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PubMed2000

Production of citric acid from starch-hydrolysate by Aspergillus niger.

The present investigation explored the possible use of a rarely used agro-industrial by-product, maize starch-hydrolysate, for economic production of citric acid. To achieve this, seventeen strains of Aspergillus niger were screened for their capacity to produce citric acid using starch-hydrolysate as a substrate. The most efficient strain, ITCC-605 was selected for further improvement in citric acid content by mutation. Mutants developed by treatment with EMS and UV, singly and in combination, produced citric acid in the range of 0.51-64.7 g kg(-1) of glucose consumed. The mutant UE-1 produced the maximum citric acid which was about 130 times more than that produced by the parent strain, ITCC-605. For further increase in citric acid production from this substrate, the cultural conditions were optimized: concentration of starch-hydrolysate, 15% (glucose equivalent); ammonium nitrate, 0.25%; KH2PO4, 0.15%; nicotinic acid, 0.0001% and initial pH of 2.0. Under these conditions, the mutant strain UE-1 yielded 490 g citric acid kg(-1) of glucose consumed in 8 days of incubation at 30 degrees C. The productivity of 341 mgl(-1)h(-1) corresponded to 49% substrate conversion to citric acid.

Aspergillus niger↗
PubMed2001

Digestion of legume starch granules by larvae of Zabrotes subfasciatus (Coleoptera: bruchidae) and the induction of alpha-amylases in response to different diets.

Zabrotes subfasciatus larvae possess three alpha-amylase isoforms as determined by in gel assays following SDS-PAGE. The two minor isoforms present lower electrophoretic mobility than the major form, and seem to occur as a heterodimer. When developed inside Vigna unguiculata (cowpea) seeds, fourth instar larvae have minor quantities of the slow-migrating forms, but when reared on seeds of Phaseolus vulgaris (common bean) or Phaseolus lunatus, the two slow-migrating forms are expressed in higher amounts, while activity of the major form was independent of the host seed. Larvae developing inside cowpea seeds at the beginning of the fourth instar were fed on flour from cotyledons of cowpea or common bean. Larvae fed on the common bean flour started to express the dimer in higher amounts when compared with the control larvae fed on cowpea flour. In an attempt to correlate differences between starch granules and the induction of alpha-amylases, a detailed study on the digestive process of the granules was conducted. Incorporation of purified starch granules into artificial diets did not induce the two minor alpha-amylases. The in vitro hydrolysis rates of purified granules and the pattern of dextrins liberated by the different alpha-amylases were similar for the two legume species. The starch granules enter the midgut extensively damaged, which may facilitate the access to the more susceptible parts of the granules to enzymatic attack.

Animals↗
PubMed2003

Change in maltose- and soluble starch-hydrolyzing activities of chimeric alpha-glucosidases of Mucor javanicus and Aspergillus oryzae.

The chimeric alpha-glucosidases of Mucor javanicus and Aspergillus oryzae, which has high activity toward not only maltooligosaccharides but also soluble starch and has high activity toward maltooligosaccharides but faint activity toward soluble starch, respectively, were constructed by shuffling the C-terminal regions where low homology is observed between the two enzymes. The chimera genes were expressed in Pichia pastoris to produce and secrete the enzymes that have predicted molecular masses in the culture medium. The two chimeric M. javanicus alpha-glucosidases, of which the N- and C-terminal regions are substituted for those of A. oryzae, respectively, decreased in soluble starch-hydrolyzing activity, however, increased in maltose-hydrolyzing activity by 2.1 and 4.9 times higher than that of the native form of M. javanicus alpha-glucosidase, respectively. The chimeric enzymes changed on the V(max) values for maltose significantly, whereas the K(m) values were similar to that of the native enzyme.

Amino Acid Sequence↗
PubMed2001

Regioselective functionalization of starch: synthesis and 1H NMR characterization of 6-O-silyl ethers.

