Microwave-assisted silication of potato starch

Silication of potato starch was performed by microwave irradiation and convectional heating of starch with sodium metasilicate. The study has shown that microwaves offered more selective silication than convectional heating. Depending on the dose of metasilicate products of either monoesterification or crosslinking esterification were formed. Increase in the amount of the silicating agent favoured crosslinking of starch. In the case of microwave irradiation, the C–O–SiO₂Na moieties were formed, whereas the convectional heating generated the C–O–Si–O–Si–O–C crosslinks.     

Carbon nanotubes in blends of polycaprolactone/thermoplastic starch

Despite the importance of polymer–polymer multiphase systems, very little work has been carried out on the preferred localization of solid inclusions in such multiphase systems. In this work, carbon nanotubes (CNT) are dispersed with polycaprolactone (PCL) and thermoplastic starch (TPS) at several CNT contents via a combined solution/twin-screw extrusion melt mixing method. A PCL/CNT masterbatch was first prepared and then blended with 20 wt% TPS. Transmission and scanning electron microscopy images reveal a CNT localization principally in the TPS phase and partly at the PCL/TPS interface, with no further change by annealing. This indicates a strong driving force for the CNTs toward TPS. Young's model predicts that the nanotubes should be located at the interface. X-ray photoelectron spectroscopy (XPS) of extracted CNTs quantitatively confirms an encapsulation by TPS and reveals a covalent bonding of CNTs with thermoplastic starch. It appears likely that the nanotubes migrate to the interface, react with TPS and then are subsequently drawn into the low viscosity TPS phase. In a low shear rate/low shear stress internal mixer the nanotubes are found both in the PCL phase and at the PCL/TPS interface and have not completed the transit to the TPS phase. This latter result indicates the importance of choosing appropriate processing conditions in order to minimize kinetic effects. The addition of CNTs to PCL results in an increase in the crystallization temperature and a decrease in the percent crystallinity confirming the heterogeneous nucleating effect of the nanotubes. Finally, DMA analysis reveals a dramatic decrease in the starch rich phase transition temperature (∼26 °C), for the system with nanotubes located in the TPS phase.     

Extrusion of pectin/starch blends plasticized with glycerol

The microstructural and thermal dynamic mechanical properties of extruded pectin/starch/glycerol (PSG) edible and biodegradable films were measured by scanning electron microscopy (SEM) and thermal dynamic mechanical analysis (TDMA). SEM revealed that the temperature profile (TP) in the extruder and the amount of water present during extrusion could be used to control the degree to which the starch was gelatinized. TDMA revealed that moisture and TP during extrusion and by inference the amount of starch gelatinization had little effect on the mechanical properties of PSG films. Furthermore, TDMA revealed that PSG films underwent a glass transition commencing at about −50°C and two other thermal transitions above room temperature. Finally, it was concluded that the properties of extruded PSG films were comparable to those cast from solution.     

Developing hydroxypropyl methylcellulose/hydroxypropyl starch blends for use as capsule materials

Blends of hydroxypropyl methylcellulose (HPMC) with up to 70% hydroxypropyl starch (HPS) were developed for use as hard capsule materials. Polyethylene glycol (PEG) was used as both a plasticizer and a compatibilizer in the blends. In order to prepare hard capsules for pharmaceutical application using the well-established method of dipping stainless steel mold pins into solution then drying at certain temperature, equilibrated solutions with higher solids concentration (20%) were investigated and developed. The solutions, films and capsules of the different HPMC/HPS blends were characterized by viscosity, transparency, tensile testing, water contact angle, SEM, as well as FTIR. The results showed that the blend system is immiscible but compatible in certain degree, especially after adding PEG. The hydroxypropylene groups grafted onto both cellulose and starch improved the compatibility between the HPMC and the modified starch. The higher viscosity of starch at lower temperature improved the viscosity balance of the system, which enlarged the operation window for the dipping–drying technique. The PEG increased the transparency and toughness of the various blends. By optimizing temperature and incubation time to control viscosity, capsules of various blends were successfully developed.     

