Examining Committee
Dr. Iris Joye, Chair
Dr. Michael Rogers, Advisor
Dr. Amanda Wright, Co-Advisor
Dr. Maria Corradini, Department Member

TITLE: LIPID CRYSTALLINITY IN O/W EMULSIONS ALTERS IN VITRO LIPID DIGESTION KINETICS

ABSTRACT: The influence of emulsion lipid droplet physical state on in vitro digestibility is compared for ten 10% oil-in-water (O/W) emulsions stabilized with 0.8 weight (wt.) % Tween 80.  The lipid phase contained palm olein (PO) and palm stearin (PS) at varying PO:PS ratios (0:100, 25:75, 50:50, 75:25 and 100:0 (PO:PS)) produced by high-pressure, hot homogenization and then tempered to be either partially crystalline (CR) (cooled from ~80 to 4°C for 30 minutes to induce crystallization) or to remain as an undercooled liquid (UC) (cooled from ~80 to 37°C and held at 37°C to maintain metastable liquid state). Initial particle characterization included size distribution, zeta potential, and microstructure are determined and evaluated over 7 days to ensure changes in lipid digestibility are reflective of changes in the crystalline state. Digestibility is measured with the TIM-1, an in vitro dynamic model simulating upper gastrointestinal (GIT) digestion, and then bioaccessibility parameters obtained from the log logistic model are correlated to differences in lipid physical state. Induction times did not vary significantly, with the exception of PO (i.e. 183.6 min for CR and 215.3 min for UC). Rate constants of digestion are significantly different between the PO (K = 1.3 x 10⁻² min⁻¹ (1 x 10⁻² - 1.2 x 10⁻² min⁻¹)) and PS (K = 9.4 x 10⁻³ min⁻¹ (0 x 10⁻² -7.8 x 10⁻³ min⁻¹) emulsions. No significant differences in digestion kinetics for blends that remained as UC liquid particles are seen. Statistically significant differences in overall bioaccessibility between PO and PS in both CR and UC emulsions were found, with the undercooled being to a lesser extent (p<0.05). In the CR emulsions the PO bioaccessible fraction was 90.58% whereas PS was 60.13% and in UC emulsions PO was 95.55% and PS was 77.48%.  Overall, these results confirm that solid fat content of lipid particles within an O/W emulsion impacts the rate and extent of lipid digestion.