Browsing by Author "Htoon, AK"

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    Effect of acid dextrinisation on enzyme-resistant starch content in extruded maize starch
    (Elsevier, 2010-05) Htoon, AK; Uthayakumaran, S; Piyasiri, U; Appelqvist, IAM; Lopez-Rubio, A; Gilbert, EP; Mulder, RJ
    The enzyme-resistant starch (ERS) content in processed high amylose and regular maize starches has been studied, with and without acid dextrinisation. The physicochemical and structural characteristics of the starches were analysed using a variety of techniques. The increase in ERS in high amylose maize starch with dextrinisation was related to the formation of a critical molecular weight fraction (MW ~ 20,000) that could rearrange structurally. Further dextrinisation reduced the processed starch MW to below where it could still form ERS. Regular maize starch containing less than 30% amylose did not increase its resistance to amylase digestibility with acid dextrinisation, probably due to impairment of amylose rearrangement by the numerous branched amylopectin chains. The ERS, which is likely to form during the enzyme-digestion process, is a linear molecule with a maximum degree of polymerisation (DP) of 30, irrespective of the starch source, processing conditions applied or type and amount of acid used. © 2010, 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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    Hydration induced structural changes in native, denatured and protected soy glycinin (11s)
    (Institute of Food Technologists, 2007-07) Appelqvist, IAM; Rout, MK; Chanvrier, H; Dezfouli, M; Kelly, M; Htoon, AK; Kealley, CS; Gilbert, EP; Strounina, E; Whittaker, AK; Gidley, MJ; Lillford, PJ
    Proteins and other biomolecules undergo a dynamic transition to a glass-like solid state with small atomic fluctuations. This dynamic transition can inhibit biological function and alter their material properties.
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    Molecular rearrangement of starch during enzyme digestion as inferred by scattering techniques
    (Australian Chemical Institute, 2007-08) Lopez-Rubio, A; Htoon, AK; Gilbert, EP
    Resistant starch (RS) is defined as the fraction of starch that escapes digestion in the small intestine, serving as a fermentation substrate for the beneficial colonic bacteria. Understanding the structure that makes these fractions resistant to digestion is of outstanding importance as it assists in the design of food products with increasing RS content. Several studies have been focussed on the description of the RS fractions from several starch varieties, but little attention has been paid to the digestion process itself, which from the present work, seems to play a key role in the understanding of what is RS.
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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