Carboxymethyl Starch Octenylsuccinate: Microwave‐ and Ultrasound‐assisted Synthesis and Properties

The synthesis of water‐soluble octenylsuccinates of carboxymethyl starch (OS‐CMS) was performed with octenylsuccinic anhydride by assistance of microwave and ultrasound irradiation using the dimethyl sulphoxide/p‐toluenesulphonic acid system and DMSO as solvents for activation of CMS as well as reaction medium of the following esterification. The prepared OS‐CMS derivatives were characterized with regard to their structural, surface‐active and performance properties. The application of both microwave and ultrasound irradiation as energy sources permitted to shorten the esterification time to several minutes from 24 h of the previously reported conventional heating [33], whereby the reaction efficiencies were high and the water‐soluble derivatives exhibited excellent emulsifying efficiency as well as surfactant performance properties tested by washing power and antiredeposition efficiency. The results indicate also the high potential of both microwave and ultrasound energy sources to innovate and increase the efficiency of technological polysaccharide esterification processes.     

Studies on the properties of citrate derivatives of cassava (Manihot esculenta Crantz) starch synthesized by microwave technique

Cassava starch citrates with degree of substitution (DS) ranging from 0.005 to 0.063 were synthesized by the microwave‐assisted reaction of cassava starch with citric acid. A response surface small composite design was used to study the effect of different reaction conditions, viz. time, temperature and reagent concentration. All these variables significantly affected the substitution level in the modified starches. The DS increased with increase in the time of reaction and temperature. However, reagent concentration had a negative effect on the DS. The modified starches showed higher viscosity with lower breakdown, lower setback and higher final viscosities in comparison to native starch. Differential scanning calorimetry showed that the modified starches exhibited a decrease in gelatinization temperatures, T_o, T_p, T_e, in comparison to native starch. However, the heat of gelatinization was not significantly affected. The citrate derivatives exhibited reduced swelling volume and enhanced water binding capacities. They were found to be less susceptible to enzyme hydrolysis than native starch. Copyright © 2007 Society of Chemical Industry     

Dynamic Rheological and Thermal Properties of Acetylated Sweet Potato Starch

Dynamic rheological and thermal properties of acetylated sweet potato starch (SPS) pastes (5%, w/w) were evaluated as a function of the degree of substitution (DS). The transition temperatures (T_o, T_p and T_c) and enthalpy of gelatinization (ΔH) of acetylated SPS, which were determined using differential scanning calorimetry, were lower than those of native starch, and significantly decreased with an increase in DS. Magnitudes of storage modulus (G′), loss modulus (G′′) and complex viscosity (η*) of acetylated SPS pastes were determined using a small‐deformation oscillatory rheometer. Dynamic moduli (G′, G′′ and η*) values of acetylated SPS pastes except for 0.123 DS were higher than those of native starch, and they also decreased with an increase in DS. The tan δ (ratio of G′′/G′) values (0.37–0.39) of acetylated SPS samples were lower than that (0.44) of native starch and no significant differences were found among acetylated SPS samples, indicating that the elastic properties of SPS pastes were affected by acetylation but did not depend on DS. The G′ values of acetylated SPS during aging at 4°C for 10 h were much lower than those of native starch, showing that the addition of acetyl groups produced a pronounced effect on the retrogradation properties of SPS.     

Determination of the mass‐specific distribution of the substituents in cationic starch derivatives

