Amylose Molecules Research Articles

Molecular properties of cassava starch modified with different UV irradiations to enhance baking expansion

Commercial cassava starch was modified with 1% (w/w) lactic acid solution and irradiated with ultraviolet radiation: UVBA (280–420 nm), UVB (310–330 nm) and UVC (254 nm) for 7–15 h. Thermal properties and molecular size distributions of the cassava starch molecules were investigated to explain structural changes responsible for baking expansion ability. The acidified starches irradiated with UVB or UVC for 7 and 9 h achieved the desired baking expansion ability and showed a significant increase in the peak temperatures determined with the differential scanning calorimeter (DSC). The results indicated formation of stable network structures suitable for the expansion. However, the transition enthalpy of these starches did not significantly decrease from that of the commercial starch. Using high performance size exclusion chromatography (HPSEC), it was found that the amylose content of the commercial starch (DPn 2173±163) was decreased to DPn 1551±62 and 1427±54 by UVB, and to DPn 1216±28 and 1096±30 by UVC irradiated for 7 and 9 h, respectively. Profiles of the molecular distributions showed that it was mainly amylose molecules that was degraded by UVB whereas both amylose and amylopectin molecules were degraded by UVC in the amorphous regions.

AFM Images of Complexes between Amylose andAspergillus niger Glucoamylase Mutants, Native and Mutant Starch Binding Domains: A Model for the Action of Glucoamylase

Atomic force microscopy has been used to investigate the complexes formed between high molecular weight amylose chains and Aspergillus niger glucoamylase mutants (E400Q and W52F), wild-type A. niger starch binding domains (SBDs), and mutant SBDs (W563K and W590K) lacking either of the two starch binding sites. The images are interpreted in terms of a favourable binding between the amylose chains and the wild-type SBDs, leading to the formation of ring-like structures, in which parallel strands of the amylose molecule bind to both binding sites on the SBDs. The SBDs are seen to form a template for the assembly of an expanded amylosic double helix. This model for amylose-SBD binding has been used to propose a molecular mechanism for the role of the SBD in the hydrolytic action of glucoamylase on starch granules. The SBDs are considered to recognise the ends of amylosic double helices formed by the short amylosic chains present as branches on the amylopectin molecules, and displayed on the face of crystalline lamellae. This allows the binding and immobilisation of chain ends by the SBD, facilitating binding and cleavage by the exo-acting catalytic domain.

Investigation of non-covalent association of single-walled carbon nanotube with amylose by molecular dynamics simulation

Functionalization of carbon nanotubes (CNTs) with the assistance of biological molecules remarkably improves the solubility of nanotubes in aqueous or organic environment and, thus, facilitates the development of novel biotechnology, biomedicine and bioengineering. In the present study, molecular dynamics (MD) simulations are performed on the complex amylose-nanotube system to study the mode of interaction between the initially separated amylose and SWNT fragments, which can be either wrapping or encapsulation. It has been found that the van der Waals force is dominant and it always plays an important role in promoting non-covalent association. The influence of the size of nanotube on MD simulation is also studied. Our study illustrates that amylose molecules can be used to bind with nanotubes and, thus, favor non-covalent functionalization of carbon nanotubes.

Effects of Na2CO3 and NaOH on Pasting Properties of Selected Native Cereal Starches

ABSTRACT: Using a Rapid Visco Analyzer (RVA), it was revealed that 2 alkalizing agents (Na2CO3 and NaOH) had a far larger effect on pasting properties of nonwaxy starches (wheat, corn, rice) compared with their effect on waxy starches (waxy corn and waxy rice). It was hypothesized that the alkalizing agents have a greater propensity to attack the amorphous regions of the nonwaxy starch granules, thereby causing increased leaching of amylose molecules and possibly also some hydrolysis of starch chains. As a result, the RVA pasting profile of a nonwaxy starch, in the presence of alkali, was drastically altered to one that more closely resembled that of its waxy counterpart without added alkali.

