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PubMed2001

Preparation of starch and other carbon fractions from higher plant leaves for stable carbon isotope analysis.

The measurement of the carbon isotope composition of starch and cellulose still relies on chemical isolation of these water-insoluble plant constituents and subsequent elemental analysis by isotope ratio mass spectrometry (EA/IRMS) of the purified fractions, while delta(13)C values of low-molecular-weight organic compounds are now routinely measured by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Here we report a simple and reliable method for processing milligram quantities of dried plant material for the analysis of the carbon isotope composition of lipids, soluble sugars, starch and cellulose from the same sample. We evaluated three different starch preparation methods, namely (1) enzymatic hydrolysis by alpha-amylase, (2) solubilization by dimethyl sulfoxide (DMSO) followed by precipitation with ethanol, and (3) partial hydrolysis by HCl followed by precipitation of the resulting dextrins by ethanol. Starch recovery for three commercially available native starches (from potato, rice and wheat) varied from 48 to 81% for the techniques based on precipitation, whereas the enzymatic technique exhibited yields between 99 and 105%. In addition, the DMSO and HCl techniques introduced a significant (13)C fractionation of up to 1.9 per thousand, while the carbon isotope composition of native starches analyzed after enzymatic digestion did not show any significant difference from that of untreated samples. The enzymatic starch preparation method was then incorporated into a protocol for determination of delta(13)C signatures of lipids, soluble carbohydrates, starch and crude cellulose. The procedure is based on methanol/chloroform/water extraction of dried and ground leaf material. After recovery of the chloroform phase (lipid fraction), the methanol/water phase was deionized by ion exchange (soluble carbohydrate fraction) and the pellet treated with heat-stable alpha-amylase (starch fraction). The remaining insoluble material was subjected to solvolysis by diglyme (cellulose fraction). The method was shown to be applicable to foliar tissues of a variety of different plant species (spruce, erect brome, maize and soybean).

Carbon↗
PubMed1991

Gravitropism and starch statoliths in an Arabidopsis mutant.

The mutant TC 7 of Arabidopsis thaliana (L.) Heynh. has been reported to be starch-free and still exhibit root gravitropism (T. Caspar and B. G. Pickard 1989, Planta 177, 185-197). This is not consistent with the hypothesis that plastid starch has a statolith function in gravity perception. In the present study, initial light microscopy using the same mutant showed apparently starch-free statocytes. However, ultrastructural examination detected residues of amyloplast starch grains in addition to the starch-depleted amyloplasts. Applying a point-counting morphometric method, the starch grains in the individual amyloplasts in the mutant were generally found to occupy more than 20% and in a few cases up to 60% of the amyloplast area. In the wild type (WT) the starch occupied on average 98% of the amyloplast area and appeared as densely packed grains. The amyloplasts occupied 13.9% of the area of the statocyte in the mutant and 23.3% of the statocyte area in the WT. Sedimentation of starch-depleted amyloplasts in the mutant was not detected after 40 min of inversion while in the WT the amyloplasts sedimented at a speed of 6 micrometers h-1. The gravitropic reactivity and the curvature pattern were also examined in the WT and the mutant. The time-courses of root curvature in the WT and the mutant showed that when cultivated under standard conditions for 60 h in darkness, the curvatures were 83 degrees and 44 degrees, respectively, after 25 h of continuous stimulation in the horizontal position. The WT roots curved significantly more rapidly and with a more normal gravitropic pattern than those of the mutant. These results are discussed in relation to the results previously obtained with the mutant and with respect to the starch-statolith hypothesis.

Arabidopsis↗
PubMed2001

Sugar utilization in the hyperthermophilic, sulfate-reducing archaeon Archaeoglobus fulgidus strain 7324: starch degradation to acetate and CO2 via a modified Embden-Meyerhof pathway and acetyl-CoA synthetase (ADP-forming).

