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At least 1,261 records · Page 70Linked to original sources
PubMed2005

Microwave processing of natural biopolymers--studies on the properties of different starches.

In this study, the influence of microwave irradiation on some physico-chemical properties and several pharmaceutical technological parameters of potato and maize starches was investigated. Changes in their habits were observed and decrease in moisture contents caused by the electromagnetic irradiation was determined. The crystalline structures and the micromorphological parameters of the starches were affected by microwave irradiation in different ways depending on the botanical origin of the samples. The tensile strengths of the compacts containing starches were decreased, their wetting properties were enhanced by the thermal process applied. Furthermore, microwave irradiation reduced the surface free energy and the polarity of the compacts significantly. Samples treated by conventional heating were used to compare the effects of microwave irradiation on the examined properties and parameters of these starches.

Biopolymers↗
PubMed2005

Improving the amylolytic activity of Saccharomyces cerevisiae glucoamylase by the addition of a starch binding domain.

Glucoamylase produced by amylolytic strains of Saccharomyces cerevisiae (var. diastaticus) lacks a starch binding domain that is present in homologous glucoamylases from Aspergillus niger and other filamentous fungi. The absence of the binding domain makes the enzyme inefficient against raw starch and hence unsuitable for most biotechnological applications. We have constructed a hybrid glucoamylase-encoding gene by in-frame fusion of the S. cerevisiae STA1 gene and DNA fragment that encodes the starch binding domain of A. niger glucoamylase. The hybrid enzyme resulting from expression of the chimeric gene in S. cerevisiae has substrate binding capability and hydrolyses insoluble starch, properties not present in the original yeast enzyme.

Aspergillus niger↗
PubMed2006

Utilization of soluble starch by a recombinant Corynebacterium glutamicum strain: growth and lysine production.

Corynebacterium glutamicum, well known for the industrial production of amino acids, grows aerobically on a variety of mono- and disaccharides and on alcohols and organic acids as single or combined sources of carbon and energy. Members of the genera Corynebacterium and Brevibacterium were here tested for their ability to use the homopolysaccharide starch as a substrate for growth. None of the 24 type strains tested showed growth on or degradation of this substrate, indicating that none of the strains synthesized and secreted starch-degrading enzymes. Introducing the Streptomyces griseus amy gene on an expression vector into the lysine-producer C. glutamicum DM1730, we constructed a C. glutamicum strain synthesizing and secreting alpha-amylase into the culture broth. Although some high-molecular-weight degradation products remained in the culture broth, this recombinant strain effectively used soluble starch as carbon and energy substrate for growth and also for lysine production. Thus, employment of our construct allows avoidance of the cost-intensive enzymatic hydrolysis of the starch, which commercially is used as a substrate in industrial amino acid fermentations.

Brevibacterium↗
PubMed2004

Bioadhesive grafted starch copolymers as platforms for peroral drug delivery: a study of theophylline release.

Nonirritant bioadhesive drug release systems based on starch-acrylic acid graft copolymers prepared by radiation of starch and acrylic acid mixtures with (60)Co were developed for buccal application. The release rate of theophylline (TPL), used as a model drug, depended on the ratio of starch to acrylic acid and on the presence of cations in the graft copolymers, but was practically not affected by the pH (between pH 3 and 7) of the dissolution medium nor by the type of starch used (corn, rice, or potato). Possible release mechanisms are discussed for specific conditions. In general, the release behavior of the graft copolymers was found to be non-Fickian, n value being between 0.6 and 0.96, suggesting that the release was controlled by a combination of tablet erosion and the diffusion of the drug from the swollen matrix. Incorporation of divalent cations into the graft copolymers led to a significant decrease in swelling erosion of the tablets as well as a substantial retardation of drug release. Highest work of adhesion was obtained with graft copolymers containing calcium ions as well as longer time of adhesion on dogs' gingiva.

Acrylates↗
PubMed2004

Evaluation of novel starch acetate-diltiazem controlled release tablets in healthy human volunteers.

Highly substituted starch acetate can be used to control drug release from directly compressed tablets in vitro. The aim of this study was to evaluate controlled release properties of starch acetate in vivo in humans. Three starch acetate tablet formulations with different in vitro release rates for diltiazem (fast, moderate and slow) were developed. An open, single dose, randomised, four treatment, four period, four sequence cross-over pharmacokinetic study was conducted in eight healthy volunteers. Diltiazem concentrations in plasma were determined by HPLC. Concentration-time profiles of the formulations differed: mean C(max) and AUC(0- infinity ) values of the fast, moderate and slow formulations were 95, 69, 31 ng/ml and 610, 511, 231 ng h/ml, respectively. In vitro-in vivo correlation (IVIVC) was analysed according to the cumulative area under the curves and in vitro release profiles. Acceptable limits of prediction errors were achieved for C(max) and AUC(0-24 h). The moderate formulation and commercial reference tablet showed similar in vitro release profiles and diltiazem concentrations in plasma. In conclusion, direct compression starch acetate formulations control drug release in humans.

