Emulsions form a major part of processed food formulations, either being the end products in themselves or as parts of a more complex food system. For the past few decades, colloid scientists have focussed mainly on the effects of processing conditions (e.g. heat, high pressure, and shear) on the physicochemical properties of emulsions (e.g. viscosity, droplet size distribution and phase stability). However, the information about the behaviour of food structures post consumption is very limited. Fundamental knowledge of how the food structures behave in the mouth is critical, as these oral interactions of food components influence the common sensorial perceptions (e.g. creaminess, smoothness) and the release of fat-soluble flavours. Initial studies also suggest that the breakdown of emulsions in the gastrointestinal tract and the generated interfacial structures impact lipid digestion, which can consequently influence post-prandial metabolic responses. This area of research needs to be intensively investigated before the knowledge can be applied to rational design of healthier food structures that could modulate the rate of lipid metabolism, bioavailability of nutrients, and also help in providing targeted delivery of flavour molecules and/or bioactive components. Hence, the objective of this research was to gain understanding of how emulsions behave during their passage through the gastrointestinal tract. In vitro digestion models that mimic the physicochemical processes and biological conditions in the mouth and gastrointestinal tract were successfully employed. Behaviour of model protein-stabilized emulsions (both positively charged (lactoferrin) as well as negatively charged [β-lactoglobulin (β-lg)] oil-in-water emulsions) at each step of simulated physiological processing (using model oral, gastric and duodenal fluids individually) were investigated. In simulated mouth conditions, oil-in-water emulsions stabilized by lactoferrin or β-lg at the interfacial layers were mixed with artificial saliva at neutral pH that contained a range of mucin concentrations and salts. The β-lg emulsions did not interact with the artificial saliva due to the dominant repulsion between mutually opposite charges of anionic mucin and anionic β-lg interfacial layer at neutral pH. However, β-lg emulsions underwent some depletion flocculation on addition of higher concentrations of mucin due to the presence of unadsorbed mucin molecules in the continuous phase. In contrast, positively charged lactoferrin emulsions showed considerable salt-induced aggregation in the presence of salts (from the saliva) alone. Furthermore, lactoferrin emulsions underwent bridging flocculation because of electrostatic binding of anionic mucin to the positively charged lactoferrin-stabilized emulsion droplets. In acidic pH conditions (pH 1.2) of the simulated gastric fluid (SGF), both protein-stabilized emulsions were positively charged. Addition of pepsin resulted in extensive droplet flocculation in both emulsions with a greater extent of droplet instability in lactoferrin emulsions. Coalescence of the droplets was observed as a result of peptic hydrolysis of the interfacial protein layers. Conditions such as ionic strength, pH and exposure to mucin were shown to significantly influence the rate of hydrolysis of β-lg-stabilized emulsion by pepsin. Addition of simulated intestinal fluid (SIF) containing physiological concentrations of bile salts to the emulsions showed competitive interfacial displacement of β-lg by bile salts. In the case of lactoferrin-stabilized emulsion droplets, there was considerable aggregation in the presence of intestinal electrolytes alone (without added bile salts) at pH 7.5. Binding of anionic bile salts to cationic interfacial lactoferrin layer resulted in re-stabilization of salt-aggregated lactoferrin emulsions. On mixing with physiological concentrations of pancreatin (mixture of pancreatic lipase, amylase and protease), significant degree of coalescence and fatty acid release occurred for both the emulsions. This was attributed to the interfacial proteolysis by trypsin (proteolytic fractions of pancreatin) resulting in interfacial film rupturing. Exchange of initial interfacial materials by bile salts and trypsin-induced film breakage enhanced the potential for lipolytic fractions of pancreatin to act on the hydrophobic lipid core. The lipid digestion products (free fatty acids and mono and/or diglycerides) generated at the droplet surface further removed the residual intact protein layers from the interface by competitive displacement mechanisms. The sequential treatment of the cationic and anionic emulsions with artificial saliva, SGF and SIF, respectively, was determined to understand the impact of initial protein type during complete physiological processing from mouth to intestine. Broadly, both the protein-stabilized emulsions underwent charge reversals, extensive droplet flocculation, and significant coalescence as they passed through various stages of the in vitro digestion conditions. Except in the simulated mouth environment, the initial charge of the emulsifiers had relatively limited influence on droplet behaviour during the simulated digestion. The results contribute to the knowledge of how structure and charge of the emulsified lipid droplets impact digestion at various stages of physiology. This information might have important consequences for developing suitable microstructures that allow controlled breakdown of droplets in the mouth and predictable release of lipids in the gastrointestinal tract.