Microwave-assisted methylation of cassava starch with dimethyl carbonate

A novel and environmentally friendly process for the methylation of cassava starch with dimethyl carbonate (DMC) could be accelerated by employing a combined strategy: using disodium hydrogen phosphate (Na₂HPO₄) as the catalyst (chemical means) and microwave irradiation as the energy source (physical means). By varying the volume of 5% sodium chloride aqueous solution between 50 and 150 mL, the amount of Na₂HPO₄ between 0 and 1.25 g, the volume of DMC between 75 and 200 mL, and the microwave time from 5 to 20 min, methyl cassava starch with degree of substitution (DS) values in the range of 0.033 and 1.087 was prepared. The chemical structure of methyl cassava starch was analyzed by ¹H NMR spectroscopy.     

Degradation of different polystyrene/thermoplastic starch blends buried in soil

Blends of PS and TPS were prepared using two different plasticizers: glycerol or buriti oil by solvent casting technique. PS/TPS blends were submitted to degradation by soil burial tests in perforated boxes for 6 months and later analyzed by TG and CPMAS ¹³C NMR. After degradation, blends with glycerol presented less stages of thermal degradation and NMR signals of minor intensity compared to the original blends. The presence of TPS at contents of 50% or greater improved the degradation of the blends. After 6 months, PS/TPS blends with buriti oil presented only one thermal degradation stage with a significant increase in mass loss. Moreover, all absorptions related to starch disappeared in NMR spectra after soil buried test, probably due to the consumption of starch by microorganisms. These results revealed that PS’s degradability can be improved when TPS plasticized with buriti oil is added to it.     

Genetic modification of cassava for enhanced starch production

To date, transgenic approaches to biofortify subsistence crops have been rather limited. This is particularly true for the starchy root crop cassava ( Manihot esculenta Crantz). Cassava has one of the highest rates of CO₂ fixation and sucrose synthesis for any C3 plant, but rarely reaches its yield potentials in the field. It was our hypothesis that starch production in cassava tuberous roots could be increased substantially by increasing the sink strength for carbohydrate. To test this hypothesis, we generated transgenic plants with enhanced tuberous root ADP-glucose pyrophosphorylase (AGPase) activity. This was achieved by expressing a modified form of the bacterial glgC gene under the control of a Class I patatin promoter. AGPase catalyses the rate-limiting step in starch biosynthesis, and therefore the expression of a more active bacterial form of the enzyme was expected to lead to increased starch production. To facilitate maximal AGPase activity, we modified the Escherichia coli glgC gene (encoding AGPase) by site-directed mutagenesis (G336D) to reduce allosteric feedback regulation by fructose-1,6-bisphosphate. Transgenic plants (three) expressing the glgC gene had up to 70% higher AGPase activity than control plants when assayed under conditions optimal for plant and not bacterial AGPase activity. Plants having the highest AGPase activities had up to a 2.6-fold increase in total tuberous root biomass when grown under glasshouse conditions. In addition, plants with the highest tuberous root AGPase activity had significant increases in above-ground biomass, consistent with a possible reduction in feedback inhibition on photosynthetic carbon fixation. These results demonstrate that targeted modification of enzymes regulating source–sink relationships in crop plants having high carbohydrate source strengths is an effective strategy for increasing carbohydrate yields in sink tissues.     

The plasticizing effect of alginate on the thermoplastic starch/glycerin blends

Corn starch and corn starch–alginate (5–15%) blends plasticized with 35% glycerin were prepared, water was intentionally excluded from the formulations. Torque rheometry measurements were carried out during the processing of the blends in a batch counterrotating twin screw mixer. A progressive decrease in the plasticization energy of the blends was observed as the alginate content was increased, with a 5-fold decrease for the blend with the higher alginate content (15%). The steady state torque of the plasticized melted blends also showed a decrease as alginate content was increased; with a drastic drop occurring for the formulation with higher alginate content. After mixing, test specimens for mechanical, thermal and microstructural testing were made by compression molding. A decrease in the elastic properties and an increase in elongation at break and impact resistance was observed when alginate content was increased in the blends. The transition of the materials towards a more viscous behavior, as alginate content was increased, was confirmed by differential scan calorimetric analysis. For the corn starch–alginate blends glass transitions were detected in the temperature range −60 to −90 °C. Scanning electron microscopy was used to examine the morphology of cryofractured surfaces of the molded test specimens. A reduction of the granular crystalline structures typical of corn starch was observed as alginate content was increased in the blends. The experimental evidence presented in this work indicates that, when water is excluded from thermoplastic corn starch preparation, alginate acts synergistically with glycerin increasing the degree and efficiency of the plasticization process.     