The Role of Hydrogen Bonding in Amylose Gelation

AbstractStudies of the rheological properties of amylose gels in mixtures of water and DMSO have shown that these properties are dependent upon the formation of intramolecular and intermolecular hydrogen bonds. In DMSO, it is proposed that amylose has a tight helical conformation which is maintained by intramolecular hydrogen bonding. When water is added it is proposed that intramolecular hydrogen bonds are replaced with intermolecular hydrogen bonds and thus the rheological properties are changed due to the more extended and flexible amylose molecules adopting an interrupted helical conformation.Because of these changes in conformation, increased water content results in strong elastic gels, commensurate with it being the dominant gel‐forming component in starch, due to its ability to form networks with water through intermolecular hydrogen bonding. The addition of various polyols to solutions of amylose in DMSO also resulted in strong elastic gels being formed. It is proposed that polyols such as 1,3‐propanediol are also able to form networks in a similar way to water.The use of intermolecular hydrogen bond breaking agents, such as urea, reduced gel strength significantly, but the intra‐molecular bond‐breaking agent, 1,1,3,3‐tetramethyl urea (TMU), was not so effective. The results of this work are further evidence of intermolecular hydrogen bonding networks between amylose and water as being of fundamental importance in the strength of starch gels.

Differently sized granules from acetylated potato and sweet potato starches differ in the acetyl substitution pattern of their amylose populations

Acetylated potato and sweet potato starches were fractionated according to granule size. From the fractions obtained amylose and amylopectin were isolated and characterized with respect to degree of substitution (DS) and degradability with α-amylase, β-amylase and amyloglucosidase. The DS of the amylose populations of differently sized granule fractions was quite constant. In contrast, the DS of the amylopectin populations originating from the differently sized fractions increased with decreasing granule size. The acetylation was confirmed to occur throughout the amorphous regions, and only take place in the outer lamellae of crystalline regions of starch granules. The amylose populations isolated from small size granule fractions of the acetylated starches tested were less susceptible to all the enzyme digestions than the amylose originating from the large granule fractions, even though the DS was similar. The acetyl populations groups over the amylose molecules are more heterogeneously distributed and located more closely to the non-reducing ends for amylose originating from small size granule fractions when compared to amylose from lager sized granules.

Diurnal-Nocturnal Changes of Assimilated Starch Structures in Sweetpotato Leaves

Sweetpotato leaves cultivated for three months were harvested at different times for two days, and starch structures in the leaves were examined. The starch content changed in a circadian rhythm, with the minimum at 05:00 and the maximum at 17:00. The starches in the leaves were extracted by maceration of the leaf debris in hot dimethyl sulfoxide and prepared by selective precipitation by iodine. Gel-permeation chromatography of the leaf starches and amylopectins on Toyopearl HW-75F revealed that the leaf starches had a higher amount of material eluted at a low molecular weight fraction compared to that of its root starch, and the low molecular weight fraction contained both amylose molecules and a large amount of small amylopectin molecules. It was also found that both molecular weight distributions of the leaf starch and amylopectin were shifted to high molecular weight during the daytime and to low molecular weight during the period from sunset to sunrise. After debranching the starches and amylopectins, the chain-length distributions and short-chain distributions were analyzed by high-performance gel-permeation chromatography and high-performance anion-exchange chromatography, respectively. The chain-length distributions of the leaf starches were clearly distinct from those of the root starch. The amylose content of the leaf starches, which was evaluated as the difference in long-chain fraction on chain-length distribution between starch and amylopectin, was low during the daytime, whereas the branch aspect of the leaf amylopectin was relatively constant throughout the whole day. Thus, the structural characteristics of the starch in sweetpotato leaf and their diurnal-nocturnal changes have been revealed.

Increased Amylose Content and Altered Molecular Structures of Wheat Starch by SGP-1 Null Mutation

