Amylose and Lipid Contents,Amylopectin Structure,and Gelatinisation Properties of Waxy Wheat (Triticum aestivum) Starch

Starch was isolated from the endosperm of three recently developed waxy wheat lines and their parents. Their amylose and lipid contents, amylopectin structures and gelatinisation properties were evaluated. The endosperm starch from waxy wheat lines is composed essentially of amylopectin. The apparent amylose (1·2–2·0 g/100 g) and lipid contents (0·12–0·29 g/100 g) are much lower than the apparent amylose (26·0–28·4 g/100 g) and lipid contents (1·05–1·17 g/100 g) of their non-waxy parents. The amylopectin of waxy wheat lines is structurally identical to that of the parents. The peak gelatinisation temperature and gelatinisation enthalpy for waxy starch are significantly higher than for non-waxy starch, but the gelatinisation enthalpy for the amylopectin fraction of waxy starch is nearly identical to that of non-waxy starch.     

The Effect of Heat–Moisture Treatment on the Structure and Physicochemical Properties of Normal Maize,Waxy Maize,Dull Waxy Maize and Amylomaize V Starches

Normal maize, waxy maize, dull waxy maize and amylomaize V starches were heat treated at 100 °C for 16 h at a moisture content of 30%. The results showed that the X-ray intensities of the major d-spacings of all starches increased on heat–moisture treatment (waxy maize > normal maize > dull waxy maize > amylomaize V). This treatment decreased the apparent amylose content (amylomaize V > normal maize), swelling factor (amylomaize V > waxy maize > dull waxy maize > normal maize), amylose leaching (amylomaize V > normal maize), pasting viscosities (amylomaize V > normal maize), acid hydrolysis (amylomaize V > normal maize > waxy maize > dull waxy maize), enzyme hydrolysis (amylomaize V > normal maize > dull waxy maize > waxy maize) and syneresis (amylomaize V > normal maize > waxy maize ≈ dull waxy maize). The gelatinization transition temperatures of all starches increased on heat–moisture treatment (amylomaize V > normal maize > waxy maize > dull waxy maize). However, the gelatinization temperature range increased only in normal maize and amylomaize V starches (amylomaize V > normal maize), while it remained unchanged in both the waxy starches. The enthalpy of gelatinization remained unchanged on heat–moisture treatment in all starches and the pasting viscosities of the two waxy starches were also unaffected. The foregoing data showed that starch chains within the amorphous and crystalline regions of the granule associate during heat–moisture treatment. However, the extent of this association was of a greater order of magnitude within the amorphous regions. DSC studies have indicated associations involving amylose chains (amylose–amylose and amylose–native starch lipids) resulted in the formation of new crystallites of different stabilities. In contrast, associations involving amylopectin chains (amylopectin–amylopectin) did not lead to crystallite formation.     

Study on melting and crystallization of short-linear chains from debranched waxy starches by in situ synchrotron wide-angle X-ray diffraction

In situ melting and crystallization of short-linear α-1,4-glucan (short-chain amylose, or SCA) from debranched waxy starches were investigated by synchrotron wide-angle X-ray diffraction. Amorphous SCA was prepared by dissolving completely debranched waxy starches in alkaline solution and neutralized by hydrochloric acid. When hydrated with 50% water at 25 °C, all amorphous SCA crystallized immediately and gave a B-type structure. The SCA from debranched waxy potato starch had a longer average chain length and a higher melting temperature but relatively lower crystallinity upon hydration; it was not completely melted at 100 °C and retained its original B-type structure during rapid cooling. In contrast, the SCA from debranched waxy wheat and waxy maize starches had a large portion of low molecular weight fractions, a higher crystallinity upon hydration, and a lower melting temperature. These differences suggest that amylopectin short chains crystallized more readily but their crystals were weaker than those of long chains. After the B-type crystals of hydrated SCA from waxy wheat and waxy maize starches melted, they reformed into the A-type polymorph upon rapid cooling. The thermal properties showed that the A-type polymorph of debranched waxy wheat and waxy maize starches had a higher melting temperature than their B-type structure.     

