Päivi Myllärinen

Effect of glycerol on behaviour of amylose and amylopectin films

Abstract The effect of water and glycerol on sorption and calorimetric Tgs 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 Tg. But in spite of the observed decrease in Tg 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.

Oxygen permeability of amylose and amylopectin films

The effects of water and glycerol contents on oxygen permeability of starch polymer films were investigated. Starch films were prepared of amylose and amylopectin by a casting technique and oxygen permeability was analysed at 20°C. Glycerol contents were 0, 10, 20 or 30% while water content varied from 8 to 36%. Under ambient humidity both amylose and amylopectin films were excellent oxygen barriers, as good as the commercial ethylene vinyl alcohol film which was studied as a reference material. It was observed that the film permeabilities were determined by water content; below 15% water both starch films were good oxygen barriers, above 20% water the barrier property was lost.

The crystallinity of amylose and amylopectin films

X-ray crystallinity of amylose and amylopectin films with 0, 10 and 30% of glycerol and stored at RH 0, 54 and 91% were studied. Films prepared of water cast dilute solutions and dried at 70°C were thin and transparent. Each fresh amylose film showed B-type crystalline structures, and depending on the glycerol and water contents the amount of crystallinity varied from 6 to 32%. No changes in the crystallinity of the amylose films were observed during storage of two months. The fresh amylopectin films were completely amorphous. After storage for two months at the highest humidity the amylopectin film with 30% glycerol showed crystalline structure (19%), but all other amylopectin films remained amorphous during ageing. The crystal formation in the highly plasticised amylopectin film was suggested to be due to its rubbery state under the storage conditions. Amylose films were stable in water unlike amylopectin films that dispersed fast in water. About 35% of the amylose films were resistant to α-amylase, whereas amylopectin films were hydrolysed wholly. Also when treated with hydrochloric acid the amylopectin films dissolved totally and fast, while one week was needed to dissolve about 50% of the amylose films. It was concluded that even if part of the amylose films were amorphous, also these amorphous regions were more resistant to hydrolysis than the amorphous amylopectin structures.

Corn starches as film formers in aqueous-based film coating.

The purpose of this study was to evaluate the film formation ability and mechanical stress–strain properties of aqueous native corn starches, using free films and film coatings applied to tablets. Free films were prepared from high-amylose corn (Hylon VII), corn and waxy corn starches, using sorbitol and glycerol as plasticizers. The tablets and pellets were film-coated using an air-suspension coater, and characterized with respect to the film coating surface topography, cross-sectional structure and thickness (SEM), and dissolution in vitro. The amylose content of the starch film formers affected both the tensile strength and the elongation. The elongations were under 5% for even the plasticized starches, and in most cases, no plasticization effect was seen by either of the plasticizers. Dissolution of native corn starch film-coated tablets (weight gain 1%) did not differ from uncoated ones. A notable delay in dissolution of the drug was found by increasing Hylon VII film coating thickness, suggesting controlled-release characteristics.

Mechanical and permeability properties of biodegradable extruded starch/polycaprolactone films

Barley starch and glycerol were mixed with polycaprolactone (PCL) powder in various combinations and plasticized in a twin-screw extruder. When possible, extrudates were processed into films in a single-screw extruder and subjected to an orientation process with the aim of improving the water durability and mechanical strength of the starch films. The mechanical properties, water vapour and oxygen permeabilities, sorption isotherms and solubility of the processed films were studied. The films containing 20% or more PCL achieved a tensile strength of 20 MPa or higher. Orientation of the film still further improved the tensile strength, and also the water vapour and oxygen barrier properties. With PCL contents of 0–20% the starch/PCL films proved to be excellent oxygen barriers. Increase in PCL content beyond this impaired the oxygen barrier properties, whilst improving the water barrier properties. Copyright

Structural analysis of starch from normal and shx (shrunken endosperm) barley (Hordeum vulgare L.)

The shx shrunken endosperm mutation of barley is the only one described with its primary effect on Type I, primer-independent soluble starch synthase (SSS). The mutant produces grains with only 31% of the normal dry weight of starch, associated with a decrease in A-granule dimensions. We investigated the structure of shx and normal cv. Bomi barley amylose and amylopectin. Surprisingly, both amylose and amylopectin from the two genotypes were very similar in all aspects examined. These findings are discussed in the light of the potential roles for the various forms of SSS and branching enzyme.

