Structure of starches extracted from near-isogenic wheat lines

High-sensitivity differential scanning calorimetry (HSDSC) and small-angle X-ray scattering (SAXS) were used to investigate the structural characteristics of starch granules with different amylose content extracted from near-isogenic wheat lines with different combinations of active granule-bound starch synthase (GBSS I) isoforms. Paracrystalline diffraction model, ‘two-state’ model of starch melting and other physico-chemical approaches were used to estimate the sizes of amylopectin clusters, the thicknesses of crystalline lamellae and the structure of amylopectin defects for investigated wheat starches. The joint analysis of SAXS and DSC data has shown that the size of amylopectin cluster, the thickness of crystalline lamellae and the structure of amylopectin defects do not depend on the differences in combinations of active GBSS I isozymes. The data obtained supposed that the amylopectin cluster size and the thickness of crystalline lamellae are, generally, the universal structural parameters for wheat starches. Additionally, the data obtained suggest that increase of amylose content is accompanied by accumulation of both amylose tie-chains, located as defects in crystalline lamellae, and amylose chains oriented transversely to the lamella stack within amorphous lamellae. Disordered ends of amylopectin double helices and/or pre-existing double helices not participating in formation of crystals are considered as amylopectin defects arranged in crystalline lamellae. The relationship between structure of wheat starches extracted from near-isogenic lines and their thermodynamic properties was recognized.     

Fractionation and characterization of starch granules using field-flow fractionation (FFF) and differential scanning calorimetry (DSC)

Starch is one of the main carbohydrates in food; it is formed by two polysaccharides: amylose and amylopectin. The granule size of starch varies with different botanical origins and ranges from less than 1 μm to more than 100 μm. Some physicochemical and functional properties vary with the size of the granule, which makes it of great interest to find an efficient and accurate size-based separation method. In this study, the full-feed depletion mode of split-flow thin cell fractionation (FFD-SF) was employed for a size-based fractionation of two types of starch granules (corn and potato) on a large scale. The fractionation efficiency (FE) of fraction-a for corn and potato granules was 98.4 and 99.4%, respectively. The FFD-SF fractions were analyzed using optical microscopy (OM) and gravitational field-flow fractionation (GrFFF). The respective size distribution results were in close agreement for the corn starch fractions, while they were slightly different for the potato starch fractions. The thermal properties of FFD-SF fractions were analyzed, and the results for the potato starch showed that the peak temperature of gelatinization (T_p) slightly decreases as the size of the granules increases. Additionally, the enthalpy of gelatinization (ΔH) increases when the granule size increases and shows negative correlation with the gelatinization range (ΔT).

     

Shear-dependent rheological properties of starch/bentonite composite gels

 Rheological properties of starch/bentonite gels (5.3–8.2% solids, 0–100% starch) were investigated at shear rates 0.0083–0.33 s^-1 (Brookfield viscometer). Prior to these measurements the strain introduced during preparation of the gel was kept as low as possible. Under these conditions six different types of structural units could be identified in the gel: bentonite particles associated in a band-type structure; bands coated with starch polymers; bundles of bands interlaced and enveloped by starch polymers (strands); individual bentonite platelets dispersed in a polymer matrix; starch polymer networks; and swollen granules. A power-law model was fitted to the experimental viscosity data: μ_app= Kγ ^n-1 . In all cases n was found to be less than 0.5. Its value decreased with the ability of the structural components to reorient under applied shear. K was found to be proportional to the compaction and/or entanglement of the structural units. These trends in K and n were further confirmed by the index of thixotropy (IT) and complex modulus of shear elasticity (G ^* ) measurements. Received: 12 August 1996 Accepted: 7 January 1997     

Influence of Amylose-Amylopectin Ratio on Properties of Extruded Starch Plastic Sheets

