Release of amino acids encapsulated in PGPR-stabilized W/O/W emulsions is affected by temperature and hydrophobicity

Double or multiple emulsions have been under study for several decades, due to the possibility of encapsulation and controlled release of various bioactive compounds. This contribution focuses on the decisive parameters for encapsulation and release in double emulsions by considering different amino acids at different environmental conditions. Laser diffraction analysis showed that the double emulsion average droplet size increased from 50 up to 90 µm after 32 days of storage. The emulsions at 4 °C showed a higher increase compared to 37 °C. Dilution in SDS solution revealed that this droplet size increase was due to aggregation rather than coalescence. The results showed that there was no significant change in the entrapped water volume fraction of the double emulsions during 2 weeks of storage. Amino acids were encapsulated within the internal aqueous phase with an efficiency of at least 80%. Regarding the release of the entrapped amino acids, it was found that both the temperature and the hydrophobicity of the amino acid had a significant effect. Fastest release was found at the highest temperature studied (i.e. 37 °C), which was thought to be due to the higher solubility and faster diffusion rate of the amino acid in the oil phase. As hydrophobicity increased, the released amino acid concentration also increased. The pH, on the other hand, did not have a significant effect on the release within the pH range considered (i.e. 7-10). The constant internal water volume fraction, together with the significant effect of temperature and hydrophobicity, indicated that the main release mechanism of amino acids in double emulsions is by direct diffusion from the internal to the external aqueous phase.