Amylose content and molecular structures of starch from a mutant of wheat (Triticum aestivum L.) that lacks a starch granule bound protein, SGP-1, have been compared with those from normal wheat (cv. Chinese Spring). Actual amylose contents, calculated by taking iodine affinity of amylopectin into consideration, for the mutant (SGP-1 null) and normal wheat starches were 34 and 26%, respectively. The amylopectins from SGP-1 null and normal starches had number-average degree of polymerization (DPn) of 4200 and 4700, respectively. Three molecular species of amylopectin with different size were observed by fluorescent labeling/GPC. Number-average chain length (CLn) of the amylopectins was close (∼21) but their CL distributions were significantly different. SGP-1 null amylopectin contained 9.5% by weight of long unit-chains having CL of >100 while such long chains were absent in amylopectin from the normal starch. Molar ratio of A chains increased slightly and that of B1 chains conversely decreased in the mutant, and the molar ratio of (A+B1)/(B2+B3) was 13.8 and 13.1 for the mutant and normal amylopectins, respectively. DPn of amylose from SGP-1 null (∼800) was lower than that for the normal (∼1000). DP distribution of the amyloses on molar and weight bases showed the ratio of smaller amyloses was higher for the mutant than the normal starch. Branched molecules of amylose consisted of 24 and 23% by mole and had average number of chains of branched molecules (NCB) 13.1 and 7.5, respectively. The above structural data on a molar basis also revealed that the mutation caused the increase in number of amylose molecules but had no effect on the number of amylopectin molecules.

Examination of the Structure of Amylose and Amylopectin by Fluorescent Labeling of the Reducing Terminal

The fluorescent labeling/HPSEC method was developed and the molar-based distribution of amylopectin unit-chains, and molecules of amylose and amylopectin from various sources was examined. The molar-based distribution of A and B chains enabled the estimation of the number of chains per cluster. Cereal amylopectins had a larger number of chains in a cluster than root and tuber amylopectins. A-Crystalline type starches contained amylopectin with a larger number of chains per cluster than B-type crystalline. The molar distribution of C chain suggested the presence of long and short C-chains, which appeared to connect two clusters and were in single cluster, respectively. Amylopectin comprised three molecular species. The large species was major in amount by mole and weight, but the medium and small species were relatively large in amount by mole but very small by weight. The three species appeared to be built up with a similar cluster in structure and differed in the number of clusters. The number of clusters suggested that the large and medium species might be blocklets in granule while the small species immature and/or degraded products of the large species. Amylose comprised several molecular species with different size, and their proportions differed by plant sources. The small amylose species was predominant in cereal amyloses while the large amylose species in root and tuber amyloses. The number-average degree of polymerization of amyloses and the number average chain length of amylopectins determined by the labeling/HPSEC method were in good agreement with those determined by conventional colorimetric methods.

Molecular Structure and Some Properties of Starches from Rhizome and Fusiform Root of Wild Turmeric (Curcuma aromatica Salisb.)

Abstract: The molecular structure and some properties of starches from rhizomes and fusiform roots of wild turmeric (Curcuma aromatica Salisb.) have been examined . Starch content of the rhizomes and fusiform roots was 9.2 and 6.5% with actual amylose content of 25 and 20%, respectively . Both starches showed a B-type Xray diffraction pattern. RVA viscograms for both starches showed small breakdown, and the rhizome starch showed two-fold higher maximum and minimum viscosities and setback . Thermal properties indicated that crystallites in the starch granules were similar in content but different in structure . The amyloses had numberaverage degree of polymerization (DPn ) of?`900 and the amyloses with DPn 400-500 were predominant on a molar basis. Branched molecules of amylose consisted of 13 and 17% by mole and had an average number of chains of branched molecule (NCB) of 4.8 and 3.4. The amylopectins had DPn of 3250 and 6040, and three molecular species with different size were observed. Number-average chain length (CL) of the amylopectins was 25 and molar ratio of unit chains, (A + B1)/(B2 + B3), was 3.8 and 5.3, respectively. The size-distribution of C chains of the wild turmeric amylopectins showed a peak at DP35 . The phosphorus content was 2200 ppm for the rhizome and 600 ppm for the fusiform-root amylopectin, and the amount of phosphorus linked to C-6 position of glucosyl residues was exceptionally low, 14 and 17 %, respectively . The esterified phosphates were found to be linked mainly to long chains (B2 and B3), and DPn of phosphorylated unit-chains was 42 and 49, respectively.

