Thermal Properties of Starch in Corn Variants Isolated After Chemical Mutagenesis of Inbred Line B73

The starch from eight ethyl methanesulfonate (EMS) treated M4 families of the corn (Zea mays L.) inbred line B73 was analyzed using differential scanning calorimetry (DSC), a Rapid Visco Analyser (RVA), a texture analyzer (TA), and scanning electron microscopy (SEM) coupled with image analysis. The eight families were chosen from 144 families previously selected for having starch with unusual DSC parameters. Apparent amylose contents of the starch from the eight families generally were lower than that of the control. According to DSC, starches from mutagenized families tended to have lower onset temperature (T₀) of gelatinization, enthalpy (ΔH) of gelatinization, and peak height index (PHI), but broader gelatinization range (R) than the B73 control. Their values for ΔH and percentage of retrograzdation (%R) were clustered around that of the control. Pasting properties from the RVA of the starches from the M4 families also were clustered around those of the control B73 starch, except for the setback values which were lower than B73 for M4 starches. Gel firmness values, as measured by TA, of all the M4 starches were generally lower than that of the B73 starch at storage treatments of one day at 25°C or seven days at 4°C. The stickiness of the gels of the M4 starches tended to be greater than that of B73 after seven days of storage at 4°C. These observations were consistent with the lower apparent amylose values for the M4 starches. SEM and image analysis data revealed no differences among the treatments in granule size and shape. Possibly, EMS treatment altered the genes, affecting internal structure of the starch granules. Starch from the mutagenized families likely had lower bonding forces among molecules and fewer long chains in the amylopectin molecules than did B73.     

Thermal Properties and Paste and Gel Behaviors of Starches Recovered from Accessions Used in the Germplasm Enhancement of Maize Project

The objective of this study was to screen starches recovered from the corn accessions used in the Germplasm Enhancement of Maize (GEM) project for unusual thermal properties and paste and gel behaviors, so that they could be exploited in corn breeding programs to enhance traits important to corn utilization. In general, the values for gelatinization temperatures and peak height indices were greater, but heat of gelatinization values were less for the starches recovered from the GEM accessions (particularly BRA 052051 (SE 32)) than for starches from commercial Dent corn hybrids (11.3 vs. 13.6 J/g). Generally, retrogradation properties were similar among the GEM accessions, although there were specific accessions (particularly Lima 13) that possessed modestly lower percentage retrogradation (34 vs. 42%). Generally, peak viscosities, cold paste viscosities, and viscosity breakdowns were greater for the starches of the GEM accessions (particularly ARZM 01150, Antiqua 3, and URZM 01089, respectively) than for the starches of commercial hybrids. Pasting temperatures were about the same for all starches. Both 1‐day and 7‐day gel strengths were considerably greater for the starches recovered from the GEM accessions (particularly BRA 052051 (SE 32), 21.0 g for 1‐day and FS8A(T), 66.2 g for 7‐day). Although the differences in starch properties were statistically different, only the higher gel strengths of the starches recovered from the GEM accessions were of practical significance to the starch industry.     

Preparation and Properties of Oxidized Corn Starches by Semi-Dry Process

Oxidized corn starch prepared by a semi-dry process using hydrogen peroxide as an oxidant was studied. The optimum oxidation conditions of corn starch were mole ratio of H₂O₂ and anhydroglucose unit (0.219); mole ratio of NaOH and anhydroglucose unit (0.144); moisture content of the reaction mixture (27.2%); and reaction temperature (65°C). Compared with oxidized corn starch produced by reacting starch with sodium hypochlorite in alkaline slurry, oxidized corn starches produced by a semi-dry process apparently had different properties. Oxidation by a semi-dry process for corn starch resulted in significant changes in the degree of crystallinity of starch and the changes increased with the increase of carboxyl content of starch. Peak viscosities of oxidized starches produced by a semi-dry process were lower than those of commercial corn starch at similar carboxyl contents, while the final viscosities and setbacks of the former were much higher than the latter. There were apparent differences for texture properties among oxidized starches prepared by different processes. Onset temperature, peak temperature, and conclusion temperature of semi-dry oxidation starches were higher than those of commercial oxidized starch, while the enthalpy of gelatinization of the former were lower than the latter.     

