Change of granular and molecular structures of waxy maize and potato starches after treated in alcohols with or without hydrochloric acid

Starches from waxy maize and potato were treated in methanol and 2-propanol either with or without 0.36% hydrochloric acid at 65 °C for 1 h. The granule morphology, molecular structure and pasting properties of the starches were determined and the effects of treatments on the granule and molecular structures of starch were investigated. Starch treated in alcohols without acid showed loss of native order through the hilum of granules, and no obvious molecular degradation was found. However, acid–alcohol treated starch showed many cracks inside granules, and both waxy maize and potato starches showed obvious molecular degradation after treated. Furthermore, the amylose chains and long chains of amylopectin of starch were more easily degraded with acid–alcohol treatment. The pasting viscosity of acid–alcohol treated starches were also obviously less than that of their counterpart native starch and starch after alcohol treatment. The extent of degradation of molecules and the decrease of pasting viscosity on potato starch after acid–alcohol treated were more obvious than that of waxy maize starch. The result indicates that the degradation preferentially occur in the amorphous region when starch treated by acid–alcohol, and the degradation of starch molecules enhances the amorphous excretion and the occurrence of cracks inside the granules.     

Effect of heat–moisture treatment on the structure and physicochemical properties of tuber and root starches

Starch from tubers potato (Solanum tuberosum), taro (Alocassia indica), new cocoyam (Xanthosoma sagitifolium), true yam (Dioscorea alata), and root cassava, (Manihot esculenta) crops was isolated and its morphology, composition and physicochemical properties were investigated before and after heat–moisture treatment (HMT) (100 °C, for 10 h at a moisture content of 30%). Native starch granules were round to oval to polygonal with smooth surfaces. The granule size (diameter) ranged from 3.0 to 110 μm.The total amylose content ranged from 22.4 to 29.3%, of which 10.1–15.5% was complexed by native lipid. The phosphorus content ranged from 0.01 to 0.1%. The X-ray pattern of potato and true yam was of the ‘B’-type. Whereas, that of new cocoyam and taro was of the ‘A’-type. Cassava exhibited a mixed ‘A+B’-type X-ray pattern. The relative crystallinity, swelling factor (SF), amylose leaching (AML), gelatinization temperature range and the enthalpy of gelatinization of the native starches ranged from 30 to 46, 22 to 54, 5 to 23%, 13 to 19 °C and 12 to 18 J/g, respectively. Susceptibility of native starches towards hydrolysis by 2.2N HCl and porcine pancreatic -amylase were 60–86% (after 12 days), and 4–62% (after 72 h), respectively. Retrogradation was most pronounced in the B-type starches. Granule morphology remained unchanged after HMT. The X-ray pattern of the B-type starches was altered (B→A+B) on HMT. However, that of the other starches remained unchanged. HMT decreased SF, AML, gelatinization enthalpy and susceptibility towards acid hydrolysis, but increased gelatinization temperatures and enzyme susceptibility. Extent of retrogradation and relative crystallinity decreased on HMT of true yam and potato starches, but remained unchanged in the other starches. The foregoing data showed that changes in physicochemical properties on HMT are influenced by the interplay of crystallite disruption, starch chain associations and disruption of double helices in the amorphous regions.     

Comparison of potato amylopectin starches and potato starches — influence of year and variety

Starches from three potato varieties and their respective transformants producing amylopectin starch were studied over a period of 3 years. The gelatinisation, swelling and dispersion properties were studied using differential scanning calorimetry (DSC), X-ray diffraction, swelling capacity measurements and a Brabender Viscograph.

The potato amylopectin starches (PAP) exhibited higher endothermic temperatures as well as higher enthalpies than the normal potato starches (NPS). PAP samples gave rise to an exceptionally sharp viscosity peak during gelatinisation and a relatively low increase in viscosity on cooling. Swelling capacity measurements showed that PAP granules swelled more rapidly, and that the dispersion of the swollen granules occurred at a lower temperature (85°C). Analysis of variance (ANOVA) also revealed that the year influenced the DSC results, and that both year and variety affect some of the Brabender parameters. Furthermore, the PAP and NPS samples were subjected to heat–moisture treatment at three different moisture levels, and the Brabender viscosity properties were studied.     

