Starch Derivatives of High Degree of Functionalization. 13. Novel Amphiphilic Starch Products

Amphiphilic starch derivatives of high degree of substitution (DS) were prepared by benzylation of pea, potato and waxy maize starch followed by the introduction of hydroxypropyltrimethylammonium and carboxymethyl moieties. The conversions were carried out under heterogeneous conditions leading to products with a total DS of up to 1.8. The starch composition regarding amylose and amylopectin influences the DS value. The structure of the products was characterized by means of elemental analysis, FTIR and NMR spectroscopy, and, in case of benzyl carboxymethyl starch by means of HPLC after complete chain degradation. The tensioactive properties depend on the DS values of hydrophilic and lipophilic groups and can be adjusted by controlling the molar ratio anhydroglucose unit to reagent during the synthesis. Surface tensions as low as 48.6 mN/m were found for benzyl hydroxypropyltrimethylammonium starch and 38.6 mN/m for benzyl carboxymethyl starch. The lowest critical micelle concentration determined is 2.1 mmol/L.     

Preparation and Evaluation of Some Cationic Starch Derivatives as Flocculants

Six types of cationic starch derivatives bearing different types of amino groups, i.e., primary, secondary and tertiary or quaternary ammonium salt, were prepared and evaluated as flocculants. Native and hydrolyzed maize starches were used as parent materials for these derivatives. The different factors affecting flocculation were studied. These factors include (a) flocculant dose, (b) pH of the flocculation medium, (c) chemical formula of the flocculant and (d) type of cationic starch, its molecular weight and nitrogen content.     

Peculiarities of Starch Cationization with Glycidyltrimethylammonium Chloride

Cationic starch derivatives containing quaternary ammonium groups with high degree of substitution are prepared by reaction of starch with glycidyltrimethylammonium chloride (GTAC) in different reaction media. In aqueous solutions of GTAC along with conventional hydrolysis of epoxy groups, their interaction with chloride ions also takes place. This resulted in formation of hydroxyl ions which accelerate both the hydrolysis of GTAC epoxy groups and can act as the internal catalyst in the reaction of GTAC with starch. Therefore, even in the absence of the external catalyst, cationic starch with a high degree of substitution can be obtained. The autocatalytic reaction of GTAC with starch proceeds more rapidly at higher temperatures but with lower reaction efficiency. Both in the absence of the external catalyst and in the case when sodium alkali is used as a catalyst the reaction of starch with GTAC proceeds only when a particular quantity of “free” water is present in the system. When the NaOH as catalyst is used the reaction efficiency is about 90%. The yield of starch cationization reaction decreases when the quantity of “free” water is twice or thrice higher than required for starch modification to begin.     

Starch Derivatives of High Degree of Functionalization. 4. Homogeneous Tritylation of Starch and Subsequent Carboxymethylation

The synthesis of monomethoxytriphenylmethyl (MMtrityl) starch and the subsequent carboxymethylation of the 6‐O‐functionalized products were investigated. The trityIation both in N,N‐dimethylacetamide (DMA)/LiCl and in dimethyl sulfoxide (DMSO) occurred homogeneously. The highest degree of substitution of trityl groups (DS_TrityI) obtained after a single conversion step was 0.77 in both solvents. A complete functionalization of primary OH‐groups was achieved only with unsubstituted triphenylmethyl chloride in these reaction media. In case of monomethoxytriphenylmethyl chloride (MMTMC) as reagent an additional conversion step is necessary to synthesize products with a DS_TrityI = 1. The structure of the products was analyzed by FTIR‐ and ¹³C‐NMR spectroscopy. Subsequent carboxymethylation of the MMtrityl starch samples leads to products with a preferred functionalization of the unprotected secondary OH‐groups. After removal of the trityl moieties, the DS_CM and the distribution of carboxymethyl groups within the anhydroglucose unit was investigated by means of HPLC and ¹H‐NMR spectroscopy. The carboxymethylation was more effective at O‐2 than at O‐3. In case of ether products with DS_Trityl < 1 a partial substitution of the primary OH group took place as well.     

