Two stage extrusion of plasticized pectin/poly(vinyl alcohol) blends

Blends of pectin with starch (high amylose and normal), poly(vinyl alcohol) (PVOH), and glycerol were extruded in a twin screw extruder, pelletized, and then further processed into blown film and extruded sheet using a single screw extruder. The samples were analyzed using tensile measurements, dynamic mechanical analysis, and scanning electron microscopy. PVOH levels of 24% or greater were necessary to successfully make blown film, while extruded sheet could be made at a level of 16% PVOH. Tensile strength and initial modulus of the extruded sheets were slightly higher in the machine direction than in the cross direction, while the reverse was true for elongation to break. For the blown films tensile strength tended to be higher in the transverse direction than in the machine direction, while the reverse was seen for initial modulus. Increased levels of PVOH led to increases in tensile strength and elongation to break, while initial modulus was decreased. Morphology as determined by SEM visually indicated stretching in the transverse direction of the blown films. The second stage extrusion appeared to promote -helix formation in the high amylose starch.     

Compression molding and tensile properties of thermoplastic potato starch materials

The mechanical and melt flow properties of two thermoplastic potato starch materials with different amylose contents were evaluated. The materials were prepared by mixing starch, glycerol, and water, mainly in the weight proportions of 10:3:4.5. Compression molding was used to produce sheets/films with a thickness in the range of 0.3-1 mm. After conditioning at 53% relative humidity (RH) and 23 C, the glycerol-plasticized sheets with a higher amylose content (HAP) were stronger and stiffer than the normal thermoplastic starch (NPS) with an amylose content typical for common potato starch. The tensile modulus at 53% RH was about 160 MPa for the high-amylose material and about 120 MPa for the plasticized NPS. The strain at break was about 50% for both materials. The stress at break was substantially higher for the HAP materials than for the NPS materials, 9.8 and 4.7 MPa, respectively. Capillary viscometry at 140 C showed that the high-amylose material had a higher melt viscosity and was more shear-thinning than the NPS. Dynamic mechanical measurements indicated a broad transition temperature range for both types of starch material. The main transition peaks for glycerol-plasticized starch were located at about room temperature with the transition for the HAP material being at a somewhat higher temperature than that of the NPS material with a lower amylose content. It was also noted that the processing conditions used during the compression molding markedly affected the mechanical properties of the starch material.     

Sorption of Monoterpenoids and Sesquiterpenoids by Natural Polysaccharides

Sorption of terpenoids (essential oil components) from aqueous solutions by six types of native food starches was studied by capillary gas chromatography. Sorption of volatile substances did not depend on amylose content in starch and specific surface of its granules. The degree of sorption was maximum (86%) for corn starch containing 25–28% amylose and decreased in the following order: tapioca starch (77%) > potato starch (74%) > wheat starch (70%) > high-amylose corn starch (58%) > amylopectin corn starch (57%). Amylopectin corn starch differed from other starches in the mechanism of sorption and selectivity to compounds with various functional groups.     

Sorption of mono- and sesquiterpenes by natural polysaccharides

Sorption of terpenoids (essential oil components) from aqueous solutions by six types of native food starches was studied by capillary gas chromatography. Sorption of volatile substances did not depend on amylose content in starch and specific surface of its granules. The degree of sorption was maximum (86%) for corn starch containing 25-28% amylose and decreased in the following order: tapioca starch (77%) > potato starch (74%) > wheat starch (70%) > high-amylose corn starch (58%) > amylopectin corn starch (57%). Amylopectin corn starch differed from other starches in the mechanism of sorption and selectivity to compounds with various functional groups.     

