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

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

Filtration Characteristics of Maize and Wheat Starch Hydrolysates

Starch hydrolysates were prepared by one- or two-stage hydrolysis with α-amylase. The filtration rate of wheat starch hydrolysates was considerably lower than that of maize starch hydrolysates. Omitting the second conversion step lowered the filtration rates of wheat and maize starch hydrolysates. Increasing the incubation time or the enzyme dosage resulted in an increase of the filtration rate of maize starch hydrolysates due to the increase in the dextrose equivalent. These process variables did not influence the filtration rate of wheat starch hydrolysates. Wheat starch hydrolysates had very poor filtration characteristics: low filtration rates, almost no removal of undesired components, and obstruction of the filter cake. On the contrary, maize starch hydrolysates showed good filtration characteristics: a high filtration rate and removal of the largest part of the undesired components. On storage, wheat starch hydrolysates separated into three layers. The intermediate fraction had a higher filtration rate than the total hydrolysate. Adding small amounts of the upper or lower layers to dextrose solutions decreased the filtration rate to that of a wheat starch hydrolysate. This was due to an increase of the protein and lipid concentration.     

Effect of Sugars on Retrogradation of Waxy Maize Starch‐Sugar Extrudates

The effect of sucrose, fructose, and xylose on the retrogradation of waxy maize starch extrudates at relatively low moisture contents (20–50 g of water/ 100 g of dry solid) at 277–353 K was investigated using X‐ray diffraction and ¹H nuclear magnetic resonance (NMR) relaxometry. The role of the sugar depended on the type of sugar and its concentration, but most importantly on the retrogradation conditions (water content and storage temperature). For the isothermal retrogradation at 313 K, fructose considerably increased the rate of retrogradation over the range of water contents investigated, and the increase was proportional to the sugar concentration. The behavior of xylose and sucrose was more complex. At 10% sugar content, both sugars enhanced starch retrogradation, while at 30% sugar content, xylose accelerated the process at <35% (mc, dsb) but decreased the rate constant when more water was present. This crossover took place at 42% mc for sucrose. Sugars enhanced the transformation of the A‐type polymorph to a so‐called pseudo‐B with an X‐ray diffractogram similar to that of B‐type starch, with the exception of the 1.6‐nm peak which was considerably depressed. The effects of these sugars on the retrogradation kinetics in variable storage temperature conditions mirrored those obtained when isothermal retrogradation was examined in the water content domain.     

Flavor Retention in Pregelatinized and Internally Flavored Starch Extrudates

Corn starch (25% amylose content) was pregelatinized in a twin-screw extruder. The extrudate was ground and reextruded after adjusting moisture content to 9, 13, or 17% (db) and blending with 5% (w/w) of flavor compounds cinnamaldehyde, eugenol, nonanoic acid, or 3-octanone. Initial moisture content significantly influenced radial expansion, specific mechanical energy, and flavor retention. Significantly higher flavor retention was obtained when flavor was injected into the extruder barrel as compared to preblending of flavors in pregelatinized starch. Flavor retention upon extrusion was lower with pregelatinized starch than with raw starch.     

Effect of Small and Large Wheat Starch Granules on Thermomechanical Behavior of Starch

The physicochemical properties of small‐ and large‐granule wheat starches were investigated to reveal whether gelatinization properties and rheological behavior differ between size classes of wheat starch. All samples contained 60% water (w/w, wb). The starch granule size and shape were examined by scanning electron microscopy in the separated A‐ and B‐type granule populations and in the whole wheat starch granule population. Differential scanning calorimetry (DSC) and electron spin resonance (ESR) analyses were performed in parallel with rheological measurements using dynamic mechanical thermal analysis (DMTA) to relate the viscoelastic changes to modifications in dynamic properties of aqueous solutions and structural disorganization of starch. The small (B‐type) granules had slightly higher gelatinization temperature and lower gelatinization enthalpy than did the large (A‐type) granules. Also, B‐type granules had higher enthalpy for the amylose‐lipid complex transition. Moreover, our results suggested that small granules have higher affinity for water at room temperature. It seems that there is a less ordered arrangement of the polysaccharide chains in the smaller granules when compared with the larger ones. These differences in functional properties of small and large granules suggested that the granule size distribution is an important parameter in the baking process.     

Effect of Wheat Starch Structure on Swelling Power

Starches were isolated from the endosperm of 12 wheat samples with a wide swelling power range in the wholemeal. Starch amylose content (24.8–34.2%) correlated negatively with the swelling power of isolated starch (18.3–26.9), but starch lipid content showed no such correlation. Higher proportions of long chains (DP ≥ 35) in amylopectins contributed to increased starch swelling. Native starch gelatinization temperatures and enthalpy measured by differential scanning calorimetry correlated positively with swelling power, which also correlated significantly with the regelatinization enthalpy of retrograded starches stored at 5°C for two and four weeks.     

