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The Role of Lipid Physical State in Determining In Vitro Digestibility and In Vivo Postprandial Metabolism

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Title: The Role of Lipid Physical State in Determining In Vitro Digestibility and In Vivo Postprandial Metabolism
Author: Thilakarathna, Surangi
Department: Department of Human Health and Nutritional Sciences
Program: Human Health and Nutritional Sciences
Advisor: Wright, Amanda
Abstract: Lipid digestibility and postprandial lipemia (PPL) have implications for health and disease, although the possible contributions of triacylglycerol (TAG) physical properties to these processes remain ill-defined. This thesis investigated the role of TAG physical state, specifically on in vitro digestibility and PPL using compositionally similar interesterified (IE) lipids with different solid fat contents (SFCs) and compositionally identical undercooled liquid (LE) and partially crystalline solid (SE) emulsion droplets. A secondary aim was to compare the in vitro and in vivo results obtained. The first study with stearic-rich IE lipids showed lower free fatty acid (FFA) bioaccessibility and higher levels of “excreted” stearic acid in the undigested TAG for non-IE vs IE blends. Those results obtained using the TIM-1 dynamic digestion simulator indicated lower digestibility for solid fat versus liquid oil and correlated well with previous postprandial TAG human data for the same lipids. Tempering was used to formulate and compare compositionally identical LE and SE emulsion droplets based on palm stearin. The droplets were similarly sized, charged, and shaped, eliminating factors that might have otherwise influenced TAG digestibility. Using a static in vitro digestion method, SE lipolysis was slower and reduced compared with LE. The presence of crystalline fat was also associated with extensive partial coalescence with exposure to simulated gastric conditions and differences in in vitro lipolysis between LE and SE were exaggerated dependent on in vitro digestion conditions, i.e. gastric pH and shear. In a randomized double-blinded crossover acute meal study with healthy male participants, SE showed a significantly delayed postprandial plasma TAG increase from baseline and a decrease in plasma TAG incremental area under the curve. Consistently, the postprandial plasma TAG parameters indicated attenuated response to SE versus LE, validating the in vitro observations. The observed differences point specifically to isolated effects of SFC on PPL. Overall, this thesis evidences that the presence of solid fat decreases digestibility compared to lipids in the liquid state. It highlights that TAG melting temperature impacts digestibility, with implications for lipemia, shown both for bulk and emulsified lipids (i.e. stearic-rich IE lipids and tempered partially crystallized and undercooled palm stearin emulsions, respectively).
Date: 2019-04-29
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