高取代度阳离子淀粉的制备方法研究

用玉米淀粉与3-氯-2-羟丙基三甲基氯化铵(CHPTMA)为原料,通过常温干法和高温干法制备高取代度季铵型阳离子淀粉醚。研究了水的用量、氢氧化钠用量、醚化剂用量、反应温度和反应时间对取代度和反应效率的影响。当淀粉用量为100g、CHPTMA用量为0.345mol、氢氧化钠用量为0.375mol、反应温度80℃、反应时间2.5h时为最佳反应条件,此时,取代度为0.445,反应效率为79.6%。     

Preparation of high‐substituted cationic starch in presence of organic bases

Cross‐linked N‐(hydroxypropyl)–N,N,N–trimethylammonium starch chlorides (CQS) with preserved microgranules, degree of substitution (DS) from 0.18 to 1.05 are prepared by reaction of starch with glycidyltrimethylammonium chloride (GTAC) accelerated by benzyltrimethylammonium hydroxide (BTMAOH) or tertiary amines–triethylamine (TEA) and dimethylbenzylamine (DMBA). When BTMAOH instead of NaOH is used as a catalyst, the reaction of cross‐linked starch (CS) with GTAC proceeds slightly slower and with a lower efficiency (RE). DMBA unexpectedly showed similar catalyst efficiency as BTMAOH. It is suggested that the reason for such phenomena is the reaction of GTAC with tertiary amines and the formation of strong bases – quaternary ammonium hydroxides. They actually catalyse starch cationization. DMBA is more active in this reaction in comparison with TEA. It is shown that, due to a higher amount of quaternary ammonium hydroxides in the liquid phase of the reaction mixture, the yield of starch cationization decreases. Cationization in the presence of organic bases provides higher sorption capabilities to the modified polysaccharide.     

半干法制备高取代度阳离子淀粉

研究了半干法制备高取代度阳离子淀粉的各种影响因素,研究表明:最佳工艺条件是:醚化剂用量ω=55%;氢氧化钠用量ω=1.0%;体系含水量ω=26%;反应温度70℃;反应时间4h;加入适量催化剂Eω=10%,能制备出取代度0.510,反应效率达88.7%的高取代度阳离子淀粉.     

高取代度阳离子淀粉的制备与应用

讨论了半干法制备高取代度阳离子淀粉的影响因素,优化出制备高取代度(DS为0.45)阳离子淀粉的最佳工艺条件,并将其作为助留剂应用于漂白麦草浆.研究结果表明,此淀粉对漂白麦草浆有很好的助留效果,当其用量为0.2%时,填料留着率可达87.6%.     

Characterisation of Fractions Obtained by Isoamylolysis and Ion‐exchange Chromatography of Cationic Waxy Maize Starch

Isoamylase hydrolysates of wet‐ (WC) and dry‐cationised (DC) waxy maize starch were fractionated by ion‐exchange chromatography on CM‐Sepharose into an unbound and four bound fractions. The amount of bound dextrins was higher in the WC than in the DC sample. The fractions were characterised by gel‐permeation chromatography and proton‐NMR spectroscopy. The unbound fraction from the WC sample consisted mainly of linear chains formed from amylopectin. The dextrins in the bound fractions contained increased amounts, from 1.2—7.9, of cationic substituents per molecule and the degree of polymerisation increased with the density of substituents. Dextrins weakly bound to CM‐Sepharose had a linear structure, whereas more tightly bound fractions were mixtures of linear and branched dextrins. In the latter, the debranching was incomplete because of sterical hindrance by substituents at or close to the branch points. Most of the dextrins were partly hydrolysed by β‐amylase, but the more highly substituted fractions possessed also a population of β‐amylase resistant dextrins, suggesting substituents at the non‐reducing ends.     

Properties of Low‐substituted Cationic Starch Derivatives Prepared by Different Derivatisation Processes

Cationic starch ethers prepared by the chemical reaction of starch with a quaternary ammonium reagent are commercially important derivatives. Cationic potato starch derivatives were produced under pilot‐scale conditions, employing four different principles. Wet cationisation was carried out by the slurry and paste processes, in which the cationic reagent and catalyst are added to the starch. Besides being prepared by these more commonly used processes, cationic starches were also produced by dry cationisation and by adding the cationic reagent during extrusion of starch. The cationic reagent used was 2,3‐epoxypropyltrimethylammonium chloride. Derivatives with three graded degrees of substitution (DS) between 0.03 and 0.12 were prepared by each process. The physical properties of the derivatives were analysed by the following methods: polarised light microscopy, X‐ray scattering, differential scanning calorimetry (DSC), solubility and swelling behaviour, and High‐Performance Size‐Exclusion Chromatography‐Multiangle Laser Light Scattering (HPSEC‐MALLS). The degree of substitution was determined by high resolution ¹³C‐NMR spectroscopy after hydrolysis with trifluoroacetic acid. The properties of the cationic starch derivatives were highly dependent on the derivatisation method. The granular structure of the starch was not visibly affected by the slurry process. Products from the semi‐dry reaction showed some granular damage, which was particularly evident after suspension of the granules in water. In the paste and extrusion processes, the starch granules were completely destroyed. Swelling temperatures and enthalpies can be determined only for starch derivatives that still retain a granular structure. As a result, samples from the paste and extrusion reactions exhibited no swelling endotherm in DSC. The samples from the slurry process showed a shift in the swelling temperature range towards lower temperature and a decrease in swelling enthalpy both as compared to native potato starch and also with increasing DS. Similar behaviour was found for the samples from the semi‐dry process. The swelling temperature region was comparable to that of the slurry samples for the same DS but the swelling enthalpy was distinctly lower, indicating that the granular structure of the starch was altered far more by the semi‐dry than the slurry process. Swelling in excess water and solubility were affected primarily by the cationisation process, while the influence of DS was of minor importance. The extrusion products had pronounced cold‐water solubility, the semi‐dry products showed increasing cold‐water solubility with increasing DS, the paste products were highly swollen in cold water and the slurry products were insoluble in cold water. All products were soluble in hot water but the state of dissolution was different. The molar mass distributions of the samples were determined after dissolution by pressure cooking. The different derivatisation methods resulted in characteristic molar mass distributions. The average molar mass decreased in the order slurry, semi‐dry‐, paste and extrusion process.     

