Inibidores de alfa amilase de feijão (Phaseolus vulgaris) foram caracterizados. O inibidor da variedade Jalo apresentou peso molecular de 50kDa (por filtração em gel), ponto isoelétrico de 4,75 e 9,6% de carboidratos. O inibidor da variedade Argentino apresentou peso molecular de 48kDa, ponto isoelétrico de 4,90 e 7,6% de carboidratos. Ambos inibidores apresentaram pH ótimo de interação com alfa amilase pancreática de porco de 5,0 e, a pH 6,9, a complexação com a mesma enzima se deu na proporção de 1:1. Esses resultados, mais a composição de aminoácidos, indicaram que as características desses inibidores são semelhantes às de outros já purificados de diferentes variedades de feijão. As principais diferenças entre o IA do Jalo e do Argentino, foram observadas através de termogramas, do teor de carboidratos e dos ensaios imunológicos. Além disso, são sintetizados entre 20 e 30 dias após a floração, sendo que o processo ocorre simultaneamente ao da síntese das proteínas de reserva do grão. Inibidores purificados das variedades Jalo, Argentino e Rico 23, em diferentes fases do desenvolvimento, indicaram ausência de grandes alterações estruturais durante esse processo. / α-amylase inhibitors of bean (Phaseolus vulgaris) were characterized. The amylase inhibitor from Jalo had molecular weight of 50 kDa (by gel filtration), an isoeletric point of 4.75 and a carbohydrate content of 9.6%. Argentino presented molecular weight of 48 kDa, an isoeletric point of 4.90 and a carbohydrate content of 7.6%. The optimum pH for inhibition of porcine pancreatic α-amylase for both inhibitors was about 5.0 and they formed 1:1 stoichiometric complex. These results and the amino acid composition indicated that these inhibitors have characteristics similar to others already purified from beans. They were synthesized between 20 and 30 days after anthesis and this process occurred simultaneously to the storage proteins synthesis. Purified inhibitors from seeds in different phases of development indicated lack of great structural changes during this process.

Inibidores de alfa amilase de feijão (Phaseolus vulgaris) foram caracterizados. O inibidor da variedade Jalo apresentou peso molecular de 50kDa (por filtração em gel), ponto isoelétrico de 4,75 e 9,6% de carboidratos. O inibidor da variedade Argentino apresentou peso molecular de 48kDa, ponto isoelétrico de 4,90 e 7,6% de carboidratos. Ambos inibidores apresentaram pH ótimo de interação com alfa amilase pancreática de porco de 5,0 e, a pH 6,9, a complexação com a mesma enzima se deu na proporção de 1:1. Esses resultados, mais a composição de aminoácidos, indicaram que as características desses inibidores são semelhantes às de outros já purificados de diferentes variedades de feijão. As principais diferenças entre o IA do Jalo e do Argentino, foram observadas através de termogramas, do teor de carboidratos e dos ensaios imunológicos. Além disso, são sintetizados entre 20 e 30 dias após a floração, sendo que o processo ocorre simultaneamente ao da síntese das proteínas de reserva do grão. Inibidores purificados das variedades Jalo, Argentino e Rico 23, em diferentes fases do desenvolvimento, indicaram ausência de grandes alterações estruturais durante esse processo. / α-amylase inhibitors of bean (Phaseolus vulgaris) were characterized. The amylase inhibitor from Jalo had molecular weight of 50 kDa (by gel filtration), an isoeletric point of 4.75 and a carbohydrate content of 9.6%. Argentino presented molecular weight of 48 kDa, an isoeletric point of 4.90 and a carbohydrate content of 7.6%. The optimum pH for inhibition of porcine pancreatic α-amylase for both inhibitors was about 5.0 and they formed 1:1 stoichiometric complex. These results and the amino acid composition indicated that these inhibitors have characteristics similar to others already purified from beans. They were synthesized between 20 and 30 days after anthesis and this process occurred simultaneously to the storage proteins synthesis. Purified inhibitors from seeds in different phases of development indicated lack of great structural changes during this process.