Administration, Oral↗
PubMed2004

Complex structures of Thermoactinomyces vulgaris R-47 alpha-amylase 1 with malto-oligosaccharides demonstrate the role of domain N acting as a starch-binding domain.

The X-ray structures of complexes of Thermoactinomyces vulgaris R-47 alpha-amylase 1 (TVAI) with an inhibitor acarbose and an inactive mutant TVAI with malto-hexaose and malto-tridecaose have been determined at 2.6, 2.0 and 1.8A resolution, and the structures have been refined to R-factors of 0.185 (R(free)=0.225), 0.184 (0.217) and 0.164 (0.200), respectively, with good chemical geometries. Acarbose binds to the catalytic site of TVAI, and interactions between acarbose and the enzyme are very similar to those found in other structure-solved alpha-amylase/acarbose complexes, supporting the proposed catalytic mechanism. Based on the structure of the TVAI/acarbose complex, the binding mode of pullulan containing alpha-(1,6) glucoside linkages could be deduced. Due to the structural difference caused by the replaced amino acid residue (Gln396 for Glu) in the catalytic site, malto-hexaose and malto-tridecaose partially bind to the catalytic site, giving a mimic of the enzyme/product complex. Besides the catalytic site, four sugar-binding sites on the molecular surface are found in these X-ray structures. Two sugar-binding sites in domain N hold the oligosaccharides with a regular helical structure of amylose, which suggests that the domain N is a starch-binding domain acting as an anchor to starch in the catalytic reaction of the enzyme. An assay of hydrolyzing activity for the raw starches confirmed that TVAI can efficiently hydrolyze raw starch.

Binding Sites↗
PubMed2001

Internal structure of the starch granule revealed by AFM.

Atomic force microscopy images of sectioned native corn starch granules show evidence of the well-known radial organisation of the starch macromolecules, with the less-ordered hilum region near to the centre. Native granules show blocks 400-500 nm in size that span the growth rings. Lintnerised starch granules, where a mild acid hydrolysis has been used to remove the amorphous and less crystalline parts of the granule, clearly show smaller 'blocklets' within the rings approximately 10-30 nm in size. This level of organisation within the growth rings corresponds to the blocklet or superhelix structures that have been proposed in the literature for the association or clustering of amylopectin helices. Mechanical property imaging techniques have provided enhanced contrast to view this morphology, and shown the deformability of the starch structure under contact mode imaging conditions.

Amylopectin↗
PubMed2003

Structure and physicochemical properties of starches from kidney bean seeds at immature, premature and mature stages of development.

Starches from kidney bean (Phaseolus vulgaris L. cv. Toramame) seeds at the immature, premature, mature stages of development were examined. The starch content increased from 94, 219 to 265 mg per seed. Starches showed the C(a)-crystalline type composed of small (<5 micrometer) and large (10-35 micrometer) granules, with the large granules largely increasing with maturity. The amylose content increased from 21, 26 to 27%, and rapid viscograms and DSC thermograms suggested that the mature-stage starch was gelatinized with ease. The amylose increased in size from DPn 820, 1000 to 1080 and a number of chains per molecule (NC) from 3.3, 4.2 to 4.5. The branched amylose was a minor component (11-18% by mole) with NC 20-22. The amylopectin was similar in CL (23), beta-amylolysis limit (59%), and chain-length distribution, but reduced in size (DPn 17,100-5270) and increased in content of phosphorus (114-174 ppm) with an increase in the amount of phosphorus linked to C-6 of the glucose residue (8-66%).

Microscopy, Electron, Scanning↗
PubMed1997

Proton NMR spectroscopy assignment of D-glucose residues in highly acetylated starch.

1H NMR spectroscopy assignments have been obtained for starch acetates using COSY and HOHAHA experiments by comparison with the spectra of amylose triacetate and of peracetylated malto-oligosaccharides (maltotriose, maltotetraose, maltoheptaose). These assignments are valuable for the location and evaluation of the substitution pattern in modified starches. The bulk of the 1H NMR spectra of highly acetylated starch strongly resembles the spectrum of amylose triacetate in which all protons are identified and display distinct chemical shifts. The resolving power of the HOHAHA experiment allowed the distinction of minor spin systems. Beside these strong signals pertaining to an average 2.3.6-tri-O-acetyl-alpha-(1-->4) linked D-glucopyranose unit in an infinite chain, the combination of COSY and HOHAHA experiments allowed the identification of these systems to the terminal, n-1, n-2, and to partially acetylated glucopyranosyl units. As an example, two different preparations of starch acetates with degrees of substitution 2.74 and 2.63 were examined. In one case, NMR demonstrates that the defects of acetylation are random on the polymeric chain (with corresponding signals for unacylated secondary hydroxyl positions at delta 3.61 and 3.40) while in another case, these signals are not detectable, probably due to the presence of clusters of non-acetylated residue forming solid-like zones.

