Browsing by Author "Flanagan, BM"
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- ItemDifferential effects of genetically distinct mechanisms of elevating amylose on barley starch characteristics(Elsevier Science Ltd, 2012-07-01) Regina, A; Blazek, J; Gilbert, EP; Flanagan, BM; Gidley, MJ; Cavanagh, C; Ral, JP; Larroque, O; Bird, AR; Li, ZY; Morell, MKThe relationships between starch structure and functionality are important in underpinning the industrial and nutritional utilisation of starches. In this work, the relationships between the biosynthesis, structure, molecular organisation and functionality have been examined using a series of defined genotypes in barley with low (<20%), standard (20–30%), elevated (30–50%) and high (>50%) amylose starches. A range of techniques have been employed to determine starch physical features, higher order structure and functionality. The two genetic mechanisms for generating high amylose contents (down-regulation of branching enzymes and starch synthases, respectively) yielded starches with very different amylopectin structures but similar gelatinisation and viscosity properties driven by reduced granular order and increased amylose content. Principal components analysis (PCA) was used to elucidate the relationships between genotypes and starch molecular structure and functionality. Parameters associated with granule order (PC1) accounted for a large percentage of the variance (57%) and were closely related to amylose content. Parameters associated with amylopectin fine structure accounted for 18% of the variance but were less closely aligned to functionality parameters. © 2012, Elsevier Ltd.
- ItemEffects of processing high amylose maize starches under controlled conditions on structural organisation and amylase digestibility(Elsevier, 2009-01-22) Htoon, AK; Shrestha, AK; Flanagan, BM; Lopez-Rubio, A; Bird, AR; Gilbert, EP; Gidley, MJThe amylase digestibility of high-amylose maize starches has been compared before and after thermo-mechanical processing. Starches were analysed for enzyme-resistant starch yield, apparent amylose content, crystallinity (X-ray diffraction), and molecular order (NMR and FTIR), both before and after treatment with (x-amylase. All samples had significant (>10%) enzyme-resistant starch levels irrespective of the type and extent of thermal or enzymic processing. Molecular or crystalline order was not a pre-requisite for enzyme resistance. Near-amorphous forms of high amylose maize starches are likely to undergo recrystallisation during the enzyme-digestion process. The mechanism of enzyme resistance of granular high-amylose starches is found to be qualitatively different to that for processed high-amylose starches. For all samples, measured levels of enzyme resistance are due to the interruption of a slow digestion process, rather than the presence of completely indigestible material. © 2008, Elsevier Ltd.
- ItemHierarchical architecture of cellulose and its interaction with other plant cell wall polysaccharides(Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-18) Martínez-Sanz, M; Lopez-Sanchez, P; Mikkelsen, D; Flanagan, BM; Gidley, MJ; de Campo, L; Rehm, C; Gilbert, EPPlant cell walls (PCWs) are extremely complex structures in which cellulose microfibrils are hier archically assembled and embedded in a multi-component matrix. While the cellulose microfibrils represent the basic building unit providing mechanical strength , the matrix components are able to tune the properties of each specific tissue [2-3], increasing the flexibility or limiting the transport of moisture, for instance. The synthesis of cellulose hydrogels by means of bacterial fermentation is an efficient approach to mimic the cell wall biosynthesis process and investigate the interactions established between cellu lose and matrix polysaccharides by incorporating the latter into the culture medium. We have char acterised cellulose hydrogels and their composites with PCW polysaccharides by means of SANS and SAXS, combined with complementary techniques such as X-ray diffraction, spectroscopy and microscopy. Furthermore, the production of partially deuterated cellulose hydrogels by using a deuterated glucose-based feedstock is presented as a strategy to enhance the neutron scattering length density contrast . The application of a multi-technique characterisation approach enabled elucidation of the complex hierarchical architecture of cellulose hydrogels and led to the development of a multi-scale model based on core-shell structures [4-8]. The model describes the multi-phase structure of cellulose microfibrils and ribbons, as well as the essential role of water at the different structural levels. In addition, USANS experiments are presented as a promising method to characterise the structure of native cellulose in the longitudinal direction, providing information on the microfibril length and ribbon twisting periodicity. PCW polysaccharides such as xyloglucan, arabinoxylan, mixed linkage glucans and pectins during cellulose synthesis have a distinct structural role and interaction mechanism with cellulose (interfering with the crystallisation process and strongly interacting with the cellulose microfibrils, or establishing interactions at the ribbons’ surface level). These results highlight the ability of small angle scattering techniques to provide valuable insights on cellulose biosynthesis and interactions with PCW polysaccharides. © The Authors.