Structure and functional properties of sorghum starches differing in amylose content

Starches were isolated from grains of waxy, heterowaxy, and normal sorghum. To study the relationship between starch structure and functionality and guide applications of these starches, amylose content, amylopectin chain-length distributions, gelatinization and retrogradation, pasting properties, dynamic rheological properties, and in vitro enzyme digestion of raw starches were analyzed. Heterowaxy sorghum starch had intermediate amylose content, pasting properties, and dynamic rheological properties. Stress relaxation was a useful indicator of cooked starch cohesiveness. Cooked heterowaxy sorghum starch (10% solids) had a viscoelastic-solid type of character, whereas cooked waxy sorghum starch behaved like a viscoelastic liquid. Amylopectin of normal sorghum starch had a slightly higher proportion of chains with degree of polymerization (DP) of 6-15 (45.5%) compared with amylopectin of heterowaxy starch (44.1%), which had a gelatinization peak temperature 2 degrees C higher than normal sorghum starch. Heterowaxy sorghum starch contained significantly lower rapidly digestible starch (RDS) and higher resistant starch (RS) than waxy sorghum starch.     

REVIEW: Developments in Our Understanding of Sorghum Polysaccharides and Their Health Benefits

The composition and structure of sorghum polysaccharides are remarkably similar to those in maize. Sorghum grain is rich in starch, cellulosic and noncellulosic polysaccharides (mainly glucuronoarabinoxylans [GAX]). Sorghum starch is similar to maize starch in terms of amylopectin, but the amylose may be more branched. This may account for sorghum starch having a generally slightly higher gelatinization temperature. The GAX in sorghum are highly substituted with glucuronic acid and arabinose, but the degree of these substitutions is lower when compared with maize GAX. Sorghum polysaccharides themselves are not sufficiently functional to allow the production of high‐quality baked goods. Sorghum has generally lower starch digestibility than maize. This is primarily due to the endosperm protein matrix, cell wall material, and tannins (if present) inhibiting enzymatic hydrolysis of the starch. Protein disulfide bond cross‐linking involving the kafirin prolamins in the protein matrix around the starch granules seems to be of major importance in reducing starch digestibility. It does not seem that sorghum polysaccharides, per se, have any unique health‐promoting effects. Any health‐promoting effects related to sorghum polysaccharides seem to be due to interactions between the polysaccharides and the endosperm matrix protein and phenolics.     

Physicochemical and digestibility properties of double-modified banana ( Musa paradisiaca L.) starches

Banana starch was chemically modified using single (esterification or cross-linking) and dual modification (esterification-cross-linking and cross-linking-esterification), with the objective to increase the slowly digestible starch (SDS) and resistant starch (RS) concentrations. Physicochemical properties and in vitro digestibility were analyzed. The degree of substitution of the esterified samples ranged from 0.006 to 0.020. The X-ray diffraction pattern of the modified samples did not show change; however, an increase in crystallinity level was determined (from 23.79 to 32.76%). The ungelatinized samples had low rapidly digestible starch (RDS) (4.23-9.19%), whereas the modified starches showed an increase in SDS (from 10.79 to 16.79%) and had high RS content (74.07-85.07%). In the cooked samples, the esterified starch increased the SDS content (21.32%), followed by cross-linked starch (15.13%). Dual modified starch (cross-linked-esterified) had the lowest SDS content, but the highest RS amount. The esterified and cross-linked-esterified samples had higher peak viscosity than cross-linked and esterified-cross-linked. This characteristic is due to the fact that in dual modification, the groups introduced in the first modification are replaced by the functional group of the second modification. Temperature and enthalpy of gelatinization decreased in modified starches (from 75.37 to 74.02 °C and from 10.42 to 8.68 J/g, respectively), compared with their unmodified starch (76.15 °C and 11.05 J/g). Cross-linked-esterified starch showed the lowest enthalpy of gelatinization (8.68 J/g). Retrogradation temperature decreased in modified starches compared with unmodified (59.04-57.47 °C), but no significant differences were found among the modified samples.     