The mass‐specific charge distribution in molar mass fractions of cationic starch derivatives was investigated. The molar mass fractions were produced by semi‐preparative SEC (SP‐SEC). The derivatives were cut into an amylopectin‐rich fraction F1, an intermediate fraction F2, containing low molar mass amylopectin and high molar mass amylose, and an amylose‐rich fraction F3. The weight‐average molar mass (M_w) and molar mass distribution (MMD) of the fractions were determined by SEC with multi‐angle laser light scattering (SEC‐MALLS). The mass‐specific charge of each fraction was calculated from the consumption of anionic titrant solution using polyelectrolyte titration (PET) in combination with particle charge detection (PCD). The difference in substituent distribution between the fractions was tested by the Student's t‐test. The weight‐average molar mass of the starch derivatives was not dependent on the degree of substitution (DS) or the derivatization process. Depending on the DS value or derivatization process, different substituent distributions were observed. The results for the mass‐specific charge distribution in different molar mass fractions of cationic starch derivatives with graded DS between 0.015 and 0.130 from the slurry process were discussed. The heterogeneity of substituent distribution decreased with increasing DS of the starch derivative. This was the case for samples from both the slurry and semi‐dry processes. The heterogeneity of derivatization was highest for low DS samples up to DS 0.03, with the amylopectin‐rich fraction incorporating more charges than the amylose‐rich fraction. This was more pronounced for the sample from the slurry process than from the semi‐dry process.     

Influence of the Cross‐linking Agent on the Gel Structure of Starch Derivatives

Hydrogels were synthesized through cross‐linking of carboxymethyl starch (CMS; Degree of Substitution DS = 0.45) using polyfunctional carboxylic acids (malic, tartaric, citric, malonic, succinic, glutaric and adipic acid). The syntheses used a cross‐linking agent ratio (ratio of the number of cross‐linking agent molecules to the number of monomer units constituting the polymer) of F_Z = 0.05. After cross‐linking the gels were dried, ground and then hydrogels of a polymer concentration of 4 mass‐% were produced. These CMS‐hydrogels were then rheologically characterized using dynamic oscillatory measurements. From measurements of the plateau region storage modulus G'_P, the network parameters molar mass between two entanglement points M_e (M_e ranging from 9.318 (citric acid) to 281.397 g/mol (tartaric acid)), the cross‐link density ν_e and the distance between two entanglement points ξ were calculated. Using carboxylic acids without other functional groups, a maximum in gel sturdiness is found at a spacer length of two CH₂‐groups. The evaluation of the loss factor tan δ for the CMS‐hydrogels showed that values of tan δ = 0.2 varied only slightly with the frequency ω. Flow curves showed a pseudopIastic flow behavior for all CMS‐hydrogels (the shear viscosity η declining over five decades in the range of the shear rate γ of 10⁻³ to 10³ s⁻¹) The different polyfunctional carboxylic acids have a strong influence on the sturdiness of the synthesized CMS‐hydrogels.     

Carboxymethyl Cocoyam Starch: Synthesis,Characterisation and Influence of Reaction Parameters

Twenty carboxymethyl starch derivatives of cocoyam starch were synthesized under different reaction conditions. The influences of sodium hydroxide concentration, sodium monochloroacetate concentration, water, type of organic solvent, reaction time and temperature were evaluated for degree of substitution (DS) and reaction efficiency (RE). The optimal ratio of moles of NaOH per mole anhydroglucose unit (AGU), n_NaOH/n_AGU was 1.62. Increases in ratio of moles of monochloroacetate (n_SMCA) to mole of AGU (n_AGU) increased the DS progressively. The ratio of water to solvent (isopropanol, IPA) in the reaction media was optimal at H₂O/IPA 0.16. Both RE and the DS increased with increase in reaction time within the studied time range (1‐4 h). Increases in temperature enhanced both reaction efficiency and DS. Among the solvents studied, an isopropanol – water medium produced the optimal result. The starch paste clarity improved remarkably after carboxymethylation. Wide angle X‐ray diffractometry revealed that starch crystallinity was reduced after carboxymethylation. ¹³C‐NMR showed peaks at δ = 180.42 ppm, 80.35 ppm, 77.77 ppm, and 71.96 ppm, which were assigned to C‐O, substituted C‐2, C‐3 and C‐6, respectively. In addition, three signals appeared at δ = 74.16 ppm, 73.42 ppm and 72.59 ppm and they were assigned to the CH₂ in the carboxylate substituents.     