Surfactant-mediated solubilisation of amylose and visualisation by atomic force microscopy

The starch polysaccharide amylose has been visualised at the molecular level by atomic force microscopy (AFM). In order to image individual amylose chains, a new method was developed for producing aqueous amylose solutions at room temperature. The method involved incubation of hot amylose solutions with iodine and the non-ionic surfactant Tween-20 (polyoxyethylene sorbitan monolaurate). This process stabilises the amylose molecules such that, after cooling to room temperature, no aggregation takes place. AFM images of the resulting sample revealed a distribution of extended chain-like molecules, and allowed for the first time, direct visualisation of a small number of branched macromolecules. Treatment of the sample with the starch-degrading bacterial α-amylase (EC 3.2.1.1) confirmed the nature of the soluble chain-like polymers.

Thermoreversible Gels of Hydrophobically Modified Hydroxyethyl Cellulose Cross-Linked by Amylose

Aqueous mixtures of hydrophobically modified hydroxyethyl cellulose (HMHEC) or unmodified hydroxyethyl cellulose (HEC), with amylose (AM) or potato amylopectin (PAP), have been investigated by rheology, turbidity, and H-1 NMR measurements. It is concluded that the AM molecules cross-link HMHEC chains by forming helical inclusion complexes with the hydrophobic side chains of HMHEC, leading to thermoreversible, elastic, and thixotropic gels at ambient temperatures. The complexation ability, the setting-melting temperature of the AM-HMHEC complexes, the strength of the association, and the viscoelastic behavior of the gels vary with the polymer concentrations, the pH, and the preparation method. AM-HMHEC complexes were obtained at a pH range of 7-12.5, but a maximum storage modulus was observed at pH approximate to 10. The AM-HMHEC complexation is modified or completely abolished by the addition of surfactant. A weak synergistic interaction was found for mixtures of PAP with HNIHEC. No complexation was observed between HEC and either AM or PAP. (Less)

Molecular characteristics of barley starches with variable amylose content

The granular and molecular characteristics of four types of hulless barley starches (normal, high amylose, waxy and zero amylose) were investigated by particle size analysis and size exclusion chromatography (SEC) with light scattering detection. Although bimodal size distribution of granules was observed for normal, waxy and zero amylose starches, the proportion of large to small granules for each type of starch differed substantially. The granular size distribution of high amylose starches was unimodal, showing the highest proportion of small granule (3 μm). For the intact starch molecules, molecular weights of high (amylopectin) and low (amylose) M w fractions were in the range from 136×10 6 to 305×10 6 and from 2.73×10 6 to 5.67×10 6, respectively. The lowest M w values were observed for amylopectin in high amylose starches. A good correlation ( r 2=0.96) between M w and R g of all amylopectins was found. After debranching of starch samples, significantly lower M w values were observed for amylose, indicating the existence of branches in amylose molecules. Debranched amylopectins exhibited trimodal distributions of long B, intermediate B and short B+A chains. The longest amylopectin branches were found in high amylose barley starches.

Role of Granule-bound Starch Synthase in Determination of Amylopectin Structure and Starch Granule Morphology in Potato

Reductions in activity of SSIII, the major isoform of starch synthase responsible for amylopectin synthesis in the potato tuber, result in fissuring of the starch granules. To discover the causes of the fissuring, and thus to shed light on factors that influence starch granule morphology in general, SSIII antisense lines were compared with lines with reductions in the major granule-bound isoform of starch synthase (GBSS) and lines with reductions in activity of both SSIII and GBSS (SSIII/GBSS antisense lines). This revealed that fissuring resulted from the activity of GBSS in the SSIII antisense background. Control (untransformed) lines and GBSS and SSIII/GBSS antisense lines had unfissured granules. Starch analyses showed that granules from SSIII antisense tubers had a greater number of long glucan chains than did granules from the other lines, in the form of larger amylose molecules and a unique fraction of very long amylopectin chains. These are likely to result from increased flux through GBSS in SSIII antisense tubers, in response to the elevated content of ADP-glucose in these tubers. It is proposed that the long glucan chains disrupt organization of the semi-crystalline parts of the matrix, setting up stresses in the matrix that lead to fissuring.

