Pasting Profiles and Solubility of Native and Cross-Linked Corn Starch inDimethylsulfoxide-Water Mixtures

The pasting profiles of native and cross-linked corn starch in dimethylsulfoxide (DMSO)–water mixtures were investigated with a Rapid Visco Analyser. The temperature profile included an isothermal step of 1 min at 30 °C, followed by a linear gradient to 75 °C in 3 min and finally an isothermal step of 20 min at 75 °C. The profiles were characterised by an initial peak (at 75 °C) followed by a trough, much as is the case with profiles of such starch in water. Increasing the DMSO concentration in the DMSO–water mixture from 70–97·5% (by weight), without changing the starch concentration, resulted in lower end-viscosities. The RVA pasting profiles of a series of sodium trimetaphosphate (STMP) and epichlorohydrin (ECH) cross-linked corn starches were investigated in 92·5% DMSO at different dry matter (d.m.) contents. At high starch concentrations (>60% d.m.), the end viscosity increased with the degree of cross-linking. At lower starch concentrations (<6% d.m.), the more highly cross-linked starches yielded lower peak- and end-viscosities than starches with lower degrees of cross-linking. The solubilisation of the starches in 92·5% DMSO was complete for the native starch and decreased considerably for the highly cross-linked starches. Light microscopy showed that the cross-linked starches, upon heating in DMSO–water, were converted to a biphasic system consisting of insoluble granule remnants and a starch solution.     

Effect of jet-cooked wheat gluten/lecithin blends on maize and rice starch retrogradation

Vital wheat gluten and lecithin (GL) (50:50, w/w) were dry blended in a coffee grinder and a 9.5% (w/v) aqueous slurry was jet-cooked (steam pressures of 65 psi/g inlet and 40 psi/g outlet) to disaggregate wheat gluten and facilitate better dispersion of the two components. The jet-cooked material was freeze-dried and stored at 0 °C for future use. The GL blend was added to pure food grade common maize and rice starch at concentrations of 0 (control), 6, 11, 16, and 21%. Starch gelatinization and retrogradation temperature transitions were determined using Differential Scanning Calorimetry (DSC). From the DSC profiles, the change in the ΔH value was used as an indication of starch retrogradation, where a higher ΔH value indicated higher retrogradation. The ΔH values of the blends at 4 °C had higher values than the −20 °C and the ambient (25 °C) storage temperatures. Overall, the 21% GL/starch blends reduced retrogradation by 50%. The lower amylose content of rice starch relative to maize starch was reflected in Rapid Visco Amylograph (RVA) measurements of peak viscosity, and similarly, Texture Analyzer (TA) measurements indicated that maize starch gel is firmer than rice starch gel. Retrogradation was also evaluated by observing G′, the shear storage modulus, as a function of time after running a standard pasting curve. Using this method, it appears that GL has a significant effect on maize starch retrogradation, since low concentrations (<0.4%, w/w) reduced G′ up to 40%. The opposite behavior was seen in rice starch, where G′ increased directly with added GL. It appears that the amylose level in the rice starch is too low to be affected by the GL, and the increase seen in G′ is most likely due to added solids.     

Macromolecular Features of Starches Determined by Aqueous High-performance Size Exclusion Chromatography

Starches from various botanical sources, having different amylose–amylopectin levels, were treated with 95% (v/v) dimethylsulphoxide and then dissolved by microwave heating in a high pressure vessel (MWHPV). This procedure led to an almost complete dissolution of the starch sample when it was subsequently taken up in water. Various treatment times were tested, and optimal conditions corresponded to 35 s heating time in MWHPV (maximum temperature 143 °C). Under these conditions, degradation of the polymers was not noticeable and the degree of solubilisation of starch in the samples was in the range 87 to 100%. High-performance size exclusion chromatography (HPSEC) in tandem with multi-angle laser light scattering and refractive index detection was used to investigate apparent weight-average molar mass ( _w) and z-average gyration radius ( _G) of the starch components. Apparent _wand _Gvalues for samples with different amylose contents (between ≈0 and 65·8%) were between 2·2±0·2×10⁸and 2·4±0·2×10⁷g/mol and between 250±10 and 163±5 nm, respectively. These values were higher than those reported previously^1,2probably due to our more complete but less severe solubilisation procedure. When the heating time was increased from 35 to 90 s (maximum temperature 211°C), the _wand _Gdecreased, demonstrating possible polymer degradation due to temperature. Partial precipitation of high amylose samples after 24 h storage was detected by modifications in chromatograms, compared with freshly prepared samples.     