Film Formation Properties of Potato Starch Hydrolysates

Native and freeze-dried potato starch granules were partially hydrolysed to produce maltodextrins with dextrose equivalents (DE) 10, 15 and 20. Freeze-drying greatly improved the enzyme accessibility of the native granules. Film formation properties of the hydrolysates were examined. Films were prepared by water casting. Especially the maltodextrins, which were produced from the native starch, were very sticky materials and could not form any films. But after removing most of the soluble saccharides from the maltodextrins, good quality films were produced by dissolving the hydrolysate in water, casting on a Teflon mould and drying the solution.

Effect of pretreatment on the film forming properties of potato and barley starch dispersions

Abstract The effects of preheating temperature, glycerol concentration and acid modification on the film-forming properties of potato and barley starches were studied in extension of the starch films and by light microscopy. In addition, the effects of heating pretreatment and acid modification were studied by size exclusion chromatography (SEC). With both starches, the starch: glycerol ratio ranged 100:5 to 100:67 of 3 wt % starch dispersions. Increasing the glycerol content increased the elongation and decreased the tensile strength of potato and barley starch films prepared after preheating at 121 °C. In the case of potato starch at 100:33 starch: glycerol ratio, raising the preheating temperature from 100 to 180 °C caused the tensile strength to increase from 2.4 to 5.0 MPa and the elongation to decrease from 104 to 5%. The mechanical properties of potato starch films underwent a notable change when the preheating temperature was 100 or 121 °C. The molecular mass of amylose decreased from 1100,000 to 670,000. A major change in the molecular mass of potato amylopectin could be detected only after heat treatment at 180 °C. At 121 °C and at 180 °C, starch dispersions exhibited a clear separation into amylose- and amylopectin-rich phases. No continuous films were obtained from acid-modified potato starches with molecular mass of amylose 20,000. With barley starch, as the preheating temperature increased from 100 to 180 °C the tensile strength increased from 2.6 to 4.9 MPa and the elongation decreased from 52 to 5%. At the same time the molecular mass of amylose decreased from 300,000 to 80,000. At 121 °C the granular structure remained, but at 180 °C no granules were left and instead the film consisted of amylopectin droplets and small amylose-rich domains.The strongest films (9.4 MPa), with 7% elongation, were obtained with acid-modified barley starch in which the molecular mass of amylose was 45,000. The tensile strength of both potato and barley starch films increased during storage reaching 9 MPa after 15 days. Elongation of both films decreased markedly during storage.

Waxy Corn Starch: A Potent Cofiller in Pellets Produced by Extrusion–Spheronization

The purpose of this study was to assess the usefulness of waxy corn (maize) starch as a cofiller and diluent in pellets produced by aqueous extrusion–spheronization. Waxy corn starch was combined with microcrystalline cellulose (MCC) in the range of 20–50% of the entire composition. Pellets containing ordinary corn starch or lactose with MCC were used as reference. The shape of pellets was characterized using an optical microscopic image analysis system. The surface and cross-sectional structure were investigated by means of scanning electron microscopy (SEM). The replacement of ordinary corn starch by waxy corn starch made it possible to increase the amount of starch from 20 to 40%. The pellets containing 50% waxy corn starch were of poorer quality but superior to those containing 30% corn starch. The surface structure became slightly more irregular with respect to the amount of either starch, and a cavity was formed inside the pellet during the spheronization. The origin of starch did not affect the surface structure of the pellets. Waxy corn starch is a potential cofiller: the amount of MCC can be reduced in pellets produced by extrusion–spheronization by using waxy corn starch as a cofiller. This enables the reduction of the manufacturing cost of pellets with low drug load.

Characterisation of Dextrins Solubilised by α-Amylase from Barley Starch Granules

α-Amylolysis of native granular starch represents a biochemical process, in which an enzyme in solution solubilises a highly organised, semicrystalline substrate. To study this process, which is very slow compared to the hydrolysis of gelatinised starch [1], it is necessary to use high concentrations of enzyme or very long incubation times. The solubilised dextrins are therefore easily hydrolysed further into small fragments, preventing a study of the products originally released from the granules. A method that enables a collection of the dextrins solubilised from starch granules by α-amylase was developed [1] and has made it possible to study the composition of the products at early stages of the process. In this method, the starch granules are packed as a thin layer in a two-compartment column [2] and a diluted enzyme solution is pumped through the starch. Before a secondary hydrolysis occurs, the enzyme is bound to an anionexchange matrix (DEAE-Sepharose) in the upper compartment of the column, whereas the solubilised dextrins are collected into fractions representing successive stages of the