<div>Shifts in the human diet to more refined foods and ingredients have contributed to the rise in metabolic disease rates associated with long-term consumption of foods causing swift rises in blood glucose response. Foods which result in a more moderate blood glucose curve are considered healthier by increasing satiety and reducing oxidative stress. Sorghum products contain naturally slowly digested starch. The matrix of sorghum porridges contains kafirin protein bodies which cross link around gelatinizing starch molecules, while similar nascent matrices in other cereals aggregate and collapse. The 3-deoxyanthocyanidin pigments unique to sorghum may be accountable for the difference in matrix stability. The density of the starch entrapped in the matrices is thought to partially inhibit α-amylase access to the starch, reducing overall starch digestion and thereby mitigating glucose response. The purpose of this work was to increase our understanding of how phenolic compounds in sorghum interact with endosperm proteins to create a stable matrix, and to explore if the knowledge might be translated to other starchy cereal products. In the first study, phenolic extracts from flours (sorghum, corn masa, white rice) were characterized for phenolic content, antioxidant activity, phenolic components, and their ability to interact with a model protein system (ovalbumin) in order to examine protein polymerization. In the second study, specific phenolic compounds in sorghums (<i>p</i>-coumaric, sinapic, and gallic acids; (+)-catechin; and apigeninidin, a 3-deoxyanthocyanidin found in sorghums) were interacted in the model protein system at different concentrations to observe extent and type of protein polymerization, and promising compounds subjected to fluorescence quenching spectroscopy to examine the nature of the interactions. The final study explored the effects of apigeninidin addition to a yellow corn flour and naturally present anthocyanin (blue corn) on starch digestion and microstructure of porridges by utilizing an <i>in vitro</i> α-amylase assay and confocal microscopy. </div><div>The slow digestion of starch in cooked sorghum products can be attributed to the 3-deoxyanthocyanidin compounds present in the grain participating in sulfhydryl-disulfide interchanges which results in extensive kafirin cross-linking surrounding starch granules. While other phenolic and redox-active components may affect matrix formation and stability, 3-deoxyanthocyanidins appear to have the most direct influence, and their ability to modify food protein matrices appears to have a direct result on starch digestion <i>in vitro</i>.</div>

ABSTRACT Influence of fenugreek gum on bread and in vitro physiological effects Keisha T. Roberts Advisors: University of Guelph Dr. S.W. Cui Professor T.E. Graham This thesis examined the effect of fenugreek gum, from Canadian grown fenugreek on bread quality, when substituted for wheat flour at 5 % and 10 %, and the in vitro physiological effects of these breads, based on models of acute and long - term feeding. Study I determined bread could be produced with 10 % fenugreek gum, while maintaining quality parameters of volume and texture, comparable to a control. This was accomplished through the development of a novel bread production method, using the lamination procedure for puff pastry production. The behavior of fenugreek gum and starch (wheat flour) was determined by rapid visco analysis (RVA), farinograph and dynamic rheological measurement, while scanning electron microscopy of bread found fenugreek gum could be identified within the bread matrix. Study 2 in vitro starch digestion found fenugreek gum at 5 % and 10 % reduced glucose liberated from bread, with 10 % fenugreek gum causing a reduction of over 30 %. RVA of fenugreek breads highlighted differences in viscosity between breads and wheat flour substituted with the gum. This was substantial as viscosity measurements by RVA are conducted on raw ingredients and not the food as consumed, which reflects the possible reduction in viscosity with food processing. This study also determined extruding fenugreek gum may have caused morphological changes to the gum, which may possibly contribute to attenuation of glucose liberated in vitro. Study 3 evaluated the accumulation of short chain fatty acids (SCFA) from the fermentation of three substrates: Extruded fenugreek gum, bread with 10 % extruded gum and control bread, based on fecal microbiota from three donors. SCFA profiles varied with substrates and donors, with fenugreek gum having the highest accumulation of SCFA after 12 hours. Donors were a caucuasian Canadian, a black Jamaican and a black Trinidadian who was the only donor culturally exposed to fenugreek. This Trinidadian’s SCFA profiles were consistently higher for fenugreek gum than the other donors. These studies collectively showed fenugreek gum, though viscous could be successfully incorporated into bread and have potential as a functional food and nutraceutical.

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.