| Summary: | According to the American Heart Association, cardiovascular disease (CVD) is the leading cause of death in the U.S., representing about 20-30% of all deaths every year in the U.S. Major risk factors for developing CVD include high blood lipid and LDL-cholesterol levels. A large number of heart attacks and strokes could be prevented by controlling these factors through lifestyle modifications and diet interventions. Epidemiological evidence shows that consumption of dry or common beans (Phaseolus vulgaris L.) has positive effects on reducing blood LDL-cholesterol and lipid levels. These health benefits are mainly attributed to the high content of dietary fiber (DF) of beans, including soluble and insoluble DF (SDF and IDF). Some proposed mechanisms to explain the cholesterol and lipid-lowering effects of DF are related to the physico-chemical properties (e.g. viscosity) of DF, and involve binding to bile salts (BS) in the small intestinal to prevent BS re-absorption which further promote cholesterol catabolism and delay lipid digestion. Nevertheless, the precise mechanisms are not fully understood yet. In addition, cooking and processing operations, and in particular high-hydrostatic pressure (HHP) processing, can modify the composition, structure and functional properties of foods; however, whether HHP affects the ability of beans to interfere with different aspects of lipid digestion remains unknown. The overall goal of this research is to understand how common beans and HHP processing impact the ability of beans to bind BS and influence lipid digestion in vitro. The specific objectives are 1) to evaluate the effect of HHP treatments (and compared it with conventional cooking (HT)) on the thermo-rheological and functional properties of dry beans; 2) to identify the impact of major bean components on the in vitro BS-binding ability of beans, the role played by the bean matrix and how this is affected by HHP processing; 3) to investigate how bean (micro)structure and fiber fractions, as well as HHP processing of dry beans, influence lipid digestion in vitro. Results showed that HT caused complete starch gelatinization and protein denaturation of beans, while HHP treatments induced partial or no starch gelatinization and a lower degree of protein denaturation, which resulted in enhanced protein solubility and emulsifying activity/stability. It was observed that, while HT treatment reduced the capacity of bean flours to retain BS because of severe disruption of the bean cell wall integrity, protein matrices, and starch granules, HHP treatments maintained or enhanced BS retention, possibly by promoting the formation of starch/protein/fiber networks able to entrap BS. Furthermore, by using an in vitro dialysis-based digestion model combined with viscosity measurements and thermal analysis, it was shown that the interaction between bean tissue materials and primary BS was not only related to viscosity but also involved hydrophobic linkages. The contribution of IDF and proteins (other than SDF) to retain BS was also significant. There was a different binding preference of beans to four primary BS with sodium glycochenodeoxycholate, the more hydrophobic BS, showing the largest retention levels while sodium taurocholate being the least effectively retained BS by beans. Diverse sequences of the same processing operations showed distinct impacts on BS-retention by dry beans. By means of an in vitro digestion model simulating conditions in the upper gastrointestinal tract, bean flours delayed the digestion of extrinsic lipids to a higher extent, compared to isolated IDF and SDF. Furthermore, HHP treatment and less severe mechanical disintegration maintained the ability of beans to modulate lipid digestion, which suggests the importance of bean structural integrity in reducing the lipolysis rate and extent by beans. Overall, this research work shows that HHP processing is a promising minimal processing technology to produce bean flours with improved functionality. It also highlights the importance of considering the structure of foods, and not just their nutrient content, when evaluating potential health impacts. This knowledge could be applied to develop a range of bean-based ingredients and formulations with desirable health benefits. This work can be extended to research the influence of beans on the gut microbiota and profile of secondary BS and short-chain fatty acids, which are also closely related to cholesterol and lipid metabolism. === Doctor of Philosophy === According to the American Heart Association, cardiovascular disease (CVD) is the leading cause of death in the U.S., representing about 20-30% of all deaths every year in the U.S. Around the world, millions of people are struggling to control the risk of CVD. Major risk factors for developing CVD include high blood lipid and LDL-cholesterol levels. A large number of heart attacks and strokes can be prevented by controlling the major risk factors through lifestyle modifications and diet interventions. Epidemiological evidence shows that consumption of dry beans (Phaseolus vulgaris L.) has positive effects on reducing blood LDL-cholesterol and lipid levels. These health benefits are mainly attributed to the high content of dietary fiber (DF) in beans. DF is carbohydrate polymers that are not hydrolyzed by the endogenous enzymes in humans. However, some of them (water-soluble DF) could increase viscosity and retain the absorption of bile salts (BS) in the small intestinal. The BS retention or the binding of BS could promote more cholesterol convert to BS (thus reduce cholesterol levels) and decrease lipid digestion. Therefore, due to the increased viscosity and BS retention ability of DF, dry beans could help to reduce the blood cholesterol and lipid levels and further help to prevent CVD. Moreover, different cooking and processing method could also affect the composition, microstructure and functional properties of foods. The purpose of this research was to determine how common beans and high hydrostatic pressure (HHP) (compared with hydrothermal (HT)) processing, a non-thermal processing, influence the ability of dry beans to retain bile salts and modulate lipid digestion in vitro. This study showed that severe HT treatment disrupted the bean cell wall integrity severally and reduced the BS retaining the efficiency of dry beans, while HHP treatment, produced minimally processed beans, improved the application properties of dry beans and maintained/enhanced BS-retention by dry beans. It also showed that the whole bean matrix (other than soluble DF) also contributes to retain BS and modulate lipid digestion, indicating the importance of retaining intact food structures. The integrity of bean structures through HHP treatment and less severe mechanical treatment could help to retain the ability of dry beans to reduce lipid digestion. These findings suggest that dry beans, with a high content of dietary fiber and resistant starch, have significant health benefits related to lowering cholesterol and lipid levels. Increasing the consumption of dry beans would definitely help to improve overall health. HHP, as a non-thermal processing technology, showed the potential to produce minimally processed bean products with enhanced health benefits and diverse application properties. This study could be extended through continuing research into the influence of beans on the gut microbiota, which are also closely related to the cholesterol and lipid metabolism regulation.
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