Bulk and interfacial interactions between hydroxypropyl-cellulose and bile salts: Impact on the digestion of emulsified lipids
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Hydroxypropyl-cellulose (HPC) is a surface-active, non-digestible polysaccharide, commonly used in food emulsions as thickener and/or emulsifier. Due to these dual characteristics, HPC is a potential ingredient to modulate lipid digestion. Since bile salts (BS) are key players during lipid digestion, the aim of this work was to investigate the impact that interactions of HPC with BS has on the digestion of emulsified lipids. We studied the effect of two BS species differing in bile-acid moiety, sodium-taurocholate (NaTC) and sodium-taurodeoxycholate (NaTDC). A Quartz-Crystal-Microbalance (QCM-D) was used to evaluate HPC-BS interfacial interactions during the sequential and simultaneous adsorption of both components at a hydrophobic surface, while microDifferential-Scanning-Calorimetry was used to examine bulk interactions. In vitro lipid digestion was studied by using a pH-stat method. Results showed that, under fed-state conditions, NaTDC micelles were more effective at displacing a pre-adsorbed HPC layer from the surface than NaTC monomers. Nevertheless, HPC was resistant to complete displacement by both BS. Additionally, HPC was more susceptible to interact with NaTDC in the bulk, compared to NaTC, which made the adsorption more competitive for NaTDC. The reduced amount of free NaTDC in solution could explain the delayed lipolysis shown by HPC-stabilized emulsions when NaTDC was used to simulate duodenal conditions. These findings show that the delay of lipid digestion by HPC is due to the combined effect of HPC-BS interfacial and bulk interactions, with BS-binding in solution mostly contributing to this effect, and the BS molecular and micellar structure playing essential roles on both situations.