Location of Starch Granule-associated Proteins Revealed by Confocal Laser Scanning Microscopy

Distinct locations of starch granule-associated proteins were revealed using a protein-specific dye with confocal laser scanning microscopy (CLSM). The dye, 3-(4-carboxybenzoyl) quinoline-2-carboxaldehyde, fluoresces only after it reacts with primary amines in proteins, thereby removing background interference from residual dye. CLSM has the capability to discern fluorescence-labelled protein distribution in an optical slice of an intact starch granule while it is still in an intact state. With these techniques, starch granule proteins were revealed to be concentrated in internal concentric spheres in potato, maize, and wheat starches. Spheres were more distinct in potato starch than in other starches. Amylose-free potato and waxy maize starches showed no protein spheres, indicating that the internal protein spheres are composed of granule-bound starch synthase (GBSS). Identification of GBSS suggests the location of biosynthesis of amylose in starch granules, as well as spatial and temporal aspects of biosynthesis.     

Extensive degradation of native starch granules by alpha-amylase from aspergillus fumigatus

Starch granules of various botanical origins were subjected to enzymic degradation by purified alpha-amylases from pig pancreas, Bacillus sp. and Aspergillus fumigatus (Aspergillus sp. K-27). With the A. fumigatus enzyme, glucose in alpha-anomeric configuration was the sole end degradation product regardless of the starch tested. The efficiency of this enzyme was very high on all native starch granules. Starches from normal and waxy maize, smooth pea and wheat were completely solubilised within 30 h using 1·34 nKat/mg of substrate. High-amylose maize, wrinkled pea and potato starches were degraded to lower extents (50, 70 and 45%, respectively). Such high enzymic efficiency was not observed with alpha-amylases from pig pancreas or Bacillus sp. With alpha-amylase from A. fumigatus, normal and waxy maize starches displayed highly eroded layered structures when observed by scanning or transmission electron microscopy during degradation. In contrast, potato and high-amylose maize starches produced a minor fraction of endo-eroded granules, whereas the rest of the granules exhibited superficial porosity.     

Effect of iodine on polymer leaching and granule swelling of starches from different botanical sources

Iodine complexation with linear glucan polymers in starch granules is a function of the length of the available polymers and their arrangement within starch granules. In previous studies, this complex formation between iodine and glucan polymers has been shown to alter the pasting properties of starches from different botanical origins. In this study, the effect of iodine on the swelling capacities of corn (CS), wheat (WS), potato (PS) and tapioca (TS) starches was investigated by heating 8% starch slurry with different levels of iodine in a Rapid Visco Analyser (RVA). Increasing concentrations of iodine had an inverse effect on the swelling capacities of starches even though the granules were highly swollen, as observed in the micrographs. Furthermore, the composition of the leachate was different for the starches, suggesting that the swelling capacity was influenced largely by an increase or decrease in the amount of leachate and the absorption spectra of the leachate. The same amounts of iodine resulted in widely different swelling capacity values for the different starches, likely, suggesting differences in their granular architecture.     

Towards an optimal process for gelatinisation and hydrolysis of highly concentrated starch–water mixtures with alpha-amylase from B. licheniformis

The enzymatic hydrolysis of starch is usually carried out with 30–35 w/w% starch in water. Higher substrate concentrations (50–70 w/w%) were reached by using a twin-screw extruder for gelatinisation and for mixing enzyme with gelatinised starch prior to enzymatic hydrolysis in a batch reactor. The aim of this study was to determine which parameters are important for gelatinisation of wheat starch and to investigate the effects of different extrusion conditions on the enzymatic hydrolysis. After extrusion, the degree of gelatinisation was measured. During hydrolysis, the carbohydrate composition, the dextrose equivalent (DE) and the alpha-amylase activity were measured. Gelatinisation measurements showed that mechanical forces lowered the temperature required for complete gelatinisation. During hydrolysis experiments, high DEs were observed even if starch was not completely gelatinised during extrusion. Due to high substrate concentrations, the residual alpha-amylase activity remained high throughout enzymatic hydrolysis, although high temperatures were used. Increased substrate concentrations did not affect the carbohydrate composition of the product. Furthermore, the time required for the batch hydrolysis step could be varied by choosing a different enzyme-to-substrate ratio. This article provides a basis for detailed optimisation of this process to develop an industrial-scale process at high substrate concentrations.     