A high regioselective 6-O silylation of starch by using thexyldimethylchlorosilane (TDSCl, chlorodimethyl-(2,3-dimethylbut-2-yl)silane) as bulky silylating agent in the reaction system N-methylpyrrolidone (NMP)/ammonia was carried out and investigated. The control of the degree of substitution (DSSi), the control of the regioselectivity, and the control of the reaction pathway are described in detail. After peracetylation of the silyl ethers of starch, the distribution of the silyl and acetyl substituents was characterized not only in the anhydroglucose repeating units (AGU) but also in the nonreducing end groups (NEG) by means of multidimensional 1H NMR techniques. In both cases, the silyl substituents were detected exclusively in the 6-O position, and the acetyl groups in the 2-O and 3-O positions of the AGU and in the 2-O, 3-O, and 4-O positions of the NEG, respectively. The described 6-O-thexyldimethylsilyl (TDS) units are potentially protecting groups of the primary OH position of starches.

Acetylation↗
PubMedDate not supplied

Plasticized waxy maize starch: effect of polyols and relative humidity on material properties.

The plasticizing effect of different polyols such as glycerol, xylitol, sorbitol, and maltitol on waxy maize starch was investigated. The concentration of plasticizer was fixed at 33 wt % (dry basis of starch). The structure and mechanical performance of resulting films conditioned at different relative humidity levels were studied in detail. The effect of the plasticizer on the glass-rubber transition temperature (T(g)) and crystallinity was characterized using differential scanning calorimetry. It was found that T(g) decreases with increasing moisture content and decreasing molecular weight of the plasticizer. The water resistance of starch increased steadily with the molecular weight of the plasticizer and was directly proportional to the ratio of the end to total hydroxyl groups. As the molecular weight of the plasticizer increased, the brittleness of the dry system increased. However, the use of high molecular plasticizer allowed good mechanical properties of the moist material to be obtained in terms of both stiffness and elongation at break.

Humidity↗
PubMedDate not supplied

Small angle X-ray scattering of resistant starch type III.

Starch fraction, which is resistant to enzymatic digestion, is produced during retrogradation. This fraction, termed resistant starch type III (RSIII), has health benefits such as pre-biotic effects, improving lipid and cholesterol metabolism, and reducing the risk of colon cancer. The work presented in this paper is aimed at investigating the colloidal structure of native high amylose corn starch (HACS) and the RSIII polymorphs produced from it using small angle X-ray scattering. Experimental scattering curves were fitted with appropriate theoretical models such as the "modified lamellar model". Our results show that retrogradation at low temperature leads to formation of polymorph B with crystallinity much lower than that of the granular form, but the lamellas are arranged in long-range periodicity. Conversely, retrogradation at high temperature leads to formation of polymorphs A and V with no defined periodicity. The degree of crystallinity is very low, and the system is better described as a dilute particulate system.

Amylose↗
PubMedDate not supplied

Mechanistic information from analysis of molecular weight distributions of starch.

A methodology is developed for interpreting the molecular weight distributions of debranched amylopectin, based on techniques developed for quantitatively and qualitatively finding mechanistic information from the molecular weight distributions of synthetic polymers. If the only events occurring are random chain growth and stoppage (i.e., the rates are independent of degree of polymerization over the range in question), then the number of chains of degree of polymerization N, P(N), is linear in ln P(N) with a negative slope, where the slope gives the ratio of the stoppage and growth rates. This starting point suggests that mechanistic inferences can be made from a plot of lnP against N. Application to capillary electrophoresis data for the P(N) of debranched starch from across the major taxa, from bacteria (Escherichia coli), green algae (Chlamydomonas reinhardtii), mammals (Bos), and flowering plants (Oryza sativa, rice; Zea mays, maize; Triticum aestivum, wheat; Hordeum vulgare, barley; and Solanum tuberosum, potato), gives insights into the biosynthetic pathways, showing the differences and similarities of the alpha-1,4-glucans produced by the various species. Four characteristic regions for storage starch from the higher plants are revealed: (1) an initial increasing region corresponding to the formation of new branches, (2) a linear ln P region with negative slope, indicating random growth and stoppage, (3) a region corresponding to the formation of the crystalline lamellae and subsequent elongation of chains, and (4) a second linear ln P with negative slope region. Each region can be assigned to specific enzymatic processes in starch synthesis, including determining the ranges of degrees of polymerization which are subject to random and nonrandom processes.