Distribution of Water between Wheat Flour Components: A Dynamic Water Vapour Adsorption Study

The water adsorption properties of hard and soft wheat flours and flour components (starch, damaged starch, gluten, soluble pentosans, and insoluble pentosans) were determined at 25 °C using a controlled atmosphere microbalance. At different levels of relative humidity (from 10% to 95%), changes in sample mass (i.e., water gain) were continuously measured versus time and described using exponential models (R²≥0·994). Water adsorption isotherms were constructed for wheat flours and flour components and described using Guggenheim-Anderson-de Boer models (R²≥0·997). It was not possible to distinguish between the selected hard and soft wheat flours by their isotherms. The water-soluble pentosans had the highest water adsorption capacity. The theoretical distribution of water between the flour components (calculated using the Guggenheim-Anderson-de Boer parameters) was starch, 88%; gluten, 10%; and pentosans, 2%.     

Structural Characterisation of Water-extractable and Water-unextractable Arabinoxylans in Wheat Bran

Water-extractable arabinoxylan (WE-AX) in wheat bran, of which only a minority originates from adherent endosperm, amounted to 6% of the total arabinoxylan (AX) content in such bran. WE-AX had an arabinose to xylose (A/X)-ratio of 0·45. Graded ethanol precipitation (20–80% range) yielded AX with an A/X-ratio increasing from 0·31 to 0·85. A population of molecular weight (MW) of 50 kDa precipitated between 0 and 40% ethanol and one with much lower apparent MW precipitated at higher ethanol concentrations. Wheat bran unextractable cell wall material (UCM) was obtained as the residue withstanding thermostable α-amylase and protease treatments and consisted mainly of AX (ca 45%) and cellulose (30–35%). Two consecutive extractions of UCM with alkaline hydrogen peroxide (AHP; 2·0%, pH 11·5, 4 h, 60 °C) resulted in a cellulose rich residue (CRR) containing 33% of the AX originally present in UCM. The average A/X-ratio of AX in CRR was lower than that in UCM. The extracted AX polymers (ca 45% of the AX originally present in UCM) had a high A/X-ratio (0·82). Their elution profiles showed two polydisperse peaks with apparent MW of respectively 100–120 kDa and 5–10 kDa. Graded ethanol precipitation resulted in a lowly substituted fraction (A/X=0·40; 0–40% ethanol) of high MW and a fraction of highly substituted AX (A/X>0·95; 40–70% ethanol) containing both low molecular weight (LMW-) as well as high molecular weight (HMW-) AX. At an ethanol concentration of 70% or more, only LMW-AX precipitated.     

Maize Starch Biphasic Pasting Curves

The pasting of commercial maize starches was found to be a biphasic phenomenon, exhibiting an expected first viscosity peak as well as an unexpected, relatively large second viscosity peak under specific cooking conditions when using a Rapid Visco Analyser (RVA). The second peak formed at long holding times (between 32 and 45 min), holding temperatures within the range of 82 to 95 °C, starch concentrations from 8 to 13% with a wide range of initial heating rates (0·5–10 °C/min) and shear conditions (150–500 rev/min). The second pasting peak is attributed to the formation of complexes between amylose and low levels of lipid present in maize starch. When lipid was partially removed by extraction with methanol-chloroform (1 : 3 v/v), the second pasting peak disappeared. When, however, the starch sample was treated with solvent and the solvent removed by evaporation, the second peak remained, but formed earlier. Increasing the holding temperature gave a slightly higher first viscosity peak, slightly earlier, and led to a decrease in the area and height of the second viscosity peak. Increasing heating rate also led to an earlier, slightly higher first peak and earlier but lower second viscosity peak. Increasing starch concentration led to an increase in height and area of both the first and second peaks and their later occurrence. Increasing shear led to a decrease in height and area of both the first and second peaks and their later appearance.     

Interaction of granular maize starch with lysophosphatidylcholine evaluated by calorimetry, mechanical and microscopy analysis

In this study we evaluated the thermo-mechanical properties of maize starch pastes (80% wt/wt) under the effect of exogenous lysophosphatidylcholine (LPC) using differential scanning calorimetry (DSC), dynamic mechanical spectrometry (DMS), and scanning electron microscopy (SEM). Particular attention was paid to the development of the amylose-LPC inclusion complex. Results from SEM and DSC showed that with no exogenous LPC, granular maize starch developed the amylose network structure for starch gelling at 80–95 °C. In comparison, at 1.86 and 3.35% of LPC, heating up to 130 °C was needed to develop the three-dimensional network required for starch gelling. Results showed that at these LPC concentrations LPC interacted mainly with amylose within the starch granule. At concentrations ≥8.26% the LPC interacted with amylose both inside the granule and on the granule's surface. At such LPC concentrations heating to 130 °C did not fully develop the starch network structure for gelling. These results suggested that a higher thermal stability was achieved by starch granules because of LPC inclusion complex formation. DSC or DMS did not detect the development of this complex, probably because its formation took place below the onset of gelatinization under conditions of limited molecular mobility. Subsequently, a lower level of organization (i.e. complex in form I) was achieved than in the complex developed at high temperature and water excess (i.e. complex in form II). On the other hand, the changes in the starch granule structure observed by SEM as a function of the time–temperature variable were well described by the phase shift angle (δ) rheograms for starch pastes with and without addition of LPC.     