Amylolysis of wheat starches. II. Degradation patterns of native starch granules with varying functional properties

Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to investigate degradation patterns of native starch granules from wheat (Triticum aestivum L.) by different starch-degrading enzymes. The starches examined were from a waxy wheat and four varieties with slightly elevated amylose content, but with different functional properties. Differences in the digestion patterns after partial α-amylolysis of starch granules were noted between the starches. The waxy starch seemed to be degraded by endocorrosion, whereas the amylose-rich starches followed a slower mode of hydrolysis starting from the granular surface. X-ray diffractograms of the amylose-rich starches were not significantly altered by 2 h of α-amylolysis, whereas partial hydrolysis of the waxy starch decreased scattering intensity at higher 2θ angles, consistent with a different mode of attack by α-amylase in the initial digestion stages of granules of waxy and amylose-rich starches. We propose these differences are due to the combined effects of the change in packing density and partial preference for hydrolysis of amorphous material. The native starch granules were also attacked by beta-amylase, isoamylase and amyloglucosidase, which indicates that α-amylase is not the only starch-degrading enzyme that is able to initiate starch hydrolysis of native granules.     

Effect of repeated heating and cooling cycles on the pasting properties of starch

The properties of starch and starch–lipid pastes have been explored using a novel extended Rapid Visco Analyser (RVA) profile, in which the heating and cooling cycles are repeated five times. Starches from four wheat varieties with amylose content ranging from 23 to 27%, and waxy starches of wheat, rice and maize were tested, alone and in mixtures with lauric acid and monopalmitin (glyceryl-1-monopalmitin). Gels of all of the starches formed and melted reproducibly during repeated heating and cooling in the RVA. The addition of lauric acid to the waxy starches had no effect on the multiple RVA profile. Monopalmitin caused an increase in viscosity during the heating stage of the second to the fifth cycles with the waxy starches, which was attributed to the presence of monopalmitin aggregates. Changes in the multiple cycle viscosity traces observed when monopalmitin or lauric acid was added to the amylose-containing starches were complex. It was concluded that RVA paste viscosities were determined by starch–lipid interactions, as well as by free lipid in the starch mixtures. The water solubility of the lipid and association of proteins with starch granules influence these interactions.     

Effect of instantaneous controlled pressure drop (DIC) on physicochemical properties of wheat, waxy and standard maize starches

Standard maize starch (SMS), waxy maize starch (WMS) and wheat starch (WTS) were hydrothermally treated by the Instantaneous Controlled Pressure Drop (DIC) process. This process consists in a short pressurisation obtained by the injection of saturated steam at fixed pressure during a predetermined time followed by a sudden pressure drop towards vacuum. The effects of DIC conditions on thermal characteristics, enzyme susceptibility, pasting (Brabender) and rheological properties of treated starches were investigated. For treated starches, an increase of transition temperatures (T_o and T_p), a narrowing of the width of gelatinization endotherms and a decrease of the gelatinization enthalpies (ΔH) were observed as the severity of processing conditions increased. WMS, SMS and WTS showed a significant increase in enzymatic hydrolysis after treatment. The saccharification yield showed an increase from 19% (native) to 44%, 21% (native) to 59% and 55% (native) to 79% for SMS, WMS and WTS, respectively. The study suggests that the structural modifications due to the previous DIC treatment influence the in-vitro hydrolysis and the access to the ultrastructure of starch granules; the susceptibility to hydrolysis increases from SMS to WMS and WTS. For all treated starches, the decrease in peak viscosity and in apparent viscosity was related to the processing conditions.     