Amylopectin Nature and Amylose‐to‐Amylopectin Ratio as Influences on the Behavior of Gels of Dispersed Starch

ABSTRACTThe importance of the nature of the amylopectin and the amylose‐to‐amylopectin ratio in the gelation of high‐amylose maize starch was examined by preparing gels of model systems using amylose (AM) from a high‐amylose maize starch mixed with an amylopectin (AP): either wx starch, acid‐hydrolyzed wx starch (AH‐wx), ae wx starch, or wx β‐limit dextrin. Mixtures of 7.5% starch in 20% dimethyl sulfoxide (DMSO) were examined by differential scanning calorimetry and dynamic oscillatory rheometry. Mixtures of 1.88 or 3.75% AM with the remainder either wx or AH‐wx developed a measurable elastic modulus (G′) within one day, more quickly than for the corresponding AP without AM. Gels of AM with either wx or AH‐wx starch developed a higher retrogradation enthalpy (ΔH) than corresponding AP without AM when the ΔH values were normalized to the amylopectin content. The G′ and ΔH of all gels containing ae wx did not change after one day. During heating of the gels to 80°C, most of the G′ at 25°C was lost, indicating that the initial gel structure was not due to a thermally stable AM network. Gelation is proposed to be due to physical junction zones (PJZ) between AM molecules (AM‐AM), between AM and amylopectin molecules (AM‐AP), and between amylopectin molecules (AP‐AP). For wx, AH‐wx, or ae wx starch, the higher G′ and ΔH of the gels with 3.75% AM compared with the gels with 1.88% AM suggests that AM‐AP PJZ are more important in gel formation when AM makes up half the starch. Gels from the mixture of 3.75% AM and 3.75% ae wx starch behaved most similarly to gels of 7.5% high‐amylose maize starch. The development of a starch gel is affected by both the nature of the amylopectin as well as the amylose‐to‐amylopectin ratio of the gel.

A Short Route to Malto-trisaccharide Synthons: Synthesis of the Branched Nonasaccharide, 6′′′-α-Maltotriosyl-maltohexaose

A short route to phenyl 1-thio-β-maltotrioside derived building blocks and their use for the synthesis of the branched nonasaccharide, 6'''-α-maltotriosyl-maltohexaose, is described. Instead of using glucose and maltose as starting materials, maltotriose was used and synthetically manipulated in a well designed strategy to obtain phenyl O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1→4)-2,3-di-O-benzyl-l-thio-β-D-glucopyranoside, phenyl O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-1-thio-β-D-glucopyranoside and phenyl O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-1-thio-β-D-glucopyranoside. The described methodology has shortened multi-step synthesis of the desired branched non-asaccharide from 40 to 23 steps. It has also provided maltotriose derived building blocks that independently or in combination with corresponding glucose or maltose derived building blocks permit synthesis of any desired part of the amylopectin or amylose molecule.

Both binding sites of the starch-binding domain of Aspergillus niger glucoamylase are essential for inducing a conformational change in amylose

The interaction of the two binding sites of the starch-binding domain (SBD) of Aspergillus niger glucoamylase 1 (GA-I) with substrate has been investigated by using atomic force microscopy (AFM) and UV difference spectroscopy in combination with site-specific mutants of both SBD and GA-I. The SBD possesses two binding sites with distinct affinities towards the soluble linear substrate maltoheptaose; dissociation constants (Kd) of 17 and 0.95 μM were obtained for W563 K (binding site 2 mutant) and W590 K (binding site 1 mutant), respectively, compared to an apparent Kd of 23 μM for the wild-type SBD. Further, the two sites are almost but not totally independent of each other for binding, since abolishing one site does not prevent the amylose chain binding to the other site. Using AFM, we show that the amylose chains undergo a conformational change to form loops upon binding to the SBD, using either the recombinant wild-type SBD or a catalytically inactive mutant of GA-I. This characteristic conformation of amylose is lost when one of the SBD binding sites is eliminated by site-directed mutagenesis, as seen with the mutants W563 K or W590 K. Therefore, although each binding site is capable of simple binding to a ligand, both sites must be functional in order to induce a gross conformational change of the amylose molecules. Taken together these data suggest that for the complex with soluble amylose, SBD binds to a single amylose chain, site 1 being responsible for the initial recognition of the chain and site 2 being involved in tighter binding, leading to the circularisation of the amylose chain observed by AFM. Binding of the SBD to the amylose chain results in a novel two-turn helical amylose complex structure. The binding of parallel amylosic chains to the SBD may provide a basis for understanding the role of the SBD in facilitating enzymatic degradation of crystalline starches by glucoamylase 1.