The hyperthermophilic, sulfate-reducing archaeon Archaeoglobus fulgidus strain 7324, rather than the type strain VC16, was found to grow on starch and sulfate as energy and carbon source. Fermentation products and enzyme activities were determined in starch-grown cells and compared to those of cells grown on lactate and sulfate. During exponential growth on starch, 1 mol of glucose-equivalent was incompletely oxidized with sulfate to approximately 2 mol acetate, 2 mol CO2 and 1 mol H2S. Starch-grown cells did not contain measurable amounts of the deazaflavin factor F420 (<0.03 nmol/mg protein) and thus did not show the F420-specific green-blue fluorescence. In contrast, lactate (1 mol) was completely oxidized with sulfate to 3 mol CO2 by strain 7324, and lactate-grown cells contained high amounts of F420 (0.6 nmol/mg protein). In extracts of starch-grown cells, the following enzymes of a modified Embden-Meyerhof pathway were detected: ADP-dependent hexokinase (ADP-HK), phosphoglucose isomerase, ADP-dependent 6-phosphofructokinase (ADP-PFK), fructose-1,6-phosphate aldolase, glyceraldehyde-3-phosphate:ferredoxin oxidoreductase (GAP:FdOR), phosphoglycerate mutase, enolase, and pyruvate kinase (PK). Specific activities of ADP-HK, ADP-PFK, GAP:FdOR, and PK were significantly higher in starch-grown cells than in lactate-grown cells, indicating induction of these enzymes during starch catabolism. Pyruvate conversion to acetate involved pyruvate:ferredoxin oxidoreductase and ADP-forming acetyl-CoA synthetase. The findings indicate that the archaeal sulfate reducer A. fulgidus strain 7324 converts starch to acetate via a modified Embden-Meyerhof pathway and acetyl-CoA synthetase (ADP-forming). This is the first report of growth of a sulfate reducer on starch, i.e. on a polymeric sugar.

Acetate-CoA Ligase↗
PubMed2001

Increased levels of adenine nucleotides modify the interaction between starch synthesis and respiration when adenine is supplied to discs from growing potato tubers.

To investigate the importance of the overall size of the total adenine nucleotide pool for the regulation of primary metabolism in growing potato tubers, freshly cut discs were provided with zero or 2 mM adenine in the presence of 1 or 100 mM [U-14C]glucose or 100 mM [U-14C]sucrose in the presence and absence of 20 mM orthophosphate (Pi). Adenine led to a 150-250% increase of the total adenine nucleotide pool, which included an increase of ADP, a larger increase of ATP and an increase of the ATP:ADP ratio. There was a 50-100% increase of ADP-glucose (ADPGlc), and starch synthesis was stimulated. Respiratory oxygen uptake was stimulated, and the levels of glycerate-3-phosphate, phosphoenolpyruvate and alpha-ketoglutarate decreased. The response to adenine was not modified by Pi. It is proposed that increased ATP stimulates ADPGlc pyrophosphorylase, leading to a higher rate of starch synthesis. The impact on starch synthesis is constrained, however, because increased ADP can lead to a stimulation of respiration and decline of glycerate-3-phosphate, which will inhibit ADPGlc pyrophosphorylase. The quantitative impact depends on the conditions. In the presence of 1 mM glucose, the levels of phosphorylated intermediates and the rate of starch synthesis were low. Adenine led to a relatively large stimulation of respiration, but only a small stimulation of starch synthesis. In the presence of 100 mM glucose, discs contained high levels of phosphorylated intermediates, low ATP:ADP ratios (< 3) and low rates of starch synthesis (< 20% of the metabolised glucose). Adenine led to marked increase of ATP and 2- to 4-fold stimulation of starch synthesis. Discs incubated with 100 mM sucrose already had high ATP:ADP ratios (> 8) and high rates of starch synthesis (> 50% of the metabolised sucrose). Adenine led to a further increase, but the stimulation was less marked than in high glucose. These results have implications for the function of nucleotide cofactors in segregating sucrose mobilisation and respiration, and the need for energy conservation during sugar-starch conversions.

Adenine↗
PubMed1985

Partially purified white bean amylase inhibitor reduces starch digestion in vitro and inactivates intraduodenal amylase in humans.