Animals↗
PubMedDate not supplied

Phosphorylation of potato starch and its electrorheological suspension.

Highly substituted potato starch phosphate (HPSP) particles were synthesized via an esterification process of potato starch with a mixture of several different concentrations of disodium hydrogen phosphate and sodium hydrogen phosphate. These particles were characterized via thermogravimetric analysis, scanning electron microscope, and inductively coupled plasma mass spectrometer. The electrorheological (ER) fluid was prepared by dispersing these HPSP particles in nonconducting silicone oil, and their ER properties were investigated. The HPSP particle-based ER fluid exhibited typical ER responses with a nonzero yield stress under an applied electric field. We examined the yield stresses for the potato starch-based anhydrous ER system by varying the degree of phosphate substitution and found that the higher polarization induced by the external electric field strength resulted in the higher values of yield stresses and shear stresses.

Carbohydrate Conformation↗
PubMedDate not supplied

Imaging of high-amylose starch tablets. 3. Initial diffusion and temperature effects.

The penetration of water into cross-linked high amylose starch tablets was studied at different temperatures by nuclear magnetic resonance (NMR) imaging, which follows the changes occurring at the surface and inside the starch tablets during swelling. It was found that the swelling was anisotropic, whereas water diffusion was almost isotropic. The water proton image profiles at the initial stage of water penetration were used to calculate the initial diffusion coefficient. The swelling and water concentration gradients in this controlled release system show significant temperature dependence. Diffusion behavior changed from Fickian to Case II diffusion with increasing temperature. The observed phenomena are attributed to the gelatinization of starch and the pseudo-cross-linking effect of double helix formation.

Amylose↗
PubMed2006

Structural transformations during gelatinization of starches in limited water: combined wide- and small-angle X-ray scattering study.

Rice flour (18-25% moisture) and potato starch (20% moisture) were heated with continuous recording of the X-ray scattering during gelatinization. Rice flours displayed A-type crystallinity, which gradually decreased during gelatinization. The development of the characteristic 9 nm small-angle X-ray scattering (SAXS) peak during heating at sub-gelatinization temperatures indicated the gradual evolution into a stacked lamellar system. At higher temperatures, the crystalline and lamellar order was progressively lost. For potato starch (B-type crystallinity), no 9 nm SAXS peak was observed at ambient temperatures. Following the development of lamellar structures at sub-gelatinization temperatures, B-type crystallinity and lamellar order was lost during gelatinization. On cooling of partially gelatinized potato starch, A-type crystallinity steadily increased, but no formation of stacked lamellar structures was observed. Results were interpreted in terms of a high-temperature B- to A-type recrystallization, in which the lateral movement of double helices was accompanied by a shift along their helical axis. The latter is responsible for the inherent frustration of the lamellar stacks.

Chemical Phenomena↗
PubMed2006

Fluorescence recovery after photobleaching as a probe of diffusion in starch systems.

The diffusion coefficients of dextran probes of various molecular weights in starch solutions over a wide concentration range were carried out using fluorescent recovery after photobleaching (FRAP), combined with a confocal microscope and tracer probe diffusion. The technique is simple to implement and can be carried out using increasingly common microscopy apparatus, giving access to a wide variety of new structural and kinetic information. The data can be rationalized in terms of the effects of probe molecular weight and on matrix starch concentration and structure. This provides a new tool to investigate the behavior of systems where starch is an ingredient that contributes to the processing and textural properties of food.

Dextrans↗
PubMed2006

Processing and characterization of porous structures from chitosan and starch for tissue engineering scaffolds.

