Cationic starch: an effective flocculating agent

A series of cationic starches (Cat St) have been developed by incorporating a cationic moiety N-(3-Chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC) onto the backbone of starch in presence of NaOH. The cationic starches are characterized by elemental analysis, FTIR spectroscopy and intrinsic viscosity measurement. The flocculation characteristics of these starches have been evaluated in 0.25 wt% silica suspension by jar test. It has been found that among the four cationic starches, the one with longer CHPTAC chains shows the best performance. The flocculation characteristics of this starch are on silica suspensions compared with various commercially available flocculants.     

Extraction of starches from tuber crops using ammonia

Ammonia solution (0·03 ) was used to extract starch from various tuber crops by the conventional settling method. It was found that there was noticeable improvement in the yield of starch from Colocasia (6–16%), while it fell for sweet potato starch and remained almost the same for the other starches. The various properties of starch, thus extracted, were compared with those for starch obtained by water extraction. It was found that total amylose of all starches were unaffected while the ‘soluble amylose’ was slightly suppressed for Colocasia starch extracted with ammonia solution. Peak viscosity was found to be increased to a large extent for Colocasia and Dioscorea esculenta starches by ammonia extraction, while it was lowered for sweet potato starch. The swelling volume of Colocasia starch extracted with ammonia was similarly enhanced by 25%, but the Dioscorea esculenta starch did not show such a tendency. Sweet Potato starch suffered a reduction in swelling volume. Phosphorus content was found to be independent of the extraction medium.     

Post functionalization of carboxymethylated starch and acrylonitrile based networks through amidoximation for use as ion sorbents

Carboxymethylation of starch provided carboxymethyl starch (CMS) and the modification was followed by grafting CMS with acrylonitrile (AN) using ammonium per sulphate-N,N,N,N-tetramethylethylene diamine as initiator–accelerator system. Crosslinked networks of CMS and AN were obtained using two crosslinkers, viz., N,N-methylenebisacrylamide and ethyleneglycoldimethacrylate. The networks were further reacted with hydroxylamine to generate metal ion active amidoxime groups. The synthesized hydrogels were characterized by FTIR, SEM, nitrogen analysis and swelling studies to evaluate water uptake and the candidate polymers were used as matrices for the sorption of Fe²⁺ ions, as a model metal ion, as a function of time, temperature, pH and ionic strength. An attempt was made to investigate the thermodynamics of its sorption behaviour.     

Process optimization for the synthesis of octenyl succinyl derivative of waxy corn and amaranth starches

Modification of starch by dicarboxylic acid anhydrides to starch esters, containing both hydrophilic and hydrophobic groups are known to improve its emulsification properties, and can also be used for encapsulation after hydrolysis. Reports on the effect of process conditions on the extent of modification of starches by using n-octenyl succinic anhydride (n-OSA) are not readily available. In the present study, the process of manufacturing of OSA starches from waxy corn and amaranth starch were studied with respect to the OSA/starch ratio, pH, temperature and time of the reaction. The effects of these parameters were evaluated on the basis of degree of substitution (DS). The concluding conditions for amaranth-OSA starches was a reaction time of 6 h at 3% OSA/starch ratio at 30 °C and pH 8.0 at 25% starch concentration. For waxy corn-OSA starch, all parameters were identical except for the reaction time of 24 h. The maximum DS achieved for both the starches was 0.02. Emulsification capacity and oil absorption capacity of the OSA-modified starches were more or less similar within the parameter chosen and also independent of starch type.     

Physicochemical characteristics and fine structure of high-amylose wheat starches isolated from Australian wheat cultivars

