Retrograded starches are commonly found in foods due to the production and/or processing conditions they have received prior to consumption. These resistant starches escape digestion in the small intestine and are fermented in the colon by the microflora present, to produce gases and SCFA in varying amounts. These are utilised by the host animal as an energy source, with a low gut pH being maintained by the production of SCFA. The fermentation of carbohydrates within the colon is beneficial to the health of the gut, as the beneficial bacterial species such as Lactobacillus and Bifidobacterium spp. are maintained, and a low pH reduces the activity of potentially harmful species such as the coliforms. The production of toxic metabolites from the breakdown of proteins will be reduced if these resistant starches persist further along the colon as a carbohydrate source. This is particularly important in the distal region of the colon, where the carbohydrate source usually becomes limited. The fermentation of both native and retrograded starches from various botanical sources containing varying amounts of the major components amylose and amylopectin, was examined. In particular, the effects on bacterial fermentation of variations in the ratios of amylose and amylopectin in starch, and of treatments such as retrogradation and/or pancreatin digestion was examined.

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.

Made available in DSpace on 2014-06-11T19:25:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-06-25Bitstream added on 2014-06-13T18:53:26Z : No. of bitstreams: 1 carbinatto_fm_me_arafcf.pdf: 2519448 bytes, checksum: 2e3afb3985cd01b53141ffd3dd03d09f (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dentre os sistemas de liberação controlada de fármacos, as matrizes hidrofílicas destacam-se pela possibilidade de incorporação de grandes quantidades de fármaco, economia e facilidade de processamento e obtenção de perfis de liberação reprodutíveis. A alta amilose e a pectina são exemplos de materiais utilizados na obtenção de matrizes hidrofílicas, ou seja, aquelas que absorvem água e formam uma camada de gel, antes de se dissolverem. No entanto, durante o intumescimento pode ocorrer a ruptura das ligações que mantêm a integridade da rede polimérica, o que compromete o controle da liberação. Tal efeito pode ser evitado através da reticulação, a qual promove a introdução de ligações intercadeias permanentes, que mantêm a integridade da rede tridimensional. Recentemente, em nossos laboratórios, a alta amilose foi reticulada com trimetafosfato de sódio (TMFS), originando sistemas sólidos não compactados que prolongaram a liberação do diclofenaco por até 24h. A pectina, polissacarídeo amplamente empregado na indústria alimentícia e farmacêutica, também pode ser reticulada pelo mesmo reagente, inclusive em misturas com a alta amilose. Sendo assim, o objetivo deste trabalho foi obter e caracterizar misturas de alta amilose e pectina em diferentes proporções, reticuladas com TMFS em diferentes graus (diferentes condições reacionais). A caracterização foi realizada por análises de reologia, intumescimento, difratometria de raios X e análise térmica. O desempenho como sistemas de liberação controlada de fármacos foi avaliado através da determinação da liberação in vitro de nimesulida a partir de comprimidos. O conjunto de resultados mostrou que todas as amostras apresentaram um comportamento de gel covalente, além de indicar a ocorrência de mudanças estruturais na rede... / Among controlled drug delivery systems, the hydrophilic matrices stand out for the possibility of incorporating large amounts of drug, economy and ease of processing, and obtaining reproducible release profiles. High amylose and pectin are examples of materials used for preparing hydrophilic matrices, i. e., those which absorb water and build a gel layer, before dissolving. However, during the swelling the rupture of the linkages that maintain the integrity of the polymer net can occur, compromising the release control. Such effect can be avoided by means of cross-linking, which introduces permanent interchain linkages, preserving the integrity of the tridimensional net. Recently, in our laboratories, high amylose was cross-linked with sodium trimethaphosphate (STMP), leadinf the formation of non compacted solid systems, which prolonged the diclofenac release for up to 24h. Pectin, polysaccharide widely used in the food and pharmaceutical industries, can be also crosslinked by the same reagent, including in mixtures with high amylose. Thus, the objective of this work was obtaining and characterizing mixtures of high amylose and pectin in different ratios, cross-linked with STMP in different degrees (different reactional conditions). Characterization included analyses of rheology, swelling behavior, X-ray diffractometria and thermal analysis. The performance of the systems in controlling drug release was assessed by the in vitro release of nimesulide from tablets. The results set showed that all samples presented a covalent gel behavior, as well as indicated the occurrence of structural changes within the tridimensional net in both the cross-linked and non cross-linked samples. However, cross-linked samples presented characteristics of stronger gel, as well as higher degree of crystallinity and and higher thermal stability. The samples... (Complete abstract click electronic access below)