Molecular Structure of a Low-Amylopectin Starch and Other High-Amylose Maize Starches

The molecular structure of two commercially available high-amylose maize starches, HYLON® V starch and HYLON® VII starch, and of a newly developed low-amylopectin starch (LAPS) was examined. These high-amylose starches give three apparent fractions as determined by gel-permeation chromatography: a high-molecular weight (mol.wt) amylopectin fraction, a low-mol.wt amylose fraction, and an intermediate-mol.wt fraction which contains both linear and branched components. The low-mol.wt amylose fraction increases from 9·4% in HYLON V starch to 17·7% in HYLON VII starch and 26·5% in LAPS, whereas the high-mol.wt amylopectin fraction decreases from 31·1% in HYLON V starch to 13·8% in HYLON VII starch and 2·5% in LAPS. The percentage of linear components in HYLON V starch, HYLON VII starch, and LAPS are 42, 54, and 80%, respectively. High-amylose starches have a large proportion of long chains in their branched fractions compared to waxy-maize and normal-maize starch. Both HYLON VII starch and the LAPS give B plus V-type X-ray diffraction patterns, but the LAPS has even a higher gelatinization temperature, lower swelling power in hot water, and is more resistant to acid digestion. With the lack of amylopectin, amylose accounts for at least part of the double helical structure in the LAPS granules.     

Plasticisation and Mobility in Starch-Sorbitol Films

The purpose of this study was to elucidate the molecular mechanism involved in the behavioural changes observed at macroscopic level in a starch-sorbitol-water system. At a low sorbitol content (<27%), maximum stress decreased and the yield at break was quite constant at around 5%. This behaviour was compared with antiplasticisation, a well-known phenomenon occurring with synthetic polymers. The study of storage loss modulus by dynamic thermal mechanical analysis (DTMA) confirmed antiplasticisation. Sorbitol at high content (>27%) acts as a plasticiser. The two relaxations observed with DTMA, α associated with glass transition (occurring at high temperature, >30 °C) and two occurring at low temperatures (<10 °C), were involved in behavioural changes. System mobility as a function of sorbitol content was determined by time domain nuclear magnetic resonance. Much of this study was performed by replacing H₂O with deuterium oxide to mask the signal from water and therefore analyse only the starch and sorbitol signals. The results show the existence of two competitive effects: one associated with a decrease in mobility and the other with the enhanced mobility of the system. The relative importance of these two effects seems to be reversed, depending on sorbitol content, which could account for the changes observed at the macroscopic level.     

Characteristics of enzymatic hydrolysis of thermal-treated wheat gluten

Effect of thermal treatment at 50–90 °C on wheat gluten hydrolysis by papain was evaluated in this study. Thermal treatment decreased the amount of sodium dodecyl sulfate (SDS) extractable protein. The treatments at 80 and 90 °C had a strong impact on protein extractability. Thermal treatment for 30 min resulted in a significant reduction in SDS extractable glutenin level in wheat gluten. A significant drop in free sulphydryl level was found in wheat gluten treated at 70 °C for 30 min. It indicated that cross-linking of glutenin through S–S occurred during thermal treatment. The treatments at 70–90 °C led to significant decreases in soluble and nitrogen level, while significant increases in peptide nitrogen amount in the hydrolysates from treated gluten were found. A time-dependent effect was observed for the changes in soluble forms of nitrogen and PN. Thermal treatment resulted in molecular mass distribution change according to gel permeation chromatography analysis. Thermal treatment significantly increased the amount of fractions with molecular mass beyond 10 K (67.2%) in the hydrolysates and greatly decreased the amounts of fractions with MM of 10–5 K and below 5 K in hydrolysates.     

