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PubMed1997

Crystallinity in starch plastics: consequences for material properties.

The processing of starches with biodegradable additives has made biodegradable plastics suitable for a number of applications. Starch plastics are partially crystalline as a result of residual crystallinity and the recrystallization of amylose and amylopectin. Such crystallinity is a key determinant of the product's properties. This article describes the influence of processing and storage conditions on starch crystallinity and offers possible explanations for the various properties of starch plastics, in particular for the problems associated with ageing, in terms of the different crystalline structures.

Biodegradation, Environmental↗
PubMed2003

Study of starch fermentation at low pH by Lactobacillus fermentum Ogi E1 reveals uncoupling between growth and alpha-amylase production at pH 4.0.

Lactobacillus fermentum Ogi E1 is an amylolytic heterofermentative lactic acid bacterium previously isolated from ogi, a Benin maize sourdough. In the present study, the effect of different pH between 3.5 and 6.0 on starch fermentation products and alpha-amylase production was investigated. Whereas a pH of 5.0 was optimum for specific growth rate and lactic acid production, growth was only slightly affected at suboptimal pH of 4.0 and 6.0. Over a pH range of 6.0 to 3.5, yields of product formation from substrate and of biomass relative to ATP were constant. These results showed that L. fermentum Ogi E1 was particularly acid tolerant, and well adapted to the acid conditions that develop during natural fermentation of cereal doughs. This acid tolerance may partly explain the dominance of L. fermentum in various traditional African sourdoughs. Surprisingly, alpha-amylase production, unlike growth, dropped dramatically when the strain was cultivated at pH 4.0 with starch. With maltose as substrate, the yield of alpha-amylase relative to biomass remained unchanged at pH 4.0 and 5.0, unlike that observed with starch. Based on the distribution of enzyme activity between extra- and intracellular fractions and fermentation kinetics, it appears that starch was first hydrolyzed into dextrins by alpha-amylase activity, and maltose was produced from dextrins by extracellular enzyme activity, transferred into the cell and then hydrolyzed into glucose by intracellular alpha-glucosidase.

Bread↗
PubMed2001

Succinylation of cyclodextrin glycosyltransferase from Thermoanaerobacter sp. 501 enhances its transferase activity using starch as donor.

A simple modification procedure, the succinylation of amino groups, was suitable to increase the transferase (disproportionation) activity of cyclodextrin glycosyltransferase (CGTase) from Thermoanaerobacter sp. 501 using different linear oligosaccharides as acceptors. On the contrary, the synthesis of cyclodextrins (CDs), the coupling of CDs with oligosaccharides, and the hydrolysis of starch decreased after chemical modification. The degree of succinylation of amino groups (45%) was accurately determined by MALDI-TOF mass spectrometry. The formation of CDs under industrial conditions was analyzed for native and succinylated CGTases, showing similar selectivity to alpha-, beta-, gamma-CD. The acceptor reaction with D-glucose using soluble starch as glucosyl donor was studied at 60 degrees C and pH 5.5. Malto-oligosaccharides (MOS) production was notably higher using the semisynthetic enzyme at different ratios (w/w) starch:D-glucose. Thus, more than 90% of the initial starch was converted into MOS (G2-G7) in 48 h employing a ratio donor:acceptor 1:2 (w/w).

Acylation↗
PubMed2001

In vitro and in vivo evaluation of starch-based hot stage extruded double matrix systems.

The objective of developing a double matrix system consisting of a hot stage extruded starch pipe surrounding a hot stage extruded and drug-containing starch core, was to obtain a monolithic matrix system applicable in the domain of sustained drug release. The behaviour of the systems was evaluated through dissolution testing and through a randomised crossover bioavailability study on nine male volunteers. All double matrix systems showed in vitro a nearly constant drug release profile after an initial slower release phase of 4 h. This initial slower release phase was avoided by loading the starch pipe with a small amount of drug. The in vitro dissolution profiles did not reflect the in vivo behaviour of the systems. Although the in vitro dissolution profiles of two selected double matrix systems were slower than the profile of a commercially available sustained release formulation, they performed less well in vivo. However, the t75%Cmax ratios of the evaluated double matrix systems versus a reference immediate release formulation indicated an acceptable sustained release behaviour, superior to that of hot stage extruded starch-based single matrices. Therefore the disclosed drug delivery systems could be applied in the domain of sustained drug delivery. Besides, the continuous production of the double matrix systems offers an advantage from a manufacturing point of view.