Changes in the molecular orientation and tensile properties of uniaxially drawn cellulose films

Cellulose films were prepared by dissolving lyocell fibers in LiCl/N,N-dimethylacetamide solvent and subsequently coagulating and drying them under ambient conditions. To introduce preferred orientation, the films were uniaxially drawn under air-dry and rewetted conditions, respectively. Preferred orientation was determined by birefringence measurements and by wide-angle X-ray scattering. Mechanical properties were characterized by means of tensile tests with films conditioned to standard temperatures and humidity. Drawing resulted in the substantial reorientation of cellulose, whereby the molecular chains in the amorphous regions exhibited clearly stronger reorientation than the crystalline fraction. The average degree of orientation was comparable to orientation achieved in spun cellulose fibers. Wet-drawing resulted in improved tensile strength and modulus of elasticity but reduced elongation at break. The mechanical properties of wet-drawn films are competitive with regard to cellophane and melt-blown cellulose films, particularly considering their high modulus of elasticity of up to 26 GPa, which is also comparable to values obtained for industrially produced cellulose fibers.     

Influence of amylose content on starch films and foams

After extraction of smooth pea starch and waxy maize starch from pure amylose and amylopectin fractions, films with various amylose contents were prepared by casting in the presence of water or water with glycerol. For unplasticized films, a continuous increase in tensile strength (40–70 MPa) and elongation (4–6%) was observed as amylose increased from 0 to 100%. Discrepancies with values obtained for native starches with variable amylose content and different botanical origins were attributable to variations in the molecular weights of components. Taking cell wall properties into account, the values obtained in the laboratory were used to improve the relation between the flexural behavior of extruded foams and the model of cellular solids with open cavities.

The properties of plasticized films were not improved by the presence of glycerol and remained constant when amylose content was higher than 40%. Results are interpreted on the basis of topological differences between amylose and amylopectin.     

Modified natural halloysite/potato starch composite films

Halloysite/potato starch composites were prepared by adding modified natural halloysite nanotubes into potato starch matrices to reenforce the mechanical properties of potato starch films. The halloysite/potato starch films were characterized by X-ray diffraction, scanning electron microscope and infrared spectrometry. Meanwhile, the mechanical properties and transparency of the films were studied. The results show that the modified halloysite nanotubes can be well distributed in the starch matrix and thus the tensile strength of the films was clearly enhanced. The flexibility of the films could be improved through adding glycerol although at the cost of reducing tensile strength. But incorporation of PVA could further improve the tensile strength of the halloysite/potato starch films.     

Characterization of films made with chayote tuber and potato starches blending with cellulose nanoparticles

The aim of this study was to characterize chayotextle starch films reinforced with cellulose (C) and cellulose nanoparticle (CN) (at concentrations of 0.3%, 0.5%, 0.8% and 1.2%), using thermal, mechanical, physicochemical, permeability, and water solubility tests. C was acid-treated to obtain CN. The films were prepared by casting; potato starch and C were used as the control. The solubility of the starch films decreased with the addition of C and CN compared with its respective film without C and CN. No statistical difference (α = 0.05) was found in the films added with different concentrations of C and CN. In general, the mechanical properties were improved with the addition of C and CN, and higher values of tensile strength and elastic modulus were determined in the films reinforced with CN. The melting temperature and enthalpy increased with the addition of C and CN, and the values of both thermal parameters were higher in the films with CN than with C; the enthalpy value of the film decreased when the concentration of C or CN increased in the composite. Low concentration of C and CN is better distributed in the matrix film. The addition of C and CN in the starch films improved some mechanical, barrier, and functional properties.     

Field performance and starch characteristics of high-amylose potatoes obtained by antisense gene targeting of two branching enzymes

Potato is an important crop for starch production, but there are limitations regarding the genetic variation of starch quality. In maize, starches with various properties have been available for a long time by mutational breeding. Amylose starch from potatoes differs from cereal amyloses in several functionally important aspects, such as a higher degree of polymerization. Areas of application in which the degree of polymerization is of importance include film forming and the polymeric properties of bioplastics. High-amylose potato lines have been achieved by inhibiting the two known branching enzyme forms of potato. A single inserted gene construct for the inhibition of both forms resulted in structural changes of the starch to levels of branching that were below the commercially available amylose standards of potato. The high-amylose potato lines were tested in multiple year field trials of agronomic performance and were used for the pilot plant production of starch. The introduced trait was confirmed to be stable over multiple years. The consequences of the modification were found to be an increased tuber yield, reduced starch content, smaller granule size and an increase in reducing sugars.     