Microwave‐assisted Synthesis of Starch Maleate by Dry Method

Starch maleate was prepared by microwave‐assisted reactions. Microwave‐assisted esterification in a dry medium for 5 min gives a reaction efficiency of 98%. Influences of reaction time, reagent molar ratio and water content of starch on the degree of substitution (DS) of the product and reaction efficiency were investigated. The structure of starch maleate was characterized by FTIR and NMR spectroscopy. Changes in the starch granules before and after modification were studied by scanning electron microscopy (SEM). Compared with the conventional heating synthesis method, microwave‐assisted synthesis in a dry medium is rapid and energy saving with high reaction efficiency.     

Characterization of Residues from Partially Hydrolyzed Potato and High Amylose Corn Starches by Pancreatic α‐Amylase

High amylose corn starch (HACS) and potato starch were hydrolyzed by pancreatic α‐amylase in vitro. Residues after hydrolysis were collected and characterized for their physicochemical properties and molecular structure. Compared with raw starches, residues had lower apparent amylose contents and higher resistant starch contents. The gelatinization enthalpy of residues from HACS increased while enthalpy of residues from potato starch decreased from 15.4 to 11.3 J/g. Peak viscosity and breakdown values of the residues from potato starch were markedly decreased but final viscosity values did not show much change. Chain length distribution of debranched amylopectin from the residues indicated that the relative portion of short chain in the residue decreased for both starches. More molecules with intermediate chain length (DP 16—31) were found in residue after 48‐h hydrolysis of potato starch.     

Physicochemical Properties of Non‐thermally Cross‐linked Corn Starch with Phosphorus Oxychloride using Ultra High Pressure (UHP)

Corn starch (20%, w/w) was non‐thermally and conventionally cross‐linked with phosphorus oxychloride (POCl₃; 0.01, 0.05, or 0.1%, based on dry weight of starch) at 400 MPa for 5, 15 and 30 min and at 45°C for 2 h, respectively. Swelling power and solubility of both non‐thermally and conventionally cross‐linked corn starches were relatively lower than those of native corn starch. The pressure holding time did not affect the solubility and swelling power of non‐thermally cross‐linked corn starches. X‐ray diffraction patterns and relative crystallinity were not significantly altered by both conventional and non‐thermal cross‐linking. DSC thermal characteristics of both non‐thermally and conventionally cross‐linked corn starches were not significantly changed indicating that the double helical structure of amylopectin was not influenced by both conventional and non‐thermal cross‐linking reactions. Both non‐thermal and conventional cross‐linking greatly affected the Rapid Visco Analyser (RVA) pasting properties, such as increase in pasting temperature and decrease in peak viscosity compared to native starch. This result suggests that in case of cross‐linking using POCl₃, both non‐thermal and conventional methods result in similar physicochemical properties and non‐thermal cross‐linking with POCl₃ can reduce the reaction time from 2 h to 15 min. This work shows the potential and possibility of non‐thermal starch modification and provides the basic and scientific information on the physicochemical properties of non‐thermally cross‐linked corn starches with phosphorus oxychloride using UHP.     