Adult↗
PubMed2003

High phosphorylase activity is correlated with increased potato minituber formation and starch content during extended clinorotation.

The major purpose of these experiments were to investigate growth of potato storage organs and starch synthesis in minitubers at slow horizontal clinorotation (2 rpm), which partly mimics microgravity, and a secondary goal was to study the activity and localization of phosphorylase (EC 2.4.1.1) in storage parenchyma under these conditions. Miniplants of Solanum tuberosum L. (cv Adreta) were grown in culture for 30 days for both the vertical control and the horizontal clinorotation. During long-term clinorotation, an acceleration of minituber formation, and an increase of amyloplast number and size in storage parenchyma cells, as well as increased starch content, was observed in the minitubers. The differences among cytochemical reaction intensity, activity of phosphorylase, and carbohydrate content in storage parenchyma cells of minitubers grown in a horizontal clinostat were established by electron-cytochemical and biochemical methods. It is shown that high phosphorylase activity is correlated with increased starch content during extended clinorotation. The results demonstrate the increase in carbohydrate metabolism and possible accelerated growth of storage organs under the influence of microgravity, as mimicked by clinorotation; therefore, clinorotation can be used as a basis for future studies on mechanisms of starch synthesis under microgravity.

Acceleration↗
PubMed1999

Spaceflight experiments with Arabidopsis starch-deficient mutants support a statolith-based model for graviperception.

In order to help resolve some of the controversy associated with ground-based research that has supported the starch-statolith theory of gravity perception in plants, we performed spaceflight experiments with Arabidopsis in Biorack during the January 1997 and May 1997 missions of the Space Shuttle. Seedlings of wild-type (WT) Arabidopsis, two reduced-starch strains, and a starchless mutant were grown in microgravity and then were given either a 30, 60, or 90 minute gravity stimulus on a centrifuge. By the 90 min 1-g stimulus, the WT exhibited the greatest magnitude of curvature and the starchless mutant exhibited the smallest curvature while the two reduced starch mutants had an intermediate magnitude of curvature. In addition, space-grown plants had two structural features that distinguished them from the controls: a greater number of root hairs and an anomalous hypocotyl hook structure. However, the morphological changes observed in the flight seedlings are likely to be due to the effects of ethylene present in the spacecraft. (Additional ground-based studies demonstrated that this level of ethylene did not significantly affect gravitropism nor did it affect the relative gravitropic sensitivity among the four strains.) Nevertheless, this experiment on gravitropism was performed the "right way" in that brief gravitational stimuli were provided, and the seedlings were allowed to express the response without further gravity stimuli. Our spaceflight results support previous ground-based studies of these and other mutants since increasing amounts of starch correlated positively with increasing sensitivity to gravity.

Arabidopsis↗
PubMed1982

A comparison of the effects of lactose and of two chemically modified waxy maize starches on mineral metabolism in the rat.