Whether commercial, bean-derived alpha-amylase inhibitor preparations failed to decrease starch digestion in humans because of insufficient antiamylase activity, destruction by gastrointestinal secretions, or decreased activity in the presence of starch is unknown. We used a simple partial purification procedure to markedly concentrate the inhibitor (sixfold to eightfold by total protein content, and 30-40-fold by dry weight). Compared with a commercial preparation and crude bean extract, this partially purified inhibitor inactivated intraduodenal, intraileal, and salivary amylase in vitro faster and more completely (p less than 0.001); its specific activity was not affected by exposure to gastric juice and was only minimally reduced by duodenal juice. Whereas the rate of amylase inhibition by inhibitor was markedly slowed in the presence of nondietary liquid starch, dietary solid starch had only a minimal effect. Consequently, the partially purified inhibitor had no effect on liquid starch digestion, but decreased in vitro digestion of dietary starch in a dose-dependent manner (p less than 0.001). Perfusion of the partially purified inhibitor (2.0, 3.5, or 5.0 mg/ml at 5 ml/min) into the duodenum of humans rapidly inhibited greater than 94%, greater than 99%, or greater than 99.9% of intraluminal amylase activity. We conclude that commercial amylase inhibitors failed to decrease starch digestion in vivo mainly because they have insufficient antiamylase activity. However, a partially purified inhibitor with increased specific activity is stable in human gastrointestinal secretions, slows dietary starch digestion in vitro, rapidly inactivates amylase in the human intestinal lumen, and, at acceptable oral doses, may decrease intraluminal digestion of starch in humans. Such an inhibitor therefore deserves study.

Adult↗
PubMed2005

Starch biosynthesis: the primer nonreducing-end mechanism versus the nonprimer reducing-end two-site insertion mechanism.

Two mechanisms are recognized for polysaccharide chain elongation: (a) the nonreducing-end, primer-dependent mechanism and (b) the reducing-end, two-site insertion mechanism. We recently demonstrated the latter mechanism for starch biosynthesis by pulsing starch granules with ADP-[14C]Glc and chasing with ADPGlc for eight varieties of starch granules. Others have reported the addition of glucose from ADPGlc to the nonreducing ends of maltose, maltotriose, and maltopentaose and a branched maltopentasaccharide. It was concluded that starch chains are biosynthesized by the addition of glucose to the nonreducing ends of maltodextrin primers. In this study, we reinvestigated the maltodextrin reactions by reacting three kinds of starch granules from maize, wheat, and rice with ADP-[14C]Glc in the absence and presence of maltose (G2), maltotriose (G3), and maltodextrin (d.p.12) and found that they inhibited starch biosynthesis rather than stimulating it, as would be expected for primers. The major product in the presence of G2 was G3 with decreasing amounts of G4-G9 and the major products in the presence of G3 was G4 and G5, with decreasing amounts of G6-G9. It was concluded that maltodextrins are acceptors rather than primers. This was confirmed by pulsing the starch granules with ADP-[14C]Glc and chasing with G2, G3, and G6, which gave release of 14C-label from the pulsed granules in the absence of ADPGlc, further demonstrating that maltodextrins are acceptors that inhibit starch biosynthesis by releasing glucose from starch synthase, rather than acting as primers and stimulating biosynthesis.

Adenosine Diphosphate Glucose↗
PubMed2006

Structural characteristics and physicochemical properties of oxidized corn starches varying in amylose content.

The effects of amylose content on the extent of oxidation and the distribution of carboxyl groups in hypochlorite-oxidized corn starches were investigated. Corn starches including waxy corn starch (WC), common corn starch (CC), and 50% and 70% high-amylose corn starches (AMC) were oxidized with NaOCl at three concentrations (0.8%, 2%, and 5%). Carboxyl and carbonyl content of oxidized starches increased with increasing NaOCl concentration. High-AMC (70%) had slightly higher carboxyl and carbonyl contents at 0.8% NaOCl, whereas WC had significantly higher carboxyl and carbonyl contents at 2% and 5% NaOCl levels. Carbohydrate profiles by high-performance size-exclusion chromatography indicate that amylose was more susceptible to depolymerization than amylopectin. Degradation of amylopectin long chains (DP >24) was more pronounced in WC and CC than in AMCs. The crystalline lamellae of WC started to degrade at 2% NaOCl, but those of the other corn starches remained intact even at 5% NaOCl level according to X-ray crystallinity. By using anion-exchange chromatography for separation and size-exclusion chromatography for characterization, carboxyl groups were found to be more concentrated on amylopectin than on amylose, particularly in AMCs. Oxidation decreased gelatinization temperature and enthalpy with WC showing the most decrease and 70% AMC showing the least. The gelatinization enthalpy of 50% AMC decreased significantly faster than those of CC and 70% AMC after 0.8% oxidation. Retrogradation of amylopectin slightly increased after oxidation with increasing oxidation level. The peak viscosities of oxidized WC and CC were higher than those of their native counterparts at 0.8% NaOCl, but this increase was not observed in AMCs. The setback viscosities of 2% NaOCl-oxidized 50% and 70% AMCs were much higher than those of the unmodified counterparts. The extent of oxidation and physicochemical properties of oxidized starches varied greatly with the amylase:amylopectin ratio of corn starches. Amylose was suggested to play an important role in controlling the oxidation efficiency.