Nous passons plus des trois quarts de notre vie dans l'état postprandial. Pourtant, une plus grande attention a été accordée à l'étude du métabolisme à jeun qu'à l'impact de l'état postprandial sur la santé.Il est prouvé scientifiquement qu'une alimentation optimale pour la santé passe par la prise en compte de l'impact glycémique des aliments au-delà de leur simple teneur en glucides. Un déterminant important de l'impact glycémique de notre alimentation est l'amidon, qui joue un rôle clé dans la nutrition humaine en fournissant jusqu'à 50% de l'apport énergétique total. S'il est établi que la cinétique de digestion des aliments riches en amidon est un élément essentiel de leur impact glycémique, les contributions de chaque étape digestive à ce processus restent un sujet de débats. Afin de mieux comprendre les facteurs qui peuvent influencer la réponse glycémique aux aliments riches en amidon, et d’identifier de nouvelles stratégies pour atténuer leur impact glycémique, il est essentiel d'élargir notre compréhension du processus digestif de l'amidon. Cette thèse visait à étudier la digestion de repasriches en amidon (pain et pâtes), à réévaluer la contribution l’amylase salivaire à l'aide de digestions semi-dynamiques in vitro, et à mener une étude chez l'Homme pour déterminer l'effet de boissons (jus de citron et thé) sur : la réponse glycémique au pain, l'apport ad libitum, et la digestion gastrique étudiée par imagerie par résonance magnétique (IRM). Nos résultats apportent une base scientifique à l'élaboration d'une stratégie simple et efficace pour réduire la réponse glycémique aux aliments riches en amidon dans des repas de tous les jours. / All of us spend over three quarters of our lives in the postprandial state. Still, more attention has been dedicated to the study of the fasting metabolism than to the impact of the postprandial state on health.Scientific evidence supports that an optimum diet for health requires consideration of the glycaemic impact of foods in preference to consideration of carbohydrate content alone. An important determinant of the glycaemic impactof our diets is starch, which plays a key role in human nutrition, supplying up to 50% of the total energy intake. If it is clear that the digestion rate of starch-rich foods is an important determinant of their glycaemic impact, the contribution of each digestive stage to this process remains controversy. To better understand the factors that can influence the glycaemic response to starch-rich foods, and to identify new strategies to attenuate the glycaemic impact of starch-rich diets, it is essential to expand our understanding of thedigestive process of starch. The aims of this PhD were to study the digestionof starch-rich meals (bread and pasta), to reevaluate the contribution of salivary amylase using semi-dynamic in vitro digestions, and to conduct a human study to determine the effect of drinks (lemon juice and tea) on: the glycaemic response to bread, ad libitum intake, and gastric digestion assessed by magnetic resonance imaging (MRI). Our results provide scientific rationale for the development of a simple and effective strategy to reduce the glycaemicresponse to starch-rich foods in everyday-life meals.

Digestion of starch in humans starts in the mouth and progresses to the small intestine. Structures from salivary and pancreatic amylases hydrolysis can impact subsequent steps of digestion at the mucosa of the small intestine. However, structures of the starch digestion products along the gut from the mouth to the small intestines – products that impact glucose homeostasis are not well understood. This thesis focuses on the luminal step of starch digestion, i.e. impact of salivary and pancreatic amylase on the structure of hydrolysis products obtained from cooked starches from different botanical sources. Normal corn (NCS), wheat (NWS) and potato (NPS) starches were cooked at 1:0.7 (T0.7) or 1:2 (T2) starch:water ratios. Cooked starches were subjected to salivary amylase at conditions mimicking oral digestion. The composition of the hydrolysates was characterised by gel-permeation chromatography. Extent of hydrolysis was lower at T0.7 compared to T2, but the amount of carbohydrates in different fractions and the molecular weight profiles within each treatment were not different between starches from different botanical sources. However, debranching of the hydrolysates revealed structural differences in extent of amylose hydrolysis and amount and profile of lower molecular weight fractions between different starches. Cooked starches were also subjected to salivary and pancreatic amylases hydrolysis. Extent of 20 min hydrolysis was lower at T0.7 compared to T2 for all the starches. Oligosaccharide composition of 120 min hydrolysates differed in amounts of DP 2, 3, 5, 6 and 7 between processing treatments and starches. NCS (T2) was treated with saliva from six participants at equal activity. Salivary amylase activities ranged from 470 x 103 to 118 x 103 U/mL among the participants. While saliva from participant 2 (high amylase activity) greatly reduced the high molecular weight fraction, saliva from participant 6 (low amylase activity) more extensively hydrolysed the starch to small molecular weight fractions of oligosaccharides. These results show that different starch hydrolysates are produced during oral digestion by saliva from different individuals and are also different based on cooking condition or botanical source of starch. Further research is therefore needed to understand how these hydrolysate structures, impact glucose homeostasis.