Properties of Some Starch Blends

Normal corn, high-amylose corn, waxy corn (waxy maize), wheat, rice, potato, cassava (tapioca), and a modified waxy corn starch were blended in various combinations and ratios. Pasting behavior, paste and thermal properties, and retrogradation tendency were determined. Differential scanning calorimetry (DSC) traces of the mixtures did not resemble those of either of the two components, nor did any DSC trace have two peaks suggestive of a mixture of two distinct starches. Amylograph data suggested that some mixtures behaved like a chemically modified starch. Observations from light microscopy suggested that intermolecular, molecular-supermolecular, and intersupermolecular interactions may be responsible for this behavior.     

Physicochemical and Structural Characteristics of Flours and Starches from Waxy and Nonwaxy Wheats

A waxy spring wheat (Triticum aestivum L.) genotype was fractionated into flour and starch by roller and wet‐milling, respectively. The resultant flour and starch were evaluated for end‐use properties and compared with their counterparts from hard and soft wheats and with commercial waxy and nonwaxy corn (Zea mays L.) starches. The waxy wheat flour had exceptionally high levels of water absorption and peak viscosity compared with hard or soft wheat flour. The flour formed an intermediate‐strength dough that developed rapidly and was relatively susceptible to mixing. Analysis by differential scanning calorimetry and X‐ray diffractometry showed waxy wheat starch had higher gelatinization temperatures, a greater degree of crystallization, and an absence of an amylose‐lipid complex compared with nonwaxy wheat. Waxy wheat and corn starches showed greater refrigeration and freeze‐thaw stabilities than did nonwaxy starches as demonstrated by syneresis tests. They were also similar in pasting properties, but waxy wheat starch required lower temperature and enthalpy to gelatinize. The results show analogies between waxy wheat and waxy corn starches, but waxy wheat flour was distinct from hard or soft wheat flour in pasting and mixing properties.     

Cross‐Linked Resistant Starch: Preparation and Properties

Resistant starches (RS) were prepared by phosphorylation of wheat, waxy wheat, corn, waxy corn, high‐amylose corn, oat, rice, tapioca, mung bean, banana, and potato starches in aqueous slurry (≈33% starch solids, w/w) with 1–19% (starch basis) of a 99:1 (w/w) mixture of sodium trimetaphosphate (STMP) and sodium tripolyphosphate (STPP) at pH 10.5–12.3 and 25–70°C for 0.5–24 hr with sodium sulfate or sodium chloride at 0–20% (starch basis). The RS₄ products contain ≤100% dietary fiber when assayed with the total dietary fiber method of the Association of Official Analytical Chemists (AOAC). In vitro digestion of four RS₄ wheat starches showed they contained 13–22% slowly digestible starch (SDS) and 36–66% RS. However after gelatinization, RS levels fell by 7–25% of ungelatinized levels, while SDS levels remained nearly the same. The cross‐linked RS₄ starches were distinguished from native starches by elevated phosphorus levels, low swelling powers (≈3g/g) at 95°C, insolubilities (<1%) in 1M potassium hydroxide or 95% dimethyl sulfoxide, and increased temperatures and decreased enthalpies of gelatinization measured by differential scanning calorimetry.     

Morphological Changes of Granules of Different Starches by Surface Gelatinization with Calcium Chloride

Native starch granules of 11 selected cultivars (potato, waxy potato, sweet potato, normal maize, high‐amylose maize, waxy maize, wheat, normal barley, high‐amylose barley, waxy barley, and rice) were treated with a calcium chloride solution (4M) for surface gelatinization. The surface‐gelatinized starch granules were investigated using light microscopy and scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). In general, those starches with larger granule sizes required longer treatment time to complete the gelatinization. The salt solution treatment of starch was monitored by light microscopy and stopped when the outer layer of the granule was gelatinized. The surface gelatinized starch granules were studied using scanning electron microscopy. On the basis of the gelatinization pattern from calcium chloride treatments, the starches could be divided into three groups: 1) starches with evenly gelatinized granule surface, such as normal potato, waxy potato, sweet potato, maize, and high‐amylose maize; 2) starches with salt gelatinization concentrated on specific sites of the granule (i.e., equatorial groove), such as wheat, barley, and high‐amylose barley; and 3) starches that, after surface gelatinization, can no longer be separated to individual granules for SEM studies, such as waxy barley, waxy maize, and normal rice. The morphology of the surface gelatinized starch resembled that of enzyme‐hydrolyzed starch granules.     