Fruit and vegetable derived polyphenols have been linked with many health benefits. In light of this, many consumers are seeking to increase their intake of polyphenols, with many turning to dietary supplements that contain concentrated doses of purified polyphenols. However, the safety of this consumption modality is not known, nor are the dose-dependent metabolic changes that may be present, especially when considering colonically generated phenolic metabolites. Using blueberry polyphenols as a model, we explored these phenomena in a rat model. Animals were dosed with blueberry polyphenols at levels up to 20 times what would be consumed in 1-2 servings of whole blueberries in an adult human. In the first study, animals were acutely dosed with blueberry polyphenols and urine and plasma pharmacokinetics measured. In the second study, animals were repeatedly dosed for 90d, with urinary metabolites monitored throughout the study and a complete necropsy performed following standard guidelines. In both studies, metabolite excretion patterns were similar: cinnamic acids accounted for a majority of the observed metabolites, followed by hippuric acids and then phenylpropionic acids (PPA). A dose-dependent shift in metabolite production was observed; as the dose increased, the relative amounts of PPA increased while hippuric acids decreased. No adverse or toxic effects were found, and, though there were several statistically significant differences in toxicological endpoints, all measured parameters remained in the normal range for these animals and thus were not deemed biologically significant. These results indicate that high doses of blueberry polyphenols, as may be present in dietary supplements, are safe for consumption. These results also demonstrate dose-dependent shifts in metabolism that may impact gut function and affect the health benefits derived from blueberry polyphenols.<br>

<p>In this study, structural specificity of flavonoids was investigated toselectively inhibit starch digestive enzymes to stimulate the ileal-brake by triggering glucagon-like peptide-1 (GLP-1) through distal small intestine starch digestion which can regulate food intake and appetite. The double bond between C2 and C3 on flavonoid’s chemical structure plays a critical role to inhibit human pancreatic α-amylase, leading to π-staking interaction. Meanwhile, the hydroxyl group at C3 on the backbone benzopyran ring is intimately related to inhibition of the mucosal α-glucosidases. This selective inhibition is likely the result of fundamental differences in the protein structures of α-amylase and α-glucosidases, as they belong to different glycosyl hydrolase Families 13 and 31 (GH13 and GH31). α-Amylase has the catalytic active siteslocated in wide and shallow grooves on the protein structure, while α-glucosidases possess the narrow and deep catalytic pocket. In an acute study done on mice, luteolin, which had thehigher degree of selectivity toward α-amylase, showed a slow and sustained postprandial glycemic response with a reduced blood glucose peak and extended high glucose profile, compared to 3’,4’-dihydroxylflavonol as the selective α-glucosidases specific inhibitor. Quercetin was inhibitory of both α-amylase and α-glucosidases.Glycemic profiles in mice confirmed in vitro analysis of the inhibitory selectivity of the flavonoids tested. Additionally, the extended glycemic response with luteolin was accompaniedthe higher secretion of GLP-1 at extended postprandial times by delivering more starch portion into the distal small intestine where the ileal-brake and gut-brain axis activation takes place. Overall, selective inhibition of α-amylase by flavonoids potentially could be considered as a key approach to control glucose release from starch with slow and extended, but still complete, digestion for improved glycemic response and minimized adverse side effects that result from severely restricting or even shutting down starch digestion by pharmaceutical grade inhibitors.<br></p>

<p>Moderating glycemic response to foods is important for the potential to control or prevent hyperglycemia-related diseases, such as diabetes and cardiovascular disease. The importance of slowly digestible carbohydrates (SDC) lies in their health effects: moderated blood glucose response, and a potential for increased satiety and reduced intake, and weight management. The research presented is on structural properties of novel, mostly soluble, a-glucans (glucose-containing oligomers and polymers with different linkage types and combinations) that are required for slow yet full digestion, and how they behave in food systems. Up to this point, little has been known regarding what structural properties of glucose-containing carbohydrates result in slow digestion, although starch structure has been well investigated and it is known that raw starch has a slowly digestible property. In addition to the structure-function aspect of the thesis work, this research contributes information about how a-glucan SDCs can be incorporated into food products that undergo heat treatment in the presence of moisture. The a-glucans maintain their SDC property while raw starch is gelatinized and becomes rapidly digestible. The rate of