Browsing by Author "Blazek, J"

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    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.
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    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.
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    Application of small-angle X-ray and neutron scattering techniques to the characterisation of starch structure: A review
    (Elsevier, 2011-05-06) Blazek, J; Gilbert, EP
    Scattering methods offer the unique potential to indirectly probe materials on length scales between the capabilities of modern crystallography and microscopy, thus bridging the gap in spatial resolution between the two groups of techniques. The most significant achievement of small-angle scattering techniques in starch science has been the quantification of the lamellar architecture of semicrystalline growth rings in native starch granules. The lamellae are structurally formed by side chains of amylopectin interspersed with amylose and their behaviour upon contact with water and varying temperature has been explained using a widely accepted 'liquid crystalline' model for starch. Scattering techniques have also been recently used to explore the structural factors in native and processed starches that determine resistance to acid and enzymatic hydrolysis. Attempts have been made to apply scattering methods in understanding more complex structures in starch-based food products. Application of these techniques that are traditionally not widely used in food materials science provides fascinating challenges and opportunities. With more basic scientific methods entering food technology, it is apparent that small-angle scattering techniques deserve their place in the multi-technique approach, which aims to understand the structural mechanisms governing starch processing and digestion, and makes it possible to design and select those processes which render desirable structural morphologies. This paper summarises previous investigations and the current status of research into the structure of native starch and starch-based systems using small-angle scattering techniques. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
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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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    Effect of enzymatic hydrolysis on native starch granule structure
    (American Chemical Society, 2010-12-13) Gilbert, EP; Blazek, J
    Enzymatic digestion of six starches of different botanical origin was studied in real time by in situ time-resolved small-angle neutron scattering (SANS) and complemented by the analysis of native and digested material by X-ray diffraction, differential scanning calorimetry, small-angle X-ray scattering, and scanning electron microscopy with the aim of following changes in starch granule nanostructure during enzymatic digestion. This range of techniques enables coverage over five orders of length-scale, as is necessary for this hierarchically structured material. Starches studied varied in their digestibility and displayed structural differences in the course of enzymatic digestion. The use of time-resolved SANS showed that solvent-drying of digested residues does not induce any structural artifacts on the length scale followed by small-angle scattering. In the course of digestion, the lamellar peak intensity gradually decreased and low-q scattering increased. These trends were more substantial for A-type than for B-type starches. These observations were explained by preferential digestion of the amorphous growth rings. Hydrolysis of the semicrystalline growth rings was explained on the basis of a liquid-crystalline model for starch considering differences between A-type and B-type starches in the length and rigidity of amylopectin spacers and branches. As evidenced by differing morphologies of enzymatic attack among varieties, the existence of granular pores and channels and physical penetrability of the amorphous growth ring affect the accessibility of the enzyme to the substrate. The combined effects of the granule microstructure and the nanostructure of the growth rings influence the opportunity of the enzyme to access its substrate; as a consequence, these structures determine the enzymatic digestibility of granular starches more than the absolute physical densities of the amorphous growth rings and amorphous and crystalline regions of the semicrystalline growth rings. © 2011, American Chemical Society.
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    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.
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    Effect of β‐glucan on technological, sensory, and structural properties of durum wheat pasta
    (American Association of Cereal Chemists, 2012-03-01) Aravind, N; Sissons, M; Egan, N; Fellows, CM; Blazek, J; Gilbert, EP
    beta-Glucan is known to have valuable properties for preventative health and is finding widespread use in foods. This study investigated the benefit of adding a commercial source of beta-glucan, Barley Balance (BB) flour, as a functional ingredient in spaghetti. Durum wheat semolina was substituted with BB at levels of 7.5, 15, and 20%, from which spaghetti was prepared on a laboratory scale. The substitution of BB increased the beta-glucan content of semolina from 0.3 to 6% in uncooked and 8% in cooked pasta. Antioxidant activity (measured by 2,2-diphenyl-1-picrylhydrazyl) increased with BB and did not decline significantly on process-ing and cooking. Compared with the control, 7.5% BB had no or minimal effect on pasta cooking loss, stickiness, water absorption, aroma, and sensory texture. However, at higher doses, pasta became less yellow and more brown, firmer, of inferior aroma, more rubbery, and chewy, but less floury to the mouth. The extent of starch digestion decreased with increasing quantities of BB, suggesting that BB may lower glycemic index, with microscopy data suggesting that this decrease was mediated through the development of a more intensive fiber or fiber/ protein matrix retarding enzymatic access to starch granules. © Copyright 2012 AACC International.
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    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.
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    Enzyme resistance and structural organization in extruded high amylose maize starch
    (Elsevier, 2010-05-05) Shrestha, AK; Ng, CS; Lopez-Rubio, A; Blazek, J; Gilbert, EP; Gidley, MJ
    Gelose 80, a high amylose maize starch, was extruded in a twin screw extruder at different feed moistures, cooled, stored for 12 days at 4°C, and cryo-milled. The raw and extruded starches were analysed for in vitro enzyme-resistant starch content (ERS), morphology, in vitro digestibility, long range (X-ray diffraction) and short range (FTIR) molecular order. Extrusion markedly increased the rate of starch digestion and reduced the ERS content, irrespective of whether B-type or B- and V-type polymorphs were present. Increasing feed moisture and storage resulted in only slight increases in ERS content, with X-ray diffraction and FTIR also showing small changes in long and short range molecular order, respectively. Analysis of residues from in vitro digestion showed the mechanism of enzyme resistance of granular and extruded high amylose starch to be markedly different, both qualitatively and quantitatively. Enzyme digestion of granular high amylose maize starch showed initial disorganization in structure followed by slow reorganization at later stages of digestion. In contrast, molecular reorganization took place throughout the enzyme digestion of extruded high amylose maize starch. Higher levels of crystallinity were found in digested extrudates compared with digested granules, showing that there is no direct correlation between starch crystallinity and enzyme digestion rates. © 2009, Elsevier Ltd.
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    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.
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    Molecular, 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, MJ
    Cereal 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.
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    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.
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    Optimisation of resistant starch II and III levels in durum wheat pasta to reduce in vitro digestibility while maintaining processing and sensory characteristics
    (Elsevier, 2013-01-15) Aravind, N; Sissons, M; Fellows, CM; Blazek, J; Gilbert, EP
    Foods with elevated levels of resistant starch (RS) may have beneficial effects on human health. Pasta was enriched with commercial resistant starches (RSII, Hi Maize (TM) 1043; RSIII, Novelose 330 (TM)) at 10%, 20% and 50% substitution of semolina for RSII and 10% and 20% for RSIII and compared with pasta made from 100% durum wheat semolina to investigate technological, sensory, in vitro starch digestibility and structural properties. The resultant RS content of pasta increased from 1.9% to similar to 21% and was not reduced on cooking. Significantly, the results indicate that 10% and 20% RSII and RSIII substitution of semolina had no significant effects on pasta cooking loss, texture and sensory properties, with only a minimal reduction in pasta yellowness. Both RS types lowered the extent of in vitro starch hydrolysis compared to that of control pasta. X-ray diffraction and small-angle scattering verified the incorporation of RS and, compared to the control sample, identified enhanced crystallinity and a changed molecular arrangement following digestion. These results can be contrasted with the negative impact on pasta resulting from substitution with equivalent amounts of more traditional dietary fibre such as bran. The study suggests that these RS-containing formulations may be ideal sources for the preparation of pasta with reduced starch digestibility. © 2013, Elsevier Ltd
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    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.
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    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.