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Thesis (Ph. D.)--University of Sydney, 2008. / Title from title screen (viewed Feb. 6, 2009). Includes graphs and tables. Includes list of publications co-authored with others. Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Agriculture, Food and Natural Resources. Includes bibliographical references. Also available in print form.

Doctor of Philosophy / In this thesis, a set of wheat varieties (Triticum aestivum L.) produced by the Value Added Wheat Cooperative Research Centre with lower swelling power as compared to commercial Australian wheat varieties were studied to enhance our understanding of the role of amylose in starch functionality. These starches originated from a heterogeneous genetic background and had a narrow range of elevated amylose content (35 to 43%) linked with diverse functional properties. Small-angle X-ray scattering together with complementary techniques of differential scanning calorimetry and X-ray diffraction have been employed to investigate the features of starch granular structure at the nanometer scale. Starch chemical structure was characterized in terms of amylose content and amylopectin chain length distribution. Starch functionality was studied by a series of swelling, pasting and enzymic digestion methods. This study showed that swelling power of flour is a simple test that reflects a number of industrially relevant characteristics of starch, and therefore can be used as an indicator of amylose content and pasting properties of starch. In contrast to waxy starches and starches with normal amylose content, wheat starches with increased amylose content displayed characteristic pasting properties that featured decreasing peak, breakdown and final viscosities with increasing amylose contents. Existence of a threshold value in amylose content, above which final viscosity of starch paste does not further increase with increasing amylose content, was proposed. Variability in amylopectin chain length distribution was shown to have an additional effect on the swelling and pasting properties of the starches. On the molecular level, increased amylose content was correlated with increased repeat spacing of the lamellae present in the semicrystalline growth rings. In agreement with current understanding of starch synthesis, amylose was shown to accumulate in both crystalline and amorphous parts of the lamella. Using waxy starch as a distinctive comparison with the other samples confirmed general trend of increasing amylose content being linked with the accumulation of defects within crystalline lamellae. Amylose content was shown to directly influence the architecture of semicrystalline lamellae, whereas thermodynamic and functional properties were proposed to be brought about by the interplay of amylose content and amylopectin architecture. Subjecting starch granules with varying amylose content to pancreatic α-amylase showed differences in their digestion patterns. Pancreatic α-amylase preferentially attacked amorphous regions of waxy starch granules, whereas these regions for initial preferential hydrolysis gradually diminished with increasing amylose content. Observed variations in the extent of enzymic digestion were concluded to be primarily determined by the level of swelling of amorphous growth rings, which can also explain observed morphologies of partly digested granules with varying amylose content. It was confirmed that access to the granular components is not a function of the extent of crystallinity but rather the spatial positioning of the crystalline regions within the granule. Digestion kinetics is governed by factors intrinsic to starch granules, whereas influence of enzyme type was shown to be critical in determining the absolute rate of hydrolysis. Wheat starches with increased amylose content offer the potential to be used as slow digestible starch, mostly in their granular form or when complexed with lipids. Differences among varieties largely diminished when starches were gelatinized or allowed to retrograde demonstrating the importance of granular structure on starch hydrolysis. Wheat varieties used in this study displayed widely differing pasting properties in a Rapid Visco Analyser (RVA) and textural characteristics of the respective retrograded starch gels. Varietal differences in starch chemical composition among wheat varieties were shown to have significant effect on the extent of the response of starch viscoelastic characteristics to the addition of monopalmitin. Amylose content was positively correlated with the increase in final viscosity, which was attributed to the presence of more amylose in non-aggregated state contributing to higher apparent viscosity of the starch paste. Comparison of stored gels obtained from amylose-rich starches with gel prepared from waxy wheat varieties confirmed the critical role of amylose on the formation of starch network and thus providing the strength of the gel. Lack of correlation between textural properties of stored gels with amylose content or rheological characteristics measured by the RVA indicated that subtle differences in starch structure may have far-reaching consequences in relation to the strength of the gels, although these differences may have only limited effect on pasting properties in the RVA Viscoelastic properties of starch paste prepared from commercial wheat starch were significantly altered depending on the chain length and saturation of the fatty acid of the monoglyceride added during repeated heating and cooling in the Rapid Visco Analyser. Varying effects of different monoglycerides on the paste viscosity were attributed to different complexation abilities of these lipids with starch. It was proposed that stability and structure of the starch-lipid complexes formed affect the viscosity trace of the paste subjected to multiple heating and cooling. Our study indicated that differing monoglycerides in combination with the number of heat-cool cycles can be used to induce form I or form II starch-lipid complexes and thus manipulate paste rheology, gel structure and resistant starch content.