The effect of gluten on the retrogradation of wheat starch

The retrogradation of amylopectin in a wheat starch and a wheat starch/gluten (10:1) blend prepared by extrusion and containing 34% water (wet weight basis) was studied using X-ray diffraction, differential scanning calorimetry and NMR relaxometry during storage at constant water content and temperature (25 °C). For both samples, amylopectin ‘fully’ retrograded after 2–3 days storage, i.e. the different parameters monitored with time to follow the retrogradation had reached their maximum value, and crystallised predominantly into the A polymorph. Under the experimental conditions used, there was no evidence of any significant effects of the presence of gluten on the kinetics, extent or polymorphism of amylopectin retrogradation.     

Muffins with resistant starch: Baking performance in relation to the rheological properties of the batter

The effect on baked muffins of progressively replacing wheat flour with resistant starch (RS) was studied. Muffin volume and height and the number and area of gas cells decreased significantly when the RS level reached about 15% (by weight of total formulation) or higher. Rheological properties of the raw batters were studied: the mechanical spectra of batters at 25 °C, the evolution of the dynamic moduli (G′ and G″) with rising temperatures (from 25 to 85 °C) and the mechanical spectra at 85 °C were obtained from oscillatory rheological tests. The decrease in the viscosity and in the elastic properties of the muffin batter as the flour was increasingly replaced by RS was related to the baking performance of the final baked products.     

Wet-milling Factors of Sorghum and Relationship to Grain Quality

Relationships of grain sorghum quality factors (proximate composition and physical properties) to laboratory wet-milling attributes (fraction yields, protein content of fractions and recovery values) of 24 grain sorghum commercial hybrids were determined. Initial water absorption rate was positively correlated with both starch and gluten recoveries (r>0·45), thus showing the greatest significance among all quality factors. The need to understand fully protein matrix breakdown relative to obtaining optimum separation of components was indicated. Positive correlations of residual protein in starch with density and percent abraded (r>0·45) were observed. Laboratory wet-milling attributes also were correlated among themselves. The highest positive correlations were observed among yield and recovery of starch and gluten (r>0·6). These four parameters had strong negative correlations with fiber/germ yield (r<−0·6). Principal component factor analysis identified five factors (named as matrix-breakdown effect, solids-leaching effect, protein-dispersion effect, protein content of gluten effect, and washing-solids effect) that explained 91% of the total variation among wet-milling attributes.     

The Effects of Storage Temperature on the Staling of Wheat Flour Tortillas

Wheat flour tortillas (31·9% moisture) were stored at −60, −12, 0, 4, 22, and 35 °C to evaluate textural changes during staling. Subjective rollability and two-dimensional extensibility tests revealed that tortillas stored at ≥0 °C had increasing force, work and modulus of deformation values during storage. Tortillas stored at ≤−12 °C retained their fresh attributes over 25 days. Tortillas staled more as defined by rheological changes when stored at 22 °C than at 0, 4, or 35 °C. Optimum storage temperatures of wheat flour tortillas are ≤−12 °C while optimum staling temperatures are between 4 and 35 °C.     

Biodegradable foam tray from cassava starch blended with natural fiber and chitosan

This work developed biodegradable foam trays from cassava starch blended with the natural polymers of fiber and chitosan. The kraft fiber at 0, 10, 20, 30 and 40% (w/w of starch) was mixed with cassava starch solution. Chitosan solution at 0, 2, 4 and 6% (w/v) was added into starch/fiber batter with 1:1. Hot mold baking was used to develop the cassava starch-based foam by using an oven machine with controlled temperature at 250 °C for 5 min. Results showed that foam produced from cassava starch with 30% kraft fiber and 4% chitosan had properties similar to polystyrene foam. Color as L^*, a^* and b^* value of starch foam tray was slightly increased. Density, tensile strength and elongation of the starch-based foam were 0.14 g/cm³, 944.40 kPa and 2.43%, respectively, but water absorption index (WAI) and water solubility index (WSI) were greater than the polystyrene foam.     

The Role of Dextrins in the Stickiness of Bread Crumb made from Pre-Harvest Sprouted Wheat or Flour Containing ExogenousAlpha-Amylase

Dextrins were extracted in water from bread made from pre-harvest sprouted wheat or standard flour supplemented with exogenousalpha-amylases. The dextrins were separated by gel permeation chromatography and the dextrin content (% of crumb weight) determined for different degree of polymerisation (DP) size classes; DP 1–2, DP 3–10, DP 11–50, DP 51–200 and DP >200. There were significant correlations between the dextrin content in each size class and crumb stickiness (r=0·84–0·91, 22 df ). The most significant correlation (r=0·96) was between total dextrin content and crumb stickiness. Addition of dextrins of various DP ranges from various sources to standard flour produced bread with sticky crumb. Again, the degree of stickiness was generally related to the amount of total dextrin in the crumb and not to size distribution of dextrins. In this instance, extensive enzymic hydrolysis of starch was not necessary to produce sticky crumb; the dextrins caused crumb stickiness directly. Addition of dextrins to reconstituted gluten–starch flour produced bread with unexpectedly low dextrin levels and correspondingly low stickiness scores. It is concluded that, to produce sticky crumb, high levels of dextrin of any size are necessary in the crumb; a sticky mass is produced when dextrins dissolve in the excess «free» water that is normally «bound» to starch, gluten and other insoluble components of bread crumb.     

