Hydrophobic modification of starch via grafting with an oxazoline-derivative

The application of starch in tailored materials is limited because of the high hydrophilicity of the polysaccharide. Thus, simple and efficient paths for the hydrophobic modification of native, cationic or thermoplastic starches by means of a radical grafting process using bifunctional fatty acid oxazoline derivatives were investigated. The modified starches can be manufactured by means of an extrusion process showing high grafting yields at adjustable grafting contents from 2.5 to 30%. Resulting starch materials are distinguished by modified water absorption properties and solubility, which is a prerequisite for their application in the paper or painting industry. Moreover the structure of the oxazoline derivative supplies the opportunity for reactive blending of different polymers carrying carboxyl, amino, mercapto or epoxy groups. This is exemplarily shown for the conversion with biodegradable polyesters, which contain carboxylic acid functions. Film forming properties of the new starch-based materials were studied. Results of the examination of manufactured shouldered test bars of starches coupled with biodegradable polyesters are presented as well.     

非对称场流分离系统的构建及其在淀粉颗粒粒径表征中的应用

淀粉颗粒粒径与分子尺寸分别在1～100μm和20～250 nm之间,是影响淀粉功能特性的重要因素之一.非对称场流分离(AF4)是一种基于样品与外力场相互作用机制的分离技术,已应用于表征淀粉分子尺寸分布.商品化的AF4系统的粒径检测范围为1 nm～10μm,对于淀粉颗粒粒径表征具有一定的局限性.该文研制了AF4分离系统;...     

酸解淀粉物理化学性质的研究

玉米淀粉和马铃薯淀粉分别在35C条件下用浓度为2．4mol／L的HCI处理不同时间,采用X射线衍射分析、差热分析和扫描电镜等测试方法对酸解后的淀粉颗粒进行结构和性能分析。结果表明,淀粉的酸解过程可分为两个阶段：首先淀粉无定形区进行水解,颗粒结晶度、结晶热稳定性和酶解速率增加;随着酸解时间的延长,结晶结构受到破坏,热稳定性降低,达到酶解平衡的时间减少。酸解4d时,玉米淀粉和马铃薯淀粉颗粒的结晶均最完整,结晶转变温度最高,分别为87．0C和93．5C。     

Studies on the properties and characteristics of starch-LDPE blend films using cross-linked, glycerol modified, cross-linked and glycerol modified starch

Corn starch was modified by cross-linking with epichlorohydrin and plasticizer glycerol. X-ray diffraction studies showed that relative crystallinity of the native and cross-linked starch were similar and were not affected by cross-linking. Different films were prepared by blending corn starch, cross-linked starch or glycerol modified starch in LDPE. The mechanical properties of the films were studied for tensile strength, elongation, melt flow index, and burst strength. The properties of the blend films were compared with LDPE films. It was observed that with the blending of 7.5% native starch, there was a decrease in tensile strength, elongation and melt flow index but burst strength increased. The tensile strength, elongation and melt flow index of the films containing cross-linked starch was considerably higher than those containing native starch but the burst strength showed a reverse trend. For native starch and cross-linked starch modified with glycerol, the elongation and melt flow index of the films increased but burst strength decreased. Surface scanning of the blend films were done by scanning electron microscope. Film containing cross-linked starch/glycerol modified starch in the blend was observed to be smoother than the native starch blend films.     

Enzyme catalysis of insoluble cornstarch granules: Impact on surface morphology, properties and biodegradability