Starch is the major constituent of matured wheat grain. The details of subtle localized differences in the evolution of the structure of starch are important for an understanding of starch biosynthesis. However, the distinct stages involved in the formation and transformation of the molecular structure of starch during starch biosynthesis are still not fully understood. In this study, starches extracted from wheat grains harvested at 3, 7, 14, 28, and 49 days after anthesis (DAA) were used as a means of examining the molecular structure of starch from developing wheat grain. Gel-permeation chromatography and high-performance anion-exchange chromatography were employed for the analysis of the structure of both whole starch and its isolated amylopectin (AP) component. Scanning electron microscopy of 3 DAA wheat grain cross-sections revealed the absence of endosperm but the presence of spherical transitory-type small starch granules in the pericarp. Endosperm was present at 7 DAA and contained lenticular-shaped developing large granules. From 14 DAA onward, spherical-shaped small granules coexisted with large granules in the endosperm. The structure of transitory pericarp starch (PS) was compared with that of matured endosperm storage starch (ES). The composition of PS and ES differed: PS granules contained 14 % apparent amylose (AAM), whereas ES granules contained 33 % AAM. The AAM fractions of PS showed characteristics similar to those of intermediate-type materials with short branches, whereas ES contained both linear and branched amylose (AM). Differences in the amylopectin component of PS and ES were also apparent, especially in their internal structures. PS amylopectin had longer chains and fewer A-chains, resulting in a structure less branched than that of ES amylopectin. Starches isolated from 7 DAA to 49 DAA were studied with respect to endosperm development. The AAM of both large and small granules increased with increasing maturity. The AAM fraction of starch granules at early maturity (7 DAA and 14 DAA) consisted of intermediate-type materials in addition to linear AM, whereas starch at later maturity stages (28 and 49 DAA) contained linear and branched AM. During granule development, the fine structure of AP varied with the maturity level as well as with the size of the granule. During the post-physiological maturity stage, when the net accumulation of sugars ceases, the grain dries out; however, structural changes occurred in AP at this stage, possibly due to the action of starch branching and debranching enzymes. In both large and small granules, the external AP structure was more organized at post-physiological maturity (49 DAA) than at pre-physiological maturity (7 DAA to 28 DAA). Compared to their characteristics at post-physiological maturity, at the pre-physiological maturity stage, isolated clusters of AP were larger with more branches and building blocks. In addition to the time-dependent discrepancies in the AP structure of developing starch, differences were also evident between large and small granules with regard to glucan trimming and the type of new chains produced. The clusters isolated from small starch granules were more tightly branched than those isolated from large granules