Amylopectin↗
PubMed2005

Effects of storage temperatures and annealing conditions on the structure and properties of potato (Solanum tuberosum) starch.

Starches were extracted from freshly harvested potatoes (12 cultivars, grown in Perthshire) and the properties of the starches of six cultivars were compared with starches extracted from the same samples but stored at 5, 25 or 55 degrees C for 7 days before extraction. The amylose (total) content of the freshly extracted starches from tubers stored at 5, 25 or 55 degrees C was on average 27.9+/-2.3, 28.3+/-1.7, 29.2+/-2.2 and 28.8+/-1.5%, respectively, with corresponding phosphorus representing 60+/-16, 64+/-9, 61+/-5 and 63+/-9 mg 100 g(-1). The unit chain distribution by chromatography of the amylopectin molecules from the starches extracted from the different conditions was very similar with an average degree of polymerisation (DP) of 26+/-2 where the two major fractions (F1 and F2) represented 54+/-2 and 19+/-1, respectively. Peak gelatinisation temperatures (Tp) and enthalpies (DeltaH) for the freshly extracted starches and from tubers stored at 5 or 25 degrees C were very similar (63.3+/-1.5 degrees C and 18.6+/-0.8 J g(-1); 63.1+/-1.0 degrees C and 17.7+/-1.5 J g(-1) and; 62.9+/-0.7 degrees C and 18.7+/-1.1 J g(-1), respectively) although starches stored at 55 degrees C were annealed, where Tp represented 71.1+/-1.1 degrees C and DeltaH 18.1+/-1.4 J g(-1). These in situ-annealed starches were comparable in terms of gelatinisation characteristics to annealed freshly extracted starches where on average, T(p) represented 72.7+/-1.0 degrees C and DeltaH 20.8+/-1.0 J g(-1). Annealing of tubers in situ prior to processing might be beneficial with respect to developing new potato-based products.

Amylopectin↗
PubMed2006

Studies on the hydrothermal modifications of new cocoyam (Xanthosoma sagittifolium) starch.

Native new cocoyam starch (nNCS) was subjected to annealing (aNCS) and heat moisture treatment at 18% moisture level (h18NCS), 21% moisture level (h21NCS), 24% moisture level (h24NCS) and 27% moisture level (h27NCS) as hydrothermal treatments. Scanning electron and light microscopy revealed round and polygonal shapes with sizes ranging from 15 to 40 microm for native and modified starches. nNCS showed "A" pattern X-ray diffraction and no significant differences were observed in the X-ray pattern of the modified starches. Swelling power and solubility reduced following heat moisture treatment. At all pH studied (2-12), unmodified new cocoyam starch exhibited higher swelling capacity and solubility than the modified derivatives. Hydrothermal modifications improved water absorption capacity but reduced oil absorption capacity. Pasting temperature of native starch shifted to higher values following annealing and heat moisture treatment. Hot paste viscosity (Hv), viscosity after 30 min holding at 95 degrees C (Hv30) and cold paste viscosity (Cv) reduced after annealing and heat moisture treatment. The result also indicates that hydrothermal treatments reduced the tendency for setback. As the number of days of storage of starch paste increased from 1 to 10, light transmittance of all the starches reduced but marked reduction of light transmittance was observed in native starch. DSC studies revealed increase in gelatinization temperature following annealing and heat moisture treatment. Starch hydrothermal modifications reduced retrogradation as enthalpies of regelatinization reduced following modifications. The regelatinization peak in the second day scanning shifted to lower temperature than the gelatinization peak in first run heating DSC curve for all samples. The regelatinization peak also became larger and shifted to higher temperature range when the storage days increased from 2 to 7.