Granular cornstarch was treated with microbial glucoamylase (50 mM sodium acetate buffer at pH 5.5 at 30 °C, 150 rpm) for up to 8 h. Treated starch was recovered and evaluated for changes in granular morphology, chemical properties, thermal properties, crystallinity and impact on its biodegradability. As the enzyme treatment progressed, reducing sugars began to accumulate in the liquid culture media (total of 6% in 8 h) and the granule suffered roughly 6% weight loss within 8 h of incubation. While the granules appeared intact morphologically, numerous small pits developed throughout the surface of the granules as a result of the enzyme treatment. Even after 8 h of enzyme treatment, the pitted granules were not disrupted and remained intact. X-ray diffraction indicated no loss of crystallinity in the enzyme treated granules but rather an increase in relative crystallinity, suggesting that the enzyme preferentially catalyzed the anhydroglucose units in amorphous regions of the granule. These findings were further supported by FTIR data suggesting that granules become more resistant to enzyme attack as amorphous amylose is hydrolyzed faster than the crystalline amylopectin domains. These results also suggest that variations in the crystallinity of different types of starches have the potential to affect their rates of biodegradation. Enzyme treated starch granules exhibited resistance to biodegradation, and the degree of resistance was related to the length of enzyme treatment. Granules treated with enzyme for a total of 7 h and subjected to biodegradation in soil produced 40-50% less CO₂ in a closed circuit respirometer compared to the untreated samples. Differential scanning calorimetry (DSC) thermograms showed an endothermic reaction with little change in the onset and peak temperatures indicating that glucoamylase started by degrading the starch granules from the surface.     

Heterogeneity of laser‐irradiated films of polyvinyl alcohol/starch blends: effect of glycerol content

The present paper reports the results of studies on the effect of laser irradiation on the morphology and thermal properties of starch/polyvinyl alcohol (PVA) blend, with varying glycerol concentration. Differential scanning calorimeter results showed that laser irradiation increased the heat of fusion (ΔH_fus), heat of crystallization (ΔH_cry), temperature of melting (T_m), temperature of crystallization (T_cry) and percentage crystallinity as a function of the amount of glycerol. It is believed that breakdown of the intermolecular hydrogen bonding between the starch and PVA causes an increase in the blend heterogeneity. These results are corroborated with the findings from thermogravimetric analysis and scanning electron microscope images. Copyright © 2013 John Wiley & Sons, Ltd.     

Gamma irradiation of sorghum flour: Effects on microbial inactivation, amylase activity, fermentability, viscosity and starch granule structure

Malted and un-malted sorghum (Sorghum bicolor (L.) Moench) flour was gamma irradiated with a dose of 10 kGy and then re-irradiated with 25 kGy. The effects of irradiation on microbial decontamination, amylase activity, fermentability (using an amylolytic L. plantarum MNC 21 strain), starch granule structure and viscosity were determined. Standard methods were used during determinations. The 10 kGy dose had no effect on microbial load of un-malted flour but reduced that of malted flour by 3 log cycles. Re-irradiation resulted in complete decontamination. Irradiation of malt caused a significant (p<0.05) reduction in alpha and beta amylase activity (22% and 32%, respectively). Irradiation of un-malted flour increased the rates of utilization of glucose and maltose by 53% and 100%, respectively, during fermentation. However, microbial growth, rate of lactic acid production, final lactic acid concentration and pH were not affected. Starch granules appeared normal externally even after re-irradiation, however, granules ruptured and dissolved easily after hydration and gelatinization. Production of high dry matter density porridge (200 g dry matter/L) with a viscosity of 3500 cP was achieved by irradiation of un-malted flout at 10 kGy. Gamma irradiation can be used to decontaminate flours and could be utilized to produce weaning porridge from sorghum.     

Structural and mechanical properties of edible films from composite mixtures of starch,dextrin and different types of chemically modified starch

Abstract

Recent regulations restricting the use of one-use-plastics open the possibility to develop starch-based edible packaging material. The objective of this work was to determine the effect of three different modified starches on starch and dextrin composite edible films by a mixture design approach on edible films’ mechanical properties. The amylose content of chemically modified starches influenced their swelling capacities, where higher amylose content was inversely related to water-power uptake and directly related to film thickness. CMS3 Nifrastarch-TS edible films, with higher amylose content, presented higher puncture force and tensile strength, but lower puncture deformation and elongation, related to a less smooth surface, according to atomic force micrographs. The use of CMS1 Gelamil-100, with lower amylose content, decreased stiffness but increased films’ stretching, presenting higher surface smoothness film topography. The use of commercial chemical modified starches in combination with starch and dextrin will allow to control of edible film thickness and hence, mechanical properties, depending on food covering necessities.     