Effect of Cooking Procedures and Storage on Starch Bioavailability in Common Beans (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L.)

Common commercial beans were cooked using two procedures: under pressure (autoclaving) and traditional cooking. Total starch extraction was higher in beans cooked with the traditional procedure (41.69–42.81%) than in the autoclaved samples (37.04–38.16%) and did not change during storage at 4 °C. However, available and total resistant starch levels in vitro were not influenced by the cooking procedure or storage. Retrograded resistant starch content was higher in beans cooked with the traditional process (2.65–2.79%) than in autoclaved beans (1.62–1.94%). The initial in vitro -amylolysis rate in freshly cooked beans was higher in the autoclaved preparation than in the beans cooked by the traditional process, but final hydrolysis indices (90 min) were similar for both samples. None of the bean samples showed statistical differences in -amylolysis behavior (=0.05) after storage at 4 °C for 96 hour.     

Changes in gelatinization and rheological characteristics of japonica rice starch induced by pressure/heat combinations

Rice starch suspensions of 10% dry matter (DM) were treated by heat (0.1 MPa at 20–85 °C) or pressure/heat combinations (100–600 MPa at 20, 40 and 50 °C) for 15 min to investigate their gelatinization and rheological characteristics. The maximum swelling index of about 12 g water per gram of DM was obtained by thermal treatment at 85 °C, meanwhile, that of 7.0 g was observed by 600-MPa pressurization at 50 °C. The higher temperatures or pressures resulted in the higher degrees of gelatinization. Furthermore, treatments of 0.1 MPa at 85 °C, 500 MPa at 50 °C and 600 MPa at various temperatures caused complete gelatinization of rice starch. The consistency index (K) and storage modulus (G′) dramatically increased from 70 °C or 400 MPa. The G′ values were higher in pressure-treated samples than those in thermal-treated samples. Therefore, an application of pressure/heat combinations as a processing method to improve the quality of rice starch products would be possible.     

Water Sorption and Dielectric Relaxations of Wheat Dough (Containing Sucrose, NaCl, and their Mixtures)

Dielectric relaxations of wheat doughs with different water contents and effects of sucrose, NaCl, and their mixture on relaxation temperatures were investigated using dielectric analysis (DEA). All ingredients were dissolved in distilled water used to prepare wheat flour doughs to optimum consistency. Before analysis, samples were stored at room temperature in vacuum desiccators over a_w range of 0·225–0·753. Dynamic DEA measurements were made at a heating rate of 2 °C/min from 40 °C below and above the observed relaxation zone. The frequencies used were 0·1, 0·5, 1, and 5 Hz. Steady state water contents varied from 3·21 to 10·89 g H₂O/100 g dm over a_w range used for the plain dough (flour+water). Added ingredients increased sorption of doughs. The tan δ of DEA showed an α-relaxation (glass transition) in all doughs at all frequencies used. The relaxation peak temperature, taken as T_g, increased with increasing frequency. Added sucrose decreased the T_g of doughs, as well as added NaCl. A dramatic depressing effect of NaCl on T_g was probably due to an increase in conductivity of doughs.     

Genetic and Environmental Variation in Sorghum Starch Properties

Starch was isolated from eight local Zimbabwean landrace varieties, an improved cultivar (SV2) and a hybrid (DC-75) of sorghum grown in four environments. Amylose content, pasting (peak (PV), hot-paste (HPV), cool-paste (CPV) viscosity), textural and thermal (gelatinisation peak temperature (T_p) and gelatinisation energy (ΔH)) properties of the starches were determined. The F -tests from analyses of variance detected significant (p<0·001) differences among genotypes and growing environments for the starch properties measured. The results indicate that a range of genetic and environmental variability exists for these traits in sorghum genotypes although the latter could be greater than varietal effects. Hybrid DC-75 largely differed in starch amylose content, pasting PV, and gel hardness from the local landrace varieties. Environments used for local landrace varieties caused significant differences in starch properties, hence selection and monitoring of growing conditions is essential if a particular genotype is to maintain minimum variation in the desired pasting, textural or thermal properties. Genotype×environment interactions indicate that in breeding programmes, selection for starch properties at a single location would be misleading.