Characterization of Corn Starch Films Reinforced with CaCO3 Nanoparticles

The characterization of corn starch (CS) films impregnated with CaCO₃ nanoparticles was investigated. Criteria such as morphology, crystallinity, water vapor permeability (WVP), opacity, and mechanical properties were the focus of the investigation. It was found that the CaCO₃ contents had significant effects on the tensile properties of the nanocomposite films. The addition of CaCO₃ nanoparticles to the CS films significantly increased tensile strength from 1.40 to 2.24 MPa, elongation from 79.21 to 118.98%, and Young’s modulus from 1.82 to 2.41 MPa. The incorporation of CaCO₃ nanoparticles increased the opacity of films, lowered the degree of WVP and film solubility value compared to those of the CS films. The results of scanning electron microscopy (SEM) showed that with the increase of CaCO₃ nanoparticles content in starch films, the roughness of the films increased, and pores or cavities were found on the surface of the films, while small cracks were observed in the structures of the fractured surfaces. X-ray diffraction showed that the addition of nanoparticles increased the peaks in the intensity of films.     

Effect of glycerol on behaviour of amylose and amylopectin films

The effect of water and glycerol on sorption and calorimetric T_gs of amylose and amylopectin films were examined. The mechanical properties of the films were also analysed under varying glycerol content at constant RH and temperature. Based on changes observed in sorption and tensile failure behaviour glycerol was strongly interacted with both starch polymers. Even though water was observed to be more efficient plasticiser than glycerol, glycerol also affected the T_g. But in spite of the observed decrease in T_g under low glycerol contents brittleness of the films increased based on changes in elongation. The increase in brittleness of both polymers was also in agreement with their actual behaviour. At around 20% glycerol great change in the rheological properties occurred. Above 20% glycerol amylose film showed much larger elongation than the low glycerol content films and was still strong but the amylopectin produced a very week and non-flexible film.     

Effect of addition of water-soluble chitin on amylose film

Amylose films blended with chitosan, which were free from additives such as acid, salt, and plasticizer, were prepared by casting mixtures of an aqueous solution of an enzymatically synthesized amylose and that of water-soluble chitin (44.1% deacetylated). The presence of a small amount of chitin (less than 10%) increased significantly the permeability of gases (N2, O2, CO2, C2H4) and improved the mechanical parameters of amylose film; particularly, the elastic modulus and elongation of the blend films were larger than those of amylose or chitin films. No antibacterial activity was observed with either amylose or water-soluble chitin films. But amylose films having a small amount of chitin showed strong antibacterial action, suggesting a morphological change in water-soluble chitin on the film surface by blending with amylose molecule. These facts suggested the presence of a molecular complex of amylose and chitosan.     

Structure–properties relationship in cross-linked high amylose starch cast films

Cross-linked high amylose starch cast films were prepared to study the effect of cross-linking degree on various properties in normal environmental conditions. Mechanical tensile properties (Young's modulus, elongation at break, tensile strength), water vapour transmission rate (WVTR) and oxygen permeability coefficients of cast films were determined as a function of cross-linking degree and percentage of free humidity. Cross-linking degree and degree of crystallinity are closely related and seem to have non-negligible opposite effect on the properties of interest. By using increased amounts of cross-linking agents, the effect of cross-linking degree tends to reduce the degree of crystallinity modulating thus mechanical properties, water vapour permeability and oxygen permeability coefficients. Yield strength, tensile strength at break, WVTR versus cross-linking degree showed a non-monotonous behaviour. Maximal values for these properties were reached for moderate cross-linking degree. Optimal crystalline/amorphous ratio in the films may induce interactions and balanced effects, which would be responsible for the non-linear behaviour of some of the investigated properties. By cross-linking with epichlorohydrin in the range 1–10 g crosslinker/100 g polymer, the mechanical properties of films are still related to water content and water vapour permeability remains high compared to some synthetic polymeric materials.     