Abstract

Starch plastic sheets were prepared by extrusion processing of mixtures of granular high-amylopectin and high-amylose starches in the presence of glycerol and water as plasticizers. Amylose content varied between 0 and 70% (w/w). Structural characterization and determination of the mechanical properties of the sheets were performed after aging the materials between 40–65% relative humidity for 2 and 35 weeks and at 90% relative humidity for two weeks. The materials were semicrystalline and viscoelastic. The materials were described as complex heterogeneous multiphase materials. They consisted of amorphous and crystalline phases of amylose and amylopectin as well as granular structures and domains of amylose, amylopectin and amylose-amylopectin helices. Single-helical type crystallinity was formed solely by amylose directly after processing while B-type crystallinity was rapidly formed in amylose-rich materials and slowly during aging of amylopectin-rich materials.

The stress-strain and stress-relaxation properties were related to differences in amylose content, degree of crystallization and water content. The amorphous amylopectin rich materials were flexible and soft but showed an increase in stiffness and a decrease in elongation due to crystallization. Amylopectin-rich materials showed unfavorable relaxation, shrinkage and cracking during aging. The materials rich in amylopectin were sensitive to water content while the amylose-rich materials were not sensitive to water in the range of 9–13% (w/w). Stress-strain relaxation behaviors of the materials were dependent on starch structure and on experimental conditions such as strain rate and extension by which the ratio of elastic and viscous response were varied. An increase in relaxation times was found with increasing amylose content and water content for the materials with solely amylose crystallinity.     

Influence of Surface-Active Compounds on Starch Dispersion in Water. Part I. Starch Pasting

The influence of native lipids and additives of surface-active compounds on starch paste rheology was investigated. The aim of the study was to gain better understanding of mechanisms involved in starch gelatinization and how these structure changes of granules later affect rheological properties of pastes and gels. Starches from three main sources—potato, maize, and wheat—were tested; sodium dodecylsulfate, oleate, and benzalkonium chloride were employed as additives. Starch pasting was examined by a rheometer to get a viscosity profile, also pastes were analyzed by differential scanning calorimetry, for particle size using a light scattering technique. Results revealed that there was a competition between native lipids and added surfactants for amylose complexation. Complexes formed during gelatinization were strongly affecting granule swelling and dissolution of starch polymers, and viscosity of pastes was mainly dependent on the particle size of a disperse phase in the paste. Addition of strong ionic surfactants to cereal starches resulted in smaller granular remnants and, therefore, decreased viscosity, while the weak anionic surfactant promoted an increase in the particle size and paste viscosity for both cereal and tuber starches. The mechanism of the effect of surfactants on the particle size in pastes is discussed.     

ESR investigation of starch gelatinization using novel spin probes

The spin probes 1,1,3,3-tetramethylisoindolin-2-yloxyl (TMIO) and the sodium salt of its sulfonate, 1,1,3,3-tetramethylisoindolin-2-yloxyl-5-sulfonate (NaTMIOS) were used to monitor the microviscosity changes of water during starch gelatinization. In cereal starch, which contains mainly A-type polymorphs, evidence was found for the amylopectin and amylose regions, the latter undergoing a transition at about 55 degrees C and a large increase in the microviscosity on cooling. Pea starch contains both A-and B-type polymorphs and this was also found to have two domains and the 55 degrees C transition was observed for the amylose phase: the less mobile amylopectin showed a reversible decrease in water microviscosity on heating.     

Identification of glucan synthetase glycosidically bound to amylopectin from cotton leaf starch

Starch-granule bound glucan synthetase was isolated from cotton leaves by a sucrose density technique. Starch granules were successively washed with 0.02 M Na-phosphate buffer containing 0.9% NaCl. The alkaline hydrolysate of washed materials and acid hydrolysate of protein-bound amylopectin were separated by use of Con A-Sepharose. Amylolytic hydrolysate of starch granules also was carried out with α-amylase and fractionated by chromatography on Sephadex G-25. Amylopectin was the only glucan glycosidically linked with proteins, in which glucan synthetase activity was identified. The amylose component was free from covalently bound proteins.     