hydrolysis of a large number of novel a-glucans was studied using a simulated upper gastrointestinal in vitro digestion utilizing porcine pancreatic α-amylase and α-glucosidases from the rat intestine, and a subset was then evaluated in a crossover design clinical trial with blood glucose monitoring. Linkage and molecular weight analysis using gas chromatography of partially methylated alditol acetates and multi-angle light scattering and refractive index (MALS-RI) detection at time points during in vitro digestion were used to elucidate the relative rate of digestion of different linkage types in new and known a-glucan carbohydrates. Rheological, turbidity, and SLS and DLS analyses were used to examine ingredient interaction between novel, enzymatically-modified α-glucans with slow digesting properties found most promising for inclusion in food products. A model nutritional beverage system was utilized containing proteins and salts. It was found that solvent and ion concentration of solutions were important for dictating aggregation formation with highly branched alternans and oligosaccharides in solution alone, or in the presence of soluble protein aggregates. Further, salts in solution proved to influence rheological and turbidity measures of all four α-glucans examined in the model system, indicating they may affect aggregation and structural conformation of such large carbohydrates. However, only tapioca maltodextrins showed in vitro rate of digestion affected by aggregation.</p><p></p> <p>These results show the chemical and molecular properties of modified carbohydrates that contribute to slow digestion rate, which is informative to develop improved or new SDCs, as well as how these novel SDCs interact with other ingredients within a model beverage system, informing applications for the food industry.</p>

<p>Findings presented in this dissertation show that polyunsaturated fatty acids of soybean oil effectively reacted with high voltage atmospheric cold plasma gas species of various gases including hydrogen, nitrogen, and oxygen at room temperature without a catalyst. Hydrogenation, nitration, and epoxidation reactions were observed along with polymerization. Unexpectedly, hydrogen gas was not the primary source of atomic hydrogen observed under these experimental conditions. Rather, it is suggested that water vapor, present as an impurity, supplied hydrogen ions to the hydrogenation reactions. Nitrogen gas modified atmosphere is an electron-rich medium that catalyze reactions. Further investigation is suggested for optimizing the process of oil hydrogenation, as well as for exploring the potential to produce bio-based gels, lubricants, and greases.</p>

<p>High-school-aged youths have limited food safety knowledge and lack safe food-handling skills. However, these youths will prepare food for themselves and are frequently employed in the food service industry, where their food-handling practices can directly impact public health. Youths’ beliefs about safe food-handling behaviors are affected by Key Influencers in their lives such as peers, classroom instructors, parents, and celebrities including popular web-content authors or video hosts. Societal changes have prompted the elimination of Family and Consumer Science courses from many schools and the reduction of food-handler role models at home, while increasing access to unregulated sources of food-handling information such as information published on web-based platforms. These societal changes largely remove peers, classroom instructors, and parents from influencing youths’ food-handling behaviors. </p> <p>The purpose of this study was to (1) evaluate the effectiveness of a researcher-developed food safety educational intervention at changing students’ food-handling behaviors specifically focusing on the role of subjective norms in generating behavior change and (2) conduct an exploratory content analysis of food safety messages delivered by blog authors and video hosts of popular web-content. </p> <p>The researcher-developed curriculum was evaluated for adherence to academic standards and overall usability in the classroom using the Delphi Technique by a panel of secondary educators who were considered experts in the education field. The curriculum was evaluated for effectiveness at changing high school students’ food-handling behaviors through self-reported surveys and observation using GoPro head mounted and stationary cameras. Finally, content analysis was performed on food safety messages disseminated by authors and video hosts of popular blogs and YouTube videos, respectively. </p> Findings from the study demonstrated that youths’ food-handling behaviors are affected by Key Influencers including their peers and classroom instructor. However, post-intervention, a role-reversal was observed and reported as students became influencers who sought to improve their Key Influencers’ food-handling behaviors. Differences in influencing power within these relationships could impact the sustainability of youths’ safe food-handling behaviors. In particular, imbalances in influencing power of celebrities in the absence of other Key Influencers could leave students vulnerable to adopting unsafe food-handling practices.

