Orientador: Aulus Cavalieiri Carciofi / Resumo: Este trabalho incluiu um estudo sobre os efeitos da adição de selênio em dietas secas extrusadas na mucosa intestinal de cães. Utilizou-se uma única formulação para produzir cinco dietas sendo uma dieta controle com adição de 0,13ppm de selenito de sódio, uma segunda dieta com 0,33ppm de selênio levedura, outra com 0,66ppm de selênio levedura, a quarta contendo 0,99ppm de selênio levedura e a quinta com 0,66ppm de selenito de sódio. Foram utilizados 30 cães em três blocos de 10 cães e cada período teve duração de 210 dias incluindo adaptação e fase experimental. Ao final de cada período foram coletadas amostras de mucosa do trato gastrintestinal por endoscopia e colonoscopia para avaliação. Um segundo estudo avaliou o efeito da gelatinização do amido na digestibilidade aparente dos nutrientes, produção de fezes e produtos de fermentação de cães alimentados com dietas extrusadas incluindo dois estudos. No estudo 1 uma mesma formulação foi processada de quatro maneiras diferentes resultando em três dietas extrusadas com moagens de 0.5, 1.8 e 2.0 mm e uma dieta peletizada com moagem de 1.8mm com diferentes graus de gelatinização. Foram utilizados 24 cães, seis por tratamento e avaliou-se a digestibilidade e os produtos de fermentação. No estudo 2 foi utilizada uma base de dados publicados e a digestibilidade de dietas preparadas para construir regressões polinomiais entre o grau de gelatinização do amido e a digestibilidade aparente dos nutrientes. No primeiro estudo a análise h... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work included a study on the effects of the addition of selenium in extruded dry diets in the gastrointestinal tract of dogs. It was used a single formulation to produce five diets and a control diet with the addition of 0,13ppm sodium selenite, a second diet with selenium yeast of 0,33ppm, another diet with 0,66ppm selenium yeast, the fourth diet containing 0, 99ppm of selenium yeast and the fifth with 0,66ppm sodium selenite. It was used a total of 30 dogs in three blocks of 10 dogs and each period lasted 210 days including adaptation and experimental phase. At the end of each period mucosa samples were collected from the gastrointestinal tract by endoscopy and colonoscopy for evaluation. A second study evaluated the effect of starch gelatinization in the apparent digestibility of nutrients, production of feces and dog fermentation products fed extruded diets including two studies. In Study 1 the same formulation was processed in four different ways, resulting in three extruded diets of grindings 0.5, 1.8 and 2.0 mm and a pelleted diet with grinding of 1.8mm with different degrees of gelatinization. Twenty-four dogs were used, six dogs per treatment and digestibility and fermentation products were evaluated. In the second study it was used a published database and diet digestibility prepared to construct polynomial regressions between the degree of starch gelatinization and apparent nutrient digestibility. In the first study histological analysis showed a significant d... (Complete abstract click electronic access below) / Mestre

Orientador: Célia Maria Landi Franco / Coorientador: Vânia Regina Nicoletti Telis / Banca: Maria Aparecida Vieira Teixeira / Banca: José Antônio Gomes Vieira / Resumo: Estabilidade de amidos frente a altas temperaturas e cisalhamento pode ser melhorada com o tratamento térmico com baixa umidade (TTBU). O objetivo deste trabalho foi investigar o efeito do TTBU sobre as características físico-químicas e reológicas dos amidos de mandioca, araruta e mandioquinha-salsa. Os amidos foram isolados e analisados quanto à composição química, teor de amilose e comprimento de cadeias ramificadas de amilopectina. Amostras de amido foram condicionadas a 28 % de umidade e submetidas a 100 ºC por 2, 4, 8 e 16 h. Os amidos nativos e modificados foram analisados quanto à morfologia dos grânulos, difração de raio-X, propriedades de pasta e térmicas, índices de absorção de água (ISA) e solubilidade (ISA) em água a 30 ºC e poder de inchamento (PI) e solubilidade (S) a 95 ºC. A transparência e sinérese dos géis de amidos nativos e modificados por 4 h, submetidos ou não a acidez e esterilização foram determinadas, e ensaios reológicos estacionários e oscilatórios dos géis foram realizados. O amido de mandioquinha-salsa apresentou o menor teor de amilose e maior proporção de defeitos em sua estrutura cristalina quando comparado com os outros amidos. O TTBU não afetou a morfologia dos grânulos, mas modificou o padrão cristalino dos amidos de mandioca e araruta de CA para A, e do amido de mandioquinha-salsa de B