Thermal, Mechanical and Microstructures Properties of Cellulose Derivatives Films: A Comparative Study

The proposal in this study was to evaluate the physical properties of different biopolymers films. The materials used were: pectin, carboxyl methylcellulose, methylcellulose, hydroxyl propylcellulose, hydroxypropyl-methylcellulose, and corn waxy starch; from these polysaccharides aqueous dispersions were prepared to 3% (w/v) for obtained films. In these biopolymer films, the thermal diffusivities (α) was evaluated by the Open Photoacoustic Cell method; also, their mechanical properties as tensile strength, elongation, and Young’s modulus were measured, their crystallinity percentage was evaluated by X-ray diffraction and microstructure through atomic force microscopy in contact mode. From the polysaccharide films, it was observed that most of them were flexible and transparent. In the case of the films, mechanical properties were found that the highest value of tensile strength and Young’s modulus corresponded to carboxyl methylcellulose with 69.17 and 1,912.20 MPa values, respectively. Also, Open Photoacoustic Cell method and X-ray diffraction measurements showed that there exist a correlation between the thermal diffusivity values and the crystallinity measured in the biopolymer films. It was also observed that α values of cellulose derived was affected by the substitution group in the molecule, reaching the highest α value, the films of carboxyl methylcellulose. Regarding the microstructural of the films, starch showed the highest roughness value (88.6 nm) whereas hydroxypropyl-methylcellulose resulted with the lowest roughness value (7.67 nm).     

Locations of hypochlorite oxidation in corn starches varying in amylose content

The general oxidation mechanism by hypochlorite on starch has been well studied, but the information on the distribution of the oxidation sites within starch granules is limited. This study investigated the locations where the oxidation occurred within corn starch granules varying in amylose content, including waxy corn starch (WC), common corn starch (CC), and 50% and 70% high-amylose corn starch (AMC). Oxidized corn starches were surface gelatinized by 13 M LiCl at room temperature to different extents (approximately 10%, 20%, 30%, and 40%). The surface-gelatinized remaining granules were separated and studied for structural characteristics including carboxyl content, amylose content, amylopectin chain-length distribution, thermal properties, and swelling properties. Oxidation occurred mostly at the amorphous lamellae. More carboxyl groups were found at the periphery than at the core of starch granules, which was more pronounced in oxidized 70% AMC. More amylose depolymerization from oxidation occurred at the periphery of CC. For WC and CC, amylopectin long chains (>DP 36) were more prone to depolymerization by oxidation. The gelatinization properties as measured by differential scanning calorimetry also supported the changes in amylopectin fine structure from oxidation. Oxidized starches swelled to a greater extent than their unmodified counterparts at all levels of surface removal. This study demonstrates that the locations of oxidation and physicochemical properties of oxidized starches are affected by the molecular arrangement within starch granules.     

Extrusion processing of high amylose potato starch materials

Thermoplastic starch was prepared by mixing native high amylose potato starch and normal potato starch in a Buss co-kneading extruder at starch to glycerol ratios of 100:45 and 100:30. The materials were also conditioned to different moisture contents at different relative humidities at 23 °C. After the mixing, the compounds were extruded into sheets with a Brabender laboratory extruder. The thermoplastic high amylose materials exhibited a higher melt viscosity than the normal potato starch materials when conditioned at 53% relative humidity. Increasing the moisture content in HAP from 27% to 30% (by weight) lowered the melt viscosity to the same level as that of normal potato starch with a moisture content of 28%. In general, the high amylose materials were more difficult to extrude than the thermoplastic material based on normal starch. The main extrusion problems encountered with the high amylose starch were unstable flow, insufficient melt tenacity and clogging of the die. By increasing the moisture content, increasing the compression ratio of the screw and increasing the rotation rate of the screw, the problems were reduced or eliminated. However, only with a starch to glycerol ratio of 100:45 was an acceptable extrusion result obtained. Extruded sheets of such high amylose materials had a stress at break of about 5 MPa at room temperature and 53% relative humidity, whereas the corresponding value for normal potato (thermoplastic) starch was 3 MPa. The elongation at break was also higher in the case of the high amylose material. The results are discussed in terms of residual crystallinity of the starch materials.     