Experimental and Modeling Studies on the Synthesis and Properties of Higher Fatty Esters of Corn Starch

This paper describes a systematic study on the synthesis of higher fatty esters of corn starch (starch laurate and starch stearate) by using the corresponding vinyl esters. The reactions were carried out in DMSO using basic catalysts (Na₂HPO₄, K₂CO₃, and Na‐acetate). The effect of the process variables (vinyl ester to starch ratio, catalyst intake, reaction temperature and type of the catalyst) on the degree of substitution (DS) of the starch laurate and starch stearate esters was determined by performing a total of 54 experiments. The results were adequately modeled using a non‐linear multivariable regression model (R²≥0.96). The basicity of the catalyst and the reaction temperature have the highest impact on the product DS. The thermal and mechanical properties of some representative product samples were determined. High‐DS products (DS = 2.26‐2.39) are totally amorphous whereas the low‐DS ones (DS = 1.45‐1.75) are still partially crystalline. The thermal stability of the esterified products is higher than that of native starch. Mechanical tests show that the products have a tensile strength (stress at break) between 2.7–3.5 MPa, elongation at break of 3–26%, and modulus of elasticity of 46–113 MPa.     

Structural Transformation of Sago Starch by Heat‐Moisture and Osmotic‐Pressure Treatment

Sago starch was modified by osmotic‐pressure treatment (OPT) and heat‐moisture treatment (HMT) and physicochemical characteristics were compared. In OPT, sago starch was suspended in saturated sodium sulfate solution and heated for 1 h at 100, 110 and 120°C, corresponding to a calculated osmotic pressure of 32,728, 33,640 and 34,552 kPa (assuming sodium sulfate dissociates completely), respectively, and in HMT, sago starch with 20% moisture content was used. Change of X‐ray diffraction pattern from C‐type to A‐type was obtained for OPT and HMT starch at 110°C and 120 °C, respectively. RVA viscograms of both OPT and HMT starch exhibited a decrease of peak and breakdown viscosity but increase of final viscosity and pasting temperature. Onset (T_o), peak (T_p), and conclusion temperature (T_c) of gelatinization of both OPT and HMT starch increased significantly with increase of treatment temperature. Biphasic broadening of T_p was observed for HMT starch indicating an inhomogeneous heat transfer during HMT. The observed narrow peaks of DSC curves indicated better homogeneity of OPT. These properties suggest that OPT starch is more suitable for large‐scale production.     

A Comparison of Some Methods for the Determination of the Degree of Substitution of Carboxymethyl Starch

The degree of substitution (DS) markedly affects the properties of sodium carboxymethyl starch (Na‐CMS). In this work Na‐CMS samples with different DS starting from both potato and corn starch were synthesized in an ethanol/water mixture and their DS was determined using three methods: direct titration of the acid form of the carboxymethyl starch (H‐CMS), Cu salt precipitation and back titration. It was found that direct titration gave smaller DS values, while the Cu salt precipitation method gave higher DS values than the back titration method, which was found to be the most accurate. The values of the DS obtained by these methods were similar for lower DS while for higher values the discrepancy was more pronounced. Under the same experimental conditions the CMS obtained from corn starch had a higher DS than the one obtained from potato starch and on average, the discrepancies between the DS values obtained by the employed analytical methods were smaller for the CMS samples synthesized from corn starch.     

Synthesis and Characterization of low DS Succinate Derivatives of Cassava (Manihot esculenta Crantz) Starch

Succinylation of cassava starch was carried out in aqueous medium to prepare derivatives with low degree of substitution (DS) and the physicochemical properties of the products were determined. A response surface design was used for the experiment with three levels of each of the three variables viz., concentration of succinic anhydride, reaction time and pH of the reaction medium. The reaction was followed in terms of the DS of the products and reaction efficiency (RE). The degree of substitution of the derivatives varied from 0.001 to 0.022 and reaction efficiency from 2.2 to 46.8%. The DS and RE showed an adequate fit to a second order polynomial model of the variables used. Succinylation brought about increase in the swelling volume, peak viscosity and paste clarity of the starch. However, the pasting temperature and solubility did not show any significant change. The in‐vitro α‐amylase digestibility of the succinylated derivatives decreased in comparison to that of native starch and this decrease correlated with a corresponding increase in DS.     