Effect of natamycin on the physicochemical properties of corn starch based films and their effect on Penicillium spp. activity

The incorporation of antimicrobials in foods by means of the use of films where they are entrapped collaborates to decrease their diffusion rate. In this work, the physicochemical properties of starch-based films loaded with 1% wt. natamycin were analyzed, and the antifungal activity of these films was evaluated against Penicillium spp..

Variations in the properties of films with 1% natamycin were minimal, leading to the conclusion that this material could be applied to avoid mold development on the surface semi-hard cheeses. Corn starch-based films containing natamycin at 1% w/w inhibited the Penicillium spp. growth in a solid matrix.     

Synthesis and characterization of corn starch based green composites reinforced with Saccharum spontaneum L graft copolymers prepared under micro-wave and their effect on thermal, physio-chemical and mechanical properties

In this paper, green composites of the corn starch were developed by using resorcinol-formaldehyde (Rf) as the cross-linking agent and reinforced with graft copolymers Saccharaum spontaneum L(Ss) and methyl methacrylates (MMA) as principal monomer and its binary mixture with acrylamide (AAm), acrylonitrile(AN), acrylic acid (AA) prepared under micro-wave. The matrix and composites were found to be thermally more stable than the natural corn starch backbone. There was improvement in physico-chemical and mechanical properties of composite were found to exhibit better than matrix. Ss-g-poly(MMA)-MW reinforced composites were found to exhibit better tensile strength, on the other hand Ss-g-poly(MMA + AA)-MW reinforced composites showed maximum compressive strength and wear resistance than other graft copolymers reinforced composite and the basic matrix. Further the matrix and composites were subjected for biodegradation studies through soil composting method. Different stages of biodegradation were evaluated through FT-IR studies and scanning electron microscopic (SEM) techniques.     

Characterizations of modified cassava starch with long chain fatty acid chlorides obtained from esterification under low reaction temperature and its PLA blending

In contrast to typical starch esterification in an aqueous solution, which are carried out at elevated to ambient reaction temperatures, a low reaction temperature was applied in this study to minimize the starch chain hydrolysis. The physical properties of the modified starch, obtained from an esterification of cassava starch with long-chain fatty acid chlorides carried out in aqueous media at 4°C, were characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and contact angle measurements. The modified starches show improvement in thermal stability and hydrophobicity, which can be further optimized by varying the types of acid chlorides and the reaction conditions. The starch products have high potential for use as fillers for biodegradable polymers, especially polylactic acid (PLA), as their tunable hydrophobicity can impose strong effect on controlling of the PLA's hydrolytic degradation rate for specific applications. Results on mechanical properties of the blends between the modified starch and PLA show an improvement in modulus of the polymer.     

The effect of chemical modification on the strength of wood and bonded wood joints

The effect of propionic, crotonic or methacrylic anhydride (MA) modification on the lab joint strength of monomer bonded veneer strips was investigated. Lap joints were formed by hot pressing veneers of modified wood with monomer in the presence of free radical initiator and bond strength was determined on an Automatic Bonding Evaluation System tensile tester. Test results indicated that chemical treatment improved bond quality between hydrophilic wood and hydrophobic monomer. Extremely strong bonds (wet and dry conditions) formed in the case of MA modified veneer strips. In addition, the effect of chemical modification on the mechanical properties of strips was also investigated. Chemical modification had a detrimental effect on the mechanical properties.     

