Digestion of dietary fat : gastrointestinal behaviour of emulsions and human physiological responses

Two in vitromodels were used to understand emulsion behavior and the subsequent formation of free fatty acids (FFA), monoglycerides (MG) and diglycerides (DG). Emulsions stabilized by whey protein isolate (WPI) or gum arabic (GA), varying in droplet size, were digested under intestinal conditions. Concentrations of FFA, MG and DG, assessed by gas chromatography, decreased with increasing droplet size. FFA release from gum arabic-stabilized emulsions was higher compared to WPI-stabilized emulsions showing an influence of the interface. Next, lipolysis of protein stabilized emulsions (i.e. WPI or lysozyme) and the influence of flocculation at the isoelectric point (pI) were investigated in a dynamic gastrointestinal model. The stomach properties including gradual acidification caused WPI-stabilized emulsions to cream during transition through the pI of the protein. This resulted in delayed intestinal lipolysis compared to the lysozyme-stabilized emulsion. Thus, since gastric passage affects emulsion behavior and intestinal lipolysis, the gastric passage should be part of digestion models. Next, in a human study emulsion behavior and resulting lipolytic products were related to the release of satiety hormones, satiety perception and ad libitumintake. Also, gallbladder volume and oral processing were studied. A delayed entry into the duodenum and lipolysis for the un-homogenized sample resulted in lower CCK, delayed GLP-1/PYY responses and barely gallbladder contraction compared to the homogenized emulsion. No difference was found between treatments on ghrelin, only the perception 'desire to eat´ was elevated for homogenized emulsions. Oral processing induced prolonged gallbladder contraction, but had no additive effect on other measures. A homogenous system as such is possibly not effective to induce pronounced satiety perceptions compared to phase separated or creamed systems using the same emulsifier. Moreover, the release of gastrointestinal hormones cannot directly be related to the satiating effect of food.