<p>It is well known that colonic microbiota is influenced by both intrinsic and extrinsic factors; out of all these, diet plays a major role. The traditional human diet has typically been high in overall dietary fiber intake, due its inherent presence in plant-derived foods. However, over the years, dietary patterns have transitioned into a low-fiber Westernized diet. This diet is increasingly implicated in colonic diseases. Dietary fiber consumption is known to increase microbial diversity, yet the mechanisms are still unclear. This is partially true because dietary fiber as a category is composed of a wide variety of structures, which may have divergent effects on the gut microbiome. The food industry has extracted, isolated, refined and purified non-digestible carbohydrates and, in some cases, modified them for improved function, which may influence their interaction with the gut microbiome. This study was developed in two phases: we first hypothesized that glucans produced by different processes were structurally distinct and that these fine structural differences in glucans would govern microbial responses to the polymers. To test this hypothesis, we first determined the structural characteristics of the glucans by gas chromatography and mass spectrometry, which revealed substantial structural differences among the glucans with respect to size and linkage patterns, consequently categorizing the glucans by structure (i.e., mixed linkage α-glucans, resistant maltodextrins, and polydextroses). The second study involved the <i>in vitro </i>fecal fermentation of these commercially available soluble glucans which are uniformly composed of glucose linked into different structural arrangements. We further hypothesized that each glucan would select for different microbiota and that there would be glucan-specific general responses across microbiomes. We were able to identify a variety of idiosyncratic metabolic patterns as well as differential organisms selecting for specific glucan structures. Although there were associations with glucan classes at the family level (e.g., <i>Bacteriodaceae </i>and <i>Lachnospiraceae </i>were discriminants of the resistant maltodextrins and polydextroses respectively), associations with glucans across individual species within these families varied. These findings suggest that microbiome responses to structurally distinct glucans depend upon both fine glucan structure and community context, and community metabolic phenotypes emerge from the interaction of the two. These findings are relevant to the food industry as they may enable optimization of synthesis to generate chemical structures that select for specific organisms and/or improve overall gut health.</p>

<p>This dissertation investigates two major structure-function relationships important to food science: vitamin stability and water-solid interactions. Thiamine, vitamin B₁, is an essential micronutrient in the human diet. While thiamine is found naturally and as a fortification supplement in many foods, it is chemically unstable on exposure to heat and some co-formulated ingredients, with degradation exacerbated in prolonged shelf-life products. The instability of thiamine is a concern for the development of dietary deficiencies, which are prevalent even in developed countries; however, thiamine stability is not widely studied in the food or pharmaceutical industries. Thiamine is commercially available in two salt forms: thiamine mononitrate (TMN) and thiamine chloride hydrochloride (TClHCl). This study focused on documenting the storage stability of thiamine in solution, considering the effects of which commercially available salt form of the vitamin was used, vitamin concentration, pH, and ions present in solution by monitoring chemical stability and degradation kinetics over a 6-month to 1-year period following storage at 25-80ºC, and expanded these studies into food systems (bread doughs). The results from these studies, including the reaction kinetics of thiamine degradation, the degradation pathway, and the sensory impacts of the degradation products formed, especially as affected by pH and food matrix, can be used to improve thiamine stability and delivery in foods.