Internal structure and physicochemical properties of corn starches as revealed by chemical surface gelatinization

The organization of amylose and amylopectin within starch granules is still not well elucidated. This study investigates the radial distribution of amylose and amylopectin in different corn starches varying in amylose content (waxy corn starch (WC), common corn starch (CC), and 50% and 70% amylose corn starches (AMC)). Corn starches were surface gelatinized by 13 M LiCl at room temperature to different extents (approximately 10%, 20%, 30%, and 40%). The gelatinized surface starch and remaining granules were characterized for amylose content, amylopectin chain-length distribution, thermal properties, swelling power (SP), and water solubility index (WSI). Except for the outmost 10% layer, the amylose content in CC increased slightly with increasing surface removal. In contrast, amylose was more concentrated at the periphery than at the core for 50% and 70% AMC. The proportion of amylopectin A chains generally decreased while that of B1 chains generally increased with increasing surface removal for all corn starches. The gelatinization enthalpy usually decreased, except for 70% AMC, whereas the retrogradation enthalpy relatively remained unchanged for CC but increased for WC, 50% and 70% AMC with increasing surface removal. The SP and WSI increased with increasing surface removal for all corn starches, with WC showing a significant increase in SP after the removal of the outmost 10% layer. The results of this study indicated that there were similarities and differences in the distribution of amylose and amylopectin chains along the radial location of corn starch granules with varying amylose contents. More amylose-lipid complex and amylopectin long chains were present at the periphery than at the core for amylose-containing corn starches.     

Granule size affects the acetyl substitution on amylopectin populations in potato and sweet potato starches

Specific enzymatic degradation in combination with chromatographic and spectrometric techniques was used to understand acetyl group distribution over the amylopectin populations of differently sized granule fractions from potato and sweet potato starches. The hydrolysates obtained after -amylase, ß-amylase, pullulanase, and the combination of pullulanase, -amylase and amyloglucosidase treatment were investigated by high-performance size-exclusion chromatography (HPSEC), high-performance anion-exchange chromatography (HPAEC) and Maldi-Tof-MS (Matrix-Assisted Laser Desorption/Ionisation Time-Of-Flight Mass Spectrometry). The acetyl groups were found to be located near the branching point, in the external chain and in the internal chain regions. The acetyl group distributions were different for amylopectin from different granule size fractions. Higher DP (degree of polymerization) fragments were present in the digests of acetylated amylopectin populations of the small size granule starches. Our studies confirmed that acetyl groups were unevenly distributed over the amylopectin populations.     

Effects of protein on crosslinking of normal maize, waxy maize, and potato starches

Channels of maize starch granules are lined with proteins and phospholipids. Therefore, when they are treated with reagents that react at or near the surfaces of channels, three types of crosslinks could be produced: protein–protein, protein–starch, starch–starch. To determine which of these may be occurring and the effect(s) of channel proteins (and their removal) on crosslinking, normal and waxy maize starches were treated with a proteinase (thermolysin, which is known to remove protein from channels) before and after crosslinking, and the properties of the products were compared to those of a control (crosslinking without proteinase treatment). After establishing that treatment of starch with thermolysin alone had no effect on the RVA trace, three reaction sequences were used: crosslinking alone (CL), proteinase treatment before crosslinking (Enz-CL), proteinase treatment after crosslinking (CL-Enz). Two crosslinking reagents were used: phosphoryl chloride (POCl₃), which is known to react at or near channel surfaces; STMP, which is believed to react throughout the granule matrix. Three concentrations of POCl₃ (based on the weight of starch) were used. For both normal maize starch (NMS) and waxy maize starch (WMS) reacted with POCl₃, the trends were generally the same, with apparent relative degrees of crosslinking indicated to be CL-Enz = CL > Enz-CL, but the effects were greater with NMS and there were differences when different concentrations of reagent were used. The basic trends were the same when potato starch was used in the same experiments. Crosslinking with STMP was done both in the presence and the absence of sodium sulfate (SS). Both with and without SS and with both NMS and WMS, the order of indicated crosslinking was generally the same as found after reaction with POCl₃, with the indicated swelling inhibition being greater when SS was present in the reaction mixture. Examination of the maize starches with a protein stain indicated that channel protein was removed by treatment with thermolysin when the proteinase treatment occurred before crosslinking with either POCl₃ or STMP, but only incompletely or not at all if the treatment with the proteinase occurred after crosslinking. Because the crosslinking reactions were less effective when the protein was removed, the results are tentatively interpreted as indicating that they involved protein molecules, although there may not be a direct relationship.     

