Collagen peptide-loaded W/O single emulsions and W/O/W double emulsions: influence of collagen peptide and salt concentration, dispersed phase fraction and type of hydrophilic emulsifier on droplet stability and encapsulation efficiency.

Bioactive peptides hold great promise as functional ingredients, but they are susceptible to hydrolysis (e.g., protease degradation) during digestion and under different physiological conditions in the human body. Thus, bioactive peptides must be encapsulated first to preserve their innate characteristics and to ensure delivery to an absorption site at the small intestine without biodegradation. The objective of this study was to formulate stable single emulsions of water in oil (W1/O) and double emulsions of water in oil in water (W1/O/W2) containing collagen peptide as core material. In this study, the influence of the following parameters was investigated: collagen peptide concentration (0-20%), salt (0% or 1% NaCl), hydrophilic emulsifiers for the outer water phase (Tween 80, lecithin, chitosan, pectin), and the use of different inner/outer water fractions (20-50% inner water, 50-80% outer water) on the droplet stability of the W1/O and W1/O/W2 emulsions during storage. In particular, the influence of the osmolytes was investigated to evaluate the change in osmotic balance and destabilization of the W1/O/W2 emulsion system as the encapsulated peptide was also osmotically active. Tween 80-stabilized W1/O/W2 emulsions showed the best droplet stability without phase separation (d90,3 = 36.6 μm) and the highest collagen peptide retention (encapsulation efficiency > 90%). During prolonged storage, collagen peptides were released from the W1/O/W2 emulsion system without significant droplet size changes, possibly due to diffusion of the collagen peptide from the inner to the outer water phase. Therefore, our findings can be utilized for preparing stable functional foods or cosmetic products from W1/O/W2 emulsions containing bioactive ingredients.