Fine Structure,Thermal and Viscoelastic Properties of Starches Separated from Indica Rice Cultivars

Starches were separated from indica rice cultivars (PR‐113, Basmati‐370, Basmati‐386, PR‐115, IR‐64, and PR‐103) and evaluated using gel permeation chromatography (GPC), X‐ray diffraction, differential scanning calorimetry (DSC) and dynamic viscoelasticity . Debranching of starch with isoamylase and subsequent fractionation by GPC revealed 9.7–28.3% apparent amylose content, 3.7–5.0% intermediate fraction (mixture of short amylose and long side‐chains of amylopectin), 20.6–26.6% long side‐chains of amylopectin and 45.8–59.4% short side‐chains of amylopectin). IR‐64 starch with the highest crystallinity had the highest gelatinization temperatures and enthalpy, T_o, T_p, T_c, and ΔH_gel being 71.8, 75.9, 82.4°C and 5.1 J/g, respectively, whereas PR‐113 starch with lower crystallinity showed the lowest gelatinization temperatures (T_o, T_p, T_c, of 60.8, 65.7 and 72.2°C, respectively). Basmati‐386 starch exhibited two endotherms during heating, the first and second endotherm being associated with the melting of crystallites and amylose‐lipid complexes, respectively. T_o, T_p, T_c and ΔH_gel of the second endotherm of Basmati‐386 starch were 99.0, 100.1, 101.1°C and 2.0 J/g, respectively. During cooling, Basmati‐386 also showed an exotherm at a peak temperature of 87°C. PR‐113 starch with the highest amylose content and the lowest content of short side‐chains of amylopectin had the highest peak storage modulus (G′= 1.6×10⁴ Pa). The granules of PR‐113 starch were the least disintegrated after heating. The effects of heating starch suspensions at different temperatures (92°C, 130°C and 170°C) on intrinsic viscosity [η], transmittance and viscoelasticity were also studied to evaluate the extent of breakdown of the molecular structure. The intrinsic viscosity of starch suspensions heated at 92, 130 and 170°C ranged between 103–114, 96–110 and 28–93 mL/g. Transmittance value of starches cooked at 92°C decreased with increase in storage duration. All starches except PR103, cooked at 130°C also showed decrease in transmittance during storage, however, at lower rate. PR103 starch heated at 130°C did not show any change in transmittance up to a storage time of 48 h. The changes in viscoelasticity of starch pastes cooked at different temperatures during cooling and reheating were also evaluated. G′ and G′′ increased with decrease in temperature during cooling cycle. Starches heated at 130°C with apparent amylose content ≤ 21.2% showed an improvement in G′ and G′′ in comparison to the corresponding starches heated at 92°C, this improvement was observed to be higher in starches with lower amylose content. All starches heated at 170°C had a higher proportion of breakdown in molecular structure as indicated by lower G′ and G′′ than the same starches heated at 130 and 92°C.     