Retrogradation of Starches from Different Botanical Sources

Retrogradation in 2% pastes prepared from unmodified commercial starches by cooking at 98–100°C under low shear, then held at 4°C for 56 days, was examined by turbidometric analysis and light microscopy. Turbidometric analysis revealed that retrogradation rates followed the order of wheat, common corn > rice, tapioca, potato ≫ waxy maize. Microstructures of stored pastes were examined both before and after centrifugation. Granule remnant morphologies and fresh and stored paste microstructures were unique to each starch examined. Fresh pastes from amylose-containing starches were dominated by networked amylose that condensed into higher density aggregates upon storage. Unique phenomena seen in some stored pastes included interactions of granular remnants with aggregated amylose, composite networks of co-associated amylopectin and amylose, and slight birefringence regained by granule remnants. Microstructural changes in stored pastes could be related to changes in turbidity and to the results of other methods used to quantitate retrogradation.     

Properties of Cross‐Linked Starch from Waxy Mutant Wheat Tanikei A6599‐4

Native starch from waxy mutant wheat Tanikei A6599‐4 is known to exhibit more stable hot paste viscosity than a typical waxy wheat (Tanikei H1881) and waxy corn. The objective of this study was to investigate the starch paste properties of Tanikei A6599‐4 after cross‐linking and compare with Tanikei H1881 and waxy corn. As an example of cross‐linking, the reaction (at 30, 60, 120, and 360 min) with sodium trimetaphosphate was used. In Rapid Visco Analyser (RVA) measurement, the unique characteristic was maintained in Tanikei A6599‐4 starch cross‐linked at low reaction time (<120 min) levels. Cross‐linking at a high reaction time (360 min) level suppressed the swelling of both Tanikei A6599‐4 and Tanikei H1881 starches but not waxy corn starch. Although unmodified Tanikei A6599‐4 starch showed the lowest paste clarity among unmodified waxy starches, this defect became unremarkable when starch was cross‐linked for ≥120 min. In gel‐dispersed dynamic viscoelasticity measurement, the order of G′ and G″ values was always Tanikei A6599‐4 > Tanikei H1881 > waxy corn. This indicates that cross‐linked Tanikei A6599‐4 and Tanikei H1881 starches have different starch properties and that swollen Tanikei A6599‐4 starch granules are more rigid than swollen Tanikei H1881 starch granules.     

Effect of Batter Solids and Starch Type on the Structure of Baked Starch Foams

The effects of starch type on the properties of baked starch foams were investigated. Starch types used for baking were normal corn, normal potato, waxy corn, high-amylopectin potato, wheat, and tapioca. Solids content of the starch batters used to bake foam trays ranged from 25 to 45%. Processing parameters and physical properties of the foams were examined. Starch-foamed trays were formed by heating a starch batter inside a closed mold. Scanning electron micrographs showed that the thin-walled foamed trays have a dense outer skin and a less dense interior with large cells. The weight of the foamed trays and density of the foam depended on the amount of batter cooked inside the mold, the percent solids of the batter, and the type of starch used. The high-amylopectin starches made the lightest trays, while the normal cereal starches made the heaviest trays. Baking time depended on percent solids of the batter, the batter volume added to the mold, and starch type. The normal cereal starches had the longest baking times and the high-amylopectin starches had the shortest baking times Strength and flexibility of the trays are correlated with tray weight and foam density. Heavier trays had greater strength and less flexibility than did lighter trays. Physical properties of the trays can be tailored to meet specific criteria by changing the starch type used and the batter solids.     

Comparison of Physicochemical Properties and Structures of Sugary‐2 Cornstarch with Normal and Waxy Cultivars

Starches from normal, waxy, and sugary‐2 (su2) corn kernels were isolated, and their structures and properties determined. The total lipid contents of normal, waxy, and su2 corn starches were 0.84, 0.00, and 1.61%, respectively. Scanning electron micrographs showed that normal and waxy corn starch granules were spherical or angular in shape with smooth surfaces. The su2 starch granules consisted of lobes that resembled starch mutants deficient in soluble starch synthases. Normal and waxy corn starches displayed A‐type X‐ray patterns. The su2 starch showed a weak A‐type pattern. The chain‐length distributions of normal, waxy, and su2 debranched amylopectins showed the first peak chain length at DP (degree of polymerization) 13, 14, and 13, respectively; second peak chain length at DP 45, 49, and 49, respectively; and highest detectable DP of 80, 72, and 76, respectively. The su2 amylopectin showed a higher percentage of chains with DP 6–12 (22.2%) than normal (15.0%) and waxy (14.6%) amylopectins. The absolute amylose content of normal, waxy, and su2 starches was 18.8, 0.0, and 27.3%, respectively. Gel‐permeation profiles of su2 corn starch displayed a considerable amount of intermediate components. The su2 corn starch displayed lower gelatinization temperature, enthalpy change, and viscosity; a significantly higher enthalpy change for melting of amylose‐lipid complex; and lower melting temperature and enthalpy change for retrograded starch than did normal and waxy corn starches. The initial rate of hydrolysis (3 hr) of the corn starches followed the order su2 > waxy > normal corn. Waxy and su2 starches were hydrolyzed to the same extent, which was higher than normal starch after a 72‐hr hydrolysis period.     