Doctor of Philosophy / In this thesis, a set of wheat varieties (Triticum aestivum L.) produced by the Value Added Wheat Cooperative Research Centre with lower swelling power as compared to commercial Australian wheat varieties were studied to enhance our understanding of the role of amylose in starch functionality. These starches originated from a heterogeneous genetic background and had a narrow range of elevated amylose content (35 to 43%) linked with diverse functional properties. Small-angle X-ray scattering together with complementary techniques of differential scanning calorimetry and X-ray diffraction have been employed to investigate the features of starch granular structure at the nanometer scale. Starch chemical structure was characterized in terms of amylose content and amylopectin chain length distribution. Starch functionality was studied by a series of swelling, pasting and enzymic digestion methods. This study showed that swelling power of flour is a simple test that reflects a number of industrially relevant characteristics of starch, and therefore can be used as an indicator of amylose content and pasting properties of starch. In contrast to waxy starches and starches with normal amylose content, wheat starches with increased amylose content displayed characteristic pasting properties that featured decreasing peak, breakdown and final viscosities with increasing amylose contents. Existence of a threshold value in amylose content, above which final viscosity of starch paste does not further increase with increasing amylose content, was proposed. Variability in amylopectin chain length distribution was shown to have an additional effect on the swelling and pasting properties of the starches. On the molecular level, increased amylose content was correlated with increased repeat spacing of the lamellae present in the semicrystalline growth rings. In agreement with current understanding of starch synthesis, amylose was shown to accumulate in both crystalline and amorphous parts of the lamella. Using waxy starch as a distinctive comparison with the other samples confirmed general trend of increasing amylose content being linked with the accumulation of defects within crystalline lamellae. Amylose content was shown to directly influence the architecture of semicrystalline lamellae, whereas thermodynamic and functional properties were proposed to be brought about by the interplay of amylose content and amylopectin architecture. Subjecting starch granules with varying amylose content to pancreatic α-amylase showed differences in their digestion patterns. Pancreatic α-amylase preferentially attacked amorphous regions of waxy starch granules, whereas these regions for initial preferential hydrolysis gradually diminished with increasing amylose content. Observed variations in the extent of enzymic digestion were concluded to be primarily determined by the level of swelling of amorphous growth rings, which can also explain observed morphologies of partly digested granules with varying amylose content. It was confirmed that access to the granular components is not a function of the extent of crystallinity but rather the spatial positioning of the crystalline regions within the granule. Digestion kinetics is governed by factors intrinsic to starch granules, whereas influence of enzyme type was shown to be critical in determining the absolute rate of hydrolysis. Wheat starches with increased amylose content offer the potential to be used as slow digestible starch, mostly in their granular form or when complexed with lipids. Differences among varieties largely diminished when starches were gelatinized or allowed to retrograde demonstrating the importance of granular structure on starch hydrolysis. Wheat varieties used in this study displayed widely differing pasting properties in a Rapid Visco Analyser (RVA) and textural characteristics of the respective retrograded starch gels. Varietal differences in starch chemical composition among wheat varieties were shown to have significant effect on the extent of the response of starch viscoelastic characteristics to the addition of monopalmitin. Amylose content was positively correlated with the increase in final viscosity, which was attributed to the presence of more amylose in non-aggregated state contributing to higher apparent viscosity of the starch paste. Comparison of stored gels obtained from amylose-rich starches with gel prepared from waxy wheat varieties confirmed the critical role of amylose on the formation of starch network and thus providing the strength of the gel. Lack of correlation between textural properties of stored gels with amylose content or rheological characteristics measured by the RVA indicated that subtle differences in starch structure may have far-reaching consequences in relation to the strength of the gels, although these differences may have only limited effect on pasting properties in the RVA Viscoelastic properties of starch paste prepared from commercial wheat starch were significantly altered depending on the chain length and saturation of the fatty acid of the monoglyceride added during repeated heating and cooling in the Rapid Visco Analyser. Varying effects of different monoglycerides on the paste viscosity were attributed to different complexation abilities of these lipids with starch. It was proposed that stability and structure of the starch-lipid complexes formed affect the viscosity trace of the paste subjected to multiple heating and cooling. Our study indicated that differing monoglycerides in combination with the number of heat-cool cycles can be used to induce form I or form II starch-lipid complexes and thus manipulate paste rheology, gel structure and resistant starch content.

The nearly unlimited applications and uses of starch for food industry make this natural polymer a unique component; no other constituent can provide consistence and storage stability to such a large variety of foods. Starch can be extracted from agricultural produce through either chemical processes or physical separation. The latter involves the application of centrifugal forces by means of hydrocyclones. A hydrocylcone is a device which separates, through physical methods, two phases of different densities. There are three flows involved: the feed (mixture introduced in the hydrocyclone), the overflow (the least dense part) and the underflow (the densest part). Normally, the underflow part, or commonly known as "heavies", is the desirable part that companies keep, this is, the starch. Despite hydrocyclones are not very expensive devices, current-based hydrocyclones demand high energy rates. This work describes the design and testing of energy-saving hydrocyclones for extracting starch from wheat. Eight prototypes were built and tested at Larsson Mekaniska Verkstad AB (Bromölla, Sweden). This company makes process equipment for the starch industry and was the one with which the author collaborated during the ellaboration of the Degree Project. Six of the eight hydrocyclones were built by Larsson; another was a commercial hydrocyclone and the last one was the one figured out after reading some literature and updates in the hydrocyclones field. The experiments consist of trying the eight hydrocyclones under different conditions, combining concentrations (153 g/L and 237 g/L) and pressures (500 Pa and 700 Pa). The experimental results proved the importance of geometry on hydrocyclone design, and showed the effect of geometrical parameters on the energy-saving properties of cyclones. Four of the eight new models behaved satisfactorily for low energy and high efficiency conditions, obtained with inlet pressures of 500 kPa and starch concentrations of 237 g/L.