- ItemMolecular interactions of a model bile salt and porcine bile with (1,3:1,4)-β-glucans and arabinoxylans probed by 13C NMR and SAXS(Elsevier, 2016-04-15) Gunness, P; Flanagan, BM; Mata, JP; Gilbert, EP; Gidley, MJTwo main classes of interaction between soluble dietary fibres (SDFs), such as (1,3:1,4)-β-d-glucan (βG) and arabinoxylan (AX) and bile salt (BS) or diluted porcine bile, were identified by 13C NMR and small angle X-ray scattering (SAXS). Small chemical shift differences of BS NMR resonances were consistent with effective local concentration or dilution of BS micelles mostly by βG, suggesting dynamic interactions; whilst the reduced line widths/intensities observed were mostly caused by wheat AX and the highest molecular size and concentrations of βG. SAXS showed evidence of changes in βG but not AX in the presence of BS micelles, at >13 nm length scale consistent with molecular level interactions. Thus intermolecular interactions between SDF and BS depend on both SDF source and its molecular weight and may occur alone or in combination. © 2015 Elsevier Ltd
- ItemMolecular rearrangement of starch during in vitro digestion: toward a better understanding of enzyme resistant starch formation in processed starches(American Chemical Society, 2008-07) Lopez-Rubio, A; Flanagan, BM; Shrestha, AK; Gidley, MJ; Gilbert, EPResistant starch (RS) is defined as the fraction of starch that escapes digestion in the small intestine, serving as a fermentation substrate for beneficial colonic bacteria. Several studies have been focused on the description of the RS fractions from different starch varieties, but little attention has been paid to the digestion process itself that, from the present work, seems to play a key role in the generation of enzyme-RS (ERS), as determined in vitro. High-amylose starch samples, extruded at two different processing conditions, have been characterized at different stages of in vitro digestion using scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), infrared spectroscopy (FF-IR), solid state C-13 NMR spectroscopy, and X-ray diffraction (XRD). Control samples kept for 18 h in the digestion solution without starch hydrolyzing enzymes (alpha-amylase and amyloglucosidase) were used for comparison purposes. An increase in molecular order was favored by the hydrolytic action of the enzymes, reflected in an increase in double helical order observed by NMR, higher crystallinity measured by XRD, and corresponding changes in FT-IR spectra. An increase in the intensity of the scattering objects was also observed by SAXS as a function of digestion. SAXS from the dry ERS fractions reveals the 001 reflection of crystallites formed during the digestion process, corresponding to a characteristic dimension of the resistant crystalline fraction of similar to 5 nm. The changes found suggest that enzyme resistant starch does not refer to a specific structure present in predigested starches, but may in fact be formed during the digestion process through the rearrangement of amylose chains into enzyme-resistant structures of higher crystallinity. Therefore, the resistance to enzyme digestion of a specific processed starch is the result of a competition between the kinetics of enzyme hydrolysis and the kinetics of amylose retrogradation. © 2008, American Chemical Society
- ItemMolecular, mesoscopic and microscopic structure evolution during amylase digestion of maize starch granules(Elsevier Science Ltd, 2012-09-01) Shrestha, AK; Blazek, J; Flanagan, BM; Dhital, S; Larroque, O; Morell, MK; Gilbert, EP; Gidley, MJCereal starch granules with high (>50%) amylose content are a promising source of nutritionally desirable resistant starch, i.e. starch that escapes digestion in the small intestine, but the structural features responsible are not fully understood. We report the effects of partial enzyme digestion of maize starch granules on amylopectin branch length profiles, double and single helix contents, gelatinisation properties, crystallinity and lamellar periodicity. Comparing results for three maize starches (27, 57, and 84% amylose) that differ in both structural features and amylase-sensitivity allows conclusions to be drawn concerning the rate-determining features operating under the digestion conditions used. All starches are found to be digested by a side-by-side mechanism in which there is no major preference during enzyme attack for amylopectin branch lengths, helix form, crystallinity or lamellar organisation. We conclude that the major factor controlling enzyme susceptibility is granule architecture, with shorter length scales not playing a major role as inferred from the largely invariant nature of numerous structural measures during the digestion process (XRD, NMR, SAXS, DSC, FACE). Results are consistent with digestion rates being controlled by restricted diffusion of enzymes within densely packed granular structures, with an effective surface area for enzyme attack determined by external dimensions (57 or 84% amylose - relatively slow) or internal channels and pores (27% amylose - relatively fast). Although the process of granule digestion is to a first approximation non-discriminatory with respect to structure at molecular and mesoscopic length scales, secondary effects noted include (i) partial crystallisation of V-type helices during digestion of 27% amylose starch, (ii) preferential hydrolysis of long amylopectin branches during the early stage hydrolysis of 27% and 57% but not 84% amylose starches, linked with disruption of lamellar repeating structure and (iii) partial B-type recrystallisation after prolonged enzyme incubation for 57% and 84% amylose starches but not 27% amylose starch. © 2012, Elsevier Ltd.
- ItemNovel approach for calculating starch crystallinity and its correlation with double helix content: a combined XRD and NMR study(Wiley-Blackwell, 2008-09) Lopez-Rubio, A; Flanagan, BM; Gilbert, EP; Gidley, MJA peak fitting procedure has been implemented for calculating crystallinity in granular starches. This methodology, widely used for synthetic polymers, is proposed to better reflect the crystalline content of starches than the method normally used, in which it is assumed that relatively perfect crystalline domains are interspersed with amorphous regions. The new approach takes into account irregularities in crystals that are expected to exist in semicrystalline materials. Therefore, instead of assuming that the amorphous background extends up to the base of diffraction peaks, the whole X-ray diffraction (XRD) profile is fitted to an amorphous halo and several discrete crystalline diffraction peaks. The crystallinity values obtained from the XRD patterns of a wide range of native starches using this fitting technique are very similar to the double helix contents as measured by C-13 solid state NMR, suggesting that double helices in granular starches are present within irregular crystals. This contrasts with previous descriptions of crystalline and noncrystalline double helices that were based on the analysis of XRD profiles as perfect crystals interspersed in a noncrystalline background. Furthermore, with this fitting methodology it is possible to calculate the contribution from the different crystal polymorphs of starch to the total crystallinity. © 2008, Wiley-Blackwell.