Two whey protein emulsion gels containing 10 mM NaCl (soft gel) or 200 mM NaCl (hard gel) were formed and subjected to sequential digestion, including an in vitro gastric step followed by an in vitro intestinal step. The breakdown of gel particles, stability of oil droplets, microstructure and free fatty acid release during digestion were examined. The results showed that after 60 and 240 min gastric digestion the digesta of both gels had different physicochemical forms. The 60 min gastric digesta of both gels was mainly composed of gel particles ranging from ~1 to ~1000 ??m. The 240 min gastric digesta of the soft gel mainly consisted of individual oil droplets and small gel particles (~10 ??m) while that of the hard gel mainly consisted of small gel particles (~10 ??m). During intestinal digestion, the breakup and coalescence of oil droplets occurred simultaneously for all gastric digesta. The remaining network structure of gel particles hindered their breakdown especially in the hard gel during intestinal digestion, which delayed lipid digestion significantly. Lipolytic products appeared to accumulate around oil droplet surfaces. Needle-shaped crystals that may be composed of free fatty acids were also found during intestinal digestion.
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