Emulsions Stabilised by Polyethylene Glycol (PEG) 40 Stearate and Lactoferrin for Protection of Lactoferrin during In Vitro Digestion

Polyethylene glycol (PEG) and its derivatives are widely used in delivery systems to protect bioactive peptides and proteins against premature degradation. In this study, we sought to understand whether or not bioactive proteins at the interface of emulsions can be protected by PEG chains during in vitro gastrointestinal digestion. We designed an emulsion stabilised by both PEG 40 stearate (PEG 40 St) and a bioactive protein, bovine lactoferrin (LF), and we monitored the fate of LF during in vitro digestion. The PEG–LF emulsions displayed a droplet diameter of 200 nm and remained colloidally and morphologically stable for at least 2 h in the simulated gastric fluid; in contrast, the control emulsions with LF alone showed droplet flocculation. After 2 h of gastric digestion, the LF in these emulsions was largely protected (84% remaining), whereas only 23% LF remained in the control emulsions. This protective effect on LF might be related to an inhibition of pepsin activity by PEG 40 St, independent of the location of the LF.Under intestinal conditions, the PEG–LF emulsions had good stability and slower lipolysis than the control emulsions, but LF was prone to immediate degradation within 5 min, regardless of the protection fromPEG 40 St, suggesting that PEG 40 St had no inhibitory effect on pancreatic proteases. Overall, this work shows promise for using PEG 40 St, a food-grade emulsifier, to prevent premature gastric digestion of bioactive proteins following oral delivery.