The influence of amylose and amylopectin characteristics on gelatinization and retrogradation properties of different starches

Physico-chemical properties of starch from wheat, rye, barley (waxy, high-amylose and normal-amylose), waxy maize, pea and potato (normal-amylose and high-amylopectin) were studied. Emphasis was given to the amylose (total, apparent and lipid-complexed) and amylopectin characteristics as well as to the gelatinization and retrogradation properties measured using differential scanning calorimetry. The total amylose content varied from ca. 1 % for waxy maize to 37% for high-amylose barley. The amylopectin characteristics were determined by high-performance size-exclusion chromatography after debranching with isoamylase. The weight-average degree of polymerization ( _w) was 26, 33 and 27 for the A-, B-, and C-type starches, respectively. In general, the potato starches exhibited the highest retrogradation enthalpies and the cereal starches the lowest, while the pea starch showed an intermediate retrogradation enthalpy. The data were analysed by principal component analysis (PCA). The _w showed positive correlation to the melting interval, the peak minimum, the offset temperatures of the retrogradation-related endotherm as well as to the gelatinization and retrogradation enthalpies. However, the high-amylose barley retrograded to a greater extent than the other cereal starches, despite low _w (24). The amylose content was negatively correlated to the onset and the peak minimum temperatures of gelatinization.     

Effects of extrusion and glycerol content on properties of oxidized and acetylated corn starch-based films

Oxidized and acetylated corn starch-based films were prepared by casting with glycerol as a plasticizer. The present study investigated the effects of extrusion prior to film-making and glycerol content on the properties of starch films. The films with extrusion exhibited lower tensile strength, higher elongation at break, higher water vapor permeability and higher oil permeability than those without extrusion. Extrusion reduced heat sealability of the films. With the increase of glycerol content, the films became more flexible with higher elongation at break and lower tensile strength. Water vapor permeability, oil permeability and the range between the onset temperature and the melt peak temperature rose as glycerol content increased. The thermograms indicated that plasticizers and biopolymers were compatible. These results suggested that extrusion did no good to starch films while glycerol content had apparent effect on the mechanical and barrier properties of the films.     

新型淀粉基全生物降解薄膜的研究

以玉米淀粉为主要原料,研究了蚋米SiO_2改性淀粉薄膜的最佳分散处理工艺,并通过测定样品的红外吸收光谱、X-射线衍射图和扫描电镜照片对该膜的结构进行了分析。结果表明:纳米SiO_2的最佳分散工艺为向2g纳米SiO_2的分散液中加入0.015g聚丙烯酰胺(PA)后,先用机械力研磨分散1h,然后置入淀粉-聚乙烯醇(ST-PVA)共混液中;纳米SiO_2在淀粉和聚乙烯醇分子间形成了均一致密的交联网状结构;所制备薄膜的各项性能均得到大幅度提高,其中拉伸强度可达34.82Mpa,断裂伸长率为331%,达到国标GB 4456—84所规定的标准。     

Targeted gene suppression by RNA interference: an efficient method for production of high-amylose potato lines

Production of high-amylose potato lines can be achieved by inhibition of two genes coding for starch branching enzymes. The use of antisense technology for gene inhibition have yielded a low frequency of high-amylose lines that mostly was correlated with high numbers of integrated T-DNA copies. To investigate whether the production of high-amylose lines could be improved, RNA interference was used for gene inhibition of the genes Sbe1 and Sbe2. Two constructs with 100 bp segments (pHAS2) or 200 bp segments (pHAS3) of both branching enzyme genes were cloned as inverted repeats controlled by a potato granule-bound starch synthase promoter. The construct pHAS3 was shown to be very efficient, yielding high-amylose quality in more than 50% of the transgenic lines. An antisense construct, included in the study as a comparator, resulted in only 3% of the transgenic lines being of high-amylose type. Noticeable was also that pHAS3 yielded low T-DNA copy inserts with an average of 83% of backbone-free transgenic lines being single copy events.