Physicochemical Properties of Carboxy-methylated Sago (Metroxylon sagu) Starch

ABSTRACT: Carboxymethyl starch (CMS) with degree of substitution (DS) ranging from 0.1 to 0.32 was prepared from sago ( Metroxylon sagu ) starch in non-aqueous medium using isopropanol as a solvent. The physico-chemical, rheological, and thermal properties of the starches were investigated. At room temperature (25 °C), CMS hydrated readily, resulting in higher swelling power compared with native (unmodified) starch. Light microscopy revealed that CMS granules imbibed more water than native starch at room temperature and thus caused a larger increase in granule size. Some of the CMS granules lost their integrity. Scanning electron microscopic observation revealed fine fissures on the surface of CMS (DS 0.32) granules compared with a relatively smooth surface of native starch granules. Carboxymethylated sago starch exhibited excellent dispersibility and cold water solubility as judged by the absence of peak viscosity in the pasting profile (determined by Rapid ViscoAnalyzer). Pasting profile of CMS was qualitatively similar to pregelatinized starch. Despite exhibiting greater swelling power, CMS showed significantly lower pasting viscosity compared with the native starch. Intrinsic viscosity was also greatly reduced by carboxymethylation. Studies using differential scanning calorimetry (DSC) showed that transition temperatures and enthalpies decreased with an increase of degree of substitution. CMS at higher substitution levels (DS 0.27 and 0.32) showed significantly lower retrogradation tendency, as indicated by lower setback, absence of DSC endotherm upon storage at 4 °C and lower syneresis upon repeated freeze-thaw cycles. The results suggested that retrogradation might be effectively retarded by the presence of the bulky carboxymethyl group.     

Combinatorial effects of mechanical activation and chemical stimulation on the microwave assisted acetylation of corn (Zea mays) starch

The changes in the physical characteristics of ball milled corn starch (BMS) after chemical modification were investigated. The SEM and XRD analysis of BMS granules showed a fragmented aspect with a total loss of their initial crystallinity and an increase of their potential hydroxyl substitution sites. This morphology facilitated the access of the esterifying solvents into the starch molecule as corroborated by the spectacular increase of the water solubility index (WSI) and water absorption index (WAI). Following the acetylation, the degree of substitution (DS) increased up to 2.83 with the augmentation of the iodine catalyst content (p = 0.011). However, under the same condition of esterification, the DS of the BMS was slightly lower in comparison to the control, due to an increase in the number of free hydroxyl groups. Consequently to the modification, a reduction in the T_g, strong hydrophobicity and important exo‐corrosion affecting the granules were noticed.     

Preparation and Properties of Octenyl Succinic Anhydride Modified Early Indica Rice Starch

Octenyl succinic anhydride (OSA) modified early indica rice starch was prepared in aqueous slurry systems and the major factors affecting the esterification were investigated systematically. The physicochemical properties of the products were determined by means of Fourier transform infrared (FT‐IR) spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction and Rapid Visco Analyser (RVA). The results indicated that the suitable parameters for the preparation of OSA starch from early indica rice starch in aqueous slurry systems were as follows: concentration of starch slurry 35% (in proportion to water, w/w), reaction period 4 h, pH of reaction system 8.5, reaction temperature 35°C, amount of OSA 3% (in proportion to starch, w/w). The degree of substitution (DS) was 0 018 and the reaction efficiency (RE) was 78%. FT‐IR spectroscopy showed characteristic absorption of the ester carbonyl groups in the OSA starch at 1724 cm^‐1. SEM and X‐ray diffraction revealed that OSA groups acted by first attacking the surface and some pores formed, but OSA modification caused no change in the crystalline pattern of rice starch up to DS 0.046. RVA results indicated that the starch derivatives gelatinized at shorter time to achieve higher viscosities with increased OSA modification.     

Effect of Osmotic Pressure on Starch: New Method of Physical Modification of Starch