Effect of dry heat modification and the addition of Chinese quince seed gum on the physicochemical properties and structure of tigernut tuber starch

To expand industrial utilization of tigernut starch and meet the demand for industrial starch, the influence of dry heat treatment (130 °C for 2 h and 4 h, 7% moisture) on the functional properties and structure of tigernut starch alone and mixed with Chinese quince seed gum (1% w/w) was investigated. Modifying the starch significantly (p < 0.05) increased peak, trough and final viscosity, and reduced the swelling power and gelatinization enthalpy. In addition, the freeze–thaw stability and pseudoplastic flow were enhanced by this modification process. Microscopic and crystalline structure results indicate that dry heat treatment without gum destroys the surface and the internal crystals of the starch granules, but when gum was present, the granule becomes more resistant to dry-heating. Overall, the treatment with dry heat and the addition of Chinese quince seed gum improved the physicochemical properties of tigernut starch, in particular by increasing freeze–thaw stability and viscosity to expand the application of the starch in food industry.     

Carboxymethylation of corn starch and characterization using asymmetrical flow field-flow fractionation coupled with multiangle light scattering

Asymmetrical flow field-flow fractionation (AsFlFFF) was coupled online with multiangle light scattering (MALS) to study the changes in the molecular weight and the size distribution of the corn starch during carboxymethylation. A corn starch was derivatized with sodium chloroacetate in alcoholic medium under alkaline condition to produce carboxymethyl starches (CMS) having various degrees of substitution (DS). The change in thermal characteristics and granule structure of the native corn starch and CMS were compared using Thermogravimetric analysis and scanning electron microscope. The ionic strength of the carrier liquid (water with 0.02% NaN₃) was optimized by adding 50 mM NaNO₃ to minimize the interactions among the starch molecules and between the starch molecules and the AsFlFFF membrane. A field-programmed AsFlFFF allowed determination of the molecular weight distribution (MWD) of starches within about 25 min. It was found that carboxymethylation of starch results in reduction in the molecular weight due to molecular degradation by the alkaline treatment. The weight-average molecular weight (M_w) was reduced down to about 4.4 × 10⁵ from about 7.2 × 10⁶ when DS was 0.14. It seems AsFlFFF coupled with MALS (AsFlFFF/MALS) is a useful tool for monitoring the changes taking place in the molecular weight and the size of starch during derivatization.     

Effect of method of solution on observed molecular weight distribution of barley starch and starch derivatives in size exclusion chromatography

Summary Samples of native barley starch and six starch derivatives were suspended (0.1% sample concentration) in four different solvents: the eluent (pH 11 buffer), dimethylsulfoxide, 0.1 M NaOH or 0.5 M NaOH and kept in a boilling water bath for 5 to 60 minutes or shaken for 60 minutes. The average molecular weight values , and the polydispersity value were determined with a TSK PW-type column using narrow standard calibration. Only a small part of the samples dissolved in the eluent. The dissolution of sample in dimethylsulfoxide was dependent on sample type. Of the NaOH solutions, 0.5 M NaOH was the only one that dissolved all the samples. Therefore, 0.5 M NaOH appears to be the solvent of choice for starch molecules.     

Effect of pH on the Redox and Sorption Properties of Native and Phosphorylated Starches

Starch is a common biopolymer that can be used for removing heavy metal ions from aqueous solutions. A valuable property of starch is its functional diversity, which can be enhanced by chemical modification. Hydroxyl groups enclosed in the starch and formed during hydrolysis act as reducing agents of Cr(VI). The sorption properties of native starch depend mainly on the presence of carboxyl groups formed during redox processes and basic centers created during acid hydrolysis, while the superiority of phosphorylated starch is related to the presence of phosphate groups binding Cr(III) ions. The effectiveness of starch depends on a series of equilibria established in its aqueous suspension and chromate ions solution, where the pH is the driving force for these processes. In this article, a systematic discussion of pH changes being the consequence of chemical reactions unraveling the extraordinary functionalities of starch was given. It also explained the influence of establishing equilibria and chemical modifications of starch on the efficiency of chromium ion removal. This allowed for the development of a comprehensive mechanism for the interaction of Cr(VI) and Cr(III) ions with native and phosphorylated starch.     