para A. Houve redução efetiva na viscosidade de quebra e aumento no set back das pastas de amido. As temperaturas de gelatinização aumentaram e os picos endotérmicos mostraram-se mais largos, enquanto as entalpias, o PI e a S dos amidos reduziram com o TTBU. Esses resultados sugeriram que o tratamento provocou uma reorganização das cadeias de amido aumentando as interações moleculares. A estrutura cristalina livre de defeitos e as forças associativas mais fortes presentes no amido de araruta contribuíram para que este fosse menos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Stability of starch in the face of high temperatures and shear can be improved by heat-moisture treatment (HMT). The objective of this study was to investigate the effect of HMT on physicochemical characteristics and rheological properties of starches from cassava, arrowroot and peruvian carrot. Starches were isolated and analyzed for chemical composition, amylose content and length of branched chains of amylopectin. Starches were conditioned at 28 % moisture and kept at 100 ºC for 2, 4, 8 and 16 h. The native starches and modified samples were analyzed for the morphology of the granules, diffraction of X-ray, pasting and thermal properties, index of water absorption (IWA) and solubility (IWS) in water at 30 ºC and swelling power (SP) and solubility (S) at 95 ºC. Transparency and syneresis of gels of native and modified starches for 4 h submitted or not to sterilization and acidity were determined, and stationary and oscillatory rheological tests were carried out of the gels. The Peruvian carrot starch had the lowest amylose content and higher proportion of defects in their crystal structure when compared with other starches. The HMT did not affect the morphology of granules, but changed the crystalline pattern of cassava and arrowroot starch from CA to A, and Peruvian carrot starch from B to A. There was a reduction effective in the breakdown viscosity and set back, and increase in the pasting of starches. The increased gelatinization temperatures and endothermic peaks were shown to be wider, while the enthalpies, SP and S starches with reduced with HMT. These results suggested that treatment caused a reorganization of the starch chains increases the molecular interactions. The crystal structure free of defects and stronger associative forces present in the arrowroot starch contributed to this were less affected by treatment. The gels of arrowroot and peruvian carrot modified... (Complete abstract click electronic access below) / Mestre

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.

Submitted by THAÍS PAES RODRIGUES DOS SANTOS null (thaispaes.btu@ig.com.br) on 2016-04-27T14:43:11Z No. of bitstreams: 1 TESE_THAIS P R DOS SANTOS.pdf: 2813733 bytes, checksum: 65a5985853cbb6a257d3371ffa95a48a (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-04-29T17:37:38Z (GMT) No. of bitstreams: 1 santos_tpr_dr_bot.pdf: 2813733 bytes, checksum: 65a5985853cbb6a257d3371ffa95a48a (MD5) / Made available in DSpace on 2016-04-29T17:37:39Z (GMT). No. of bitstreams: 1 santos_tpr_dr_bot.pdf: 2813733 bytes, checksum: 65a5985853cbb6a257d3371ffa95a48a (MD5) Previous issue date: 2016-02-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Amidos pré-gelatinizados podem ser usados em aplicações de produtos de conveniência pela indústria de alimentos, pois apresentam maior solubilidade em água fria e menor temperatura de gelatinização. As modificações físicas por spray drying e por extrusão são métodos que podem resultar em alterações na região cristalina, com mudanças nas propriedades térmicas e de pasta dos amidos. Objetivou-se neste trabalho verificar as alterações estruturais e funcionais provocadas, pelos métodos de modificações físicas citados, nos amidos de mandioca, mandioquinha-salsa e batata-doce. A modificação por spray drying foi realizada com aquecimento da suspensão à 57 °C e concentração de 8 % de amido, com temperatura de saída e vazão no spray dryer, respectivamente, de 105 °C e 0,5 L h-1. A modificação por extrusão foi realizada no amido a 20 % de umidade, temperaturas de 25, 50 e 75 ºC, respectivamente, na 1a zona, 2ª zona e 3ª zona do extrusor e rotação de 245 rpm. Após a finalização deste experimento, os resultados evidenciaram que a modificação por spray drying provocou alterações menos severas nas características dos amidos estudados. Sendo assim, foi realizado um segundo experimento com os amidos de mandioca e batata-doce a fim de determinar as melhores condições de processo da modificação por spray drying, seguindo planejamento experimental central composto rotacional nos dois ensaios experimentais. Os amidos