Static in vitro Digestibility Impacted by Emulsion Crystallinity Under Different Experimental Conditions

Understanding better how triacylglycerol (TAG) crystallinity alters lipid digestion should help to clarify the contributions of dietary lipids to postprandial lipemia. The static in vitro digestibility of o/w Span 60 emulsions with similarly sized (~ 500 nm in diameter) palm olein (PO) control or palm stearin (PS) droplets tempered to contain maximal (PS-SE) and partial (PS-SE-25 °C) crystallinity or to remain undercooled (PS-LE) at 37 °C was compared. With low shear and no preceding gastric phase, duodenal lipolysis quantified using a commercial enzymatic assay did not differ up to 10 minutes (p> 0.05) while particle size also did not differ (p> 0.05). Lipolysis then trended higher for the liquid emulsions (i.e., PO and PS-LE), but ultimately did not differ between samples. With low shear gastro-duodenal digestion, PO hydrolysis was unexpectedly lower compared to PS-SE and PS-LE throughout the duodenal phase potentially due to higher particle diameter and stabilizing effects of TAG crystallinity on colloidal properties. Higher shear in the gastro-duodenal digestion attenuated early lipolysis for all PS emulsions but not PO which was digested faster up to 60 minutes and differed from the other samples (p< 0.05). The results were related to differences in particle size such that the extra shear redispersed the acidic-flocculated PO droplets and this may have occurred to a lesser extent in the presence of crystalline TAG. The PS-LE sample, although liquid initially, experienced low level crystallization during digestion which led it to differ from the liquid control PO. Therefore, particle size measured during in vitro digestion indicated that TAG crystallinity differences affected colloidal behaviour and had an overall attenuating effect on lipid digestibility under the most physiologically relevant conditions. The work has relevance to postprandial lipemia since lipid digestibility may modulate lipemic response.