<p>The nearly unlimited applications and uses of starch for food industry make this natural polymer a unique component; no other constituent can provide consistence and storage stability to such a large variety of foods. Starch can be extracted from agricultural produce through either chemical processes or physical separation. The latter involves the application of centrifugal forces by means of hydrocyclones. A hydrocylcone is a device which separates, through physical methods, two phases of different densities. There are three flows involved: the feed (mixture introduced in the hydrocyclone), the overflow (the least dense part) and the underflow (the densest part). Normally, the underflow part, or commonly known as "heavies", is the desirable part that companies keep, this is, the starch. Despite hydrocyclones are not very expensive devices, current-based hydrocyclones demand high energy rates. This work describes the design and testing of energy-saving hydrocyclones for extracting starch from wheat. Eight prototypes were built and tested at Larsson Mekaniska Verkstad AB (Bromölla, Sweden). This company makes process equipment for the starch industry and was the one with which the author collaborated during the ellaboration of the Degree Project. Six of the eight hydrocyclones were built by Larsson; another was a commercial hydrocyclone and the last one was the one figured out after reading some literature and updates in the hydrocyclones field. The experiments consist of trying the eight hydrocyclones under different conditions, combining concentrations (153 g/L and 237 g/L) and pressures (500 Pa and 700 Pa). The experimental results proved the importance of geometry on hydrocyclone design, and showed the effect of geometrical parameters on the energy-saving properties of cyclones. Four of the eight new models behaved satisfactorily for low energy and high efficiency conditions, obtained with inlet pressures of 500 kPa and starch concentrations of 237 g/L.</p>

<p> The research in this thesis investigated the effects of different vitamin C forms [ascorbic acid (Asc), sodium ascorbate, and calcium ascorbate] on gelatinization, pasting, and short-term retrogradation of wheat starch. Vitamin C is the third most supplemented nutrient in the U.S. and necessary for prevention or treatment of many illnesses. Asc is also used in food products as an acidulant that decreases microbial growth and extends shelf-life, flavoring agent that promotes sour taste, and bread improver that increases gluten development and dough strength in wheat doughs. Ascorbate salts are used as vitamin C sources when a sour taste or pH decrease is undesirable. The gelatinization temperature (Tgel) of wheat starch in solutions of the vitamin C forms and related acids and salts at 0.5, 1.0, and 1.5 M concentrations (or equivalent) was measured using a differential scanning calorimeter and, compared to starch in water, was increased by all the salt solutions and decreased only by Asc. Calcium ascorbate increased Tgel more than the other salts due to hydrogen bonds between ascorbate and starch and strong hydration by water of Ca2+ that stabilized the starch-water structure and inhibited gelatinization. Asc decreased starch Tgel while similarly acidic solutions did not because Asc caused more extensive starch hydrolysis, which promoted granule swelling and amylose leaching. The paste viscosity values of wheat starch in solution were measured with a rapid visco analyzer and, compared to starch in water, were increased by all salt solutions except NaCl and increased by all acidic solutions until breakdown, then decreased. Ascorbate salts increased paste viscosities significantly more than chloride salts due to the stabilization effect of ascorbate hydrogen bonds that increased the amount of larger starch structures, which increased the viscosity during pasting and short-term amylose retrogradation. Ascorbate-containing acidic solutions increased starch peak viscosity and decreased trough and final viscosities more than HCl because increased granular swelling and amylose leaching results in a more rapid and greater initial increase in viscosity and subsequent decrease in viscosity when granular breakdown overtakes swelling. The results of this work could be used by food researchers and product developers to supplement or fortify vitamin C in a starch-based food and/or modify the functions of starch within that food.  </p>

Master of Science / Department of Grain Science and Industry / Jon M. Faubion / Endosperm texture is an important characteristic in determining wheat processing and end-use. The presence of puroindoline proteins on the starch surface is the biochemical marker for wheat hardness. Near-isogenic samples over expressing puroindolines have been used to assess the effect of wheat hardness on final product characteristics. The objective of this study was to determine differences among starch isolated from near-isogenic samples and to investigate the role starch surface components play in pasting. The use of near-isogenic samples over expressing puroindolines combined with the use of two methods of starch isolation (batter and dough) was an effective means to create samples with varied amounts of surface components. Starch thermal properties were characterized and surface proteins and lipids were quantified. Starch isolated from hard wheat cultivars presented more similarities with starch isolated from its soft near-isogenic line when a dough method was used than when a batter method was used. Starch from soft experimental lines isolated using a batter method showed increased MVA peak viscosity, breakdown and swelling power. Increased levels of LysoPC in starch isolated from hard wheat cultivars or soft experimental lines by dough method could have complexed with amylose and restricted granule swelling. Thereby, decreasing peak viscosity, breakdown and swelling power.