Nano clay reinforced PCL/starch blends obtained by high energy ball milling

Sodium montmorillonite was incorporated into a poly(ε-caprolactone)–starch blend by means of a ball mill. The structural organization and physical (mechanical, thermal and barrier) properties were analyzed and correlated with the milling conditions. Scanning electron microscopy and X-ray characterization show that the milling process can improve the compatibilization between the PCL and the starch phases, while promotes the dispersion of clay minerals at nanometric level. The milling time strongly influences the mechanical and barrier properties. In particular, the best results in terms of elastic modulus and permeability coefficient were achieved with a complete delamination of the pristine clay structure. In summary, the milling process not only has demonstrated to be a promising compatibilization method for immiscible PCL–starch blends, but it can be also used to improve the dispersion of nanoparticles into the polymer blends.     

Enzymatic modification of cassava starch by bacterial lipase

Enzymatic modification of starch using long chain fatty acid makes it thermoplastic suitable for a myriad of industrial applications. An industrial lipase preparation produced by Burkholderia cepacia (lipase PS) was used for modification of cassava starch with two acyl donors, lauric acid and palmitic acid. Reactions performed with palmitic acid by liquid-state and microwave esterification gave a degree of substitution (DS) of 62.08% (DS 1.45) and 42.06% (DS 0.98), respectively. Thermogravimetric analysis showed that onset of decomposition is at a higher temperature (above 600°C) for modified starch than the unmodified starch (280°C). Modified starch showed reduction in α-amylase digestibility compared to native starch (76.5–18%). Swelling power lowered for modified starch as esterification renders starch more hydrophobic, making it suitable for biomedical applications as materials for bone fixation and replacements, carriers for controlled release of drugs and bioactive agents. Thus enzymatic esterification is ecofriendly.     

Detection of synergistic interactions of polyvinyl alcohol–cassava starch blends through DSC

The synergistic interaction of polyvinyl alcohol (PVOH) and cassava starch was studied by differential scanning calorimetry (DSC) method. Film of the PVOH–cassava starch blends were prepared by solution cast method. Originally, cassava starch film did not show presence of any endothermic peaks in DSC thermogram. However, after adding PVOH to cassava starch, the PVOH–cassava starch blend films showed obvious endothermic peaks with onset and end-point temperatures higher than neat PVOH film. In addition, the PVOH–cassava starch blends have experimental enthalpy of melting higher than theoretical values. This evidence shows that the interactions between PVOH and cassava starch molecules are extensively strong. Due to the synergistic interactions of PVOH and cassava starch, it is postulated that incorporation of 65–75 wt.% of PVOH in cassava starch blend has physical bonding equivalent to neat PVOH.     

Biological denitrification using cross-linked starch/PCL blends as solid carbon source and biofilm carrier

A novel kind of cross-linked starch/polycaprolactone (SPCL11) was prepared and used as carbon source and biofilm attachment carrier for denitrifying bacteria. The results showed that the average denitrification rate was 0.027 mg NO?-N/(g·h) in batch tests. The continuous fixed-bed experiments indicated that more than 90% NO?-N was removed, the denitrification rate reached 26.86 mg NO?-N/(L·h), and NO?-N concentration was below 0.16 mg/L. The formation of NH?-N was observed, but usually below 1.0 mg/L. Rapid biodegradation of starch on the surfaces of SPCL11 granules could cause an initial excess release of dissolved organic compound (DOC), and shortening HRT from 2h to 1h can result in sharp decrease of DOC.     