Diets containing 30% by weight of waxy maize starch, lactose monohydrate, acetylated distarch phosphate (EEC No. 1414) or acetylated distarch adipate (EEC No. 1422) were fed to weanling female Specified Pathogen-Free Sprague-Dawley rats for 1 yr and to similar 9-month-old rats for 34 wk. Behaviour and general health were unaffected by the different diets and there were no diet-related differences in food consumption. AT the end of the experiment with 9-month-old rats the mean body weight of the animals receiving lactose was significantly lower than that of the controls receiving starch. The animals receiving the modified starches were slightly but not significantly heavier than the controls at the end of both experiments. The main treatment-related changes in rats on the three test diets were (1) caecal enlargement, (2) increased urinary excretion of calcium, (3) increased renal calcification as measured by chemical analysis of renal tissue obtained at autopsy and (4) increased medullary and pelvic nephrocalcinosis as assessed histopathologically. Acetylated distarch adipate had a slightly greater effect on the above parameters than acetylated distarch phosphate but both modified starches had less effect than lactose. The calcium content of the kidneys, as measured by chemical analysis or histopathology, increased with age, even in the animals receiving the control diet. This change may be due to excessively high concentrations of calcium and phosphorus in all the diets, including the control diet. Cortico-medullary mineral deposits were not a feature in these studies possibly because the diets were not deficient in magnesium. The importance of correct dietary formulation in long-term toxicity studies is emphasized.

Animals↗
PubMed1997

Dietary sucrose and starch affect dysplastic characteristics in carcinogen-induced aberrant crypt foci in rat colon.

To study whether dietary carbohydrates affect dysplasia in aberrant crypt foci (ACF), rats treated with 1,2-dimethilhydrazine (DMH) were fed for three months with diets containing 46% sucrose or corn starch. The number of ACF/colon in the two dietary groups was similar (P = 0.58), but ACF were smaller in the starch than in sucrose group (P < 0.05). ACF in the starch group also showed less severe goblet cell dysplasia, more sulphomucins and less sialomucins than in the sucrose group (P < 0.05), indicating that corn starch protects against colon carcinogenesis while sucrose in the diet is detrimental, promoting the dysplasia of preneoplastic lesions like ACF.

1,2-Dimethylhydrazine↗
PubMed2006

Analysis of genotype x environment interaction effects for starch pasting viscosity characteristics in Indica rice.

Milled rice (Oryza sativa L.) is composed of approximately 90% starch. The properties of starch have considerable effects on cooked rice palatability and consumer acceptability. Starch pasting viscosity parameters serve as important indices in the estimation of eating, cooking, and processing qualities of rice. In the present study, four cytoplasmic male-sterile (CMS) lines and eight restorer (R) lines have been used in an incomplete diallel cross to analyze seed effects, cytoplasmic effects, maternal gene effects, and their genotype x environment (GE) effects on the following starch pasting viscosity parameters: breakdown (BD), consistency (CS), and setback (SB). The results demonstrated that the total main genetic variances (V(G)) accounted for over 64% of the total genetic variance (V(G) +V(GE)) for the three traits, indicating that these traits were mainly controlled by the main genetic effects in addition to the GE interaction effects. The estimated total narrow-sense heritability were 67.8%, 79.5%, and 79.5% for BD, CS, and SB, respectively. The general heritability (h(2)(G)) accounted for over 75% of the total heritability (h(2)(G) +h(2)(GE)), indicating that early selection would be effective for those traits and the selection efficiencies were relatively stable in different environments.

Cytoplasm↗
PubMed2003

Preparation and characterization of biodegradable poly-3-hydroxybutyrate-starch blend films.

Bacterial polyesters have attracted much attention as biodegradable biocompatible polymers. Poly-3-hydroxybutyrate, a microbially produced thermoplastic, has similar material properties to polypropylene. Its potential application as biodegradable and biocompatible plastics is well documented. However, due to high cost it is used mainly in biomaterials for medical applications. Materials with useful properties may result from blending bacterial polyhydroxybutyrate (PHB) with other polymers. In this paper, the compatibility of PHB with starch for improved properties and cost reduction is discussed. The thermal and mechanical properties of the blended films were studied by means of thermogravimetry, differential scanning calorimetry and an automated material testing system. The results revealed that blend films had a single glass transition temperature for all the proportions of PHB:starch tested. The nature of all combinations was found to be crystalline. The tensile strength was optimum for the PHB:starch ratio of 0.7:0.3 (wt/wt). The variation in tensile strength, Young's modulus, extension needed to break, thermal stability, glass transition temperature, melting temperature, for the different proportions of PHB:starch are discussed.