A new method of physical modification of starch in the presence of high concentrated salt solution is presented, called “Osmotic Pressure Treatment” (OPT). OPT was introduced in order to produce the same physically modified products as obtained by conventional heat‐moisture treatment (HMT) of starch. Potato starch was selected for the comparative study of the two methods. For the OPT method, potato starch was suspended in a saturated solution of sodium sulfate and heated in an autoclave at 105°C and 120°C ,which corresponded to the calculated osmotic pressures of 328 and 341 atm (332 and 345 bar, respectively) (assuming sodium sulfate dissociates completely) for 15, 30 and 60 min, respectively. For the HMT method, starch with 20% moisture content was placed in a Duran bottle, then the same heat treatment method in the autoclave was applied. Light and scanning electron microscopy (SEM) showed that OPT of starch changed the shape of the starch granules to a folded structure, while the starches remained unchanged after HMT. The RVA viscogram for the OPT starch exhibited a decrease in the peak viscosity without a breakdown and an increase of the pasting temperature when increasing the temperature and time, which was in an agreement with the viscosity patterns for the HMT starches. X‐ray diffraction patterns were altered from B to A+B for the HMT and from B to A type for the OPT starch when treated at 120°C. After OPT, the gelatinization temperatures (T_o, T_p, and T_c) of the starch increased significantly with increasing temperature and time, whereas only the T_c of starch increases after HMT. The biphasic broadening of the peaks (high T_c‐T_o) can be explained by an inhomogeneous heat transfer during HMT. Narrow peaks in the DSC curve can be an indication for a better homogeneity of the OPT samples. However, both methods provide a similar decrease in the gelatinization enthalpy (ΔH). The amylose‐amylopectin ratio calculated from the HPSEC patterns was strongly increased for HMT starches at 105°C for 60 min and 120°C for 30 min and decreased after treatment at 120°C for 60 min. For OPT starches the ratio was strongly increased at 120°C for 15 min and decreased after prolong heating. The OPT provides a uniform heat distribution in the starch suspension. This allows the modified starch to be produced on a larger scale.     

Effect of Heat‐Moisture Treatment on Structural and Thermal Properties of Rice Starches Differing in Amylose Content

Starches from glutinous rice (1.4% amylose), Jasmine rice (15.0% amylose) and Chiang rice (20.2% amylose) were exposed to heat‐moisture treatment (HMT) at 100 °C for 16 h and at different moisture levels (18, 21, 24 and 27%). The effect of heat‐moisture treatment on structural and thermal properties of these three rice starches was investigated. The HMT did not change the size, shape and surface characteristics of rice starch granules. The A‐type crystalline pattern of rice starches remained unchanged after HMT. The relative crystallinity (RC) and the ratio of short‐range molecular order to amorphous (RSA) of heat‐moisture treated glutinous and Jasmine rice starches decreased with increasing moisture level of the treatments. In contrast, the RC of the treated Chiang rice starch remained practically unchanged. A peak of crystalline V‐amylose‐lipid complexes was clearly presented in all treated Chiang rice starches. The peak became progressively stronger with increasing moisture level of the treatment. Differential scanning calorimetry (DSC) of all treated rice starches showed a shift of the gelatinization temperature to higher values. Increasing moisture level of the treatments increased the onset gelatinization temperature (T_o) but decreased the gelatinization enthalpy (ΔH) of rice starches. A broad gelatinization temperature range (T_c‐T_o) with a biphasic endotherm was found for all treated Chiang rice starches and Jasmine rice starch after HMT₂₇ (HMT at 27% moisture level). Additionally the (T_c‐T_o) of treated Chiang rice starches increased linearly with increasing moisture level of the treatments.     

Chemical and Physical Characterisation of Grain Tef [Eragrostis tef (Zucc.) Trotter] Starch Granule Composition

Chemical and physical properties of starch granules isolated from five grain tef (Eragrostis tef) varieties were characterised and compared with those of maize starch. Endogenous starch lipids extracted with hot water‐saturated n‐butanol and total starch lipids extracted with n‐hexane after HCl hydrolysis were 7.8 mg/g (mean) and 8.9 mg/g (mean), respectively, slightly lower than in the maize starch granules. The starch phosphorus content (0.65 mg/g) was higher than that of maize starch but virtually the same as reported for rice starch. The starch granule‐swelling factor was lower than that of maize starch and extent of amylose leaching was higher. The starch X‐ray diffraction pattern was characteristic of A type starch with a mean crystallinity of 37%, apparently lower than the crystallinity of maize starch and more similar to that reported for rice and sorghum starches. The starch DSC gelatinisation temperature was high, like for other tropical cereals; T_o, T_p, T_c and ΔH were in the range 63.8—65.4, 70.2—71.3, 81.3—81.5 °C and 2.28—7.22 J/g, respectively. The lower swelling, apparently lower percentage crystallinity and lower DSC gelatinisation endotherms than maize starch suggest that the proportion of long amylopectin A chains in tef starch is smaller than in maize starch.     

