Browsing by Author "Copeland, L"

Now showing 1 - 8 of 8
  • No Thumbnail Available
    Item
    Amylolysis of wheat starches. I. Digestion kinetics of starches with varying functional properties
    (Elsevier, 2010-05) Blazek, J; Copeland, L
    The susceptibility of wheat (Triticum aestivum L.) starches to hydrolysis by pancreatic α-amylase in vitro was investigated using a series of 35 starches with slightly enriched amylose content within a narrow range (36–43%), but widely differing functional properties. After 2 h of incubation with α-amylase, native starch granules were digested to different extents, but there were no differences between any of the starches once they were gelatinized. Cooling the starch for 72 h at 4°C after cooking reduced the susceptibility of all of the starches to enzymic digestion by a similar extent, whereas addition of monopalmitin decreased the digestibility of the starches that contained amylose, but did not affect the digestibility of waxy starches that were also included in the study. Amylopectin chain length distribution of partly digested starch granules displayed increased proportion of short and medium chains and decreased proportion of long chains in comparison to native granules. Separated large (A) and small (B) starch granules from three of the starches differed significantly in their susceptibility to in-vitro digestion. A predictive model of the susceptibility of starch in the different forms was developed from the physico-chemical and functional properties of the starches. © 2010, Elsevier Ltd.
  • No Thumbnail Available
    Item
    Amylolysis of wheat starches. II. Degradation patterns of native starch granules with varying functional properties
    (Elsevier, 2010-09-01) Blazek, J; Copeland, L
    Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to investigate degradation patterns of native starch granules from wheat (Triticum aestivum L.) by different starch-degrading enzymes. The starches examined were from a waxy wheat and four varieties with slightly elevated amylose content, but with different functional properties. Differences in the digestion patterns after partial α-amylolysis of starch granules were noted between the starches. The waxy starch seemed to be degraded by endocorrosion, whereas the amylose-rich starches followed a slower mode of hydrolysis starting from the granular surface. X-ray diffractograms of the amylose-rich starches were not significantly altered by 2 h of α-amylolysis, whereas partial hydrolysis of the waxy starch decreased scattering intensity at higher 2θ angles, consistent with a different mode of attack by α-amylase in the initial digestion stages of granules of waxy and amylose-rich starches. We propose these differences are due to the combined effects of the change in packing density and partial preference for hydrolysis of amorphous material. The native starch granules were also attacked by beta-amylase, isoamylase and amyloglucosidase, which indicates that α-amylase is not the only starch-degrading enzyme that is able to initiate starch hydrolysis of native granules. © 2010, Elsevier Ltd.
  • No Thumbnail Available
    Item
    Effect of monopalmitin on pasting properties of wheat starches with varying amylose content.
    (Elsevier, 2009-08-04) Blazek, J; Copeland, L
    The influence of varietal differences among wheat (Triticum aestivum L.) starches on properties of starch pastes and gels was studied. Wheat varieties with elevated total amylose content within a narrow range (36-43%) displayed widely differing pasting properties in a Rapid Visco Analyser (RVA). The pasting properties of the wheat starches were influenced significantly by the addition of monopalmitin. Increase in final RVA pasting viscosity of starch-monopalmitin mixtures was correlated positively with increasing amylose content. The textural characteristics of the respective retrograded starch gels also differed greatly and were affected by varietal differences between the starches. There was no correlation between textural properties of aged gels with amylose content or the viscoelastic characteristics measured by the RVA. The strength of gels may be affected by subtle differences in starch structure that influence retrogradation, but have only limited effect on starch pasting properties. © 2009, Elsevier Ltd.
  • No Thumbnail Available
    Item
    Effects of monoglycerides on pasting properties of wheat starch after repeated heating and cooling
    (Elsevier, 2011-07-01) Blazek, J; Gilbert, EP; Copeland, L
    The effects of repeated heating and cooling on the properties of pastes prepared from a commercial wheat starch (Triticum aestivum L.) with added monoglycerides were studied using a Rapid Visco Analyser (RVA). The nanostructure of the freeze-dried pastes was determined by X-ray diffraction and small-angle X-ray scattering. Pastes prepared from the wheat starch alone, or from the starch mixed with tripalmitin, which does not form complexes with starch, produced regular viscosity profiles in the RVA when subjected to multiple heat-cool cycles. In comparison, the effects of adding monoglycerides (or monoacylglycerols) depended on the chain length and saturation of the fatty acid of the monoglyceride. Repeated heat-cool cycles in the RVA of the starch with different monoglycerides induced the formation of complexes of varying stability that influenced the viscosity trace of the paste during multiple heating and cooling cycles. Small-angle X-ray scattering in combination with X-ray diffraction proved useful in describing the nanostructural changes in the RVA pastes induced by monoglycerides and temperature cycling. The results indicate that the functional properties of starch pastes may be manipulated through the strategic selection of an added monoglyceride. (C) 2011 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Form and functionality of starch.