Influence of Jet‐Cooking Temperature and Ionic Strength on Size and Structure of Cationic Potato Amylopectin Starch as Measured by Asymmetrical Flow Field‐Flow Fractionation Multi‐Angle Light Scattering

Asymmetrical flow field‐flow fractionation (AsFlFFF) in combination with multi‐angle light scattering (MALS) was applied to cationic potato amylopectin (CPAP) to investigate how molar mass, root‐mean‐square (r.m.s.) radius and shape was influenced by different conditions of jet‐cooking. The effect of different jet‐cooking temperatures in the range 110°C – 140°C was studied in an excess steam jet‐cooker. This equipment is used in the industry for dissolution of starch and starch derivatives before technical application. The effect of different ionic strengths conditions was examined in the range of 10–200 mM. The weight‐average molar mass decreased from about 34×10⁷ g/mol to 2.6×10⁷ g/mol when the jet‐cooking temperature was increased from 110°C to 140°C. Concurrently the root‐mean‐square radius decreased from ca 380 nm to 90 nm. The decrease in size was reflected by a decrease in viscosity with increasing temperature. The root‐mean‐square radius was reduced when increasing the ionic strength. This decrease in size was correlated with a decrease in viscosity. Conformation and Kratky plots showed that at low ionic strength (≤ 10 mM) CPAP behaved as a flexible chain with high degree of branching, close to hyperbranching. Increase of the ionic strength gave a more compact structure and changes in the internal structure were observed as well. Consequently, by using AsFlFFF – MALS the effect of technical processing on the molar mass, molecular radius, conformational structure, and shape could be determined in a size region where standard methodology commonly fails.     

Isolation of a Recombinant Bacillus sp. TS‐23 α‐Amylase by Adsorption‐Elution on Raw Starch

A Bacillus sp. TS‐23 α‐amylase produced by recombinant Escherichia coli was adsorbed onto raw starch and the adsorbed enzyme was eluted with maltose or maltodextrin in 50 mM Tris/HCl buffer (pH 8.5). The adsorption‐elution procedure resulted in a yield of 53% α‐amylase activity and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS/PAGE) analysis showed that the eluted α‐amylase had a molecular mass of approximately 64 kDa. Raw starch could be used repeatedly in the adsorption‐ elution cycle with good reproducibility. Scanning electron microscopy of the isolated corn starch exhibited a smooth appearance of the granules before adsorption and only a small change in appearance after three adsorption‐elution cycles. These results suggest that the raw starch adsorption‐elution technique has a great potential in the isolation of Bacillus sp. TS‐23 α‐amylase from the culture broth of recombinant E. coli.     

Physicochemical,Microstructural, and Antibacterial Properties of β‐Chitosan and Kudzu Starch Composite Films

Abstract: This study investigated physicochemical, microstructural, and antibacterial properties of β‐chitosan–kudzu starch composite films with addition of 0%, 20%, 60%, or 100% kudzu starch (w starch/w chitosan) in 1% chitosan solution. Molecular interactions between chitosan and kudzu starch and the crystal structure of the films were also determined. Adding 60% kudzu starch reduced water vapor permeability and solubility of pure β‐chitosan film by about 15% and 20%, respectively, whereas mechanical strength and flexibility of the film were increased about 50% and 25%, respectively. Micrograph showed that β‐chitosan film was totally amorphous, and the composite films generally became rougher with more starch added. Fourier transform infrared and X‐ray diffraction spectra showed that the 2 film‐forming components were compatible with each other. Pure β‐chitosan film resulted in 9.5 and 11.5 log CFU/mL reduction in Escherichia coli and Listeria innocua based on plate count method, respectively. Addition of kudzu starch reduced the antibacterial activity of film, but still achieved 8.3 and 10.3 log CFU/mL reduction in E. coli and L. innocua, respectively when kudzu starch to chitosan weight ratio was 1:1. Reduced antibacterial activity might attribute to the interaction of amino groups in β‐chitosan with the hydroxyl groups in kudzu starch. This study demonstrated that kudzu starch effectively improved water barrier of β‐chitosan film, and the composite films retained strong antibacterial ability. Practical Application: One percent of β‐chitosan containing 60% kudzu starch (w/w chitosan) composite films possessed better mechanical and water barrier properties than pure β‐chitosan films, and showed strong antibacterial activity against both Gram‐positive and Gram‐negative bacteria. The films may be used as wraps or coatings to prolong the shelf life of different foods or other similar applications.     

Grafting of 2‐(Dimethylamino)ethyl Methacrylate onto Potato Starch Using Potassium Permanganate/Sulfuric Acid Initiation System

Graft copolymerization of 2‐(dimethylamino)ethyl methacrylate onto potato starch was carried out in an aqueous medium using a potassium permanganate/sulfuric acid initiation system. The grafting percentage and grafting efficiency were determined as functions of the concentrations of potassium permanganate, sulfuric acid and the monomer, and also polymerization temperature and time. The IR spectrum of the graft copolymer showed the peaks characteristic of the grafted chains. The grafting percentage and grafting efficiency increased and then decreased with increasing the concentrations of potassium permanganate, sulfuric acid, and the monomer, as well as polymerization temperature. The grafting reaction was characterized by an initial fast rate followed a lower rate which leveled off after a certain time. The overall activation energy for the grafting was estimated to be 66.9 kJ/mol.