Natural biodegradable polymers were processed by different techniques for the production of porous structures for tissue engineering scaffolds. Potato, corn, and sweet potato starches and chitosan, as well as blends of these, were characterized and used in the experiments. The techniques used to produce the porous structures included a novel solvent-exchange phase separation technique and the well-established thermally induced phase separation method. Characterization of the open pore structures was performed by measuring pore size distribution, density, and porosity of the samples. A wide range of pore structures ranging from 1 to 400 microm were obtained. The mechanisms of pore formation are discussed for starch and chitosan scaffolds. Pore morphology in starch scaffolds seemed to be determined by the initial freezing temperature/freezing rate, whereas in chitosan scaffolds the shape and size of pores may have been determined by the processing route used. The mechanical properties of the scaffolds were assessed by indentation tests, showing that the indentation collapse strength depends on the pore geometry and the material type. Bioactivity and degradation of the potential scaffolds were assessed by immersion in simulated body fluid.

Amylopectin↗
PubMed2000

Internal structure of normal maize starch granules revealed by chemical surface gelatinization.

Normal maize starch was fractionated into two sizes: large granules with diameters more than 5 microns and small granules with diameters less than 5 microns. The large granules were surface gelatinized by treating them with an aqueous LiCl solution (13 M) at 22-23 degrees C. Surface-gelatinized remaining granules were obtained by mechanical blending, and gelatinized surface starch was obtained by grinding with a mortar and a pestle. Starches of different granular sizes and radial locations, obtained after different degrees of surface gelatinization, were subjected to scanning electron microscopy, iodine potentiometric titration, gel-permeation chromatography, and amylopectin branch chain length analysis. Results showed that the remaining granules had a rough surface with a lamella structure. Amylose was more concentrated at the periphery than at the core of the granule. Amylopectin had longer long B-chains at the core than at the periphery of the granule. Greater proportions of the long B-chains were present at the core than at the periphery of the granule.

Amylopectin↗
PubMedDate not supplied

Microbial desizing using starch as model compound: enzyme properties and desizing efficiency.

A film of sizing agents protects yarn during weaving. Its removal in a subsequent washing process causes 50% of the organic effluent load of textile finishing processes and requires large amounts of auxiliary chemicals (e.g., surfactants). Microbial desizing is a new bioprocess that uses the acidifying culture of a two-phase anaerobic digestion plant for the removal and partial degradation (acidification) of the sizing agent. Soluble starch is used in this study to characterize the enzymatic properties in the supernatant of the desizing culture and to link them to desizing efficiencies. The supernatant of the culture (grown at 37 degrees C, pH 5.5) displayed the highest enzymatic activity between pH 4 and 5 and in a broad temperature range (20-80 degrees C). Highest metabolization rates were determined with the substrate amylose. Short chain dextrins (average of 5 and 10 glucose units) and amylopectin were converted significantly more slowly. At 37 degrees C the half-life time of the enzymatic activity in the supernatant was 45 h. In a desizing test a decisive reduction of the chain length was found already after 1 h (allowing starch solubilization). A microbial desizing experiment with dyed, native maize starch demonstrated the efficiency of the proposed bioprocess.

Bacteria, Anaerobic↗
PubMedDate not supplied

Hydrolysis of nonstarch carbohydrates of wheat-starch effluent for ethanol production.

A (polysaccharide-rich) waste stream derived from a combined starch and ethanol factory was investigated regarding hydrolysis of the nonstarch carbohydrates for ethanol production. The material was characterized and processed to yield the maximum amount of sugars. The starch fraction was hydrolyzed with amylolytic enzymes, and the resulting fibrous material was separated by filtration. This material, denoted starch-free fibers (SFF), was subjected to heat treatment followed by enzymatic hydrolysis to recover the other major carbohydrate components, namely, cellulose and hemicellulose, in monomeric form. Heat treatment in a microwave oven efficiently solubilized a fraction of these polysaccharides and made the material more accessible to the cellulolytic and hemicellulolytic enzymes used in the subsequent enzymatic hydrolysis. The maximum sugar yield after enzymatic hydrolysis, achieved with pretreatment at 170 degrees C for 40 min, was 34.1 g per 100 g SFF, comprising 12.8 g glucose, 13.9 g xylose and 7.4 g arabinose, corresponding to 66%, 71% and 51% of the theoretical, respectively.