Influence of Soluble Polymer Residues in Crosslinked Carboxymethyl Starch on some Physical Properties of its Hydrogels

Crosslinked carboxymethyl starch (CMS) was synthesized from potato starch in a single‐step procedure with mono‐ (MCA) and dichloroacetic acid (DCA), using the well‐known Williamson reaction. The products varied in their degree of substitution DS (average number of carboxymethyl groups per monomer unit) and crosslinker ratio F_z (number of crosslinker molecules offered per monomer unit). After neutralizing and removal of the formed salt, one part of the synthesized CMS networks was pre‐swollen in water in an additional purification step in order to wash out unlinked, soluble polymer chains. The rest of the product remained unwashed. Different swelling experiments were performed with the two samples, before being dried and ground. Both, the Free Swelling Capacity (FSC) and the Absorption Capacity Under Mechanical Load (AUL) of the hydrogels were strongly influenced by chemically unlinked CMS chains that were only physically entangled in the network structure. These mobile polymer segments were responsible for a significant weight loss of the swollen, unwashed hydrogels over the course of time. Rheological oscillatory experiments showed that, in order to achieve comparable values for the storage and loss moduli (G′ and G′′), the polymer content of an unwashed hydrogel had to be more than twice as high as that of the corresponding purified product. By using a special rheological test procedure with a cyclic temperature program, the long‐term stability of CMS gels could be measured and verified.     

Synthesis of Higher Fatty Acid Starch Esters using Vinyl Laurate and Stearate as Reactants

This paper describes the synthesis of long‐chain fatty esters of corn starch (starch laurate and starch stearate) with a broad range in degree of substitution (DS = 0.24−2.96). The fatty esters were prepared by reacting the starch with vinyl laurate or vinyl stearate in the presence of basic catalysts (Na₂HPO₄, K₂CO₃, and Na acetate) in DMSO at 110°C. The yellowish products were characterized by ¹H‐, ¹³C‐NMR and FT‐IR. The DS of the products is a function of the carbon number of the fatty acid chain, vinyl ester to starch ratio and the type of catalyst. When performing the reactions using Na₂HPO₄ as the catalyst, the DS for the starch laurate compounds is higher than for the corresponding starch stearates. For low vinyl ester to starch ratios, an increase in the vinyl ester concentration leads to higher product DS values. At higher ratios, the DS decreases, presumably due to a reduction of the polarity of the reaction medium. K₂CO₃ and Na acetate are superior catalysts with respect to activity compared to Na₂HPO₄ and products with DS values close to 3 were obtained.     

The relationship between entanglement concentration and physicochemical properties of potato and sweet potato starch dispersions

Entanglement concentration (c_e) is defined as the onset of overlap and interpenetration of random‐coil chains in a polymer solution and is important in determining rheological, dynamic and fracture properties. However, few studies have reported in detail how c_e influences physicochemical properties of starch dispersions. So, the effects of c_e on the physicochemical properties of the potato and sweet potato starch dilute and semi‐dilute dispersions were investigated. The results showed that for the two starch dispersions with concentrations ≥c_e, the gelatinisation temperature increased more significantly with increasing concentrations, and storage modulus increased faster than loss modulus with increasing frequency. The potato starch dispersion with concentrations ≥c_e possessed higher entanglement density of the chain segments. The two starch dispersions with concentrations >c_e exhibited shear thinning with increasing frequency. The two starches could only form film at concentrations ≥c_e. So, c_e will be a suitable concentration for regulating the concentration of starch dispersions to obtain the expected physicochemical properties.