玉米淀粉微晶结构在加热和高压作用下的变化

对照研究了玉米淀粉微晶结构在高压和加热单独作用下的变化。玉米淀粉加压或加热后，在偏振光显微镜下均有偏光十字消失现象，说明玉米淀粉的微晶结构发生了相同的变化，且均已被破坏，即加热和加压均可使淀粉糊化     

高压对玉米淀粉糊化度影响的研究

采用差热扫描量热法（ＤＳＣ）研究了不同压力及保压时间对玉米淀粉糊化度的影响。在７００ＭＰａ压力下，保压２ｍｉｎ即可使８６．８％玉米淀粉糊化，达到一般食品加工要求；保压５ｍｉｎ，可使玉米淀粉１００％糊化，这是高压食品加工的一大优点     

Effect of Ferulic Acid and Catechin on Sorghum and Maize Starch Pasting Properties

The effects of ferulic acid and catechin on starch pasting properties were studied as part of an investigation into the structure and functionality of phenolics in starch‐based products. Commercial maize starch, starches from sorghum cultivars (SV2, Chirimaugute, and DC‐75), and the phenolic compounds ferulic acid and catechin were used in the investigation. Pasting properties were measured using rapid viscosity analysis. Ferulic acid and catechin (up to 100 mg each) were added to maize or sorghum starch (3 g, 14% mb) in suspensions containing 10.32% dry solid content. Addition of catechin resulted in pink‐colored pastes, whereas ferulic acid had no effect on paste color. Ferulic acid and catechin decreased hot paste viscosity (HPV), final viscosity, and setback viscosity of maize and sorghum starch pastes, but had no influence on the peak viscosity (PV) of the former. Both phenolics increased breakdown viscosity. Ferulic acid had greater influence on HPV, final viscosity, breakdown, and setback than catechin. Addition of catechin under acidic conditions (pH 3) decreased HPV, final viscosity, and setback of maize starch, but alkaline conditions (pH 11) slightly increased setback. Both acidic and alkaline conditions resulted in increased breakdown. Investigations on model‐system interactions between ferulic acid or catechin and starch demonstrated that phenolic type and pH level both significantly influence starch pasting properties, with ferulic acid producing a more pronounced effect than catechin. The significance of these interactions is important, especially in food matrices where phenolics are to be added as functional food ingredients.     

Capillary Rheometry of Corn Endosperm: Glass Transition,Flow Properties,and Melting of Starch

A capillary rheometer was manufactured to study the properties of corn endosperm. Samples were tested at or near the pressures and temperatures encountered in high-temperature, short-time extrusion. The rheometer was designed to prevent moisture loss during testing. At a set pressure, raising the temperature caused corn endosperm particles to soften and change shape, resulting in a pressure drop as the voids in the sample were reduced. The temperature at which the pressure drop occurred was considered the glass transition temperature. Continued heating caused the pressure to rise and drop a second time as the sample softened and flowed through the capillary. Thermal analysis by differential scanning calorimetry showed that complete melting of starch crystals was not necessary to permit capillary flow. Pressure and temperature conditions sufficient to initiate flow were measured for opaque and vitreous corn flours and expressed as a boundary curve defining the flow region. The position of the curve shifted as a function of sample moisture content. The vitreous corn sample had a rough (unstable) flow that could be eliminated by addition of a small amount (2% w/w) of vegetable oil. When isolated corn starch was studied in the capillary rheometer, results showed that, under certain conditions, starch crystal melting was affected by pressure and time. A model was developed to account for the effects of pressure, temperature, time, and sample moisture on starch crystal melting.     

Consequence of Starch Damage on Rheological Properties of Maize Starch Pastes

Waxy and normal maize starches were damaged to different extents by ball milling, with waxy starch notably more susceptible to damage. Starch damage caused substantial decreases in shear stress or apparent viscosity in both waxy and normal maize starch pastes at a wide range of shear rates (5.6 to 400 1/sec). Shear stress or apparent viscosity decreases were more evident in waxy than in normal maize starch pastes at the same ball milling times. Values of storage moduli were much higher than values of loss moduli, and storage moduli decreased with increase in starch damage in both waxy and normal maize starches, indicating decrease in elastic property. The study showed that starch damage causes substantial rheological changes in gelatinized pastes and that waxy starch undergoes more pronounced changes than normal starch. These results can be used to understand the general behavior of damaged normal and waxy starches in processed foods.     

