristics of an A-type starch. Canaryseed starch was also more susceptible to α-amylase hydrolysis and more soluble in dimethyl sulfoxide as compared with wheat starch. Based on its ease of extraction and functional properties, canaryseed starch could have potential for food and non-food uses.     

Scanning Electron Microscopy Studies of Wheat,Potato and Corn Starch during Gelatinization

The gelatinization of a commercial wheat and potato starch and two types of corn starch (Amaizo Amylomaize VII and Amaizo Amioca Pearl starch) was examined by the scanning electron microscope. Concomitantly, the loss of birefringence in the wheat, potato and corn starch was followed with the light microscope. Swelling and deformation of the starch granules observed in the scanning electron microscope correlated with the loss of birefringence in the light microscope. The gelatinization range of the starches was detected with the scanning scope. Swelling of the wheat starch granules was first observed in the larger A-type granules. Amylomaize VII retained granular structure until approximately 95 °C even though birefringence changes were observed as low as 69°C. Some evidence of structural changes were evident at 83°C. Amioca Pearl underwent structural changes at approximately 68°C and abruptly lost granular structure at approximately 71 °C.