Bacteria↗
PubMed2006

A novel type carbohydrate-binding module identified in alpha-glucan, water dikinases is specific for regulated plastidial starch metabolism.

The phosphorylation of the amylopectin fraction of starch catalyzed by the alpha-glucan, water dikinase (GWD, EC 2.7.9.4) plays a pivotal role in starch metabolism. Limited proteolysis of the potato tuber (Solanum tuberosum) GWD (StGWD, 155 kDa) by trypsin primarily produced stable fragments of 33 and 122 kDa, termed the SBD fragment and N11, respectively, as generated by trypsin cleavage at Arg-286. SBD and N11 were generated using recombinant DNA technology and purified to near homogeneity. Tandem repeat sequences, SBD-1 and SBD-2, of a region that is significantly similar in sequence to N-terminal regions of plastidial alpha-amylases are located in the N-terminus of StGWD. The SBD-1 motif is located within the sequence of the SBD fragment, and our results demonstrate that the fragment composes a new and novel carbohydrate-binding module (CBM), apparently specific for plastidial alpha-glucan degradation. By mutational analyses of conserved Trp residues located within the SBD-1 motif, W62 and W117, we show that these aromatic residues are vital for carbohydrate binding. N11 still possessed starch phosphorylating activity, but with a 2-fold higher specific activity compared to that of wild type (WT) StGWD using potato starch as the glucan substrate, whereas it had double the K(m) value for the same substrate. Furthermore, investigation of the chains phosphorylated by WT StGWD and N11 shows that N11 exhibits a higher preference for phosphorylating shorter chains of the amylopectin molecule as compared to WT. From analyses of the glucan substrate specificity, we found up to 5-fold higher specific activity for N11 using amylose as the substrate.

Peptide Fragments↗
PubMedDate not supplied

Peculiarities of aqueous amaranth starch suspensions.

Among the starches the granules from amaranth starch (a. hypochondriacus, amylopectin type) are singular because of their extremely small size of 1-3 microm and high uniformity. However, large spherical particles of 30-80 microm in diameter were observed from spray-dried amaranth starch by environmental scanning electron microscopy (ESEM) which exhibited a characteristic fine structure. After the mixture was stirred in cold water, the large particles disintegrate into small ones of 1-3 microm diameter. The particles from the stirred suspension were characterized by static and dynamic light scattering and viscometry. Almost the same diameters were found by the three techniques which were 1.76 times larger than those for the dry starch particles investigated by ESEM. The difference in size is explained by reversible uptake of water. A molar mass of M(w,granule) = 177 x 10(9) g/mol was measured for the granular particle. After dissolution in 0.5 N sodium hydroxide a molar mass M(w,amylopectin) = 104 x 10(6) g/mol of the amylopectin was obtained that agreed satisfactorily with that of waxy maize. Thus the granule consists on average of 1700 amylopectin molecules. Furthermore, rheological measurements were carried out with aqueous suspensions at room temperature. A shear gradient dependence was found for concentrations higher than 6% (w/v) of granules. At c > 19% reversible gel formation was observed with G'(omega) > G"(omega) and a plateau over 2 decades. The zero shear viscosity as a function of c[eta] shows behavior similar to glycogen and to latex particles. The granules, however, differ from common latex particles because of their capability to gel formation.

Amaranthus↗
PubMed2000

Physical stabilization of starch-allylurea blends by EB-grafting: a compositional and structural study.

