Multiple-layered coatings on l-glutamine solid microparticles for the retention during storage and enteric delivery during in vitro digestions

The objective of this work was to study delivery systems of water-soluble bioactive compounds using solid/oil/water emulsions to minimize the release during storage and gastric digestion. Spray-dried glutamine solid particles were suspended in milk fat that was emulsified by whey protein isolate or sodium caseinate at neutral pH as primary emulsions, followed by deposition of pectin at pH 3.0 to obtain secondary emulsions. Zeta-potential results verified the preparation of secondary emulsions. Secondary emulsions showed a higher efficiency of encapsulating glutamine and retaining glutamine during storage. For emulsions reconstituted from spray dried secondary emulsions, <20% release of glutamine was observed at pH 2.0–7.0 after 2-week refrigerated storage. The secondary emulsions retained glutamine during the 2-h simulated gastric digestion better than primary emulsions and showed gradual release to >90% after the subsequent 4-h simulated intestinal digestion. Therefore, the solid/oil/water secondary emulsions can be used as delivery systems of water-soluble bioactive compounds.