</p><p></p><p>The studies of water-solid interactions in this dissertation covered two topics: 1) the effects of formulating a variety of food-relevant additives on the crystallization tendency of amorphous sucrose; and 2) the effects of formulation on the moisture sorption behaviors and physical stability of spices, herbs, and seasoning blends. Sucrose lyophiles were co-formulated with a variety of additives and stored at 11-40% relative humidity (RH). The structural compatibility of sucrose with the additive, and related intermolecular interactions, dictated the tendency of the additive to either delay, prevent, or accelerate sucrose crystallization. Spices, herbs, and seasoning blends were exposed to increasing RH (23-75%) and temperature (20-50ºC) to determine the effect of storage and formulation on a variety of physical properties. In general, as complexity of blends increased, physical stability decreased. While this dissertation covers a wide variety of food chemistry and food materials science topics, including vitamin chemical stability, amorphous sucrose physical stability, and moisture sorption behaviors of spices, herbs, and seasoning blends, the findings provide valuable information on the chemical and physical stability of ingredient systems and how the structure-function relationships of the systems can be controlled for optimal ingredient functionality.</p><p></p>

<div> <div> <div> <p>As a major part of the dietary fiber classification, plant polysaccharides often have chemically complex structures which may differ by genera and species, and perhaps even by genotype and growing environment. Arabinoxylans from cereal cell walls are known to differently impact human gut microbiota composition and fermentation metabolites due to variability in chemical structure, though specificities of structure to these functions are not known at the level of genotype ́ environment. In the first study, corn bran arabinoxylan (CAX) extracted from 4 genotypes ́ 3 growing years at the Purdue Agronomy Farm was compared in human fecal fermentations to test the hypotheses that, 1) CAXs extracted from brans from different corn genotypes and grown over different years (environments) show distinct structures, and 2) these cause differences in gut microbiota response and fermentation metabolites. Monosaccharides and linkage analysis revealed that CAXs had different structures and the differences were genotype-specific, but not significantly due to environment. PCA analysis revealed that both short chain fatty acid production and the microbial community shifted also in a genotype-specific way. Thus, small structural changes, in terms of sugar and linkage compositions, cause significant changes in fermentation response showing very high specificity of structure to gut microbiota function. </p> <p>Insoluble fermentable cell wall matrix fibers have been shown to support beneficial butyrogenic Clostridia, but have restricted use in food products due to their insoluble character.</p></div></div> </div> <div> <div> <div> <p>In the second study, a soluble fiber matrix was developed that exhibited a similar fermentation effect as fermentable insoluble fiber matrices. Low arabinose/xylose ratio CAX was extracted with two concentrations of sodium hydroxide to give soluble polymers with relatively low and high residual ferulic acid (CAX-LFA and CAX-HFA). After laccase treatment to make diferulate crosslinks, soluble matrices were formed with average size of 3.5 to 4.5 mer. In vitro human fecal fermentation of CAX-LFA, CAX-HFA, soluble crosslinked ~3.5 mer CAX-LFA (SCCAX- LFA), and ~4.5 mer SCCAX-HFA revealed that the SCCAX matrices had slower fermentation property and higher butyrate proportion in SCCAX-HFA. 16S rRNA gene sequencing showed that SCCAX-HFA promoted OTUs associated with butyrate production including Unassigned Ruminococcaceae, Unassigned Blautia, Fecalibacterium prausnitzii, and Unassigned Clostridium. This is the first work showing the fabrication of soluble crosslinked fiber matrices that favors growth of butyrogenic bacteria. </p> <p>Moreover, these same SCCAXs exhibited an interesting gel forming property on simple pH reduction, which is similar in gelling property to low acyl gellan gum, though is differently readily soluble in water. Both of the SCCAXs formed gels at pH 2, with SCCAX-HFA forming the stronger gel. Gels showed shear-thinning behavior and a thermal and pH reversible property. A gel forming mechanism was proposed involving noncovalent crosslinking including hydrogen bonds and hydrophobic interaction among the SCCAX complexes. This mechanism was supported by structural characterization of SCCAX complexes using a Zeta-sizer and FT-IR spectroscopy. SCCAX-HFA could be used in low sugar gels and has the above property of promoting butyrogenic bacteria in the gut. </p> <p>In conclusion, gut microbiota responds differentially to CAXs with various fine structures. This probably due to dietary fiber-gut microbiota relationships have been evolved over time to be highly specific. Forming soluble fiber matrices could be a good strategy to promote butyrogenic bacteria and improve gut health, in a readily usable form in beverages.</p></div></div></div>