Pasting,thermal and rheological properties of octenylsuccinylate modified starches from diverse small granule starches differing in amylose content

Waxy maize (a standard starch of normal granule size) and five small granule starches from different botanical sources (rice, wheat B type, oat, quinoa and amaranth) were subjected to 2-octenyl-1-succinic anhydride (OSA) modification. Changes of pasting, gel texture, thermal and rheological properties were investigated. Different small granule starches showed quite different property changes after OSA modification. Pasting viscosity was generally increased in OSA starches, among which OSA oat starch had notably high peak and breakdown viscosity but low setback viscosity. Gel hardness of rice, wheat B type, oat and quinoa starches was reduced by OSA treatment, whereas that of waxy maize and amaranth starches was increased. Amylose content was considered to be the major factor influencing pasting, gel and thermal property of OSA starches. Esterification increased pseudoplastic flow behavior of all starches, while OSA oat starch uniquely had reduced flow consistency coefficient. The dynamic rheological properties were also changed differentially among OSA starches. Viscoelastic properties of rice, wheat B type, oat and quinoa starches were increased after OSA treatment, whereas those of waxy maize and amaranth starches were decreased. This study showed that diverse functionalities from OSA small granule starches may fulfil different demands in product development.     

Morphologies and microstructures of cornstarches with different amylose–amylopectin ratios studied by confocal laser scanning microscope

The morphologies and microstructures of cornstarches with different amylose–amylopectin ratios (waxy: 0/100; maize: 23/77; Gelose 50: 50/50; and Gelose 80: 80/20) were studied by a confocal laser scanning microscope (CLSM). The temperature-induced changes of the cornstarch granules in excess of water were also studied under CLSM. Acid hybridization of starch by HCl was used to enhance the difference between amorphous and crystalline ranges. It was found that the high-amylose starches (G50 and G80) were brighter than those of low-amylopectin starches (waxy and maize) under confocal laser light, and the average (decreasing) fluorescence intensity sequence of the granules was G80 > G50 > maize > waxy. Waxy and maize starches showed clear internal cavities and channels, whilst G50 and G80 had bright cores. Sharp growth ring structures can be clearly observed for low-amylose starches (waxy and maize) after acid hydrolysis. Gelatinization of all starches starts at the hilum and the adjacent of the channels, and spreads rapidly to the periphery. This work is the first time that three-dimensional images of partly gelatinized granules have been constructed and presented from different confocal images, which allows further exploration of the mechanisms of gelatinization.     

Texture determinants of cooked,parboiled rice. II: Physicochemical properties and leaching behaviour of rice

This paper reports the pasting, gelatinisation and leaching behaviour of 11 cultivars of rice, the starch structural properties of which were determined in the preceding paper. The results show that the contents of leached amylose in the cooking water, as determined by both size exclusion–high performance liquid chromatography (SE–HPLC) and iodine colorimetry, were correlated positively with the texture of cooked rices, which possessed total amylose contents in the range 18·4–29·5%. The amount of leached amylose depended on the total amylose content of the rice. A similar correlation between the conventional «setback» value, measured using the Viscoamylograph, and the texture of cooked rice may be a result of the leached starch content. The gelatinisation temperatures of rice starches determined by differential scanning calorimetry (DSC) were not correlated with the texture of cooked rice, but were significantly related to the crystallinity of the rice starch. The longest chain population (92–98 DP_n), which had been detected previously in the hard rice samples, was not found in their corresponding leached starches. This observation may well support the suggestion in the preceding paper that the longest amylopectin chains could interact with other components in rice, the resultant complexes being retained in the cooked grain and inhibiting softening.     