Physical blends of starch graft copolymers as matrices for colon targeting drug delivery systems

Colon targeting drug delivery systems have attracted many researchers due to the distinct advantages they present such as near neutral pH, longer transit time and reduced enzymatic activity. Moreover, in recent studies, colon specific drug delivery systems are gaining importance for use in the treatment of local pathologies of the colon and also for the systemic delivery of protein and peptide drugs.In previous works, our group has developed different types of hydrophilic matrices with grafted copolymers of starch and acrylic monomers with a wide range of physicochemical properties which have demonstrated their ability in controlled drug release. Since the cost of synthesizing a new polymeric substance and testing for its safety is enormous, polymer physical blends are frequently used as excipients in controlled drug delivery systems due to their versatility. So, the aim of this work is to combine two polymers which offer different properties such as permeability for water and drugs, pH sensitivity and biodegradability in order to further enhance the release performance of various drugs. It was observed that these physical blend matrices offer good controlled release of drugs, as well as of proteins and present suitable properties for use as hydrophilic matrices for colon-specific drug delivery.     

Crystallinity and morphology in films of starch, amylose and amylopectin blends

Films of potato starch, amylose, and amylopectin and blends thereof were prepared by solution casting and examined using X-ray diffraction, light microscopy, transmission electron microscopy, and differential scanning calorimetry. Amylose films had a relative crystallinity of about 30% whereas amylopectin films were entirely amorphous. Blending of amylose and amylopectin resulted in films with a considerably higher degree of crystallinity than could be predicted. This is explained by cocrystallization between amylose and amylopectin and possibly by crystallization of amylopectin. The crystallized material gave rise to an endotherm detected with differential scanning calorimetry. The enthalpy and peak temperature of the transition also increased as the water content decreased. When the amylose proportion in the blends was low, separate phases of amylose and amylopectin were observed by light microscopy. At higher amylose proportions, however, the phase separation was apparently prevented by amylose gelation and the formation of a continuous amylose network. The amylose network in the films, observed with transmission electron microscopy, consisted of stiff strands and open pores and became less visible as the amylose proportion decreased. The water content of the films was dependent on the microstructure and the crystallinity.     

Miscibility study of chitosan/2-hydroxyethyl starch blends and evaluation of their effectiveness as drug sustained release hydrogels

Polymeric matrices of chitosan (CS), 2-hydroxyethyl starch (HES) and their blends prepared by solvent evaporation technique, have been tested as sustained release hydrogels of ropinirole drug. X-Ray diffraction (XRD), infrared spectroscopy (FT-IR) and viscometry measurements showed that the two polymers can form miscible blends. This miscibility is owed to formed hydrogen bonds taking place between the reactive groups of CS and HES and one glass transition is recorded in all blends. Neat polymers were used to prepare solid dispersion formulations with ropinirole drug. It was found that drug was released immediately within 15-30 min from HES while the release was slower from CS matrix. Completely different were the release rates from ropinirole with physical mixtures using neat polymers and their blends. Due to the different solubility and swelling behaviour of CS and HES the release rates showed a sustained profile from the blends containing high amounts of CS.     

Mechanical properties and water vapor transmission in some blends of cassava starch edible films

The continuous increase of consumer interest in quality, convenience and food quality has encouraged further research into edible films and coatings from natural polymers, such as polysaccharides. Ecoefficient products are the new generation of biobased products prepared with sustainable materials, that agree with ecological and economic requirements including environmentally acceptable disposal of post-user waste. The numerous potential applications of natural polymers such as polysaccharides stimulated the study with edible films based on cassava starch. Blends of glycerol (GLY) and polyethylene glycol (PEG) as plasticizers, and glutaraldehyde (GLU) as crosslinking agent were prepared in order to determine the mechanical properties and water vapor transmission of those films. A response surface methodology was applied on the results to identify the blend with the best mechanical properties and lowest water vapor transmission. The crosslinking effect of glutaraldehyde in the films can be observed. The plasticizing action of polyethylene glycol was restrained by more than 0.5 g of glutataraldehyde. The use of glycerol was less evident for this property even after 284 h of contact time with water vapor.     

