Browsing by Author "Topping, DL"

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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.
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    Structural modifications of granular starch upon acylation with short-chain fatty acids
    (Elsevier, 2009-10) Lopez-Rubio, A; Clarke, JM; Scherer, B; Topping, DL; Gilbert, EP
    Low (LAMS) and high (HAMS) amylose maize starches acylated with acetic, propionic and butyric acids at three different degrees of substitution (DS) have been structurally characterized. SEM, XRD, SAXS and FT-IR were used to ascertain the effects of the molecular size of the esterified acid, the composition of the base maize starch and the DS on their structural properties. LAMS and HAMS did not differ significantly at the microscopic level. However, substantial differences were found at the nanostructural levels as a function of the esterified fatty acid, highlighting the importance of these length scales for the understanding of the macroscopic functional characteristics. Although the crystal unit cell remained practically unchanged, as deduced from the similar X-ray diffraction patterns, an increase in long-range order was observed with increasing fatty acid chain length. Conversely, shorter acyl chain lengths were related to greater decreases in the electron density difference between the amorphous and crystalline lamellae, suggesting the introduction of defects in the lamellar structure. From the SAXS results, it appears that the longer esterified chains are able to be accommodated within the crystalline lamellar regions so that the nanostructure is affected less by butyrylation than by the addition of acetyl or propionyl groups. © 2009, Elsevier Ltd.