High-amylose starch is a source of resistant starch (RS) which have great impact on human health like dietary fiber. Nowadays, high-amylose wheat has been produced by genetic backcrossing, which enhances apparent amylose content and generates altered amylopectin. In this study, the high-amylose wheat starches isolated from various high-amylose wheat cultivars grown in Australia were characterized for understanding their physicochemical properties and fine structure of starch. The physicochemical characteristics of the high-amylose wheat starches are significantly different among the cultivars. Amylose contents of these cultivars were in a range of 28.0–36.9%, which is significantly higher than that of the normal wheat starch (25.6%). The high-amylose wheat starches also had higher blue value but lower λ_max than the normal wheat starch. Gelatinization temperature of the high-amylose wheat starches is higher than that of the normal wheat starch but transition enthalpy is lower. X-ray diffraction showed that the high-amylose wheat starch had C-type crystals close to A-type crystal. Pasting properties of the high-amylose wheat starches were varying depending on the cultivars. However, almost high-amylose wheat starches had lower peak and final viscosities and higher setback viscosity than did the normal wheat starch. Fine structure of amylose and amylopectin was different among the high-amylose wheat cultivars and related to the physicochemical properties of starch. These results help to understand well the characteristics of the high-amylose wheat starches before application for food processing.     

Structural studies of starches with different water contents

The proportion of double helices in starches from a series of pea [rb, rug4-b, rug3-a, and lam-c mutants, and the wild type (WT) parental line], potato and maize (normal and low amylose), and wheat (normal) lines, ranged from about 30-50% on a dry weight basis. In relatively dry starch powders, only about half of the double helices were in crystalline order, this proportion being higher for A-type than for B-type starches. Using starch from WT pea as an example, it was found that increasing water content results in an increase in total crystallinity. When the water content was raised to a level similar to that in excess water, the proportion of crystallinity was close to the proportion of double helices (DH). Measuring crystallinity in starches with a high water content is difficult using traditional methods such as x-ray diffraction. A method was developed, therefore, for determining starch structural characteristics in excess water by measuring the enthalpy of gelatinization transition in quasi-equilibrium differential scanning calorimetry (DSC) experiments. It is suggested that DH% = DeltaH(sp)/DeltaH(DH) x 100%, where DeltaH(sp) and DeltaH(DH) represent the specific enthalpies of gelatinisation transition, DeltaH(sp) being measured as J/g dry starch weight and DeltaH(DH) as J/g DH, in starch. Studies on potato and maize starches in excess water and in 0.6M KCl showed, respectively, that DeltaH(DH) was 36.3 and 35.6 J/g for B-type polymorphs and 33.0 and 35.0 J/g for A-type polymorphs. For C-type starches, such as those from pea, intermediate values of DeltaH(DH), related to the proportions A-/B-polymorphs, should be used. The type of crystallinity in starch can be determined by the shift in peak temperature for thermograms in excess water and in excess 0.6M KCl. For B-polymorphs this shift was found to be approximately 2-3 degrees C and for A-polymorphs approximately 7-12 degrees C. The ratio between ordered areas with both A- and B-polymorphs can be determined from the enthalpies of disruption of each area. These enthalpies can be obtained by deconvolution of bimodal thermograms produced by C-type starches in excess 0.6M KCl. This methodical approach can be applied to all starches that give a sharp gelatinisation thermogram in excess water. Using a range of methods, including DSC, it was found that starch granules from the mutant peas are constructed in a similar way to those from the WT, with B-polymorphs in the centre and A-polymorphs at the periphery of all granules. The proportion of A/B-polymorphs, however, differed between the mutants. It was found that in addition to increasing the total crystallinity, increasing the water content within the granules also resulted in an increase in the proportion of B-polymorphs.     

Development of waxy cassava with different Biological and physico-chemical characteristics of starches for industrial applications

The quality of cassava starch, an important trait in cassava breeding programs, determines its applications in various industries. For example, development of waxy (having a low level of amylose) cassava is in demand. Amylose is synthesized by granule-bound starch synthase I (GBSSI) in plants, and therefore, down-regulation of GBSSI expression in cassava might lead to reduced amylose content. We produced 63 transgenic cassava plant lines that express hair-pin dsRNAs homologous to the cassava GBSSI conserved region under the control of the vascular-specific promoter p54/1.0 from cassava (p54/1.0::GBSSI-RNAi) or cauliflower mosaic virus (CaMV) 35S (35S::GBSSI-RNAi). After the screening storage roots and starch granules from field-grown plants with iodine staining, the waxy phenotype was discovered: p54/1.0::GBSSI-RNAi line A8 and 35S::GBSSI-RNAi lines B9, B10, and B23. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that there was no detectable GBSSI protein in the starch granules of plants with the waxy phenotype. Further, the amylose content of transgenic starches was significantly reduced (<5%) compared with the level in starch granules from the wild-type (about 25%). The inner structure of the waxy starch granules differed from that of the untransformed ones, as revealed by transmission electron microscopy analysis as well as morphological changes in the iodine-starch complex. Endothermic enthalpy was reduced in waxy cassava starches, according to differential scanning calorimeter analysis. Except B9, all waxy starches displayed the A-type X-ray diffraction pattern. Amylogram patterns of the waxy cassava starches were analyzed using a rapid viscosity analyzer and found to have increased values for clarity, peak viscosity, gel breakdown, and swelling index. Setback, consistency, and solubility were notably reduced. Therefore, waxy cassava with novel starch in its storage roots was produced using the biotechnological approach, promoting its industrial utilization.     