Acetylation↗
PubMed1999

Activity of blood coagulation and fibrinolysis during and after hydroxyethyl starch (HES) colloidal volume replacement.

OBJECTIVES: To examine the effect of medium molecular weight hydroxyethyl starch on protein C levels and the changes in the activation state of blood platelets, coagulation and fibrinolyis during and after 5 day of its infusion. DESIGN AND METHODS: Fifty male patients (mean age: 47 years, range 45-50 years) who required prostatectomy for benign prostatic hyperplasia were divided into two equal groups. One group was given 15 mL/kg body weight (mean volume 1000 mL +/- 100 mL) of 6% hydroxyethyl starch (HES) 200/0.5, the other received an equal volume of 5% human albumin during the operation. Blood samples were collected immediately before infusion (baseline values) and at 20, 40, 60, 90, 240, and 480 min after the infusion started then daily for the next 5 days postoperatively. Hematocrit, factor VIII:C, thrombin-antithrombin III complex; the anticoagulant protein C levels; the fibrinolytic parameters tissue type plasminogen activator (t-PA), and the fibrinolytic product D-Dimer and the platelet aggregation activity were measured. RESULTS: The data obtained did not detect any significant differences between HES and human albumin in the plasma levels of thrombin-antithrombin III complex, protein C, tissue-type plasminogen activator and the fibrin split products D-Dimer. Factor VIII:C and platelet aggregation were significantly lower in the hydroxyethyl starch group in comparison with albumin. Baseline values were attained postoperatively for factor VIII:C and platelet aggregation by the first and fifth days, respectively. CONCLUSION: The lowering effect of medium molecular weight hydroxyethyl starch on factor VIII:C would not be attributed to increased proteolytic activity of protein C on this coagulation cofactor because there is a nonsignificant change in protein C levels.

Antithrombin III↗
PubMed1975

Starch and chemotaxis. A histological study in the mouse.

Primary interest in inflammation centers around the mechanism by which polymorphonuclear leucocytes emigrate from the circulating blood to an area of injury, a process apparently first designated as "chemotaxis" in 1888. Recent experimental studies have emphasized the role of ions in the pathogenesis of thrombi in the circulatory system following the implantation of plastics. The negatively charged leucocytes are attracted by positively charged plastics. Starch granules have a positive charge and, when implanted subcutaneously in the mouse, attract the negatively charged leucocytes. Sixty minutes after the subcutaneous implantation of starch granules in the subcutaneous tissue of mice polymorphonuclear leucocytes had begun to emigrate to the area. The number of leucocytes rapidly increased for 24 to 72 hours and then progressively decreased. By the 5th experimental day the number of leucocytes had decreased markedly and continued to decrease in their emigration to the granules of starch. The positive ionic charge associated with the granules of starch is neutralized by the adsorption of the negatively charged plasma protein ions. It is suggested that chemotaxis is an electrochemical phenomenon.

Animals↗
PubMed2001

Optimization of experimental conditions for the separation of small and large starch granules by gravitational field-flow fractionation.

Separation of small and large barley starch granules by gravitational field-flow fractionation was investigated from the point of view of sample pre-treatment, amount of injected sample, and elution conditions. The sample pre-treatment study resulted in the conclusion that it is reasonable to soak the starch granules for at least 24 h prior to separation. The experiments with different amounts of injected sample show that it is possible to increase as well as decrease twofold the sample amount usually used without any change in retention ratios. The implementation of flow-rate gradients for elution of the starch granules reduced total separation time. However, the applied flow-rate gradients did not improve the resolution of peaks A and B compared with the generally used constant flow-rate. Thus, for barley starch granules, the constant flow-rates within the range from 0.8 to 1.0 ml/min seem to provide the best compromise of total separation time, peak resolution and instrumental expense.

Chemical Fractionation↗
PubMed1985

Rapid analysis of starch, amylose and amylopectin by high-performance size-exclusion chromatography.

Starch components, amylose and amylopectin, were analyzed by high-performance size-exclusion chromatography. These two-components were separated using a two-column system (E-Linear and E-1000) and dimethyl sulphoxide as the mobile phase. The void volume (V0 = 2.22 ml) was measured using tobacco mosaic virus. Column calibration was accomplished with dextrans of known average molecular weight (Mw range = 10,100-2,000,000). The elution volume of amylopectin (Ve = 2.5 ml) indicated that this starch component was fractionated on the column system despite its very large molecular size. Standard curves were prepared from various mixtures of purified corn and wheat amylose and amylopectin. From the linear relationships obtained, the percentages of both components in corn and wheat starches were determined. The method developed proved useful to monitor the purity of amylose and amylopectin preparations, and to estimate rapidly the amylose:amylopectin ratio of starch samples.

