EMULSIFICATION AND LIPOLYSIS OF TRIACYLGLYCEROLS ARE ALTERED BY VISCOUS SOLUBLE DIETARY-FIBERS IN ACIDIC GASTRIC MEDIUM IN-VITRO

This in vitro study was designed to test the hypothesis that soluble d ietary fibres can alter the process of intragastric lipid emulsificati on and possibly subsequent triacylglycerol lipolysis. Three guar gums, two pectins and gum arabic were dissolved in acidic gastric medium in the concentration range 0.3-2.0% (w/v). Viscosities of fibre solution s were measured and apparent viscosities varied over a wide range (0.7 -77 mPa . s). Emulsification of a lipid mixture (triolein/phosphatidyl choline/cholesterol) was performed under mild conditions in the presen ce of increasing concentrations of soluble fibres. The amount of emuls ified lipid was not affected whereas the size of the emulsified drople ts was increased by raising the concentration of viscous fibres only, The droplet size (r = 0.75, P = 0.006) and overall droplet surface are a (r = -0.69, P = 0.009) were strongly correlated with the medium visc osity in the range 0-20 mPa . s. The addition of solutions of viscous fibres to a preformed standard emulsion did not change the initial vel ocity of human gastric lipase reaction. Conversely, when emulsions pre pared in the presence of fibres (i.e. with different droplet sizes) we re incubated with excess gastric enzyme for 2 h, the high-viscosity gu ar gum significantly reduced the extent of triacylglycerol lipolysis, as compared with control and low- or medium-viscosity fibres, In concl usion, the data obtained show that reducing emulsification of dietary lipids in the mildly acid medium found in the stomach is a mechanism b y which soluble viscous fibres can alter lipid assimilation.