modificados no primeiro experimento foram analisados em relação as características estruturais e propriedades de pasta e térmica. A modificação por spray drying não provocou alterações no teor de amilose, massa molecular e raio médio de giro, assim como na distribuição dos comprimentos das cadeias ramificadas de amilopectina, mostrando que não houve degradação das ligações glicosídicas. Houve redução dos picos do padrão de difração de Raios X dos amidos, refletindo na diminuição na cristalinidade relativa. A morfologia dos grânulos apresentou aglomerados para os amidos de mandioca e mandioquinha-salsa, indicando gelatinização parcial dos grânulos. O amido de mandioquinha-salsa modificado por spray drying apresentou aumento na viscosidade a frio e diminuição da viscosidade de pico e final. Para todos os amidos, houve aumento no setback (tendência a retrogradação). As temperaturas de gelatinização não sofreram alterações significativas, porém a variação da temperatura diminuiu, assim como a variação da entalpia. Os amidos modificados por extrusão não apresentaram alteração no teor de amilose e na distribuição dos comprimentos das cadeias ramificadas da amilopectina, no entanto, houve alteração na massa molecular e no raio médio de giro, indicando provável rompimento das ligações glicosídicas. Os amidos modificados por extrusão apresentaram redução total dos picos do padrão de difração dos amidos, indicando total gelatinização. Nas imagens de microscopia eletrônica de varredura não foram observados grânulos para todos os tratamentos, confirmando a gelatinização total do amido com perda da estrutura granular durante o processo de extrusão, o que também foi observado pela ausência de curva de gelatinização na análise de propriedade térmica. Tais alterações levaram a um aumento na viscosidade a frio. As modificações por spray drying e extrusão resultam em amidos com diferentes propriedades, sendo que o amido modificado por spray drying seria indicado para produtos que necessitem de consistência mais firme, enquanto o amido modificado por extrusão seria indicado para produtos com viscosidade a frio e com consistência mais fluída. Em relação aos amidos estudados, o amido de mandioquinha-salsa apresentou maior sensibilidade ao processo, devido sua temperatura de gelatinização ser próxima às temperaturas utilizadas, e também, pelo defeito na área cristalina. Os resultados obtidos no segundo experimento evidenciaram que as melhores condições de modificação dos amidos de mandioca e de batata-doce por spray drying são: alta temperatura (60 °C) e baixa concentração (5 %). Nas condições citadas, podem ser obtidos amidos modificados por spray drying com boas características de pasta e térmica, como leve viscosidade a frio, consistência no produto final e temperatura de gelatinização uniforme, refletindo em melhor utilização de energia no processo. / Pregelatinized starches can be used in applications of convenience products by the food industry, since they have greater solubility in cold water and low gelatinization temperature. The physical modification by spray drying and extrusion are methods which can result in changes in the crystalline region, with changes in the thermal and pasting properties of starch. The aim of this work was to verify the structural and functional changes caused by physical modification methods mentioned in starches from cassava, Peruvian carrot and sweet potato. The modification by spray drying was performed using temperature of 57 °C and concentration of 8 %, with outlet temperature and feed rate in spray dryer of 105 °c and 0.5 L h-1, respectively. The modification by extrusion was carried out with 20 % of starch moisture, with temperatures of 25 °C, 50 °C and 75 °C in the 1st zone, 2nd zone and 3rd zone respectively, and rotation 245 rpm. After completion of this experiment, the results show that the modification by spray drying caused less severe changes in the characteristics of the studied starches. Thus, it was conducted a second experiment with starches from cassava and sweet potato, in order to determine the best process conditions of modification by spray drying, following experimental design central composite rotational in both experimental tests. The modified starches of the first experiment were analyzed for structural characteristics and thermal and pasting properties. The modification by spray drying caused no changes in the amylose content, molecular weight and the average gyration radius, and distribution branch chains-length of amylopectin showing that there was no degradation of glycosides bonds. There was reduction of the peaks of the diffraction pattern