Emulsions with partially crystalline solid (SE) and undercooled-liquid (LE) droplets with equivalent droplet sizes (centering ∼416 nm), surface charges (∼-56 mV), and spherical morphologies were prepared by hot microfluidization based on 10% palm stearin and 0.4% Span 60. Lipid crystallinity attenuated early gastroduodenal lipolysis in vitro ( p < 0.05), both with and without inclusion of a gastric phase ( p < 0.05). Gastric exposure, in particular acidic pH, led to partial coalescence of SE and flocculation and partial crystallization of LE, and it attenuated the rate and extent of lipolysis in both samples. In vitro shear conditions further impacted colloidal stability, particularly for SE, with implications for digestibility. Although lipid crystallinity consistently attenuated early lipolysis, gastric-phase SE partial coalescence had a relatively greater impact on digestibility than did droplet physical state. These findings show that a complex interplay exists among a droplet's physical state, colloidal properties, and digestion conditions, which combine to impact emulsion in vitro lipolysis.
Keywords: colloidal stability; emulsions; in vitro digestion; lipolysis; physical state.