Effects of structure and modification on sustained release properties of starches

Starches of different sources and compositions were investigated to determine the effect of structure and chemical modification on the sustained release properties of the resultant modified starches. Starches were cross-linked with epichlorohydrin and substituted with carboxymethyl or aminoethyl groups at different levels. Substitution efficiency was overall higher for waxy corn and potato starches than for Hylon VII, and was higher for starches at low cross-linking levels than those at high cross-linking ones. Waxy corn starch displayed better sustained release properties when cross-linked to a lower level, whereas Hylon VII showed better performances when cross-linked to a higher level. Matrices substituted with carboxymethyl and aminoethyl groups at the high level showed better sustained release properties than those substituted at the low level. The proportion and structure of amylose and amylopectin in starches from different botanical sources strongly influenced the level of modification required to produce a satisfactory sustained release matrix.     

Effect of microwave radiation on physico-chemical properties and structure of potato and tapioca starches

The time-temperature profiles of selected starch-water systems subjected to microwave processing were established and the effect of microwave radiation on the physico-chemical properties and structure of potato and tapioca starches was studied. The experimental starch samples were examined by the Brabender rheological method, light microscopy, scanning electron microscopy and X-ray diffractometry. Microwave radiation was evidenced to affect the temperature and moisture contents of the experimental starches, with a strong correlation between the moisture content and the rate of temperature rise. An isothermal transformation was revealed with the samples of moisture contents over 20%, causing a rise in the gelatinisation temperature of the starch and a drop in its solubility in water. The most pronounced change was observed in the case of potato starch: its crystal structure changed from type B to type A. The tapioca starch underwent similar but less marked changes.     

Solid state NMR studies on the structural and conformational properties of natural maize starches

Natural maize starches having a range of amylose contents have been characterised by CP/MAS NMR spectroscopy. Chemical shifts, relative resonance intensities, line-widths and spectral shapes were compared at different moisture contents. At 10% moisture content, these parameters showed few significant differences across a range of apparent amylose levels from 0 to 84%. After hydration of the granules to ≈30% moisture, it was found that the amylose content significantly affected the relative signal intensities and line-widths especially of C-1 and C-4 resonances. Narrower line-widths after hydration were attributed to (i) an increased degree of crystallinity, and (ii) disappearance of the signals of amorphous material which, on becoming more mobile, became invisible to the CP/MAS experiment. The enhanced resolution at higher moisture levels revealed signals which were assigned to the amylose–lipid complex, i.e. V-type amylose. The amount of V-amylose detected by NMR increased with both amylose content and lipid content of the granule. Prolonged treatment of the granules with iodine vapour significantly increased the amount of V-type amylose in the high amylose samples, but caused a decrease in their degree of crystallinity. Waxy-maize starch was barely affected by iodination. The results provide evidence that amylose tends to disrupt the structural order within amylopectin crystallities. This effect is enhanced by the formation of the amylose–iodine complex, indicating that V-amylose could be a major crystallite-disrupting agent in native starch granules.     

A simple and rapid method for evaluation of Mark–Houwink–Sakurada constants of linear random coil polysaccharides using molecular weight and intrinsic viscosity determined by high performance size exclusion chromatography: application to guar galactomannan

A rapid method for establishing the constants in the Mark–Houwink–Sakurada equation, relating intrinsic viscosity and molecular weight (MW), of guar galactomannan is described. Following partial acid hydrolysis, the galactomannan was analyzed using high performance size exclusion chromatography employing viscosimetry and right angle light scattering detectors. In this way, a large number of samples of polysaccharides with a wide range of MW distributions were prepared, without need for isolation, and intrinsic viscosity and MW rapidly determined. The a and K values found for guar galactomannan were 0.72 and 5.13×10⁻⁴ ([η] in dl/g) respectively, in good agreement with previously published values.     