Effect of Hot-water-soluble Components on the Rheological Properties of Rice Starch

The hot-water-soluble components of 2.5% indica (Taichung Sen 17, TCS17 and Kaohsiung Sen 7, KSS7) and japonica (Tainung 67, TNu67) rice starches were prepared by heating from 45 to 70, 80, and 90 °C, respectively and were analyzed by gel-permeation chromatography. Two major peaks (FI and FII) were detected on the chromatogram. The presence of the FI fraction showed that low molecular weight amylopectin and intermediate fraction were solubilized at 70- 80 °C. The size of the solubilized amylose molecules and the ratio of FI to FII increased as temperature rised. The effects of hot-water-soluble components on the rheological properties of rice starch were evaluated by dynamic rheometry. For clarifying the contributions to starch gelation from starch granules and hot-water-soluble components, suspensions of modified waxy rice starch (Taichung waxy 70, TCW70) with the addi-tion of 2% hot-water-soluble components were used as samples. The addition of hot-water-soluble components retarded the swelling of the starch granules and the gelation was dominated by starch granules dur-ing heating. However, the hot-water-soluble components increased the storage modulus (G ') and decreased tan δ of 10% modified waxy rice starch gel during cooling and aging at 25 °C for 3.5 h. The influence of the hot-water-soluble fractions prepared at high temperature on the rheological properties was more profound than that of the fractions prepared at low temperature. The increments of G ' by adding 80 °C fractions were: TCS17 > KSS7 ETNu67 during aging. However, the differences among the 90 °C fractions of the different varieties were: TCS17 EKSS7 > TNu67. Therefore, it is concluded that the fine structure of the hot-water-soluble components will affect the starch rheological properties, and hot-water-soluble components with high molecular weight promote the starch retrogradation more effectively than those with low molecular weight.

Effect of Hot-water-soluble Components on the Rheological Properties of Rice Starch

The hot-water-soluble components of 2.5% indica (Taichung Sen 17, TCS17 and Kaohsiung Sen 7, KSS7) and japonica (Tainung 67, TNu67) rice starches were prepared by heating from 45 to 70, 80, and 90 °C, respectively and were analyzed by gel-permeation chromatography. Two major peaks (FI and FII) were detected on the chromatogram. The presence of the FI fraction showed that low molecular weight amylopectin and intermediate fraction were solubilized at 70- 80 °C. The size of the solubilized amylose molecules and the ratio of FI to FII increased as temperature rised. The effects of hot-water-soluble components on the rheological properties of rice starch were evaluated by dynamic rheometry. For clarifying the contributions to starch gelation from starch granules and hot-water-soluble components, suspensions of modified waxy rice starch (Taichung waxy 70, TCW70) with the addi-tion of 2% hot-water-soluble components were used as samples. The addition of hot-water-soluble components retarded the swelling of the starch granules and the gelation was dominated by starch granules dur-ing heating. However, the hot-water-soluble components increased the storage modulus (G ') and decreased tan δ of 10% modified waxy rice starch gel during cooling and aging at 25 °C for 3.5 h. The influence of the hot-water-soluble fractions prepared at high temperature on the rheological properties was more profound than that of the fractions prepared at low temperature. The increments of G ' by adding 80 °C fractions were: TCS17 > KSS7 ETNu67 during aging. However, the differences among the 90 °C fractions of the different varieties were: TCS17 EKSS7 > TNu67. Therefore, it is concluded that the fine structure of the hot-water-soluble components will affect the starch rheological properties, and hot-water-soluble components with high molecular weight promote the starch retrogradation more effectively than those with low molecular weight.

Influence of processing methods on starch properties

Native potato starch was prepared using different processing methods. The samples were characterized by wide-angle X-ray scattering (WAXS), optical microscopy, differential scanning calorimetry (DSC), and microhardness. Compression molding of the starch granules led to sintered relatively brittle materials. Here, the amylopectin crystals of the native powder remained grossly preserved. Preparation of dry films from aqueous gels resulted in disintegration of the structure of the native starch granules and in the formation of a new semicrystalline structure comprised of crystallized amylose molecules. Injection molding of native starch was found to be a processing method that gives rise to amorphous materials with superior mechanical properties.