Low α-Amylase Starch Digestibility of Cooked Sorghum Flours and the Effect of Protein

The comparably low starch digestibility of cooked sorghum flours was studied with reference to normal maize. Four sorghum cultivars that represent different types of endosperm were used. Starch digestibilities of 4% cooked sorghum flour suspensions, measured as reducing sugars liberated following α-amylase digestion, were 15–25% lower than for cooked maize flour, but there were no differences among the cooked pure starches. After the flours were predigested with pepsin to remove some proteins, the starch digestibility of cooked sorghum flours increased 7–14%, while there was only 2% increase in normal maize; however, there was no effect of pepsin treatment on starch digestibility if the flours were first cooked and then digested. After cooking with reducing agent, 100 mM sodium metabisulfite, starch digestibility of sorghum flours increased significantly while no significant effect was observed for maize. Also, starch solubility of sorghum flours at 85 and 100°C was lower than in maize, and sodium metabisulfite increased solubility much more in sorghum than in maize. Differential scanning calorimetry results of the flour residue after α-amylase digestion did not show any peaks over a temperature range of 20–120°C, indicating that sorghum starches had all undergone gelatinization. These findings indicate that the protein in cooked sorghum flour pastes plays an important role in making a slowly digesting starch.     

Comparison of the gelatinization behavior of organic and conventional spelt starches assessed by thermal and rheological analyses

The objective of this study was to compare gelatinization properties and molecular composition of starches extracted from locally grown organic and conventional spelt using thermal, rheological, and SEC analyses, along with Concanavalin A method. Organic and conventional spelt was planted in six replicated plots, and the extracted starch was analyzed for their gelatinization properties. DSC showed that the gelatinization temperature ranged from 56.7 to 68.8 °C with an average peak of 62.4 °C, with no evidence for statistical difference in gelatinization properties between treatments. Rheological behavior variation among samples was more pronounced than that between the two growing conditions. The amylose content ranged from 23.0% to 29.8%. There was no significant difference in the molecular weight of amylose and amylopectin irrespective of the plot locations, although a significant difference was found between the amylopectin molecular weight of organic and conventional spelt starches when analyzed collectively. The organic spelt starch studied may substitute the conventional starch when gelatinization behavior is considered.     

Thermal Properties of Corn Starch Extraction Intermediates by Differential Scanning Calorimetry

Thermal properties of corn starch extraction intermediates from four types of corn were studied using differential scanning calorimetry. Starch at four different stages of extraction, including a standard single-kernel starch isolation procedure and three starch extraction intermediates, was isolated from mature corn kernels of B73 and Oh43 inbreds and the mutants of waxy (wx) and amylose extender (ae) in an Oh43 background. Differences in thermal properties and moisture and protein contents of starch from the extraction stages were statistically analyzed. Most thermal properties (gelatinization and retrogradation onset temperatures, gelatinization and retrogradation ranges, gelatinization and retrogradation peak temperatures, gelatinization and retrogradation enthalpies, peak height index, and percentage of retrogradation) of starches extracted at stage 3 intermediate (a procedure that did not include a final washing step) were similar to those of starch extracted by the standard single-kernel isolation procedure. Values for gelatinization peak temperature, gelatinization enthalpy, and peak height index were different between the standard and the stage 3 intermediate. The values obtained from starches extracted at stage 3, however, were consistent and predictable, suggesting that this extraction intermediate might be used in screening programs in which many starch samples are evaluated. By using the stage 3 extraction, samples could be evaluated in three rather than four days and the procedure saved ≈0.5 hr of labor time. The other two starch extraction intermediates, which excluded filtering and washing or filtering, washing, and steeping, produced starch with thermal properties generally significantly different from starch extracted by the standard single-kernel isolation procedure.     