Impact of Cassava Starch Varieties on the Physiochemical Change during Enzymatic Hydrolysis

The enzymatic modification of starch extends its industrial use to flavor delivery and probiotic encapsulants, among other uses. However, it is not known how starch from different cassava varieties responds to enzymatic hydrolysis. Starches from two Ecuadorian cassava varieties (INIAP 650, an edible starch, and INIAP 651, an industrial starch) were partially modified at three enzymatic hydrolysis degrees (0%, 30%, and 50%), and their physicochemical properties were assessed. The structural analysis revealed that both varieties showed progressive structural damage as hydrolysis increases, probably due to exo-hydrolysis. However, deeper pores were observed in INIAP 651 with the SEM analysis. The crystallinity percentage obtained by XRD analyses remained constant in INIAP 651 and decreased (by 26%) in INIAP 650 (p < 0.05). In addition, the amylose–lipid complex index in INIAP 650 remained constant, while INIAP 651 increased (p < 0.05) at 30% hydrolysis (by 93%). In both varieties, hydrolysis increased (p < 0.05) the water holding capacity (WHC) (by 10–14%) and the water binding capacity (WBC) (by 16%), but 50% hydrolysis of INIAP 650 was needed to significantly affect these properties. No differences were observed in the varieties’ thermal properties. Regarding the rheological properties, the variety did not influence the changes in the storage module (G′) and the loss modulus (G″) with the hydrolysis (p > 0.05). However, the phase angle decreased significantly (p < 0.05) with the hydrolysis, being higher in the INIAP 650 variety than in the INIAP 651 variety. In general, the results indicate that the variety affects the response of the starch granule to enzymatic hydrolysis (noticeable in the principal component analysis, PCA) and opens up the possibility to modulate starch properties.     

Effect of environment on the degradation of starch and pro-oxidant blended polyolefins

The aim of this study was to understand the rate of degradation of commercial pro-oxidant blended and starch blended High Density Polyethylene (HDPE), pro-oxidant blended Low Density Polyethylene (LDPE), and starch blended polypropylene in three different environments, namely under direct sunlight, buried in soil and immersed in marine waters for a period of 150 days. The bio-fouling parameters were also monitored in the case of polymers deployed in sea water. Exposure to sunlight showed highest weight loss (>10%) and samples buried in soil showed the lowest (∼1%). Pro-oxidant blended HDPE showed higher weight loss when compared to starch blended (22.7 as against 11%). Scanning electron microscopy revealed surface deterioration and decrease in contact angle indicated reduction in surface hydrophobicity. Increase in the carbonyl and hydroxyl groups in the infra-red spectrum of the exposed samples suggested abiotic degradation. Starch blended PP exposed to sunlight showed the highest thermo gravimetric weight loss (63.8%) followed by the same polymer buried in soil (46.1%).     

The effect of various potato cultivars at different times during growth on starch content determined by DSC

Differential scanning calorimetry (DSC) was used to determine the starch content of potato dry matter isolated from various cultivars at different times during growth. When potato dry matter was heated in the presence of excess water, a symmetrical endothermic peak resulted, which was similar to the gelatinization peak of pure starch. From the enthalpy value of potato dry matter and pure potato starch at a moisture content of 70%, the starch content in the potato dry matter can be determined. Starch content increased as growth progressed to a maximum and then decreased. The effect of moisture content and sample mass on gelatinization of dry matter and starch was also investigated. Compared to other starch analysis technique, DSC is a simple and more rapid method.     

Kinetic studies on the addition of dipropylamine to starch acrylate

Summary The kinetics of nucleophilic addition of dipropylamine to vinyl groups of starch acrylate has been investigated. The reactions were carried out under pseudo-first order conditions in tetrahydrofuran with excess amine within the temperature range from 25 to 45^oC. Pseudo-first-order rate constants for addition and the activation energy have been determined.