    (Elsevier, 2008-08) Copeland, L; Blazek, J; Salman, H; Tang, MCM
    Starch is a macro-constituent of many foods and its properties and interactions with other constituents, particularly water and lipids, are of interest to the food industry and for human nutrition. Starch varies greatly in form and functionality between and within botanical species, which provides starches of diverse properties but can also cause problems in processing due to inconsistency of raw materials. Being able to predict functionality from knowledge of the structure, and explain how starch interacts with other major food constituents remain significant challenges in food science, nutrition, and for the starch industry generally. This paper describes our current understanding of starch structure that is relevant to its functionality in foods and nutrition. Amylose influences the packing of amylopectin into crystallites and the organization of the crystalline lamellae within granules, which is important for properties related to water uptake. Thermal properties and gel formation appear to be influenced by both amylose content and amylopectin architecture. While amylose content is likely to have an important bearing on the functional properties of starch, subtle structural variations in the molecular architecture of amylopectin introduces uncertainty into the prediction of functional properties from amylose content alone. Our ability to relate starch granule structure to suitability for a particular food manufacturing process or its nutritional qualities depends not only on knowledge of the genetic and environmental factors that control starch biosynthesis, and in turn granule morphology, but also on how the material is processed. © 2008, Elsevier Ltd.
  • No Thumbnail Available
    Item
    New insights on the mechanism of acid degradation of pea starch
    (Elsevier, 2012-02-14) Wang, S; Blazek, J; Gilbert, EP; Copeland, L
    The degradation of pea starch granules by acid hydrolysis has been investigated using a range of chemical and structural methods, namely through measuring changes in amylose content by both the iodine binding and concanavalin A precipitation methods, along with small angle X-ray scattering (SAXS), wide angle X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The relative crystallinity, intensity of the lamellar peak and the low-q scattering increased during the initial stages of acid hydrolysis, indicating early degradation of the amorphous regions (growth rings and lamellae). In the first 2 days of hydrolysis, there was a rapid decline in amylose content, a concomitant loss of precipitability of amylopectin by concanavalin A, and damage to the surface and internal granular structures was evident. These observations are consistent with both amylose and amylopectin being located on the surface of the granules and attacked simultaneously in the early stages of acid hydrolysis. The results are also consistent with amylose being more concentrated at the core of the granules. More extensive hydrolysis resulted in the simultaneous disruption of amorphous and crystalline regions, which was indicated by a decrease in lamellar peak intensity, decrease in interhelix peak intensity and no further increase in crystallinity. These results provide new insights into the organization of starch granules. (C) 2011 Elsevier Ltd.
  • Thumbnail Image
    Item
    Structural characterization of wheat starch granules differing in amylose content and functional characteristics
    (Elsevier, 2009-02-24) Blazek, J; Salman, H; Rubio, AL; Gilbert, EP; Hanley, TL; Copeland, L
    Small-angle X-ray scattering (SAXS) together with several complementary techniques such as differential scanning calorimetry and X-ray diffraction, have been employed to investigate the structural features that give diverse functional properties to wheat starches (Triticum aestivum L.) within a narrow range of enriched amylose content (36-43%). For these starches, which come from a heterogeneous genetic background. SAXS analysis of duplicate samples enabled structural information to be obtained about their lamellar architecture where differences in lamellar spacing among samples were only several tenths of nanometer. The SAXS analysis of these wheat starches with increased amylose content has shown that amylose accumulates in both crystalline and amorphous parts of the lamella. Using waxy starch as a distinctive comparison with the other samples confirmed a general trend of increasing amylose content being linked with the accumulation of defects within crystalline lamellae. We conclude that amylose content directly influences the architecture of semi-crystalline lamellae, whereas thermodynamic and functional properties are brought about by the interplay of amylose content and amylopectin architecture. © 2008, Elsevier Ltd.
  • No Thumbnail Available
    Item
    Structure-function relationships in A and B granules from wheat starches of similar amylose content
    (Elsevier, 2009-02-11) Salman, H; Blazek, J; Lopez-Rubio, A; Gilbert, EP; Hanley, TL; Copeland, L
    Five wheat (Triticum aestivum L.) starches, from the varieties Sunco, Sunsoft, SM1118. and SM1028, with similar amylose content, and a waxy wheat were separated into large (A) and small (B) granules. The unfractionated starches, and isolated A and B granules, were characterized structurally and evaluated for their functional properties. The amylopectin chain length distribution revealed that A granules had a lower proportion of short chains with degree of polymerization (DP) 6-12 and a higher proportion of chains with DP 25-36 than B granules. X-ray diffraction (XRD) patterns showed predominantly A-type crystallinity for all of the starches. No differences in the crystallinity were found between unfractionated, A and B granules. Small-angle X-ray scattering (SAXS) patterns of the starches at 55% hydration showed that the lamellar repeat distance in A granules was larger than that of B granules for all the starches examined. However, the lamellar distances of both A and B granules from the waxy wheat were smaller than those of Sunco, Sunsoft, SM1118 and SM1028 starches. The swelling power of the B granules was greater than that of A granules from all five starches. The kinetics of digestion of A and B granules with α-amylase in vitro were complex, with B granules initially digested to a greater extent than A granules. After 4 h of incubation, A granules showed greater digestibility than B granules, except in the case of waxy starch where unfractionated and fractionated granules had similar in vitro digestibility. Correlations between structural and functional parameters were more significant for the isolated A and B granules than for the unfractionated starches. This study demonstrates that A and B granules differ in structure and functionality, and that some correlations between these properties could be masked in unfractionated starches with bimodal granule size distribution. © 2008, Elsevier Ltd.