Composition,Molecular Structure,Properties, and In Vitro Digestibility of Starches from Newly Released Canadian Pulse Cultivars

Pulse starches were isolated from different cultivars of pea, lentil, and chickpea grown in Canada under identical environmental conditions. The in vitro digestibility and physicochemical properties were investigated and the correlations between the physicochemical properties and starch digestibility were determined. Pulse starch granules were irregularly shaped, ranging from oval to round. The amylose content was 34.9–39.0%. The amount of short A chains (DP 6‐12) of chickpea starch was much higher than the other pulse starches, but the proportions of B1 and B2 chains (DP 13‐24 and DP 25‐36, respectively) were lower. The X‐ray pattern of all starches was of the C type. The relative crystallinity of lentil (26.2–28.3%) was higher than that of pea (24.4–25.5%) and chickpea starches (23.0–24.8%). The swelling factor (SF) in the temperature range 60–90°C followed the order of lentil ≈ chickpea > pea. The extent of amylose leaching (AML) at 60°C followed the order of pea ≈ chickpea > lentil. However, in the temperature range 70–90°C, AML followed the order of lentil > pea > chickpea. The gelatinization temperatures followed the order of lentil > pea > chickpea. The peak viscosity, setback, and final viscosity of pea starch were lower than those of the other starches. Lentil starch exhibited lower rapidly digestible starch (RDS) content, hydrolysis rate, and expected glycemic index (eGI). The resistant starch (RS) content of both lentil cultivars was nearly similar. However, pea and chickpea cultivars exhibited wide variations in their RS content. Digestibility of the pulse starches were significantly correlated (P < 0.05) with swelling factor (60°C), amylose leaching (60°C), gelatinization temperature, gelatinization enthalpy, relative crystallinity, and chain length distribution of amylopectin (A, B1, and B2 chains).     

Rheological and physicochemical properties of starches from moist- and dry-type sweetpotatoes

Although starch makes up from 50 to 70% of sweetpotato (SP) dry matter, its role in cooked texture is unknown. The purpose of this research was to characterize raw starches isolated from SP cultivars and experimental selections (C/S) with a wide range of textural properties when cooked and to investigate the relationship between textural properties of the cooked roots and characteristics of the isolated starches. Shear stress measured by uniaxial compression of cooked SP cylinders served as an objective measure of SP texture. Starches were isolated from C/S representing three SP texture types: moist (Jewel and Beauregard); intermediate (NC10-28 and NC2-26); and dry (NC6-30 and NC8-22). The following parameters of isolated starches were measured: amylose content by colorimetric and differential scanning calorimetric (DSC) methods; swelling power, solubility, gelatinization enthalpy (DeltaH), and pasting properties by Brabender amylograph (BA) and rapid viscoanalyzer (RVA). Pasting temperatures for SP C/S measured by BA and RVA were significantly correlated. Due to high shear degradation in RVA, RVA viscosities of starch suspensions decreased as much as 40% during cooking at 95 degrees C, whereas the BA viscosities changed little at this temperature. There were no statistically significant differences among the C/S for amylose or DeltaH. However, significant C/S differences in swelling power, solubility, and pasting properties were observed. Although differences in some rheological and physical properties were observed for C/S starches, shear stress was statistically correlated only with DSC onset temperature (r = 0.78), indicating that factors other than the properties measured on isolated starches are mainly responsible for the texture of cooked SP C/S.     