大米淀粉糊化过程的光谱分析

采用衰减全反射傅立叶变换红外光谱仪跟踪测定了不同品种大米淀粉的糊化过程,同时与X-射线衍射仪测定的淀粉结晶度相对比,研究了淀粉颗粒内结晶结构在糊化过程中变化的详细情况.利用红外光谱仪计算出天然大米淀粉及其在糊化过程中各个阶段代表结晶区特征的1047cm-1和代表非晶区特征的1022cm-1两处红外吸收峰强度的比值.结果表明,天然淀粉的结晶区主要由支链淀粉侧链的双螺旋结构所形成;在加热过程中淀粉的结晶结构被破坏,并且直链淀粉含量越高,其结晶结构在糊化过程中破坏越慢,说明直链淀粉能抑制淀粉结晶结构的破坏.利用X-射线衍射仪测定了大米淀粉糊化过程各个阶段的结晶度,进一步验证了淀粉的结晶结构在糊化过程中的损失.虽然,两种测定方法对"结晶度"的定义不同,但对于淀粉结晶程度的测定具有相关性和可比性,能为研究淀粉的糊化行为提供有利的补充信息.     

Rapid analysis of starch, amylose and amylopectin by high-performance size-exclusion chromatography

Starch components, amylose and amylopectin, were analyzed by high-performance size-exclusion chromatography. These two-components were separated using a two-column system (E-Linear and E-1000) and dimethyl sulphoxide as the mobile phase. The void volume (V0 = 2.22 ml) was measured using tobacco mosaic virus. Column calibration was accomplished with dextrans of known average molecular weight (Mw range = 10,100-2,000,000). The elution volume of amylopectin (Ve = 2.5 ml) indicated that this starch component was fractionated on the column system despite its very large molecular size. Standard curves were prepared from various mixtures of purified corn and wheat amylose and amylopectin. From the linear relationships obtained, the percentages of both components in corn and wheat starches were determined. The method developed proved useful to monitor the purity of amylose and amylopectin preparations, and to estimate rapidly the amylose:amylopectin ratio of starch samples.     

Electrosprayed maize starch and its constituents (amylose and amylopectin) nanoparticles

Starch consists of amylose and amylopectin. Properties such as being natural and highly hygroscopic as well as biodegradability have opened a considerable range of applications for amylose, amylopectin and starch. The performance of particles is highly dependent on their size which in turn determines the specific surface area. This work studies the application of electrospraying to fabricate maize starch and its constituents: amylose and amylopectin nanoparticles. This study showed that electrospraying technique is capable of producing amylose, amylopectin and starch nanopowder with an average particle size around 100 nm. FTIR analysis showed no reaction or interaction occurring in amylose, amylopectin and starch nanoparticle compared with their natural form. Basically, lower concentration, lower viscosity and lower surface tension of the electrospraying solution as well as higher nozzle–collector distance, higher voltage and lower feed rate lead to smaller nanoparticle size. Copyright © 2015 John Wiley & Sons, Ltd.     

Construction of Porous Starch-Based Hydrogel via Regulating the Ratio of Amylopectin/Amylose for Enhanced Water-Retention

The performance of hydrogels prepared with traditional natural starch as raw materials is considerable; the fixed ratio of amylose/amylopectin significantly limits the improvement of hydrogel structure and performance. In this paper, starch hydrogels were prepared by physical blending and chemical grafting, with the aid of ultrasonic heating. The effects of different amylose/amylopectin ratios on the microstructure and water retention properties of starch hydrogels were studied. The results show that an increase in amylopectin content is beneficial to improve the grafting ratio of acrylamide (AM). The interaction between the AM grafted on amylopectin and amylose molecules through hydrogen bonding increases the pores of the gel network and thins the pore walls. When the amylopectin content was 70%, the water absorption (swelling 45.25 times) and water retention performance (16 days water retention rate 44.17%) were optimal. This study provides new insights into the preparation of starch-based hydrogels with excellent physical and chemical properties.     