Surface modification of maize starch films by low-pressure glow 1-butene plasma

Plasma polymerisation was used to modify the surface of maize starch films in order to reduce their water affinity. Films were prepared by casting starch suspensions heated for different periods of time. Glycerol was added as a plasticiser. To produce a hydrogenated-carbon coating, films were exposed to low-pressure glow plasma generated in 1-butene gas from a radio frequency diode sputtering system. Atomic force microscopy (AFM) was used to investigate possible changes in surface morphology and roughness of plasma-coated films in relation to the corresponding substrates. AFM phase contrast images at high magnification revealed characteristic features at the surfaces of plasma-coated starch films. Water absorption experiments and contact angle measurements were carried out to verify the effect of deposited layers on the water sensitivity of those surface-modified films. The results indicated that the coating process reduced significantly the hydrophilic character of starch films.     

Citric acid and maleic anhydride as compatibilizers in starch/poly(butylene adipate-co-terephthalate) blends by one-step reactive extrusion

Starch/poly(butylene adipate-co-terephthalate) films were obtained by one-step reactive extrusion using maleic anhydride (MA) and citric acid (CA) as compatibilizers. The mechanical, structural, optical and barrier properties of the films were analyzed when glycerol (GLY), CA and MA were added to the starch/PBAT (55:45, w/w) according to mixture design. FTIR analysis showed that CA and MA were able to promote esterification/transesterification reactions and that CA induced them more efficiently. When a greater proportion of compatibilizer (1.5 wt%) was used, the resulting films were more opaque and had a greater tensile strength. A greater proportion of GLY (10.0%, w/w) improved the elongation at the break of the films. The barrier properties to water vapor of the films were improved by high levels of CA (1.5 wt%) and intermediate levels of GLY (9.25 wt%). The inclusion of compatibilizers resulted in blends with improved properties, representing a potential replacement for non-biodegradable films.     

Effect of nixtamalization on the modification of the crystalline structure of maize starch

Endosperm of nixtamalized corn was analyzed using X-ray diffraction. Relative crystallinity changed with lime concentration and steeping. Diffractograms showed peaks corresponding to V-type crystalline structures, indicating formation of complexes during cooking and steeping. Diffraction patterns of the soluble fraction showed that complexed amylose can be leached out during solubilization. While diffraction patterns of the insoluble fraction suggested that some of the formed complexes remain in this fraction. During alkali steeping, release of amylose is strongly inhibited as indicated by the pronounced decrease in the starch–I₂ absorbance of the lime treated samples compared to the lime-free treated sample. This decrease is interpreted as evidence of starch cross-linking during the nixtamalization process. Differences in starch–I₂ absorbance and in X-ray diffraction patterns of the soluble fractions suggested that lime treatment could also modified formation of amylose complexes with lipids.     

Microwave-assisted extraction of cyclotides from Viola ignobilis

Cyclotides are an interesting family of circular plant peptides. Their unique three-dimensional structure, comprising a head-to-tail circular backbone chain and three disulfide bonds, confers them stability against thermal, chemical, and enzymatic degradation. Their unique stability under extreme conditions creates an idea about the possibility of using harsh extraction methods such as microwave-assisted extraction (MAE) without affecting their structures. MAE has been introduced as a potent extraction method for extraction of natural compounds, but it is seldom used for peptide and protein extraction. In this work, microwave irradiation was applied to the extraction of cyclotides. The procedure was performed in various steps using a microwave instrument under different conditions. High-performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI–TOF) results show stability of cyclotide structures on microwave radiation. The influential parameters, including time, temperature, and the ratio of solvents that are affecting the MAE potency, were optimized. Optimal conditions were obtained at 20 min of irradiation time, 1200 W of system power in 60 °C, and methanol/water at the ratio of 90:10 (v/v) as solvent. The comparison of MAE results with maceration extraction shows that there are similarities between cyclotide sequences and extraction yields.