Effect of acid–alcohol treatment on the molecular structure and physicochemical properties of maize and potato starches

The molecular structure and physicochemical properties of acid–alcohol treated maize and potato starches (0.36% HCl in methanol at 25 °C for 1–15 days) were investigated. The yields of the modified starches were ranging from 91 to 100%. The average granule size of modified starches decreased slightly. The solubility of starches increased with the increase of treatment time, and the pasting properties confirmed the high solubility of modified starches. The gelatinization temperatures and range of gelatinization increased with the increase of treatment time except T_o (onset temperature) of maize starch. Molecular structures of modified starches suggested the degradation of starches occurred mostly within the first 5 days of treatment, and degradation rate of potato starch was higher than maize starch both in amylopectin and in amylose. Maize starch was found less susceptible to acid–alcohol degradation than potato starch.     

Physico-chemical and morphological characteristics of New Zealand Taewa (Maori potato) starches

The physico-chemical, morphological, thermal, pasting, textural, and retrogradation properties of the starches isolated from four traditional Taewa (Maori potato) cultivars (Karuparera, Tutaekuri, Huakaroro, Moemoe) of New Zealand were studied and compared with starch properties of a modern potato cultivar (Nadine). The relationships between the different starch characteristics were quantified using Pearson correlation and principal component analysis. Significant differences were observed among physico-chemical properties such as phosphorus content, amylose content, swelling power, solubility and light transmittance of starches from the different potato cultivars. The starch granule morphology (size and shape) for all the potato cultivars showed considerable variation when studied by scanning electron microscopy and particle size analysis. Starch granules from Nadine and Moemoe cultivars showed the presence of large and irregular or cuboid granules in fairly high number compared with the starches from the other cultivars. The transition temperatures (T_o; T_p; T_c) and the enthalpies (ΔH_gel) associated with gelatinization suggested differences in the stability of the crystalline structures among these potato starches. The Moemoe starch showed the lowest T_o, while it was higher for Tutaekuri and Karuparera starches. Pasting properties such as peak, final and breakdown viscosity and texture profile analysis (TPA) parameters of starch gels such as hardness and fracturability were found to be higher for Nadine and Huakaroro starches. The Nadine and Huakaroro starch gels also had lower tendency towards retrogradation as evidenced by their lower syneresis (%) during storage at 4 °C. Principal component analysis showed that the Tutaekuri and Nadine cultivars differed to the greatest degree in terms of the properties of their starches.     

Photoelectron spectroscopic studies of cellulose, starch and their oxidation products, in powdered form

The use of X-ray photoelectron spectroscopic techniques (XPS or ESCA) in the characterization of cellulose, starch and their oxidation products is discussed. The ESCA results obtained from these materials in the finely powdered state are presented and compared to the results obtained with celluloses in the fibrous form. A far greater amount of surface impurities were found to be present for the powdered polysaccharides due to their greater surface area. Also, it has been shown that a high full-width at half-maximum (f.w.h.m.) value for the C_1s signal is obtained with 100% periodate oxidized maize starch, while a smaller value was found for 11% periodate oxidized cellulose powder. Finally, cellulosic powders seem to produce the O_1s signal 0·8 eV downfield (i.e. higher binding energy value) as compared to the starches and this may be related to the rigid, crystalline and linear structure of the cellulose molecule as compared to the more amorphous and branched structure of the starches.     

