Comparative interfacial in vitro digestion of protein and polysaccharide oil/water films.

The behaviour of proteins (β-lactoglobulin (βlg) and soy protein isolate (SPI)) and a surface active polysaccharide (hydroxypropylmethylcellulose, HPMC) o/w interfacial films under simulatedgastrointestinal conditions using the interfacial tensiometer Octopus were compared and related to the performance of the emulsions (using the same emulsifiers) under in vitro digestion. Theevolution of interfacial tension (γ) was used to investigate the effect of gastrointestinal fluids on o/w interfacial films. Clear differences were observed among these emulsifiers. During thegastric phase, HPMC showed the lowest change in γ values as compared to protein films. The most important changes occurred during the intestinal stage where it was observed an important decrease of γassociated with the rapid penetration of BS, followed by a lower rate of decrease attributable to the accumulation of FFA at the interface. In the last stage, the subphase was exchanged by bufferalone, to remove the reversibly adsorbed digestion products. SPI formed the most resistant interface to the remotion of digestion products, followed by HPMC and finally by βlg. The results agree withthe degree of lipolysis reported for the emulsions stabilized by these emulsifiers, which suggest that lipid digestion could be modulated by the ability of emulsifiers to prevent the BS activity (toadsorb at the O/W interface or remove the inhibitory digestion products from the interface). Thus, emulsifiers-BS interactions appears as a key factor in controlling the lipolysis.

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