of starches, reflecting in decrease of relative crystallinity. The morphology of the granules showed agglomerates for the starches of cassava and Peruvian carrot, indicating partial gelatinization of the granules. Modified starch of Peruvian carrot by spray drying showed increase in cold viscosity and decrease in peak and final viscosity. For all starches, there was increase in setback. The temperatures of gelatinization no showed significant changes, although the temperature range decrease, as well as the enthalpy change. Modified starches by extrusion no show change in the amylose content and the distribution of branch chains-length of amylopectin, however, changes were observed in the molecular weight and the average gyration radius, indicating likely breaking of glycosidic bonds. Modified starches by extrusion showed total reduction in peaks of the diffraction pattern of the starches, indicating complete gelatinization of starches. In scanning electron microscopy observed no granules, confirming complete gelatinization of the starch, with loss of granular structure during the extrusion process, which also were observed by absence of gelatinization curve in thermal analysis. These changes leaded to increase of cold viscosity. The modifications by spray drying and extrusion resulted in starches with different properties, being the modified starch by spray drying can be indicated to apply in products that need of firmness consistency, and the modified starch by extrusion may be indicated to apply in products with cold viscosity and less consistency. Among of studied starches, Peruvian carrot starch showed be more susceptible for both process, due to its gelatinization temperature to be near the temperatures used in these experiments, and due to its defect in crystalline area. The results obtained in the second experiment show that the best conditions for modification of starches of cassava and sweet potato by spray drying are: high temperature (60 °C) and low concentration (5%). In these conditions can be obtained modified starches by spray drying with good pasting and thermal properties, as the cold viscosity, consistency in final product and gelatinization temperature uniform between the granules, reflecting in better utilization of energy by process.

Les aliments à base de plantain, connu comme riche en amidon résistant, sont largement consommés dans les pays du sud. Le contrôle de la digestibilité de l'amidon du plantain cuit implique la maîtrise de ses propriétés physicochimiques qui varient en fonction des conditions de cuisson et qui résultent de processus de transport (énergie, eau), de transformations et de réactions. Ces travaux de recherche ont pour but de mieux comprendre ces processus. Pour y parvenir, l'effet combiné de la température (T) et de la teneur en eau (X) sur le degré de gélatinisation (α) a été mesuré par DSC. Les proportions d'amidon rapidement digestible (RDS) et résistant (RS) mesurées par une méthode enzymatique in vitro, ont été étudiées sur un aliment modèle (farine + eau) à partir des variétés Dominico Harton et Harton. Les deux diagrammes d'état de l'amidon ont été représentés par un modèle de Weibull. Les effets combinés de T et X sur RDS ou RS peuvent être regroupés dans α; quel que soit l'historique thermohydrique de l'amidon. Ainsi, deux relations adimensionnées sont proposées pour prévoir le RDS et le RS en fonction uniquement d'α. Les écarts de comportement (gélatinisation et digestibilité) de l'amidon de l'aliment modèle et d'un morceau de plantain ont été mesurés et attribués aux effets de structures. Le modèle de prédiction de la digestibilité a été couplé à un modèle 2D traduisant les transferts d'énergie et d'eau durant la cuisson de cylindres de plantain. Le modèle simule bien les profils de température, de taux de gélatinisation et de gain en eau. Une diffusion de type capillaire a été observée en début de cuisson à 50 °C alors qu'au-delà (75 – 100 °C), le transport d'eau s'opère par diffusion moléculaire. La digestibilité est essentiellement pilotée par les transferts d'énergie. Ainsi pour du plantain prêt à être consommé, les degrés de liberté pour moduler le RDS et le RS sont limités ; en revanche, pour des produits pré-gélatinisés, des cuissons à températures intermédiaires (75 – 80 °C) permettraient d'obtenir des produits à faible impact glycémique. Toutefois, la sélection variétale du type de plantain est certainement le moyen en amont le plus souple pour contrôler la digestibilité des produits.Mots clés : plantain, amidon, gélatinisation, digestibilité, modélisation. / Plantain-based foods are widely consumed in southern countries. Plantain