Understanding and influencing starch biochemistry

Starch is one of the most important products synthesized by plants that is used in industrial processes. If it were possible to increase production or modify starches in vivo, using combinations or either genetically altered or mutant plants, it may make them cheaper for use by industry, or open up new markets for the modified starches. The conversion of sucrose to starch in storage organs is, therefore, discussed. In particular the roles of the different enzymes directly involved in synthesizing the starch molecules on altering starch structure are reviewed, as well as the different models for the production of the fine structure of amylopectin. In addition, the process of starch phosphorylation, which is also important in determining the physical properties of starches, is reviewed. It is hoped that detailed knowledge of these processes will lead to the rational design of tailored starches. Starch degradation is also an important process, for example, in the cold-sweetening of potato tubers, but outside of cereal endosperm little is known about the processes involved. The enzymes thought to be involved and the evidence for this are discussed.     

Starch biosynthesis: sucrose as a substrate for the synthesis of a highly branched component found in 12 varieties of starches

D-[14C]glucose was incorporated into starch when 12 varieties of starch granules were incubated with [14C]sucrose. Digestion of the 14C-labeled starches with porcine pancreatic alpha amylase showed that a high percentage (16.1-84.1%) of the synthesized starch gave a relatively high molecular weight alpha-limit dextrin. Hydrolysis of the 12 varieties of starch granules by alpha amylase, without sucrose treatment, also gave an alpha-limit dextrin, ranging in amounts from 0.51% (w/w) for amylomaize-7 starch to 8.47% (w/w) for rice starch. These alpha-limit dextrins had relatively high molecular weights, 2.47 kDa for amylomaize-7 starch to 5.75 kDa for waxy maize starch, and a high degree of alpha-(1-->6) branching, ranging from 15.6% for rice starch to 41.1% for shoti starch. ADPGlc and UDPGlc did not synthesize a significant amount (1-2%) of the branched component, suggesting that sucrose is the probable substrate for the in vivo synthesis of the component and that sucrose is not first converted into a nucleotide-glucose diphosphate intermediate.     

Effects of processing high amylose maize starches under controlled conditions on structural organisation and amylase digestibility

The amylase digestibility of high-amylose maize starches has been compared before and after thermo-mechanical processing. Starches were analysed for enzyme-resistant starch yield, apparent amylose content, crystallinity (X-ray diffraction), and molecular order (NMR and FTIR), both before and after treatment with α-amylase. All samples had significant (>10%) enzyme-resistant starch levels irrespective of the type and extent of thermal or enzymic processing. Molecular or crystalline order was not a pre-requisite for enzyme resistance. Near-amorphous forms of high amylose maize starches are likely to undergo recrystallisation during the enzyme-digestion process. The mechanism of enzyme resistance of granular high-amylose starches is found to be qualitatively different to that for processed high-amylose starches. For all samples, measured levels of enzyme resistance are due to the interruption of a slow digestion process, rather than the presence of completely indigestible material.     

Developmental Changes in the Structure of Endosperm Starch of Rice (Oryza sativa L.)

The developmental changes in the structure and properties of endosperm starches were investigated using the near-isogenic lines for wx alleles of rice. The amylose content in nonwaxy starch was increased during the development of rice grains. Because the accumulation of amylose in endosperm stopped earlier than that of amylopectin during development, the percentages of amylose reached a maximum at the 17th day after flowering in nonwaxy endosperm. Since the distributions of the unit-chain length of amylopectin in waxy and nonwaxy starches were unchanged with the development of the grains, these amylopectins would be synthesized in a similar manner through development. The structure and properties of endosperm starches were reconfirmed to be conspicuously affected by the temperature at the early developmental stages of the grain-filling period, namely, they appeared to be characterized by the temperature at which the starch was accumulated in the endosperm.     