Effect of Cross‐Linked Resistant Starch on Wheat Tortilla Quality

Resistant starch (RS) ingredients are an attractive option to increase dietary fiber in baked products. This study determined the effect of two forms of cross‐linked and pregelatinized cross‐linked RS, Fibersym‐RW (Fsym) or FiberRite‐RW (FRite), respectively, from wheat on dough and tortilla quality and acceptability. Refined wheat tortillas with 0% (control) to 15% RS (flour basis) were made using a standard baking process. Tortillas with 100% whole white wheat were also made. Physical and rheological properties of dough and tortillas, and sensory profile of tortillas were evaluated. Dough with whole wheat and 15% FRite were significantly harder and less extensible than the control dough; this was related to high water absorption of these doughs. Tortillas with whole wheat and 10–15% FRite were less puffed and denser than the control; however these levels of FRite significantly increased tortilla weight (by up to 6.2%). Dough and tortillas with Fsym were comparable to the control. Dietary fiber (g/100 g, db) increased from 2.8 ± 0.3 in control to 14.3 ± 0.5 and 13.6 ± 0.5 in 15% Fsym and 15% FRite tortillas, respectively. Tortillas with whole wheat were less acceptable than the control in appearance, flavor, and texture, while tortillas with 15% Fsym had higher overall acceptability than the control. Incorporation of 15% cross‐linked wheat RS to increase tortilla dietary fiber is feasible without negatively affecting dough handling and tortilla quality.     

Effect of Surfactant Structure on the Pasting Properties of Wheat Flour and Starch Suspensions

Systematic studies were performed on the effect of the surfactant alkyl chain length (10–16 carbon atoms) and the head group charge/structure (anionic, cationic, nonionic) on the pasting properties of wheat flour and starch aqueous suspensions by means of a Rapid Visco Analyser (RVA). An excellent agreement was observed between the effect of surfactants on the onset temperature of the pasting process (PT) and the time to reach peak viscosity (t_peak) of wheat flour and wheat starch suspensions. Moreover, a correlation was found between the effect of different surfactants on these two parameters. With the exception of the cationic surfactants (alkyl trimethyl ammonium bromides), the effect of surfactants (alkyl sulfates, maltosides, monoglycerides, and sucrose esters) was found to be strongly dependent on the surfactant chain length. Shorter chain surfactants (C10–C12) induced an earlier pasting, while longer chain surfactants (C14–C16) had the opposite effect. The effect of surfactants on PT and t_peak of flour suspensions was enlarged when the surfactant concentration was increased from ≈1% to 15% (w/w) on a dry starch basis.     

Evaluation of Compatibility of Rice Starch and Pectins by Glass Transition and Sub‐Tg Endotherms and the Effect of Compatibility on Gel Viscosity and Water Loss

Differences in molecular structure and hydrophilicity may affect the compatibility of food components in a highly concentrated solution. Mixtures of TNuS19 rice starch (RS) and pectins with three different degrees of esterification (22, 64, and 92%) were used as a model system to evaluate the components' compatibility in a low‐moisture system. When analyzed individually by differential scanning calorimetry (DSC), RS, low methoxyl pectin (LMP), intermediate methoxyl pectin (IMP), and high methoxyl pectin (HMP) showed the presence of a glass transition temperature (T_g) at 75.2, 96.2, 96.4, and 93.5°C, respectively. Among mixtures, the compatible RS‐HMP exhibited only a single T_g between the T_g values of the two components, whereas the incompatible RS‐LMP showed two T_g values that were close to those of the individual components. The sub‐T_g endotherms of all three mixtures (1:1) were lower than the means of the corresponding components. The degree of decrease was more pronounced in the RS‐HMP mixture than in the others. The above results imply that the interaction, which led to close contact between side chains of the two components, was more intense in the compatible RS‐HMP mixture than in the RS‐IMP and RS‐LMP mixtures. The decrease of the sub‐T_g endotherm can be used as an index to evaluate the degree of compatibility as well as the interaction occurring between the two molecules. The above findings were further verified by dynamic mechanical analyses. Both viscosity and water retention of the compatible RS‐HMP mixed gel were significantly higher than those of the RS‐IMP and RS‐LMP mixed gels. This evidence further suggests that RS and HMP are compatible and exhibit a strong intermolecular interaction that increases gel viscosity and decreases water loss during high‐temperature heating.     

Biochemical Characterization of the Wheat Waxy A Protein and Its Effect on Starch Properties

Granule bound starch synthase1 (GBSS1) is a key enzyme in amylose biosynthesis and is encoded by the A, B and D GBSS1 wx loci in wheat. Wheat lines with mutations at the three GBSS1 loci have been identified. We have characterized and compared the grain starch of CDCW6 wheat line (null B and D for GBSS1) with PI235238 (null A and B for GBSS1), waxy (null A, B and D for GBSS1), and AC Reed (wild type wheat) grain starches. The grain starch of waxy, CDCW6, PI235238, and AC Reed lines contained ≈0, 12, 23, and 25% amylose (w/w), respectively. Waxy, partially waxy, and wild wheat grain starches showed significant differences in onset and peak transition temperatures as determined by differential scanning calorimetric analysis. Grain starches extracted from waxy, CDCW6, and PI235238 also had higher enthalpy of gelatinization values than did wild wheat starch. X-ray diffraction analysis revealed the highest crystallinity for starch extracted from waxy wheat, followed by CDCW6. The starch produced from the CDCW6 line may find special food and industrial applications because of its relatively low amylose concentration.     

