Browsing by Author "Bird, AR"

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    Differential 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, MK
    The 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.
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    Effects 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, MJ
    The 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.
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    Processing of novel elevated amylose wheats: functional properties and starch digestibility of extruded products
    (American Chemical Society, 2007-11-15) Chanvrier, H; Appelqvist, IAM; Bird, AR; Gilbert, EP; Htoon, AK; Li, ZY; Lillford, PJ; Lopez-Rubio, A; Morell, MK; Topping, DL
    Different types of novel wheat lines with different starch contents and amylose/amylopectin ratios, relating to defined alterations in the number and activity of starch synthase IIa genes, were processed by pilot-plant extrusion. Two types of products were produced: pure wholemeal products and breakfast cereals made from wholemeal/maize blends. Lower apparent shear viscosity was obtained in the extruder with lower starch content and higher amylose/amylopectin ratio flours (SSIIa-deficient line). The bulk density of the products decreased with increasing extrusion temperature and was always higher for the triple-null line. The bulk density was not completely explained by the melt shear viscosity, suggesting the importance of the fillers (fibers, brans) in the process of expansion and structure acquisition. The different mechanical properties were explained by the density and by the material constituting the cell walls. Enzyme-resistant starch (RS) content and hydrolysis index (HI) were not correlated to the extrusion temperature, but RS was higher in pure wholemeal products and in the SSIIa-deficient line. These results are discussed in terms of starch molecular architecture and product microstructure. © American Chemical Society
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    Structural characterization of acylated starches with increased delivery of short-chain fatty acids
    (Royal Australian Chemical Institute, 2007-08) Lopez-Rubio, A; Gilbert, EP; Topping, DL; Bird, AR; Cobiac, L; Clarke, JM
    Short-chain fatty acids (SCFA), mainly acetic, propionic and butyric acids, are produced during fermentation of carbohydrates in the human colon and are critical for the maintenance of bowel health and colonic function (Topping and Clifton, 2001). However, an increased delivery of specific SCFA to the large bowel can also be obtained by acylation of carbohydrates, using a CSIRO proprietary technology. Understanding the effects of structure on functionality is essential for the design and manufacture of acylated starches with specific health and therapeutic effects. The aim of the present study is to determine the effects of the level of acylation (degree of substitution), the molecular size of the esterified acid and the composition of the base maize starch on the structure of the acylated starch. Low and high amylose maize starches acylated with acetic, propionic and butyric acids at three degrees of substitution were compared with the structure of the unmodified maize starches.