Structure of starches extracted from near isogenic wheat lines

Differential scanning calorimetry (DSC), acidic hydrolysis and different physico-chemical approaches were used to study thermodynamic and structural characteristics of starches from near-isogenic wheat lines to establish the effect of different combinations of active granule-bound starch synthase isoforms, taking part in amylose biosynthesis, on the structure and thermodynamic properties of starches. Obtained results suggest that the effect of different GBSS I combinations is realized through altered amylose localization within starch granules, reflecting in changes of melting temperature of crystalline lamellae (T _m) and rates of acidic hydrolysis. It has also been demonstrated that changes in T _m values for native wheat starches are determined by amylose content in amylopectin clusters.     

In vitro and in vivo digestibility of native maize starch granules varying in amylose contents

Digestibility of maize starch granules with different amylose content (AL-0, 22, 54, 68, 80, or 90%) was investigated. Measurement of the in vivo resistant starch (RS) content of the starches was performed using surgically prepared ileorectostomized rats. The rats were fed a purified diet containing one of the starches at 652.5 g/kg diet. The in vivo RS content was determined based on the fecal starch excretion. The dietary fiber (DF) value increased as a function of the amylose content in the starch and showed a positive linear correlation with the gelatinization temperature of the granules. In contrast, the in vitro RS content was likely to depend on both the surface area and amylose contents of the starch granules. The maximum in vitro RS content was obtained with AL-68 (54.4%). In vivo RS content showed a significant correlation with the amount of in vitro RS but not in respect to the DF detected. The in vivo RS content of AL-68 (43.4%) was higher than that found in AL-90 (37.8%). A profound gap was observed for AL-54 between the amount of DF (6.4%) and RS (in vitro = 46.6% and in vivo = 40.9%) present. The results suggest that both in vitro and in vivo digestibility of maize starch is affected by the amylose content and surface area of the granules. The current evaluation suggests that the physiological occurrence of RS from maize starch might be predictable by reference to the in vitro RS value.     

Thermoplastic starch revisited. Structure/property relationship for “dialed-in” biodegradability

Starch, totally biodegradable polysaccharide biosynthesized by numerous plants, is one of the most abundant renewable resources known to man. Composed mostly from linear amylose and highly branched amylopectin, the starch, in its granular form, is a crystalline material. When mixed with limited amount of water and subjected to heat and shear, starch undergoes spontaneous destructurization. Homogeneous melt, possessing thermoplastic character is formed, called thermoplastic starch. It absorbs between 5 and 30 % of water at relative humidity range 0 to 90 %. Water is principal plasticizer of this material changing its original stiffness from glass-like to natural gumlike substance. This plasticization is accompanied by significant dimensional changes. Many polymers, both hydrophilic and hydrophobic, were blended with starch to modify its moisture sensitivity. To illustrate influence of admixed polymers on its moisture sensitivity and its effect on properties and biodegradability, poly(vinyl alcohol), poly(ethylene-co-vinyl alcohol) and poly(ethylene-co-methacrylic acid) were added to potato starch. This paper discusses results and observed trends.     

Comparative Study on the Structural and Physicochemical Properties of Flour and Starch from Dioscorea opposita Thunb

The objective of this work was to investigate and compare the structural and physicochemical properties of Dioscorea opposita Thunb. flour(DF), starch(DS) and purified starch(PDS). DS and PDS showed higher total starch and amylose content as compared to DF. Starch granules of DF were oval shape with rough surface while DS and PDS were relatively smooth by SEM. According to XRD measurements, FT-IR spectroscopy and 13 C CP/MAS NMR spectroscopy, all samples displayed C-type crystalline pattern, and PDS displayed the highest relative crystallinity and short-range order structure. However, DF contained the greatest content of the amorphous-phase. DF displayed the absorption peaks at 1730 and 1560 cm~(-1) related to the characteristic groups of lipid and protein using FT-IR spectroscopy. Furthermore, DF exhibited significantly higher pasting temperature while DS displayed the great peak and breakdown viscosity, as well as PDS had the highest setback and final viscosity, presumably due to the chemical composition and structural differences. DF exhibited the highest gelatinization temperature whereas PDS displayed the greatest gelatinization enthalpy. The pasting and gelatinization properties of flour and starch might be related to the relative crystallinity, short-range order structure or the interactions between starch and its associated compounds. The results allow the improvement in the manufacture of Dioscorea opposita Thunb. flour and starch with desirable pasting and gelatinization properties.     