Calorimetry, Differential Scanning↗
PubMed2006

Thermal and rheological properties of nixtamalized maize starch.

The effect of nixtamalization process on thermal and rheological characteristics of corn starch was studied. Starch of raw sample had higher gelatinization temperature than its raw counterpart, because, the Ca(2+) ions stabilize starch structure of nixtamalized sample; however, the enthalpy values were not different in both samples. The temperature of the phase transition of the retrograded starches (raw and nixtamalized) were not different at the storage times assessed, but the enthalpy values of the above mentioned transition was different, indicating a lower reorganization of the starch structure in the nixtamalized sample. The viscoamylographic profile showed differences between both starches, since raw starch had higher peak viscosity than the nixtamalized sample due to partial gelatinization of some granules during this heat treatment. Rheological test showed that at low temperature (25 degrees C) the raw and nixtamalized starches presented different behaviour; however, the elastic characteristic was more important in the starch gel structure. The nixtamalization process produced changes in thermal and rheological characteristics becoming important in those products elaborated from nixtamalized maize.

Alkalies↗
PubMed1997

Wheat starch intolerance in patients with celiac disease.

OBJECTIVE: Evaluate in patients with celiac disease the tolerance of prolonged consumption of small amounts of gliadin contained in products containing wheat starch. DESIGN: Open 1-year trial of the addition of wheat starch to a gluten-free diet in a cohort of adult patients with biopsy-proven celiac disease who had never consumed wheat starch. The control group consisted of patients with celiac disease who tolerated wheat starch. SUBJECTS: Seventeen patients with celiac disease and 14 control patients, all diagnosed according to criteria of the European Society of Pediatric Gastroenterology and Nutrition, were recruited from the Canadian Celiac Association and the Quebec Celiac Foundation. SETTING: The study was conducted in the outpatient clinic of the Gastroenterology and Nutrition Service of Ste Justine Hospital, Montreal, Quebec, Canada. INTERVENTIONS: Patients were asked to consume four to six portions daily of a wheat starch-containing product, mainly bread, for up to 1 year. MAIN OUTCOME MEASURES: The gliadin content of the wheat starch product used in this trial was quantified by enzyme-linked immunosorbent assay. Patient outcome measures included symptoms, nutritional parameters (anthropometric data, complete blood count, serum folate and iron levels), and immunologic parameters (antigliadin antibody and antiendomysium antibody titers). RESULTS: A quantifiable amount of immunoreactive gliadin (0.75 mg/100 g) was found in the wheat starch. The majority of the patients with celiac disease (11 of 17) who had never consumed wheat starch previously developed symptoms, which resolved within weeks of discontinuing the product. Relapse of skin lesions was seen in two of three patients with coexisting dermatitis herpetiformis. No weight loss or biochemical changes were observed. Despite the presence of symptoms, antigliadin antibody and antiendomysium antibody determinations were not useful to detect the clinical intolerance. APPLICATIONS: The innocuousness of the long-term ingestion of "gluten-free" products containing wheat starch is still unproven, and prolonged use of such products by patients with celiac disease cannot be recommended.

Adolescent↗
PubMed2000

The substitution pattern in cationised and oxidised potato starch granules.

The distribution pattern of substituents within the granules and the components of two cationised and two oxidised potato starches was studied. The level of crystallinity in wet-cationised (WC) and hypochlorite oxidised (HO) starch granules was similar to that of native starch granules but lower in dry-cationised (DC) and peroxide oxidised (PO) granules. However, the melting temperature of DC granules remained similar to native granules but was decreased in the other samples. With all modified starches, the initial rate of acid hydrolysis (lintnerisation) was increased compared to native granules. The degree of substitution decreased only slightly in WC granules after the lintnerisation, whereas virtually all the substituted glucosyl units in DC starch were hydrolysed already at initial stages. The decrease of substituents in the HO and PO starches was intermediate. The starches were partly resistant to the action of isoamylase and the successive beta-amylolysis, suggesting that substituents were found both close to the branches and near the nonreducing ends in the amylopectin component. It is suggested that the DC starch was preferentially cationised at the surface of the granules, whereas WC and oxidised starches were modified throughout the granules.