Composition and Reactivity of A‐ and B‐type Starch Granules of Normal,Partial Waxy,and Waxy Wheat

Wheat has great potential to make inroads into starch markets with the advent of partial waxy and waxy starches of diverse composition and properties. The majority of isolated starch utilized in food applications is chemically modified to improve starch properties according to the intended use. Therefore, it is critical to understand factors that affect wheat starch reactivity. This work investigated the relative reactivities of normal, partial waxy, and waxy wheat starches and their respective A‐ and B‐type starch granule fractions. Native starch isolated from four closely related soft wheat lines (normal, partial waxy, and full waxy) was modified through 1) substitution (propylene oxide analog) and 2) cross‐linking (phosphorus oxychloride) reactions to generate both types of modified starch products for each wheat line. Characterization of the unmodified starch fractions confirmed compositional differences among the cultivars and their respective granule types. In cross‐linking reactions, B‐type granules were slightly more reacted than A‐type granules for all cultivars, while the waxy starch generally exhibited higher reactivity compared with normal and partial waxy starches. For the substituted starches, no differences in reactivity were observed among the cultivars or between the two granule types.     

Functional Properties of Cross-Linked and Hydroxypropylated Waxy Hull-less Barley Starches

Waxy hull-less barley (HB) starches containing 0 or 5% amylose were cross-linked with phosphorus oxychloride and the cross-linked starches were hydroxypropylated with propylene oxide. For comparison, waxy corn and potato starches were similarly modified. For all starches, cross-linking inhibited granule swelling and prevented swollen granules from disintegration, resulting in dramatic improvement in pasting properties and tolerance to cooking shear and autoclaving. Cross-linked waxy HB starches were more tolerant to cold storage and cooking shear than cross-linked waxy corn starch. Hydroxypropylation of the cross-linked starches reduced granule crystallinity and gelatinization temperature, and improved granule swelling, paste clarity, and freeze-thaw stability. The double-modified waxy HB starches showed higher cold tolerance than similarly modified waxy corn and potato starches, as judged by freeze-thaw stability and clarity after cold storage. These results indicated that the cross-linked and double-modified waxy HB starches together may have a wide range of food applications. This study indicated that the behavior of granule swelling and disintegration of swollen granules played an important role in governing paste viscosity, clarity, and freeze-thaw stability of waxy HB starches.     

Effect of Source and Proportion of Waxy Starches on Pasta Cooking Quality

Starches from the endosperm of three types of total‐waxy cereals (bread wheat, maize, and barley) were used in reconstitution studies of durum wheat semolinas to investigate the effect of waxy starch on pasta cooking quality. The chemical composition and the pasting and gelatinization properties of the starches used in this study were evaluated to define the functional properties of each waxy starch. The rheological properties of dough semolinas were evaluated by small‐scale mixograph. Spaghetti was prepared using a small‐scale pasta extruder and its cooking quality was assessed using a texture analyzer. Cooked pasta firmness, resilience, and stickiness were measured. The substitution of semolina starch with waxy starches from different sources changed the functional properties of dough and their pasta quality. A decrease in firmness was detected in all the semolinas reconstituted with waxy starches. An increase in stickiness was found when semolinas with waxy starch from wheat were evaluated. No improvement in pasta quality should be expected if the waxy character is introduced in durum wheat.     

Effect of Amylose Content on Gelatinization,Retrogradation, and Pasting Properties of Starches from Waxy and Nonwaxy Wheat and Their F1 Seeds

We studied the effect of amylose content on the gelatinization, retrogradation, and pasting properties of starch using wheat starches differing in amylose content. Starches were isolated from waxy and nonwaxy wheat and reciprocal F1 seeds by crossing waxy and nonwaxy wheat. Mixing waxy and nonwaxy wheat starch produced a mixed starch with the same amylose content as F1 seeds for comparison. The amylose content of F1 seeds ranged between waxy and nonwaxy wheat. Nonwaxy‐waxy wheat had a higher amylose content than waxy‐nonwaxy wheat. Endothermic enthalpy and final gelatinization temperature measured by differential scanning calorimetry correlated negatively with amylose content. Gelatinization onset and peak temperature clearly differed between F1 and mixed starches with the same amylose content as F1 starches. Enthalpy for melting recrystallized starches correlated negatively with amylose content. Rapid Visco Analyser measurement showed that F1 starches had a higher peak viscosity than waxy and nonwaxy wheat starches. Mixed starches showed characteristic profiles with two low peaks. Setback and final viscosity correlated highly with amylose content. Some of gelatinization and pasting properties differed between F1 starches and mixed starches.     