Effect of Resistant Starch on Hydrolysis and Fermentation of Corn Starch for Ethanol

Starch samples with 0% or 30% amylose were subjected to four different liquefaction enzyme treatments (at various temperature and pH conditions) followed by simultaneous saccharification and fermentation (SSF). Resistant starch (RS) measurements were conducted for the initial starch sample, after liquefaction and after SSF. Initial RS was higher for 30% amylose starch samples (16.53 g/100 g sample) compared with 0% amylose (0.76 g/100 g sample). Higher initial RS resulted in lower conversion of starch into sugars and lower final ethanol yields. The four enzymes hydrolyzed RS, but in varying amounts. Higher temperature liquefaction hydrolyzed a larger portion of RS, resulting in higher ethanol concentrations and lower final residual solids (non-fermentables), whereas lower temperature liquefaction hydrolyzed a smaller portion of RS and resulted in lower ethanol concentrations and higher final residual solids. Decreases in resistant starch after high temperature liquefaction were 55% to 74%, whereas low temperature liquefaction decreases were 11% to 43%. For all enzyme treatments, RS content of starch samples decreased further after SSF.     

Effect of Microwave Irradiation on Acid Hydrolysis of Faba Bean Starch: Physicochemical Changes of the Starch Granules

Starch is the most abundant carbohydrate in legumes (22–45 g/100 g), with distinctive properties such as high amylose and resistant starch content, longer branch chains of amylopectin, and a C-type pattern arrangement in the granules. The present study concentrated on the investigation of hydrolyzed faba bean starch using acid, assisted by microwave energy, to obtain a possible food-grade coating material. For evaluation, the physicochemical, morphological, pasting, and structural properties were analyzed. Hydrolyzed starches developed by microwave energy in an acid medium had low viscosity, high solubility indexes, diverse amylose contents, resistant starch, and desirable thermal and structural properties to be used as a coating material. The severe conditions (moisture, 40%; pure hydrochloric acid, 4 mL/100 mL; time, 60 s; and power level, 6) of microwave-treated starches resulted in low viscosity values, high amylose content and high solubility, as well as high absorption indexes, and reducing sugars. These hydrolyzed starches have the potential to produce matrices with thermo-protectants to formulate prebiotic/probiotic (symbiotic) combinations and amylose-based inclusion complexes for functional compound delivery. This emergent technology, a dry hydrolysis route, uses much less energy consumption in a shorter reaction time and without effluents to the environment compared to conventional hydrolysis.     

Properties of High-Swelling Native Starch Treated by Heat–Moisture Treatment with Different Holding Times and Iterations

Tapioca and potato starches were used to investigate the effect of heat–moisture treatment (HMT; 95–96 °C, 0–60 min, 1–6 iterations) on gelatinization properties, swelling power (SP), solubility and pasting properties. Tapioca starch had similar content and degree of polymerization of amylose, but a higher amylopectin short/long chain ratio, to potato starch. After HMT, the gelatinization temperature range was narrowed for tapioca starch, but was widened for potato starch. Decreases in SP and solubility were less for tapioca than potato starches, coinciding with a progressive shift to the moderate-swelling pasting profile for tapioca but a drastic change to the restricted-swelling profile for potato. Moreover, decreasing extents of SP and maximum viscosity for HMT tapioca starch were, respectively, in the range of 47–63% and 0–36%, and those of HMT potato starch were 89–92% and 63–94%. These findings indicate that the granule expansion and viscosity change of starch during gelatinization can be tailored stepwise by altering the HMT holding time and iteration.     