Rapid Isolation of Sorghum and Other Cereal Starches Using Sonication

High‐intensity ultrasound (sonication) was investigated as a method to rapidly purify starch from sorghum and other cereal grains. To improve the process, buffers were optimized to solubilize sorghum proteins in combination with the sonication. Protein content and starch color were determined to evaluate the efficiency of the extraction process. Sonication times, SDS concentration, different types and concentrations of reducing agents (sodium metabisulfite, dithiothreitol, and β‐mercaptoethanol), and centrifugation speeds of the starch washing procedure were tested. Protein content of isolated sorghum starch was reduced to 0–0.14% (db) after 2 min of sonication (using any of the reducing agents tested). Sodium metabisulfite was chosen as the preferred reducing agent because of its lower toxicity and odor compared with other reducing agents tested. The optimum conditions for producing high‐purity sorghum starches (0.06% protein) were obtained using the following conditions: 2 min of sonication time with 12.5 mM sodium borate buffer, pH 10, containing 0.5% SDS (w/v) and 0.5% sodium metabisulfite (w/v) using 1,500 rpm centrifugation speed during starch washing. Starches separated by this method showed significantly less protein content and b values (yellowness) compared with starches separated by enzymatic methods or methods using NaCl solutions and protein extraction buffers with multiple washing steps, both of which take several hours to complete. Differential scanning calorimetry thermogram values for starches isolated by three different methods showed similar patterns, except that starches obtained with the enzymatic method had slightly higher values of T_o, T_p, and ΔH. Other cereal starches from whole wheat meal, wheat flour, corn, rice, and barley were also obtained rapidly using sonication.     

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.     

Effects of Starch Isolation,Drying, and Grinding Techniques on Its Gelatinization and Retrogradation Properties

The effects of two different methods of starch isolation, drying, and grinding on gelatinization and retrogradation properties were investigated. Starch was isolated from whole wheat and flour of four hard red spring wheat cultivars. Portions of each starch isolate were freeze-dried or air-dried and portions of each dried starch were ground using a mortar and pestle or a Wiley Jr. mill. Less starch damage was obtained for freeze-dried starch regardless of isolation method or grinding technique and for all starches derived from whole wheat. Highest starch damage was obtained for air-dried starch isolates. Wiley-milled starch isolates showed higher water-binding. Whole wheat starch isolates had higher peak, lower trough, and lower final viscosities, as determined by starch paste viscosity analysis, than did starch isolates derived from flour. Major effects of all treatments on differential scanning calorimetry gelatinization properties showed lower onset temperature for flour starch isolates, lower peak temperature for freeze-dried starches, and no effects due to grinding. Endotherms of all starches after refrigerated storage and freezethaw cycling were lower than those for gelatinization.     

Partial Characterization of Buckwheat (Fagopyrum esculentum) Starch

Laboratory-isolated buckwheat (Fagopyrum esculentum) starch was compared to commercial corn and wheat starches. Buckwheat starch granules (2.9–9.3 μm) were round and polygonal with some holes and pits on the surface. Buckwheat starch had higher amylose content, waterbinding capacity, and peak viscosity, and it had lower intrinsic viscosity when compared with corn and wheat starches. Buckwheat starch also showed restricted swelling power at 85–95°C and lower solubility in water at 55–95°C and was more susceptible to acid and enzymatic attack. Gelatinization temperatures, determined by differential scanning calorimetry, were 61.1–80.1°C for buckwheat starch compared to 64.7–79.2°C and 57.1–73.5°C for corn and wheat starches, respectively. A second endotherm observed at 84.5°C was an amylose-lipid complex attributed to the internal lipids in buckwheat starch, as evidenced by selective extraction. The retrogradation of buckwheat, corn, and wheat starch gels was examined after storage at 25, 4, and -12°C for 1–15 days. In general, buckwheat starch retrogradation was slower than that of corn and wheat starch, but it increased as storage time increased, as did that of the other starch pastes. When the values of the three storage temperatures were averaged for each storage period analyzed, buckwheat starch gels showed a lower percentage of retrogradation than did corn and wheat starch gels. Buckwheat starch also had a lower percentage of water syneresis when stored at 4°C for 3–10 days and had better stability to syneresis after three freeze-thaw cycles at -12 and 25°C.     