A structural and compositional study of thermoplastic blends prepared from native potato starch (NPS) and various amounts of allylurea (AU) was performed to gain a better understanding of possible radiochemical routes to physically stable materials. The blends, mixed at ca. 130 degrees C, were studied in the form of 150 microns-thick films. Upon aging at room temperature, the samples obtained from these blends exhibit macroscopic phase separation under the form of allylurea blooming at their surface. The maximal compatibility of allylurea in amorphized potato starch was assessed by gravimetry and compared to that of urea in mixtures with NPS prepared in similar conditions. Physical aging of the unstable blends was monitored for various initial AU contents. Electron beam (EB) processing of fresh films with AU content above the solubility limit was shown to prevent phase separation, essentially as a consequence of radiation grafting onto starch of the unsaturated additive. X-ray diffractometry was performed to control (i) the effective amorphization of starch upon mixing, (ii) the recrystallization of the incompatible AU fraction from untreated blends in the tetragonal form, and (iii) the retardation or the suppression of this phenomenon after EB processing. The physical stability of the blends treated with a sufficient radiation dose (400-800 kGy) was confirmed by dynamic thermomechanical analysis of samples submitted to various hygrometric conditioning.

Crystallography, X-Ray↗
PubMedDate not supplied

Surface composition and morphology of starch, amylose, and amylopectin films.

The surfaces of solution-cast films of starch, amylose, and amylopectin were examined with scanning electron microscopy (SEM), atomic force microscopy (AFM), electron spectroscopy for chemical analysis (ESCA), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The surface topography visualized by SEM showed that amylopectin films were very smooth whereas amylose and starch films were rougher. It appears that crystallinity or phase separation in the bulk of the film affects the surface topography. AFM showed that the outmost surfaces of all films were covered with small protrusions, 15-35 nm wide and 1-4 nm high. Studies with ESCA revealed the presence of 3-8% nitrogen on the surfaces. ToF-SIMS indicated that the nitrogen originates from protein because ionic fragments from amino acids and the peptide backbone were found. Extracts from the top surface layer of the starch film showed protein bands in gel electrophoresis (SDS-PAGE) around 60 kDa, which is in the same molecular weight range as the biosynthesizing enzyme GBSS I present in starch granules. The proteins apparently phase separated during film formation and migrated to the surface, resulting in an extensive enrichment of proteins in the film surface, where about 8% of the protein is present in the top 0.01% of the film. We believe that the protrusions observed with AFM could be one or a few proteins aggregated side by side.

Amylopectin↗
PubMedDate not supplied

Use of (13)c MAS NMR to study domain structure and dynamics of polysaccharides in the native starch granules.

To investigate the domain structure and dynamics of polysaccharides in the native starch granules, a variety of high resolution, solid-state (13)C NMR techniques have been applied to all three (A-, B-, and C-) types of starch with different water content. Both single-pulse-excitation magic-angle-spinning (SPEMAS) and cross-polarization-magic-angle-spinning (CPMAS) methods have been employed together with the PRISE (proton relaxation induced spectral-editing) techniques to distinguish polysaccharide fractions in different domains and having distinct dynamics. It has been found that, for all three types of dry starch granules, there are two sets of NMR signals corresponding to two distinct ordered polysaccharides. Hydration leads to substantial mobilization of the polysaccharides in the amorphous regions, but no fundamental changes in the rigidity of the polysaccharides in the crystalline (double) helices. Full hydration also leads to limited mobility changes to the polysaccharides in the amorphous lamellae (branching zone) within the amylopectin clusters and in the gaps between the arrays of the amylopectin clusters. Under magic-angle spinning, proton relaxation-time measurements showed a single component for T(1), two components for T(1rho), and three components for T(2). PRISE experiments permitted the neat separation of the (13)C resonances of polysaccharides in the crystalline lamellae from those in the amorphous lamellae and the amylose in the gaps between amylopectin clusters. It has been found that the long (1)H T(1rho) component ( approximately 30 ms) is associated with polysaccharides in the crystalline lamellae in the form of double helices, whereas the short T(1rho) component (2-4 ms) is associated with amylose in the gaps between amylopectin clusters. The short (1)H T(2) component ( approximately 14 micros) is associated with polysaccharides in the crystalline lamellae; the intermediate component (300-400 micros) is associated with polysaccharides in the amorphous lamellae and amylose in the gaps between amylopectin clusters. The long T(2) component is associated with both mobile starch protons and the residue water protons.