Effects of Extrusion on Dietary Fiber and Isoflavone Contents of Wheat Extrudates Enriched with Wet Okara

Okara is the residue left after soymilk or tofu production. In North America, okara is used either as animal feed, fertilizer, or landfill. The purpose of this study was to use wet okara to produce and enrich extruded cereal products and to study the effects of extrusion on the dietary fiber and isoflavone contents. Wet okara was combined with soft wheat flour to produce two different formulations (33.3 and 40% okara) and extruded using four combinations of two screw configurations and two temperature profiles. Various physicochemical properties, dietary fiber by enzymatic-gravimetric method, and isoflavone content by HPLC were analyzed. The radial expansion ratio decreased as fiber content increased. On the other hand, both bulk density and breaking strength increased as fiber content increased. Combining okara with soft wheat flour resulted in increased protein, dietary fiber, and isoflavone contents compared with soft wheat flour alone. Extrusion of the formulations resulted in decreased insoluble fiber (≤25.5%) and increased soluble fiber (≤150%) contents of extrudates. Extrusion decreased the total detectable isoflavones (≤20%) and altered the distribution of the six detected isoflavones.     

Effect of Corn Moisture on the Properties of Pet Food Extrudates

Corn moisture (9.5–13.5%) was significantly correlated to extrudate properties, even though water was added at the extruder to compensate for the differences in moisture. Water addition was more effective at the preconditioner than at the extruder, and longer retention preconditioner improved expansion. Water added to the pet food formula apparently was absorbed by the other formula ingredients and not the corn. Controlling the specific mechanical energy did not compensate for differences in corn moisture.     

Effects of Wheat Starch and Gluten on Tortilla Texture

Wheat starches were isolated from three wheat flours. Two vital wheat glutens, one from a commercial source and another one isolated from straight-grade flour, were combined with wheat starches to form reconstituted flours with a protein level of 10%. Several characteristics of tortillas made with the hot-press method were measured. No significant difference (P < 0.05) occurred in texture of tortillas made with hard wheat gluten and soft wheat gluten. Wheat starches did not have any significant (P < 0.05) effect on tortilla stretchability or foldability. Analysis of variance confirmed that wheat starch and gluten had limited effects on tortilla texture. The possible reasons were that the solubles of wheat flour were not included, and the shortening in the tortilla formula interfered with the interaction of gluten and starch.     

Hydrodynamic Chromatography of Waxy Maize Starch

A hydrodynamic column packed with solid beads chemically bonded with N-methyl-d -glucamine residues was used with 90% dimethylsulfoxide (DMSO)-H₂O mobile phase as part of a chromatographic system to characterize jet-cooked waxy maize starch. Software calculations based on signals from refractive index and dual-angle light-scattering detectors indicated the column could fractionate molecular weights up to ≈5 × 10⁸. Calculated molecular weight values for the highest molecular weight sample was greatest at the lowest flow rate of 0.1 mL/min. Values of molecular weights and radii of gyration determined by the in-line dual-angle light-scattering detector were significantly less than those determined with an off-line multiangle light-scattering detector that examined samples that had not traveled through the hydrodynamic column. This work has demonstrated the feasibility of using a hydrodynamic column to characterize waxy maize amylopectins. However, considerations of sample shear sensitivity and questions of in-line light scattering detection show that further efforts are required to develop and optimize a chromatographic system to characterize very high molecular weight amylopectins.     

Effects of Processing Parameters on Physical Properties of Corn Starch Extrudates Expanded Using Supercritical CO2 Injection

Corn starch was extruded with a corotating twin-screw extruder (24:1 L/D ratio, 31-mm screw diameter) and supercritical CO₂ was injected as a blowing agent. The effects of barrel temperature (80–90°C), screw speed (150–250 rpm), and water injection (30–54 g/min) on specific mechanical energy (SME) input for the process and the physical properties of extrudates, such as expansion ratio, water absorption (WA), water solubility (WS), breaking stress, and elastic modulus, were examined using a response surface methodology. Barrel temperature had the greatest effect on physical properties of extrudates but not on SME input, whereas screw speed and water injection had significant effects on SME input. Extrudates had a smooth surface, and air cells were uniform and closed, providing low WA and WS. Using superimposed contour plots, optimum barrel temperature, screw speed, and water injection rate, based on maximum expansion ratio and minimum SME input, were 94–96°C, 155–175 rpm, and 36–39 g/min, respectively.