Packing Characteristics of Starch Granules

The rheological properties of granular materials and dispersions of solid particles in fluids are dependent on the packing characteristics of the particles. Maximum packing fractions (Φ_m) have been measured for corn, wheat, rice, potato, and amaranth starches, in the dry state and dispersed in either ethanol or hexane, using a tapping method. The observed maximum packing fraction increases with tapping time to a constant value. Values measured for dry starches were lower than those measured in liquids and reflect the effects of granule shape and intergranular friction. Values measured in fluids for potato, corn, and wheat starches were all similar in magnitude, and in the range of values (0.58–0.63) for random loose packing and random close packing of monodisperse spheres. Values for amaranth and rice starches were significantly lower due to agglomeration and clumping of individual granules. Blends of corn and potato starches show a slight enhancement of packing, with some Φ_m values greater than potato starch, consistent with data for bimodal blends of spheres. Blends of rice and potato starches displayed enhanced packing above ideal mixing but did not exceed the packing fraction of the potato starch. Knowledge of starch packing fractions is required for fundamental understanding of the rheological properties of granular starch‐filled materials and important for predicting processing characteristics.     

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.     

Modification of Starch by Dry Heating with Ionic Gums

Waxy maize (native and hydroxypropylated [HP]) and potato starches were impregnated with ionic gums (sodium alginate, CMC, and xanthan, 1% based on starch solids) and heat‐treated in a dry state for 0, 2, or 4 hr at 130°C. Effects of the dry heating on paste viscosity (RVA) and clarity (light transmittance) were examined. Heat treatment with sodium alginate and CMC raised the paste viscosities of native and HP waxy maize starches, but decreased that of potato starch. Xanthan provided the most substantial changes in paste viscosity among the tested gums. It appeared to heavily restrict granule swelling of the waxy maize starches, but it increased swelling of potato starch granules. Dry heating raised the paste viscosity of all the starch‐gum mixtures tested, except the potato starchalginate mixture. The final viscosity at 50°C of a 7% paste was raised in all other starches by ≈500–1,000 cP by this treatment. The paste of waxy maize starch‐gum products became opaque and shorter textured by the heat treatment, regardless of the gum type, whereas potato starch‐gum products did not show any obvious change in paste clarity. Ionic gums could behave as cross‐linking agents as well as form graft copolymers through heatinduced ester formation. This simple heating process with ionic gums could be used as a modification method for starch.     

Physicochemical Properties of Zero Amylose Hull-less Barley Starch

Zero amylose starch isolated from hull-less barley (HB) showed a typical A-type diffraction pattern. The X-ray analysis suggested that granules of zero amylose (SB94794) and 5% amylose (CDC Candle) HB starches had lower crystallinity than did commercial waxy corn starch. Differential scanning calorimetry showed lower transition temperatures and endothermal enthalpies for the HB starches than for the waxy corn starch. The zero amylose HB starch showed a Brabender pasting curve similar to that of waxy corn starch, but with lower pasting and peak temperatures and a higher peak viscosity. Noteworthy characteristics of zero amylose HB starch were its low pasting temperature and high paste clarity and freezethaw stability, which make this starch useful for many food and industrial applications.     

Effects of Granular Structures on the Pasting Behaviors of Starches

Japonica (Tainung 67 [TNu67]) and waxy (Taichung 70 [TCW70]) rice, normal and waxy corn, and cross-linked waxy rice and corn starches were used in an investigation of the influence of the granular structure on the pasting behavior of starch, using small amplitude oscillatory rheometry. Both normal corn and normal rice (TNu67) starches had the highest storage moduli (G′), followed by their cross-linked versions; native waxy corn and rice starches had the lowest. Native waxy starches showed paste characteristics (G′ < 500 Pa; tan δ > 0.2) at concentrations of up to 35%. However, cross-linked waxy starches exhibited gel behavior at 10% concentration (cross-linked TCW70) or higher (cross-linked waxy corn starch). The degrees of swelling power were in the order: TCW70 > native waxy corn > TNu67 ≅ cross-linked TCW70 ≅ normal corn ≅ cross-linked waxy corn starches. Solubilities were in the order: normal corn > TNu67 > native waxy > cross-linked waxy starches. The addition of 2% purified amylose from indica rice (Kaohsiung Sen 7) did not induce gelation of waxy corn starch. Swelling powers of normal corn, TNu67, and crosslinked waxy starches were similar, but normal corn and TNu67 had much higher G′ value. Such results implied that the formation of gel structure was governed by the rigidity of swollen granules and that the hot-water soluble component could strengthen the elasticity of the starch gel or paste.     