<p>  </p> <p>The world has experienced an unprecedented change in the systems responsible for food production, distribution, and commercialization with concurrent changes in diets. In developed and developing countries, the shift in consumption patterns has moved towards a Western diet pattern which has been linked to negative health outcomes including obesity, diabetes and associated non-communicable diseases. Traditional African diets have previously been associated with protective effects against the development of the above-mentioned conditions. Yet, the underlying reasons for this is not clear. One dietary factor that may contribute to its protective effect is the principal available carbohydrate, starch, which in traditional African staples is considered to contain slowly digestible carbohydrates (SDCs) and some amount of resistant starch (RS). We reported that traditional African staple starchy foods (sorghum and millet) had markedly slower gastric emptying than introduced modern starchy foods (rice, pasta and potatoes). This response was attributed to activation of enteroendocrine cells of the small intestine (L-cells) with potential to trigger physiological, hormonal, and neurological processes that affect digestion time and perception of hunger; effect known as the ileal brake. Moreover, at least in mice models, consumption of SDCs has shown to have beneficial effects on the rate and type of fuel (e.g. carbohydrate vs fat) used for metabolic processes.</p> <p>The first thesis study compared the effect of diets (cohorts in the USA and Kenya) on gastric half-emptying time and metabolic fuel utilization in healthy adults. Our findings showed that gastric emptying time was not different between cohorts and that diet did not influence gastric emptying time; however, calculated respiratory exchange ratio (RER) (which is a measure of metabolic fuel utilization at the cellular level, e.g. carbohydrate vs fat) and metabolic flexibility (which is the ability to switch between metabolic fuel sources upon demand or need) was higher for the Kenyan cohort. Multivariant models were developed and corrected for multicollinearity of some diet variables. Carbohydrate and protein in multivariate model 1; total fiber, added sugars and starch in multivariate model 2; and diet quality (measured as the Healthy Eating Index based on 2015-2020 dietary guidelines, or HEI-2015) in multivariate model 3, were significantly and independently correlated with RER and metabolic flexibility.   </p> <p>The second study assessed if slow gastric emptying and improve metabolic fuel utilization could be induced through SDC supplementation. The objective of this study was to determine if continual consumption of SDC for 21 days delayed the rate of gastric emptying, moderated postprandial glycemic response, decreased hunger, and/or improved metabolic fuel utilization in subjects with low diet quality (HEI-2015<65). Our results indicated that supplementation with SDC did not slow gastric emptying time or acute measures of metabolic fuel utilization; however, continuous consumption of SDC had a modest but significant effect on improving metabolic flexibility and decreasing hunger scores. </p> <p>The last two chapters of this thesis focused on the use of a low-cost, high-pressure, high temperature extruder suitable for processing in Africa of whole grain pearl millet (<em>Pennisetum glaucum</em>). In Africa, emerging, entrepreneurial companies are increasingly gaining share of local markets by manufacturing and distributing high-quality locally sourced processed foods made with indigenous grains. Whole pearl millet is particularly susceptible to development of rancidity. The objective of our third study was to assess the use of the extruder on the stability and sensory attributes of whole grain pearl millet extruded flours to be used for instant thin and thick porridges. Findings showed that extrusion fully gelatinized the starch in pearl millet and prevented hydrolytic rancidity in the instant flour products. However, extrusion cooking did not stop oxidative rancidity. We concluded that while extrusion cooking is a versatile technology for whole grain processing, refinement of extrusion conditions used in the experiment and the evaluation of other unit operations (e.g. steeping, germination) in combination with extrusion cooking may improve the sensory properties of final products.</p> <p>Finally, extrusion cooking has been showed to promote the formation of beneficial amylose-lipid complexes (ALCs). The objective of the last study was to evaluate the formation of ALCs in whole grain pearl millet extruded flours, characterize their composition, and assess their ability to slowly digest <em>in vitro</em>. Extrusion promoted the formation ALCs and these flours exhibited a slow enzymatic digestion <em>in vitro</em>. The findings from this thesis provide insights into the role of diets and metabolic fuel utilization, and improvement of processed pearl millet foods in Africa.</p>