Carbohydrates↗
PubMed2001

Pressure-temperature phase transition diagram for wheat starch.

Wheat starch suspensions in water (5% dry matter) were subjected to various pressures (0.1-600 MPa) and temperatures (-20 to 96 degrees C) for 15 min. The gelatinization rate was measured after treatment by using microscopic measurements of the loss of birefringence of the granules. This method was previously calibrated by differential scanning calorimetry. Curves of isogelatinization were found to be quite similar to a pressure-temperature (P-T) diagram of unfolding proteins. Results were first analyzed by considering the thermodynamic aspects related to the dT/dP curve shifts. On the basis of equations already shown for proteins, the P-T gelatinization diagram of wheat starch would show different kinds of thermal contributions, suggesting endothermic, athermic, or exothermic melting reactions. Second, as a practical consequence, these previous P-T areas corresponded to specific gelatinization conditions as confirmed by hydration evaluation measured by starch swelling index. Depending on the pressure-temperature conditions, gelatinization would involve hydration. Lowering the pressure and temperature resulted in a complete gelatinization with less hydration in comparison with a thermal treatment at atmospheric pressure. A hydration model based on an energetic approach was proposed.

Birefringence↗
PubMed2001

Glycemic response to a food starch esterified by 1-octenyl succinic anhydride in humans.

To evaluate the glycemic response to a food starch esterified by 1-octenyl succinic anhydride (OSA), 30 healthy nondiabetic adult subjects were studied in a double-blind crossover design. After an overnight fast, subjects consumed a product containing either 25 g of glucose or 25 g of OSA-substituted starch. Finger-prick capillary blood was obtained at baseline and 15, 30, 45, 60, 90, and 120 min postprandial for glucose measurement. After OSA treatment, the rise in blood glucose was reduced (P < 0.05) at 15 and 30 min and tended (P < 0.08) to be lower at 45 min. Mean peak rise in glucose was reduced 19% (P < 0.01) by OSA (3.30 +/- 0.19 versus 2.66 +/- 0.16 mmol/L) compared to glucose, but time to peak did not differ between treatments. Net incremental area under the curve was also lower (P < 0.05) on OSA compared to glucose. Minimal effects on gastrointestinal symptoms (intensity and frequency of nausea, cramping, distention, and flatulence) were noted for both products, with no clinically significant difference between products. In conclusion, starch substitution with OSA attenuated the postprandial glycemic excursion compared to an equivalent glucose challenge and was well tolerated by fasting healthy adult subjects.

Adult↗
PubMed2003

Analysis of the retrogradation of low starch concentration gels using differential scanning calorimetry, rheology, and nuclear magnetic resonance spectroscopy.

The retrogradation of 5, 10, 15, and 25% corn starch gels was measured using differential scanning calorimetry (DSC), rheology, and an array of NMR spectroscopy techniques. During the initial (<24 h) stage of retrogradation, an increase in G' corresponding to an increase in the number of solid protons participating in cross-relaxation (M(B)(0) was observed for all four concentrations studied. During the latter (>24 h) stage of retrogradation, amylopectin recrystallization becomes the dominant process as measured by an increase in deltaH(r) for the 25% starch gel, which corresponded to a further increase in. A decrease in the molecular mobility of the liquid component was observed by decreases in (17)O T(2), (1)H D(0), and T(2A). The value for T(2B) (the solid transverse relaxation time) did not change with concentration or time indicating that the mobility of the solid component does not change over time despite the conversion of the highly mobile starch fraction to the less mobile solid state during retrogradation.

Amylopectin↗