Structural Changes of Debranched Corn Starch by Aqueous Heating and Stirring

Aqueous dispersions (2 mg/mL) of debranched corn starches of different amylose contents (waxy, normal, and high‐amylose) were subjected to extensive autoclaving and boiling‐stirring, and then the changes in starch chain profile were examined using medium‐pressure, aqueous, size‐exclusion column chromatography. As autoclaving time increased from 15 to 60 min, weight‐average chain length (CL_w) of waxy, normal, and high‐amylose corn starches determined using pullulan standards decreased from 46 to 41.2, from 122.1 to 96.3, and from 207.3 to 151.8, respectively. Number‐average chain length (CL_n) measured by the Nelson‐Somogyi method also decreased from 23.0 to 18.4, from 26.4 to 21.8, and from 66.5 to 41.5, respectively, indicating that thermal degradation of starch chains occurred. The CL_w/CL_n ratio for normal corn starch was higher than that for waxy corn starch, indicating an increase in polydispersity of the amylose fraction. Thermal degradation was also observed when the debranched starch was subjected to the boiling‐stirring treatment (0–96 hr). During 96 hr, the CL_w and relative proportion of B≥2 chains of amylopectin released by debranching waxy corn starch increased, whereas those of B1 chains decreased. This change may indicate physical aggregation of B1 chains. But branches from normal and high‐amylose corn starches showed increases in CL_w and the proportion of both B1 and B≥2 chains, along with substantial decreases in those of amylose chains. Therefore, thermal degradation of amylose was greater than that of amylopectin.     

Morphological,Structural, and Thermal Properties of Starch Nanocrystals Affected by Different Botanic Origins

Six types of starch nanocrystals were prepared from corn, barley, potato, tapioca, chickpea, and mungbean starches with an acid hydrolysis method. The yields and morphological, structural, and thermal properties of starch nanocrystals were characterized. Starch nanocrystals had yields ranging from 8.8 to 35.7%, depending on botanical origin. During acid hydrolysis, amylose was effectively degraded, and no amylose was detected in any starch nanocrystal. Shape and size of native starch granules varied between starches, whereas there was no obvious difference in shape among different types of starch nanocrystals. The average particle size of starch nanocrystals was mainly related to crystalline type of native starches. Compared with their native starch counterparts, changes in crystalline diffraction patterns of starch nanocrystals depended on the original botanical source and crystalline structure. Degree of crystallinity, melting temperature, and enthalpy of starch nanocrystals increased, whereas their thermal decomposition temperature decreased. Of six produced starch nanocrystals, potato starch nanocrystal had the lowest yield, degree of crystallinity, and onset and melting temperatures, the largest particle size, and obvious changes in crystalline diffraction pattern.     

Starch Characteristics of Waxy and Nonwaxy Tetraploid (Triticum turgidum L. var. durum) Wheats

Manufacture of pasta products is paramount for durum wheat (Triticum turgidum L. var. durum). The recent development of waxy durum wheat containing starch with essentially 100% amylopectin may provide new food processing applications and present opportunities for value‐added crop production. This investigation was conducted to determine differences in some chemical and functional properties of waxy durum starch. Starch was isolated from two waxy endosperm lines and four nonwaxy cultivars of durum wheat. One of the waxy lines (WX‐1) was a full waxy durum wheat whereas the other line (WX‐0) was heterogeneous, producing both waxy and nonwaxy seed. Effects on starch swelling, solubility, pasting, gelatinization, and retrogradation were examined. The full waxy starch had four times more swelling power than the nonwaxy durum starches at 95°C, and was also more soluble at three of the four temperatures used. Starch pasting occurred earlier and peak viscosities were greater for starches from both waxy lines than for the nonwaxy starches, but their slurries were less stable with continued stirring and heating. Greater energy was required to melt gelatinized waxy starch gels, but no differences were found in either refrigerated storage or freeze‐thaw retrogradation, as determined by differential scanning calorimetry. The results of this investigation showed some significant differences in the starch properties of the waxy durum wheat lines compared to the nonwaxy durum wheats.