Effect of sorbitol addition on the physicochemical characteristics of starch–fatty acid systems

Aqueous maize starch dispersions (20%) were heated at 100 °C, in the presence of myristic, palmitic or stearic acid potassium salts as well as of sorbitol added at concentrations up to 60% (dry starch). Flow behaviour measurements at 100 °C indicated that interactions took place between the starch–fatty acid systems and sorbitol resulting in viscosity increase which was more pronounced as the sorbitol content increased. Water solubility measurements showed that a major part of sorbitol was easily extracted by excess water whereas sorption experiments revealed that the moisture uptake rate was proportional to sorbitol content of the starch systems examined. Thermomechanical studies indicated that the starch–fatty acid samples containing sorbitol up to 40% exhibited antiplasticizing behaviour. Scanning electron microscopy studies revealed that at sorbitol concentrations over 30%, free sorbitol crystals were formed on the surface of starch–fatty acid samples, whereas the percentage crystallinity as well as the crystallite size of samples were proportional to sorbitol content.     

Influence of growth temperature on the structure and thermodynamic parameters of barley starches

Barley starches grown at different temperatures were investigated using high sensitivity differential scanning microcalorimetry and X-ray diffraction. By applying physico-chemical approaches, thickness of crystalline lamellae, thermodynamic and structural characteristics (such as gelatinisation) of cooperative units and parameters characterising thermodynamic properties of crystal surfaces were determined. It was established that a difference of growth temperature experienced by plants during development does not lead to changes in the thickness of amylopectin crystalline lamellae and hence constituent double helix length. The role of defects in structural organisation of native barley starches is discussed. It is suggested that not all fatty acids necessarily form crystalline inclusion complexes.     

Studies on tuber starches III. Impact of annealing on the molecular structure,composition and physicochemical properties of yam (Dioscorea sp.) starches grown in Sri Lanka

This study reports the impact of one step annealing on the composition, molecular structure, granule morphology and physicochemical properties of starches isolated from cultivars of Dioscorea esculenta (kukulala, java-ala-nattala) and Dioscorea alata (hingurala, raja-ala), yam tubers grown in Sri Lanka. In all starches, granule morphology (shape, size, surface appearance), birefringence patterns, acid hydrolysis profile and X-ray patterns remained unchanged on annealing. Crystallinity remained unchanged on annealing in hingurala, kukulala and java-ala. However, crystallinity of raja-ala and nattala increased and decreased, respectively, on annealing. In all starches, annealing decreased the gelatinization temperature range (kukulala ～ hingurala > nattala ～ raja-ala > java-ala), amylose leaching (raja-ala > nattala > hingurala > kukulala > java-ala), granular swelling (raja-ala ～ hingurala > kukulala > java-ala > nattala), peak viscosity (raja-ala > hingurala > kukulala > java-ala > nattala), enthalpy of retrogradation (kukulala ～ java-ala ～ nattala ～ hingurala ～ raja-ala) and susceptibility towards acid hydrolysis (java-ala > raja-ala > hingurala ～ nattala > kukulala). However, annealing increased gelatinization temperatures (kukulala ～ java-ala ～ nattala ～ raja-ala ～ hingurala) and the enthalpy of gelatinization (kukulala > hingurala > java-ala > nattala > raja-ala). Set-back viscosity increased in nattala, but decreased in the other starches (raja-ala > hingurala > kukulala > java-ala) on annealing. The study showed that the different responses shown by the cultivars of the Dioscorea starches towards annealing were to a large extent influenced by their composition and molecular structure.     

Yield stress components of waxy corn starch–xanthan mixtures: Effect of xanthan concentration and different starches

Yield stress of 6% (w/w) waxy maize (WXM), cross-linked waxy maize (CLWM), and cold water swelling (CWS) starches in xanthan gum dispersions: 0%, 0.35%, 0.50%, 0.70%, and 1.0% was measured with the vane method at an apparent shear rate of 0.05 s⁻¹. The intrinsic viscosity of the xanthan gum was determined to be: 112.3 dL/g in distilled water at 25 °C. Values of the static (σ_0s) and dynamic (σ_0d) yield stress of each dispersion were measured before and after breaking down its structure under continuous shear, respectively. The WXM and CWS starches exhibited synergistic behavior, whereas the CLWM starch showed antagonistic effect with xanthan gum. The difference (σ_0s − σ_0d) was the stress required to break the inter-particle bonding (σ_b). The contributions of the viscous (σ_v) and network (σ_n) components were estimated from an energy balance model. In general, values of σ_b of the starch–xanthan gum dispersions decreased and those of σ_n increased with increase in xanthan gum concentration.     