Amylopectin↗
PubMed2000

Platelet aggregation during abdominal surgery in an experimental pig model: the effects of presurgical antibiotic protocols and volume replacement with hydroxyethyl starch.

The effect of presurgical antibiotic protocols in combination with hemodilution on platelet aggregation was studied. Thirty pigs were randomly assigned to three groups. Group 1 received amoxicillin/clavulanic acid, group 2 metronidazole+cefuroxime, and group 3, as a control, sodium chloride. They underwent laparotomy, massive blood loss, and volume replacement with hydroxyethyl starch 200, followed by an anaphylactoid reaction. Platelet aggregation was measured by the turbidometric method. Neither antibiotic protocols had any effect on platelet aggregation as compared with the control group. In all three groups, aggregation to ADP and collagen was significantly reduced after volume replacement with hydroxyethyl starch. In contrast, the sensitivity to the aggregating effects of collagen was increased as assessed by a higher frequency of responses to low concentrations of collagen and a shortened latency of the aggregation response after collagen addition. Further in vitro studies revealed that dilution of plasma with hydroxyethyl starch specifically induced the changes seen after in vivo volume replacement. The results suggest that the plasma substitute hydroxyethyl starch 200 increases the sensitivity to low doses of collagen, an effect never described before and considered of clinical relevance.

Abdomen↗
PubMed2000

SANS study of the distribution of water within starch granules.

This study describes contrast variation small angle neutron scattering (SANS) experiments which focus on the role which the intra-granular room temperature distribution of water and carbohydrate plays in determining the native structure and subsequent functionality of starch. It is shown that variations in botanical origin and amylose content do not correlate with significant differences in room temperature composition of A-type starch granules. In turn, variations in the gelatinisation behaviour of A-type starches do not correlate with variations in room temperature water distribution. In contrast, the room temperature water content is found to differ significantly between granules of potato (B-type) and a range of A-type starch cultivars. A correlation is found between these compositional differences and variations in crystal structure, which has implications for biological growth conditions and gelatinisation behaviour.

Amylose↗
PubMed1997

Starch granule surface imaging using low-voltage scanning electron microscopy and atomic force microscopy.

High resolution imaging of wheat and potato starch granule surfaces has been performed using low-voltage scanning electron microscopy and atomic force microscopy. The complimentary images of uncoated granules demonstrate that the two starch types possess substantially different surface topologies; potato starch has many protrusions (100-300 nm in diameter), above a flatter surface containing 20-50 nm structures, whilst wheat starch possesses far fewer protrusions and generally has a smoother surface composed of approximately 20 nm structures. The protrusions are believed to be carbohydrate in nature and thus represent the ends of amylopectin side-chain clusters at the granule surface.

Microscopy, Atomic Force↗
PubMed1998

Starch granules: structure and biosynthesis.

The emphasis of this review is on starch structure and its biosynthesis. Improvements in understanding have been brought about during the last decade through the development of new physicochemical and biological techniques, leading to real scientific progress. All this literature needs to be kept inside the general literature about biopolymers, despite some confusing results or discrepancies arising from the biological variability of starch. However, a coherent picture of starch over all the different structural levels can be presented, in order to obtain some generalizations about its structure. In this review we will focus first on our present understanding of the structures of amylose and amylopectin and their organization within the granule, and we will then give insights on the biosynthetic mechanisms explaining the biogenesis of starch in plants.

Carbohydrate Conformation↗
PubMed1999

Characterization of a crosslinked high amylose starch excipient.

A controlled release excipient based on sodium trimetaphosphate (STMP) crosslinked high amylose starch has been examined by 13C CP/MAS NMR. The dry excipient powder is pressed to a hard tablet whose volume increase in H2O runs parallel to the STMP concentration used. The known polymorph resonances of single helix 'V' starch (hydrated) and double helix 'B' starch (hydrated) both contribute to the spectrum corresponding to the swollen tablet. The wet tablet when loaded with a pharmaceutical agent provides a near zero-order release profile for up to 20 h. The swelling and drug release behaviour is explained in terms of self-assembly of the STMP treated starch nanomolecular particles. These particles are drawn together by "self-assembly" due to formation of amylose double helices as water penetrates the tablet. An optimum level of chemical crosslinking ensures the integrity of the swollen tablet whose sponge-like structure enclosed by a membranous surface is responsible for sustained release.

Amylose↗