Effect of process conditions and amylose/amylopectin ratio on the pasting behavior of maize starch: A modeling approach

The effects of different process conditions on the pasting behavior of the 14%, w/w suspensions of high amylose, waxy and normal maize starches at mixing speeds of 50, 160 and 250 rpm with the heating rates of 2.5, 5 and 10 °C/min were investigated. In addition, the impact of the starch mixture with an amylose-amylopectin ratio of 0–70% at 160 rpm and a heating rate of 5 °C/min on the pasting parameters was studied. According to the results, when stirring speed decreased from 250 rpm to 50 rpm, the peak viscosity dramatically increased. Furthermore, both heating and stirring rates significantly affected the pasting properties (p < 0.05). The amylose content of maize starch had a negative correlation with peak viscosity, trough viscosity, breakdown viscosity, final viscosity, and setback viscosity. Besides, syneresis values decreased as amylose content decreased from 70% to 0%. According to the kinetic modelling of pasting curves, starch coefficients were found to be higher than 1 for all starches, indicating that the penetration of water into starch granules increased granule swelling rate. The findings of the present study confirmed that both process conditions and amylose/amylopectin ratio can be optimized without necessity of starch modification to obtain the products with the desired quality.     

Pasting characteristics and in vitro digestibility of γ-irradiated RS4 waxy maize starches

The effect of γ-irradiation on the physicochemical properties of cross-linked waxy maize resistant starches was examined. The cross-linked waxy maize starches contained resistant starch (RS) of 56.1 and 63.5%, respectively for 5 and 10% sodium trimetaphosphate (STMP)/sodium tripolyphosphate (STPP) cross-linking, and the RS contents slightly decreased as the irradiation dose increased whereas the RS content in unmodified waxy maize starch increased with an increase in irradiation dose. For both native and cross-linked starches, the rapidly digestible starch (RDS) content increased and the slowly digestible starch (SDS) content decreased by the irradiation. The solubility of the native and cross-linked starches increased as the irradiation dose increased. The cross-linked starches did not swell in boiling water without showing pasting viscosity. However, the starches became swellable, forming pastes by irradiation, and the pasting viscosity gradually increased with an increase in irradiation dose. The crystallinity as determined by an X-ray diffraction analysis remained unchanged upon cross-linking and γ-irradiation. However, the gelatinization enthalpy of the cross-linked starches decreased in proportion with irradiation dose. The melting temperatures of cross-linked starches gradually decreased and the temperature range for melting increased with an increase in irradiation dose.     

Effect of zein extrusion and starch type on the rheological behavior of gluten-free dough

Previous research has shown that zein, above its glass transition temperature, may adopt molecular structures that are able to form doughs with viscoelastic properties comparable to those of wheat gluten. It is hypothesized that extrusion can promote molecular changes in zein and favor interactions with starch that enhance dough viscoelasticity. Thus, the effects of extruding zein at 90–160 °C on the rheological properties of doughs prepared with potato, rice, and maize starches were determined.Formulations were optimized to provide similar mixing profiles to that of a standard wheat dough. For all zein samples, creep-recovery tests demonstrated that doughs prepared with maize and potato starches were less elastic when compared to doughs prepared with rice starch. Zein doughs produced using rice starch were comparable to wheat-dough. Extensional tests showed that zein extruded at 160 °C provided a larger increase in strain-hardening behavior, which is important for bread production. These samples also exhibited larger extensional stresses. Gel electrophoresis of zein extruded at 160 °C revealed an increase in protein aggregates and the presence of smaller peptides when compared to samples subjected at lower extrusion temperatures.Scanning electron micrographs of doughs containing zein showed starch granules embedded within an amorphous material and fibrous structures, which is attributed to elongated zein.     