Carbohydrate Conformation↗
PubMedDate not supplied

Production of starch foams by twin-screw extrusion: effect of maleated poly(butylene adipate-co-terephthalate) as a compatibilizer.

Free-radical-initiated grafting of maleic anhydride (MA) onto poly(butylene adipate-co-terephthalate) (PBAT), a biodegradable aliphatic-aromatic copolyester, was performed by reactive extrusion. 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane was used as the free-radical initiator. The peroxide concentration was varied between 0.0 and 0.5 wt % at 3.0 wt % MA concentration; the MA concentration was varied between 1.0 and 5.0 wt % at 0.5 wt % peroxide concentration. The reaction temperature was maintained at 185 degrees C for all experiments. Under these conditions, between 0.194% and 0.691% MA was grafted onto the polyester backbone. Size-exclusion chromatography, melt flow index, intrinsic viscosity measurements, thermal gravimetric analysis, and differential scanning calorimetry were used to characterize the maleated copolyester. Increasing the initiator concentration at a constant MA concentration of 3% resulted in an increase in the grafting of MA while decreasing the molecular weight of the resulting polymer. Increasing the feed MA concentration also increased the grafting percentage. The maleation of the polyester proved to be very efficient in promoting strong interfacial adhesion with high amylose cornstarch in starch foams as prepared by melt blending. Thus, the use of maleated copolyester as a compatibilizer between starch and PBAT allowed the reduction of the density of resulting starch foams to approximately 21 kg/m3 and improved the resilience from 84% to as high as 95%. Also, the resulting starch foams exhibited improved hydrophobic properties in terms of lower weight gain and higher dimensional stability on moisture sorption.

Biodegradation, Environmental↗
PubMedDate not supplied

Optimization of the preparation of aqueous suspensions of waxy maize starch nanocrystals using a response surface methodology.

Response surface methodology was used to investigate the effect of five selected factors on the selective H(2)SO(4) hydrolysis of waxy maize starch granules. These predictors were temperature, acid concentration, starch concentration, hydrolysis duration, and stirring speed. The goal of this study was to optimize the preparation of aqueous suspensions of starch nanocrystals, i.e., to determine the operative conditions leading to the smallest size of insoluble hydrolyzed residue within the shortest time and with the highest yield. Therefore empirical models were elaborated for the hydrolysis yield and the size of the insoluble residues using a central composite face design involving 31 trials. They allowed us to show that it was possible to obtain starch nanocrystals after only 5 days of H(2)SO(4) hydrolysis with a yield of 15 wt % and having the same shape as those obtained from the classical procedure after 40 days of HCl treatment, with a yield of 0.5 wt %.

Biotechnology↗
PubMedDate not supplied

Structural processes during starch granule hydration by synchrotron radiation microdiffraction.

Starch granule hydration has been examined on the level of a single potato starch granule by static and dynamic synchrotron radiation (SR) microdiffraction techniques. A cryofrozen, hydrated granule was mapped through a 5 microm SR-beam in order to investigate its internal organization. The edge of the granule showed fiber texture scattering due to radially oriented amylopectin helices. The variation of fiber texture across the granule center supports the model of concentric shells. The crystalline phase appears, however, to increase strongly toward the granule center due to a random amylopectin fraction, which could be related to crystallization of short-range ordered amylopectin during hydration. During gelatinization, the shell structure breaks down and remaining fiber-textured amylopectin domains belong probably to the swollen starch granule envelope. Hydration of a granule was initiated by a microdrop generator and followed in situ by SR-microdiffraction. A fast hydration process with a half time of about 7 s seems to reflect the porous nature of starch granules. The size of the hydrated domains suggests that this process is limited to the level of amylopectin side chain clusters. Longer hydration times are assumed to involve remaining short-range ordered amylopectin and results in larger domains.

Kinetics↗