is well known for its high resistant starch content. Controlling the digestibility of cooked plantain starch involves managing its physicochemical properties. These vary depending on the cooking conditions and are a consequence of transport processes (energy, water), transformation and reactions. This research work aims to further our understanding of the different processes. To achieve this, the combined effect of temperature (T) and water content (X) on the degree of starch gelatinization (α) was measured by DSC. The proportions of Rapidly Digestible Starch (RDS) and Resistant Starch (RS) were measured using an in vitro enzymatic method and studied using a model food (flour + water) based on Dominico Harton and Harton varieties. Both starch state diagrams where represented using a Weibull model. The combined effects of T and X upon RDS or RS can be summarized by α, irrespective of the thermohydric history. Thus, two dimensionless relations were proposed to predict RDS and RS as a function of α. The difference in the starch behaviour (gelatinization and digestibility) between the model and a piece of plantain were measured and determined as structural effects. The digestibility prediction model was coupled with a 2D model that predicts the energy and water transfer during the cooking of the plantain cylinders. The model provides satisfactory simulations for temperature, degree of gelatinization and water gain profiles. A capillary-type diffusion was observed at the start of cooking at 50 °C, whereas at higher temperatures (75 – 100 °C), water transport is controlled by molecular diffusion. Digestibility is essentially driven by energy transfers. Thus, for ready-to-eat plantain, the freedom to modulate RDS and RS is limited. However, for pre-gelatinized products, products with a low glycemic impact could be obtained at intermediate cooking temperatures (75 – 80 °C). Prior selection of the plantain variety is certainly the easiest way to control product digestibility.Key words: plantain, starch, gelatinization, digestibility, model.

<p>Low moisture baked goods (cookies, biscuits, etc.) are known for their high sugar content, low water content, and characteristic texture. The added sugar in baked goods has been a concern of health advocates due to the negative health implications of overconsumption of sugar. To minimize these health implications and support healthier food products, the replacement of sugar, sucrose, in low moisture baked goods with alternative sweeteners is of interest. The goal of this study was to improve understanding on how sweetener alternatives and dietary fiber interact with cookie ingredients and the subsequent cookie texture compared to sucrose containing cookies to aid in developing health-conscious low moisture baked goods.</p><p> The replacement of sucrose with sucrose replacers (SRs) encompassing a variety of structural and physicochemical properties (high fructose corn syrup (HFCS), amorphous sucrose, maltitol, allulose, isomalt, Benefiber, Miralax, fructooligosaccharides (FOS), and isomalto-oligosacchrides (IMO)) in wire-cut cookies was investigated in terms of starch thermal properties, model cookie formulations, and sensory descriptive analysis. Starch thermal properties were investigated using differential scanning calorimetry (DSC) while wire-cut cookie parameters were analyzed through a_w, color (<i>a, b, L</i>), moisture loss, cookie dimensions (height, width, length), and cookie hardness (N) assays. Sensory descriptive analysis was used to ascertain texture perception of wire-cut cookies through five attributes (hardness, fracturability, pastiness, cohesiveness, and crumbliness).</p> The onset gelatinization temperature (T_gel) was increased to a greater extent than sucrose by Miralax and FOS, and to the same extent by IMO, maltitol, and Benefiber at high concentrations (60%w/w). The SRs which performed similar to sucrose in wire-cut cookie baking (spread, moisture loss, hardness) and texture intensity ratings were amorphous sucrose, maltitol, and allulose. No significant differences in descriptive analysis intensity scores were found in crumbliness, cohesiveness, and pastiness between SRs and sucrose formulated wire-cut cookies. FOS, IMO, and Benefiber displayed significantly larger fracture intensity scores compared so sucrose and isomalt cookies were significantly less hard than sucrose cookies. Principal component analysis (PCA) related SRs effect on starch gelatinization, cookie baking properties, and descriptive analysis intensity scores, and indicated the mostly likely candidates for use in reduced sugar cookies are maltitol and allulose.