Molecular basis of the gelatinisation and swelling characteristics of waxy barley starches grown in the same location during the same season. Part II. Crystallinity and gelatinisation characteristics

Nine waxy barley samples (grown at the same site during the same season) were investigated to identify those molecular aspects of amylopectin structure and architecture which define the order and gelatinisation characteristics. Using ¹³C CP-MAS/NMR it was confirmed that the number of double helices within the starches were approximately constant although differences in crystallinity were identified by X-ray diffraction. These differences in terms of amount of crystalline order correlated well with gelatinisation temperatures. The onset (T_o), peak (T_p) and conclusion (T_c) gelatinisation temperatures were 53.4, 59.2 and 68.1 °C on average with the associated enthalpy (ΔH) of 11.0 and 13.5 J g⁻¹ on a starch and amylopectin basis. Annealing of the starches below T_o elevated T_o, T_p and T_c by +11.9, +8.2 and +5.1 °C on average and sharpened the gelatinisation range (T_c−T_o). Acid hydrolysis after annealing increased T_o, T_p and T_c (especially T_c) by +2.3, +17.4 and +34.7 °C on average. Annealing in the presence of α-amylase elevated similarly the gelatinisation parameters by +10.2, +7.1 and +2.8 °C for T_o, T_p and T_c, respectively. Crystalline lamellae lengths were found to be 5.2±0.7 and 6.2±0.4 nm using high sensitivity differential scanning micro-calorimetry and differential scanning calorimetry, respectively.     

Amylolysis of wheat starches. I. Digestion kinetics of starches with varying functional properties

The susceptibility of wheat (Triticum aestivum L.) starches to hydrolysis by pancreatic α-amylase in vitro was investigated using a series of 35 starches with slightly enriched amylose content within a narrow range (36–43%), but widely differing functional properties. After 2 h of incubation with α-amylase, native starch granules were digested to different extents, but there were no differences between any of the starches once they were gelatinized. Cooling the starch for 72 h at 4 °C after cooking reduced the susceptibility of all of the starches to enzymic digestion by a similar extent, whereas addition of monopalmitin decreased the digestibility of the starches that contained amylose, but did not affect the digestibility of waxy starches that were also included in the study. Amylopectin chain length distribution of partly digested starch granules displayed increased proportion of short and medium chains and decreased proportion of long chains in comparison to native granules. Separated large (A) and small (B) starch granules from three of the starches differed significantly in their susceptibility to in-vitro digestion. A predictive model of the susceptibility of starch in the different forms was developed from the physico-chemical and functional properties of the starches.     

Hydrothermal modification of wheat starch. Part 2. Thermal characteristics of pasting and rheological properties of pastes

Water suspensions of starch (with the concentration of 8 g/100 g) were prepared in a measuring vessel of a Brabender viscograph and heated to temperatures of 74, 76.5, 79, 81.5, 84, 86.5, 89, 91.5 or 94 °C under continuous stirring. The resultant solution was cooled and frozen, and then defrosted. Thermal characteristics of re-pasting, rheological properties of produced pastes, starch solubility in water and swelling power were determined.The heating and freezing of the wheat starch suspension induced changes in its properties, with tendency and extent of these changes depending on temperature of pre-heating. The thermal characteristics of the analyzed starches revealed three peaks that corresponded to transitions proceeding during solubilization of retrograded amylopectin and retrograded amylose and solubilization of amylose–lipid complexes. Retrogradation of amylose induced by starch pre-heating followed by its freezing affected also the consistency coefficient and yield stress of the pastes formed by the analyzed starches. Values of these rheological parameters were higher at higher temperatures of pre-heating, compared to the pastes prepared from native starch, and were changing accordingly to the determined second order polynomial function. Amylose retrogradation occurring during the production of starch preparations diminished their solubility in water and increased their swelling power compared to native starch.     

Thermal dissolution of maize starches in aqueous medium

Starches are insoluble in neutral water at room temperature. However, if they are heated beyond the boiling point of water in a closed container, they eventually dissolve. The dissolution profile depends on the type of starch. The dissolution processes of maize starches were monitored in real time by measuring the transmittance of starch dispersion/solution while it was heated. It was found that the dissolution of starches in water results from the degradation of the two components of starches, amylopectin and amylose. Starches from both normal maize and waxy maize were fully dissolved in water when their aqueous solution was heated to approximately 174 °C. Upon cooling to room temperature, amylopectin remained in a solubilized state while amylose molecules were retrograded. For starch solutions that have been heated to higher than 191 °C, the color turned brown and the retrogradation of amylose was not observed.