Physico-chemical characterisation of sago starch

The physico-chemical characteristics of various sago starch samples from South East Asia were determined and compared to starches from other sources. X-ray diffraction studies showed that all the sago starches exhibited a C-type diffraction pattern. Scanning electron microscopy showed that they consist of oval granules with an average diameter around 30 μm. Proximate composition studies showed that the moisture content in the sago samples varied between 10.6% and 20.0%, ash between 0.06% and 0.43%, crude fat between 0.10% and 0.13%, fiber between 0.26% and 0.32% and crude protein between 0.19% and 0.25%. The amylose content varied between 24% and 31%. The percentage of amylose obtained by colourimetric determination agreed well with the values obtained by fractionation procedures and potentiometric titration. Intrinsic viscosities and weight average molecular weight were determined in 1M KOH. Intrinsic viscosity for amylose from sago starches varied between 310 and 460 ml/g while for amylopectin the values varied between 210 and 250 ml/g. The molecular weight for amylose was found to be in the range of 1.41×10⁶ to 2.23×10⁶ while for amylopectin it was in the range of 6.70×10⁶ to 9.23×10⁶. The gelatinisation temperature for the sago starches studied varied between 69.4°C and 70.1°C. The exponent ‘a’ in the Mark–Houwink equation and the exponent ‘’ in the equation R_g=kM was found to be 0.80 and 0.58, respectively for amylose separated from sago starch and these are indicative of a random coil conformation. Two types of pasting properties were observed. The first was characterised by a maximum consistency immediately followed by sharp decrease in consistency while the second type was characterised by a plateau when the maximum consistency was reached.     

Interpretation of small angle x-ray scattering from starch on the basis of fractals

Using small-angle X-ray scattering, the behaviour of corn and potato starches during gelatinization, swelling, and rétrogradation was investigated. The scattering patterns were analysed on the basis of the fractal concept. The main scattering source from low moisture starches could be interpreted as a ‘surface fractal’ obeying a power law with an exponent of ca —4. When the starch swelled, the surface fractal characteristic was recognised only at very low angles, and on heating it disappeared at ca 80 °C. For gelatinised starches, the whole scattering pattern obeyed the power law with the power around -2.0. This result suggests that the physical arrangement of gelatinised starch molecules is a ‘mass fractal’, i.e. a self-similar structure, in nature. Further, it was found that the scattering of the retrograded starch showed a shoulder like peak superimposed the background scattering representing the mass fractal. The corresponding Bragg spacing was estimated to be 31˜15nm.     

Starch derivatives of high degree of functionalization. 1. Effective, homogeneous synthesis of p-toluenesulfonyl (tosyl) starch with a new functionalization pattern

Pure p-toluenesulfonyl (tosyl) starch with an insignificant formation of chlorodeoxy groups was prepared by reacting starch dissolved in the solvent system N,N-dimethyl acetamide in combination with LiCl. Interestingly, the viscosity of the starch dissolved in the solvent system increases with the increasing amount of LiCl. The tosyl starch samples obtained were characterized by means of elemental analysis, FITR and ¹³C NMR spectroscopy. The degree of substitution (DS_Tos) of the products can be controlled in range from 0.4 to 2.0 by adjusting the molar ratio of tosyl chloride per anhydroglucose unit up to 6.0 mol/mol. The tosyl starch samples are readily soluble in various organic solvents. As revealed by means of ¹³C NMR analysis as well as by analysis of the corresponding 6-iodo-6-deoxy derivatives, a faster tosylation at position 2 than at positions 6 and 3 takes place. The thermal stability of tosyl starch increases with increasing DS_Tos and degradation starts at 166°C for the sample of DS_Tos of 0.61. The remaining OH groups of tosyl starch are reactive and can be additionally modified by acetylation reactions.     

Preparation and characterization of soluble starches having different molecular sizes and composition,by acid hydrolysis in different alcohols