Effects of β-amylolysis on the resistant starch formation of debranched corn starches

Retrograded amylose is resistant to digestion by amylolytic enzymes, which is known as resistant starch type III (RS3). In this study we investigated the effect of β-amylase hydrolysis on the formation and physicochemical properties of RS3 from debranched corn starches. Three types of corn starch (Hylon VII, Hylon V, and common corn) were first gelatinized and then hydrolyzed using β-amylase to varying degrees. The resultant hydrolyzed starch was debranched with isoamylase and then exposed to temperature cycling to promote RS formation. A broad endotherm from approximately 45 to 120 °C and a small endotherm above 150 °C were noted for all retrograded starches. All three corn starches had increased RS contents after moderate β-amylolysis, with Hylon V having the highest RS content at 70.7% after 4 h of β-amylolysis. The results suggest that RS3 formation is affected by the starch composition as well as the starch structure and can be increased by moderate β-amylolysis.     

Physicochemical Properties of Normal and Waxy Job's Tears (Coix lachryma-jobi L.) Starch

Physicochemical properties of starches from eight coix (Coix lachrymajobi L.) accessions were investigated. There was considerable variation in most measured traits, generally corresponding to the separation into waxy and normal amylose types. The amylose contents of five normal coix ranged from 15.9 to 25.8%, and those of three waxy coix were 0.7–1.1%. Swelling power of waxy coix starches varied between 28.6 and 41.0 g/g, generally higher than waxy maize. Normal coix starches had significantly higher gelatinization peak temperature (T_p) than the normal maize, 71.9–75.5°C. The T_p of waxy coix starches was 71.1–71.4°C, similar to waxy maize. Rapid Visco-Analyser (RVA) pasting profiles of normal coix showed little variation and closely matched the normal maize starch profile. Pasting profiles of waxy coix showed more variation and had lower peak viscosities than waxy maize starch. Waxy coix starches formed very weak gels, while the gel hardness of normal coix starches was 11.4–31.1 g. Amylose content was the main factor controlling differences in starch properties of the coix starches.     

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.     

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.     

Morphological, structural, thermal, and rheological characteristics of starches separated from apples of different cultivars

The starches were separated from unripe apples of five cultivars (Criterion, Ruspippum, Red Spur, Skyline Supreme, and Granny Smith) and evaluated using scanning electron microscopy (SEM), gel permeation chromatography (GPC), X-ray diffraction, differential scanning calorimetry (DSC), and dynamic viscoelasticity. SEM showed the presence of round granules as well as granules that had been partially degraded, probably by amylases. The starch granules in different apple starches ranged between 4.1 and 12.0 mum. Debranching of starch with isoamylase and subsequent fractionation of debranched materials by GPC revealed the presence of an apparent amylose, an intermediate fraction (mixture of amylose and amylopectin), long side chains of amylopectin, and short side chains of amylopectin in the range of 28-35.2, 3.6-4.4, 20-21.3, and 39.9-47.1%, respectively. The swelling power of starches ranged between 14.4 and 21.3 g/g. X-ray diffraction of apple starches showed a mixture of A- and B-type patterns. All apple starches showed peak intensities lower than that observed for normal corn and potato starch, indicating the lower crystallinity. The transition temperatures (onset temperature, T(o); peak temperature, T(p); and conclusion temperature, T(c)) and enthalpy of gelatinization (deltaH(gel)) determined using DSC ranged between 54.7 and 56.2 degrees C, between 57.1 and 59.1 degrees C, between 60.2 and 63.5 degrees C, and between 3.3 and 4.2 J/g, respectively. The viscoelastic properties of starch from different cultivars measured during heating and cooling using a rheometer differed significantly. Red Spur and Criterion starches with larger granule size showed higher G' and G' ' values, whereas those containing smaller size and amylolytically degraded granules showed lower G' and G' '.