Effect of hexafluoroisopropanol alcohol on the structure of melittin: a molecular dynamics simulation study

The molecular mechanism by which HFIP stabilizes the alpha-helical structure of peptides is not well understood. In the present study, we use melittin as a model to gain insight into the details of the atomistic interactions of HFIP with the peptide. We have performed extensive comparative molecular dynamics simulations (up to 100 nsec) in the absence and in the presence of HFIP. In agreement with recent NMR experiments, the simulations show rapid loss of tertiary structure in water at pH 2 but much higher helicity in 35% HFIP. The MD simulations also indicate that melittin adopts a highly dynamic global structure in 35% HFIP solution with two alpha-helical segments sampling a wide range of angular orientations. The analysis of the HFIP distribution shows the tendency of HFIP to aggregate around the peptide, increasing the local cosolvent concentration to more than two times that in the bulk concentration. The correlation of local peptide structure with HFIP coating suggests that displacement of water at the peptide surface is the main contribution of HFIP in stabilizing the secondary structure of melittin. Finally, a stabilizing effect promoted by the presence of counter-ions was also observed in the simulations.     

Effect of high hydrostatic pressure on the formation of radicals in maize starches with different amylose content

Native and high pressure-treated (water suspensions, 650 MPa) waxy maize starch, containing mainly amylopectin, and Hylon VII, rich in amylose, were studied for their ability to generate free radicals upon thermal treatment at 180–230 °C. The electron paramagnetic resonance (EPR) spectroscopy was used to characterize the nature, number and stability of radicals. Various stable and short living (stabilized by N-tert-butyl-α-phenylnitrone (PBN) spin trap) radical species were formed. It was found, that at given conditions the waxy maize starch reveals higher ability to generate radicals, than Hylon VII. The presence of water and high pressure pretreatment of starches, both resulted in the reduction of the amount of thermally generated radicals. The decrease in crystallinity of waxy maize starch and of Hylon VII, occurring upon high pressure treatment, leads to the increase of the relative amount of fast rotating component in the EPR spectrum of both types of starches.     

The influence of alterations in ADP-glucose pyrophosphorylase activities on starch structure and composition in potato tubers

In order to examine whether alterations in the supply of precursor molecules into the starch biosynthetic pathway affected various characteristics of the starch, starch was isolated from potato (Solanum tuberosum L.) tubers containing reduced amounts of the enzyme ADP-glucose pyrophosphorylase (AGPase). It was found that although the type of crystalline polymorph in the starch was not altered, the amylose content was severely reduced. In addition, amylopectin from the transgenic plants accumulated more relatively short chains than that from control plants and the sizes of starch granules were reduced. The starch granules from the transgenic plants contained a greater amount of granule-bound starch synthase enzyme, which led to an increase in the maximum activity of the enzyme per unit starch tested. The K _m for ADP-glucose was, at most, only slightly altered in the transgenic lines. Potato plants containing reduced AGPase activity were also transformed with a bacterial gene coding for AGPase to test whether this enzyme can incorporate phosphate monoesters into amylopectin. A slight increase in phosphate contents in the starch in comparison with the untransformed control was found, but not in comparison with starch from the line with reduced AGPase activity into which the bacterial gene was transformed. Received: 2 February 1999 / Accepted: 25 March 1999     

Molecular weight characterization of high molecular weight dextran with multiangle light scattering in on‐line and off‐line mode

This work reports the molecular weight (MW) analysis of high MW dextran using multiangle light scattering (MALS) in both chromatography and automated batch measurement mode. The results show that the chromatographic columns alter the high MW native dextran and cause underestimation of the MW as a consequence. Alternatively, a batch MALS measurement (without columns) provides more accurate MW values. The batch MALS measurement was automated with the incorporation of an automatic sample dilution and injection device. This automation reduces the sample preparation time and minimizes concentration errors introduced by manual sample dilution. To the best of our knowledge, this is the first study using an automated batch MALS in the analysis of high MW dextran. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 387–392, 2015.