Size separations of starch of different botanical origin studied by asymmetrical-flow field-flow fractionation and multiangle light scattering

Asymmetrical-flow field-flow fractionation combined with multiangle light scattering and refractive index detection has been revealed to be a powerful tool for starch characterization. It is based on size separation according to the hydrodynamic diameter of the starch components. Starch from a wide range of different botanical sources were studied, including normal starch and high-amylose and high-amylopectin starch. The starch was dissolved by heat treatment at elevated pressure in a laboratory autoclave. This gave clear solutions with no granular residues. Amylose retrogradation was prevented by using freshly dissolved samples. Programmed cross flow starting at 1.0 mL min(-1) and decreasing exponentially with a half-life of 4 min was utilised. The starches showed two size populations representing mainly amylose and mainly amylopectin with an overlapping region where amylose and amylopectin were possibly co-eluted. Most of the first population had molar masses below 10(6) g mol(-1), and most of the second size population had molar masses above 10(7) g mol(-1). Large differences were found in the relative amounts of the two populations, the molar mass, and hydrodynamic diameters, depending on the plant source and its varieties.     

Isothermal microcalorimetric studies on starch retrogradation

In the present study, isothermal microcalorimetry was introduced as a tool to investigate properties of starch retrogradation during the first 24 h. The study was made on purified amylose and amylopectin from corn, as well as on native starches, such as wheat, potato, maize, waxy maize and amylomaize, differing in their amylose content. The results were obtained in the form ofP-t traces (thermal powervs. time), and integration of these traces gave a net exothermic enthalpy of reaction, caused by the crystallization of amylose and amylopectin. TheP-t traces reflected the quantities of amylose and amylopectin in the starch studied. Depending on the amylose content and the botanical source of the starch, the rate of crystallization of amylose was high and predominated over that of amylopectin during the first 5–10 h. The contribution from amylose crystallization to the measured exothermic enthalpy was very substantial during this period. After 10 h, amylose crystallized at a lower constant rate. During the first 24 h, amylopectin crystallized at a low steady rate. The exothermic enthalpies obtained by the isothermal microcalorimetric investigations during the first 24 h of retrogradation were generally low in relation to the endothermic melting enthalpies observed by differential scanning calorimetry (DSC) measurements after 24 h of storage. The discrepancies in enthalpy values between the two methods are discussed in relation to phase separation and the endothermic effects owing to the decrease in polymer-water interactions when polymer-rich regions in the starch gel separate. Besides the exothermic enthalpies obtained, theP-t traces also made it possible to study the initial gelation properties of amylose from different botanical sources. The present study further demonstrated that isothermal microcalorimetry can provide a possible way to investigate the antistaling effect of certain polar lipids, such as sodium dodecylsulphate (SDS) and 1-monolauroyl-rac-glycerol (GML), when added to starches of different botanical origin. The net exothermic heat of reaction for starch retrogradation during the first 24 h was decreased when GML or SDS was added to the starch gels. The recordedP-t traces also showed how the effect of the added lipid influenced different periods during the first 24 h of starch retrogradation, and that the effect depended mainly on the amylose content, the botanical source of the starch, and the type of lipid used. When GML or SDS was added to waxy maize, the isothermal microcalorimetric studies clearly indicated some interaction between amylopectin and the polar lipids. These results concerning the action of anti-staling agents are further discussed in relation to the helical inclusion complexes formed between amylose-polar lipid and amylopectin-polar lipid.The authors thank Eva Qvarnström at the Dept. of Thermochemistry and Eva Tjerneld at the Dept. of Food Technology for valuable practical assistance. Financial support was obtained from the Swedish Council for Forestry and Agricultural Research (SJFR) and the Swedish Farmer's Foundation for Agricultural Research (Stiftelsen Lantbruksforskning).