Calorimetry, Differential Scanning↗
PubMed2001

Amylopectin aggregation as a function of starch phosphate content studied by size exclusion chromatography and on-line refractive index and light scattering.

Starches with a natural 65-fold span in covalently bound phosphate content were prepared from five different crops including sorghum, cassava, three potato varieties and an exotic ginger plant, Curcuma zedoaria, with extreme starch phosphate content. These starches were subjected to size exclusion chromatography with refractive index detection (SEC/RI). A simple and rapid method for starch solubilisation was used. The conditions during solubilisation (2 M NaOH) and separation (10 mM NaOH, 50 degrees C) were such as enabling > 94% recovery of the starch without detectable degradation. The aggregation properties of the starch was investigated using on line refractive index/multi angle laser light scattering (RI/MALLS) detection. Three major regions in the SEC profile were identified, consisting of large amylopectin aggregates, amylopectin particles with radius of gyration (Rg) of approx 200 nm (400 nm blocklets) and amylose. A procedure for correction of light scattering signals spread over the SEC profile as a result of aggregate tailing was developed. The significance of the relative amounts of these three molecular species on standard starch pasting parameters, as measured by a Rapid Visco Analyzer (RVA), was investigated. Starches with a high amount of amylopectin aggregates showed high peak viscosities. Moreover, very high amounts of starch bound phosphate or amylose appears to suppress the content of large aggregates resulting in low viscosity.

Amylopectin↗
PubMed2001

Preparation and characterization of biodegradable copolyester-starch based foams.

Regular (25% amylose) and waxy corn starches blended to various ratios with Eastar Bio Copolyester 14766 (EBC) were extruded into loose-fill foams using a twin screw extruder. Included in this study were two types of corn starch, three levels of EBC content, and three levels of starch moisture content. Waxy starch produced foams with greater radial expansions and lower unit and bulk densities than regular starch. Regular starch foams had lower water solubility indices (WSIs) than waxy starch foams. Foams made of both types of starch possessed similar mechanical properties. No differences were observed in compressibilities and spring indices of either waxy or regular starch foams. Higher levels of EBC addition resulted in less radial expansion and higher unit and bulk densities. Foams made with 10% EBC had higher compressibility than foams containing 25% EBC. Spring indices of single-piece samples and compressibilities and spring indices of bulk samples were not affected by the differences in the level of EBC addition. At 19% and 22% of moisture contents, foams had greater radial expansion than at 25% moisture content. Unit and bulk densities were not affected by variations in moisture content. At 22% moisture content, a lower WSI of 18.5% was obtained. At 22% moisture content, softer foams were produced. At all three levels of moisture content, no differences were detected in the spring indices.

Biocompatible Materials↗
PubMed2001

Molecular characteristics of amylose and starch in dimethyl sulfoxide.

The aim of this work was the molecular characterization of starch polysaccharides to determine solution structure. Studies of amylose and potato starches of different origins were carried out by the static light scattering, dynamic light scattering, and HPSEC-MALLS methods. Molecular parameters such as Mw, Rg, A2, molar mass distribution, Dz, Rh, the structure-dependent rho-parameter, and osmotic modulus for amylose were determined. The Mw of amylose was found to be in the range from 1 x 10(5) to 1 x 10(6) g mol-1. The Mw of potato starches was much higher, that is, in the range of 23-37 x 10(6) g mol-1. The Rg of the amylose samples was in the range of 24-71 nm, and that of the potato starches was between 130 and 150 nm. The intensity-time correlation function showed one diffusive relaxation motion for amylose as well as for starch. The diffusion coefficients of the amylose prepared from starch by several methods were in the range of 2.7-9.1 x 10(-8) cm2 s-1, and those of the starches were 1 magnitude lower between 4.8 and 6.7 x 10(-9) cm2 s-1. The rho-parameter of amylose was calculated as having values between 1.5 and 2.2, and that of starches was calculated to be an average value of 0.62. The assumed solution behavior of amylose in dimethyl sulfoxide corresponds to that of a flexible chain, while the behavior of starch more closely resembles that of a spherelike structure.

Amylose↗
PubMedDate not supplied

In vitro assessment of the enzymatic degradation of several starch based biomaterials.