Potato and waxy-maize starches were separately modified for 1 h at 65° with 0.36% hydrochloric acid in methanol, ethanol, 2-propanol, and 1-butanol. All of the modified starches were readily soluble in hot water, to give crystal-clear solutions up to a concentration of at least 20% (w/v). The modified granules were studied by light-microscopy and iodine-iodide staining. All of the modified starches retained their granule appearance, although with various degrees of damage that progressively increased from methanol to 1-butanol. Both hydrolysis and alcoholysis occurred, but to different extents in the different alcohols. The highest proportion of alcoholysis occurred in methanol where 50% of the resulting molecules were glycosides, the lowest in 1-butanol where 6% were glycosides. The number-average molecular weights of the modified starches also progressively decreased from 126,670 for the methanol-modified waxy-maize starch to 4,750 for the 1-butanol-modified potato starch. The methanol- and ethanol-modified potato starches were fractionated into amylose and amylopectin components. The 2-propanol- and 1-butanol-modified potato starches gave only an amylopectin component. The amylose components were characterized by gel-permeation chromatography on Bio-Gel A-5m, and the amylopectin components, on Bio-Gels A-150m and A-0.5m. The molecular sizes of the amylose and amylopectin components progressively decreased from methanol- to 1-butanol-modified starches. Furthermore, the polymodal composition of the amylopectin component was decreased to give a more homogeneous product. Waxy-maize starch was modified in methanol and 2-propanol and gave products that were of lower molecular size and more homogeneous than the polymodal native starch. It is shown that the differential effect of the different alcohols on the modification of the starch granules is produced by effecting different concentrations of acid inside the granule, where hydrolysis occurs in the 10–12% of water contained in the granule. It is postulated that 2-propanol and 1-butanol dissolve the double-helical, crystalline regions in the starch granule to give different types of products under otherwise identical conditions of modification.     

An investigation of the action of porcine pancreatic alpha-amylase on native and gelatinised starches

The action of pancreatic alpha-amylase (EC 3.2.1.1) on various starches has been studied in order to achieve better understanding of how starch structural properties influence enzyme kinetic parameters. Such studies are important in seeking explanations for the wide differences reported in postprandial glycaemic and insulinaemic indices associated with different starchy foodstuffs. Using starches from a number of different sources, in both native and gelatinised forms, as substrates for porcine alpha-amylase, we showed by enzyme kinetic studies that adsorption of amylase to starch is of kinetic importance in the reaction mechanism, so that the relationship between reaction velocity and enzyme concentration [E0] is logarithmic and described by the Freundlich equation. Estimations of catalytic efficiencies were derived from measurements of kcat/Km performed with constant enzyme concentration so that comparisons between different starches were not complicated by the logarithmic relationship between E0 and reaction velocity. Such studies reveal that native starches from normal and waxy rice are slightly better substrates than those from wheat and potato. After gelatinisation at 100 degrees C, kcat/Km values increased by 13-fold (waxy rice) to 239-fold (potato). Phosphate present in potato starch may aid the swelling process during heating of suspensions; this seems to produce a very favourable substrate for the enzyme. Investigation of pre-heat treatment effects on wheat starch shows that the relationship between treatment and kcat/Km is not a simple one. The value of kcat/Km rises to reach a maximum at a pre-treatment temperature of 75 degrees C and then falls sharply if the treatment is conducted at higher temperatures. It is known that amylose is leached from starch granules during heating and dissolves. On cooling, the dissolved starch is likely to retrograde and become resistant to amylolysis. Thus the catalytic efficiency tends to fall. In addition, we find that the catalytic efficiency on the different starches varies inversely with their solubility and we interpret this finding on the assumption that the greater the solubility, the greater is the likelihood of retrogradation. We conclude that although alpha-amylase is present in high activity in digestive fluid, the enzymic hydrolysis of starch may be a limiting factor in carbohydrate digestion because of factors related to the physico-chemical properties of starchy foods.     

Characterization of Molecular Structure of Starch Granules in Suspension-cultured Cells from Ipomoea cordatotriloba Denn.

The molecular structure of starch granules formed in suspension-cultured cells of Ipomoea cordatotriloba Denn. was characterized by its chain length distribution, which was compared to those of the starches from the root and leaf of the original plant. The cultured cell starches were spherical and had a very small granule size (about 2 μm). The debranched starches roughly separated into three fractions during gel-permeation chromatography, and the fractions were defined as Fr.1, 2, and 3, respectively. The chain length distribution of the debranched cultured cell starch showed that the high molecular weight fraction (Fr.1), referred to as an amylose fraction, was much less than those of the root and leaf starches. The ratio of the two lower fractions (Fr.3/Fr.2) of the cultured cell starch, which was mainly derived from unit chains of amylopectin, was greatest among the starches, suggesting that the amylopectin from the cultured cell starch has much shorter unit chains. By X-ray diffraction analysis, it was found that both cultured cell and leaf starch granules have low crystallinity.