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Whole-grain, high-fiber, or decorticated extrudates of excellent properties were made from white (nonwaxy, heterowaxy, waxy) sorghums or brown tannin-sorghums. Intact grains or prepared raw materials (cracked, cracked and sifted, decorticated) were extruded in a high-temperature, short-time (HTST) extruder. Waxy extrudates expanded less and were softer than those from nonwaxy or heterowaxy sorghums. Waxy extrudates had bigger air cells and thicker cell walls. Low moisture used in this type of extrusion and its interaction with the different amylose contents were the causes of the differences. Whole-grain extrudates from white sorghum had similar sensory acceptability to those from white decorticated sorghum. They had bland flavor and appearance and texture characteristic of whole-grain products. Extrudates from tannin sorghums were reddish brown due to their high levels of phytochemicals. The more expanded, softer products from whole-grain tannin sorghum were obtained when the grain was cracked and sifted. Decreased expansion was caused by higher levels of fiber and greater particle sizes (as in the extruded intact grain), and by reduced particle sizes (as in the cracked non-sifted grain). Expansion was correlated to smaller air cells with smooth walls. A simple enzymatic method was developed that isolates the 'gritty' particles from whole-grain/high-fiber extrudates, which closely correlated with expansion. Gritty particles were fiber (bran) plus undegraded starchy material. Whole grain/high fiber extrudates from white and tannin sorghums are an excellent option for food processors because of their excellent taste, appearance and texture.

Limited information exists regarding the effects of light pearling on the properties of physical grain characteristics, composition, and technological and sensory properties of selected varieties of Western Canadian barley especially hulless barley genotypes with modified starch characteristics. Nine barley genotypes with different hull (hulled and hulless) and starch characteristics (normal, waxy, and high amylose (HA)) were pearled to three differing levels. Scanning electron micrographs showed that the pericarp, testa, aleurone, and subaleurone layers were completely removed in heavily pearled barley whereas only a few outer layers were removed in minimally pearled barley. Waxy starch genotype Fibar and HA starch genotypes, SH99250 & SB94893 contained high levels of soluble β-glucan (9-11%). Waxy starch genotypes exhibited higher β-glucan solubility when cooked compared to normal and HA starch genotypes. However, HA starch genotypes had lower in vitro starch digestibility which may provide a lower glycemic response in humans.

Limited information exists regarding the effects of light pearling on the properties of physical grain characteristics, composition, and technological and sensory properties of selected varieties of Western Canadian barley especially hulless barley genotypes with modified starch characteristics. Nine barley genotypes with different hull (hulled and hulless) and starch characteristics (normal, waxy, and high amylose (HA)) were pearled to three differing levels. Scanning electron micrographs showed that the pericarp, testa, aleurone, and subaleurone layers were completely removed in heavily pearled barley whereas only a few outer layers were removed in minimally pearled barley. Waxy starch genotype Fibar and HA starch genotypes, SH99250 & SB94893 contained high levels of soluble β-glucan (9-11%). Waxy starch genotypes exhibited higher β-glucan solubility when cooked compared to normal and HA starch genotypes. However, HA starch genotypes had lower in vitro starch digestibility which may provide a lower glycemic response in humans.