Rice is an important human staple food for over half of the world’s population. Amylose content (AC), gelatinization temperature (GT), grain protein content (GPC), percentage grain chalkiness (PGC), and mineral content are important parameters for evaluating rice quality, which attracts customers and breeders. Only limited genes or QTLs (OsAAP6, OsGluA2, OsASN1, Chalk5, OsHMA3, etc.) are reported regulating rice GPC, PGC, and mineral content due to the lack of genetic knowledge and molecular markers. To dissect the genetic architecture of rice grain quality regulation, genome wide association studies (GWAS) were performed using two populations (USDA-mini core collection and a panel of 662 rice accessions from the 3K Rice Genomes Project). A total of 28, 11, 4, 3, 40, 3, 4, 3, and 10 QTLs were identified associated with Cd, Co, Cu, K, Mo, Ni, Rb, Sr, and Zn under flooded environment, while, 23, 7, 7, 7, and 3 QTLs were detected to be associated with Cd, Fe, Mo, Ni, and Zn under unflooded environment, respectively. Moreover, 6, 5, and 2 significant QTLs were tightly associated with kernel length, kernel rate, kernel width, respectively. Furthermore, 44, 7, 27, and 20 QTLs were identified associated with AC, GT, GPC, and PGC, respectively. Overall, 53 (~ 20.08%) of the 264 QTLs were coinciding with previously reported QTLs/genes, and 211 (~ 79.92%) were novel QTLs. A candidate gene, OsPCAT (putative cationic transporter), associated with GPC in the dry season was selected for further analysis. The OsPCAT gene belongs to the amino acid transporters (AATs) family with nine closely related members reported in Oryza Sativa. The classification and evolution of the CAT family (a subgroup of AATs family) using 61 species were studied. The over-expression lines (OsPCAT-OX) and CRISPR-Cas9 knock-out lines (OsPCAT-KO) were developed to study the function of OsPCAT gene. The preliminary results showed the GPC in OsPCAT-OX lines was increased and OsPCAT-KO lines were decreased compared to WT. Overall, a large number of new and reported QTLs associated with rice grain quality have been identified. This work lays the foundation for marker development in breeding and further investigation on rice grain quality regulation.

Due to the high cost of wheat importation in countries where the climatic conditions do not favour its cultivation, alternative sources of bread baking flour are required. Maize is a suitable alternative because it is by far the most important crop produced in Africa. However, it lacks gluten, the protein that is formed in wheat dough which is responsible for the desirable quality attributes (high loaf volume, soft and open crumb structure) of wheat bread. Therefore the need arises to improve maize bread quality. The effects of three types of non-wheat bread methods on the quality of maize bread were investigated. The first was a traditional sourdough method used in Lesotho for making steamed bread. This involved addition of spontaneously fermenting sorghum malt sourdough (equivalent to 15% of the total maize flour) and pre-gelatinization of the starch in the maize flour with boiling water. The second was a Food and Agriculture Organization method which involved pre-gelatinization of the starch in 10% of the maize flour by cooking. The third method was a modern gluten-free sourdough method which involved fermenting 75% of the maize flour with a multiple strains starter culture or Lactobacillus plantarum plus the natural flora in the maize. The modern sourdough method produced maize bread with a more open crumb structure and a significant increase in loaf volume compared to the other methods. This was probably related to the high percentage of fermented maize flour in the recipe, which was probably sufficient to modify the dough properties satisfactorily enough to impact positively on the maize bread quality. Based on these findings, the modern sourdough method was investigated further. Maize sourdoughs were prepared (as described) and compared to chemically acidified maize dough. Sourdough maize bread had an approx. 