Factors affecting lipase digestibility of emulsified lipids using an in vitro digestion model: Proposal for a standardised pH-stat method

The control of lipid digestibility within the human gastrointestinal tract is important for the development of many functional food and pharmaceutical products. The influence of product composition and microstructure on lipid digestibility is typically studied using in vitro digestion methods. This article focuses on the impact of various experimental factors on lipid digestion in oil-in-water emulsions, using a pH-stat method that simulates the small intestine. The rate and extent of lipid digestion were found to increase with: increasing lipase (from 0 to 4.8 mg/ml), decreasing bile extract (from 20 to 0 mg/ml), increasing CaCl2 (from 0 to 20 mM), decreasing lipid (from 2.5 to 0.1 wt.%); decreasing droplet diameter (from d = 800 to 200 nm), and decreasing fatty acid molecular weight (medium chain triglycerides versus corn oil). These affects are interpreted in terms of the surface area of lipid exposed to the aqueous phase, and factors affecting the accumulation of reaction products (fatty acids) at the oil–water interface. Based on our own and others’ work, we propose a standardised in vitro digestion model to test emulsified lipids, based on pH-stat titration. This study has important implications for designing and testing delivery systems that control lipid digestion using the pH-stat method.