In vitro study of intestinal lipolysis using pH-stat and gas chromatography

Developing healthy products requires in-depth knowledge of digestion. This study focuses on lipid digestion in relation to emulsion properties typically followed by pH-stat. Although this is a fast and easy method to follow the overall digestion, it provides no details on lipid digestion products. Thus, the aims of the present study were to use gas chromatography (GC) to determine all products present during lipolysis, i.e. monoglycerides (MG), diglycerides (DG) and triglycerides (TG), and to compare this method with the pH-stat method for free fatty acids (FFA). Fine, medium and coarse emulsions stabilized with two different emulsifiers (whey protein isolate (WPI) or gum arabic) were digested under in vitro intestinal conditions. Although the amount of FFA increased for both methods for WPI stabilized emulsions, the amount of FFA was 2–3 times higher when determined by GC compared with pH-stat. GC analysis showed decreasing amounts of MG and DG with increasing droplet size for both emulsions. Molar ratios of FFA/DG and MG/DG were twofold higher for WPI than for gum arabic stabilized emulsions. This indicates that the total production of lipolytic products (i.e. FFA + MG + DG) depends on the droplet size and the emulsifier but their proportions only depend on the emulsifier. Although pH-stat provides a fast measure of FFA release, it is influenced by the emulsifier type at the oil–water interface and therefore care should be taken when interpreting pH-stat results. We suggest combining this method with GC for accurate FFA determination and further evaluation of all lipolytic products