The susceptibility of starch-based biomaterials to enzymatic degradation by amylolytic enzymes (glucoamylase and alpha-amylase) was investigated by means of incubating the materials with a buffer solution, containing enzymes at different concentrations and combinations, at 37 degrees C for 6 weeks. Two polymeric blends of corn starch with poly(ethylene-vinyl alcohol) copolymer and poly(epsilon-caprolactone), designated by SEVA-C and SPCL, respectively, were studied. The material degradation was characterized by gravimetry measurements, tensile mechanical testing, scanning electron microscopy (SEM), and Fourrier transform infrared-attenuated total reflectance (FTIR-ATR). The degradation liquors were analyzed for determination of reducing sugars, as a result of enzyme activity, and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to identify the degradation products. All of the analysis performed showed that starch polymeric blends are susceptible to enzymatic degradation, as detected by increased weight loss and reducing sugars in solution. alpha-Amylase caused significant changes on the overall mechanical properties of the materials, with a decrease of about 65% and 58% being observed in the moduli for SEVA-C and SPCL, respectively, when compared with the control (samples incubated in buffer only). SEM analysis detected the presence of fractures and pores at the material's surface as a result of starch degradation by amylolytic enzymes. FTIR spectra confirmed a decrease on the band corresponding to glycosidic linkage (-C-O-C-) of starch after incubation of the materials with alpha-amylase. In contrast, the incubation of the polymers in buffer only, did not cause significant changes on the material's properties and morphology. Comparing the two materials, SEVA-C exhibited a higher degradability, which is related to the physicochemical structure of the materials and also to the fact that the starch concentration is higher in SEVA-C. The identification of the degradation products by HPAEC-PAD revealed that glucose was the major product of the enzymatic degradation of starch-based polymers. alpha-Amylase, as expected, is the key enzyme involved in the starch degradation, contributing to major changes on the physicochemical properties of the materials. Nevertheless, it was also found that starch-based polymers can also be degraded by other amylolytic enzymes but in a smaller extent.

Bacteria↗
PubMedDate not supplied

Starch graft poly(methyl acrylate) loose-fill foam: preparation, properties and degradation.

Starch graft poly(methyl acrylate) (S-g-PMA) was prepared by ceric ion initiation of methyl acrylate in an aqueous corn starch slurry (prime starch) which maximized the accessibility of the starch for graft polymerization. A new ceric ion reaction sequence was established as starch-initiator-methyl acrylate followed by addition of a small amount of ceric ion solution when the graft polymerization was almost complete to quench the reaction. As a result of this improved procedure, no unreacted methyl acrylate monomer remained, and thus, essentially no ungrafted poly(methyl acrylate) homopolymer was formed in the final grafted product. Quantities of the high purity S-g-PMA so prepared in pilot scale were converted to resin pellets and loose-fill foam by single screw and twin screw extrusion. The use of prime starch significantly improved the physical properties of the final loose-fill foam, in comparison to foam produced from regular dry corn starch. The S-g-PMA loose-fill foam had compressive strength and resiliency comparable to expanded polystyrene but higher bulk density. The S-g-PMA loose-fill foam also had better moisture and water resistance than other competitive starch-based materials. Studies indicated that the starch portion in S-g-PMA loose-fill foam biodegraded rapidly, whereas poly(methyl acrylate) remained relatively stable under natural environmental conditions.

Acrylic Resins↗
PubMed2006

Slow digestion property of native cereal starches.

The slow digestion property of native cereal starches, represented by normal maize starch, was investigated. The in vitro Englyst test showed that 53.0% of the maize starch is slowly digestible starch (SDS), and scanning electron microscopy (SEM) revealed that SDS starts from an increase of pore size until almost complete fragmentation of starch granules. However, similar amounts of SDS ( approximately 50%) were shown for partially digested fragmented starch residuals, which would normally be considered resistant to digestion based on the Englyst assay. Molecularly, both amylopectin (AP) and amylose (AM) contributed to the amount of SDS as evidenced by a similar ratio of AP to AM at different digestion times. Consistently, similar degrees of crystallinity, comparable gelatinization behavior, and similar debranched profiles of starch residuals following different digestion times indicated that the crystalline and amorphous regions of starch granules were evenly digested through a mechanism of side-by-side digestion of concentric layers of semicrystalline shells of native starch granules.

Crystallization↗