25-26% increase in loaf volume and a more open crumb structure with large gas cells. This showed that the maize bread quality improvement was not due to low pH. Confocal laser scanning microscopy revealed a cohesive dough structure in the sourdoughs. Larger cells and a more uniform crumb structure were also observed in maize breads with maize sourdough. This indicated an improvement in the maize dough properties with sourdough. Differential scanning calorimetry showed that maize sourdough had a slightly lower peak temperature than straight maize dough, an indication of starch modification. Rheological analysis showed that maize sourdough had a shorter relaxation time, an indication that it was less elastic. Strain sweep analysis revealed that maize sourdoughs had the lowest elastic modulus, also indicating a less elastic dough. Temperature sweep analysis showed an initial less elastic dough and a final high tan delta, suggesting that the maize dough could withstand gas expansion pressure during baking without crumbling. The dominant lactic acid bacteria in the sourdoughs were identified as L. plantarum. In the two sourdoughs, the L. plantarum present were gram-positive, catalase negative and exhibited proteolytic activities. However, only the L. plantarum in the multiple strains starter culture fermented maize sourdough exhibited amylolytic activities. It is proposed that proteolytic activity of the L. plantarum degraded the endosperm protein matrix and hydrolysed the proteins soluble in the dough liquid, thereby allowing increased accessibility of water to the starch granules. It is further proposed that the amylolytic activity of the L. plantarum slightly hydrolysed the starch granules, increasing water absorption by the starch granules. It is proposed that improvement in maize bread quality by sourdough fermentation is due to starch modification (increase water accessibility and water absorption by the starch granules due to the proteolytic and amylolytic activities of the dominant lactic acid bacteria in the sourdoughs) which made the dough less elastic. This in-turn improves the ability of the dough to trap and withstand the pressure of the expanding carbon dioxide in the fermenting dough and bread. / Thesis (PhD)--University of Pretoria, 2014. / gm2015 / Food Science / Unrestricted

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<p>Sorghum [<i>Sorghum bicolor</i> (L.) Moench] is a staple food for millions of people in Africa and South Asia. It is mainly consumed for its starch. The starch composition and structure in the seed endosperm determines cooking properties, processing quality, and starch digestibility. </p> <p>An assay to measure the alkali spreading value (ASV) of sorghum is described. The assay was used to identify sorghum EMS mutants with variation in starch composition. The ASV mutants (ASV+) exhibited a range of starch thermal properties with starch gelatinization temperatures (GT) being lower or higher than samples from Tx623 or Sepon82. The ASV+ phenotypes were found to be correlated with starch related traits such as enthalpy (r = −0.53) and range of starch GT (T_c-T_o) (r = 0.60). </p> <p>Genes controling the ASV phenotype of sorghum and their impact on starch quality traits are described. Whole genome re-sequencing of sorghum EMS mutants exhibiting an ASV+ phenotype was used to identify single nucleotide polymorphisms (SNPs) in candidate genes <i>Sobic.004G163700</i> and <i>Sobic.010G093400</i>. The two genes were identified as a <i>SbeIIb</i>, a putative sorghum homolog of <i>amylose extender,</i> and as a <i>SSIIa</i>, respectively. Linkage analysis showed that the mutations in <i>Sobic.010G093400</i> and <i>Sobic.004G163700</i> co-segregated with the ASV phenotype. The <i>ssIIa</i>-mutants exhibited normal amylose values, lower starch GT and lower final viscosity than the wild type. The <i>sbeIIb</i>-mutants exhibited higher amylose content, higher starch GT and lower peak and final viscosity with poor gel consistency compared to the wild type and <i>ssIIa</i>-mutants. An allele dosage test indicated that the <i>sbeIIb</i>-mutants had an allele dosage dependent effect on amylose content. Double mutants of <i>sbeIIb</i> and <i>ssIIa</i> showed that amylose content, starch thermal properties and paste viscosity profiles resemble the <i>sbeIIb</i> parent. </p> <p>A study of ASV phenotypes in a panel of more than 750 sorghum conversion lines revealed genetic variation for the ASV phenotype. A few SC-lines exhibiting stable expression of the ASV+ phenotype over two growing seasons. Most of these lines were described as belonging to the working group Nandyal, durra types from India described as producing ‘glutinous grains’. Whole genome resequencing discovered common SNPs in genes associated with starch biosynthesis. A genome wide association study (GWAS) identified a significant SNP that could be associated with the starch biosynthesis gene <i>Sobic.010G273800</i>, and with candidate genes <i>Sobic.010G274800</i> and <i>Sobic.010G275001</i> both annotated as glucosyltransferases. Grain samples from SC489, SC491, SC587 and SC589 exhibited a consistent ASV+ phenotype with lower or similar starch GT, similar amylose content, and similar high viscosity and gel consistency compared to controls.</p> <p> </p>