Ethylcellulose oleogel as a prolonged release delivery system for probiotics. Development and validation of a cold-mixing method

Ethylcellulose thickened oil (EC oleogels) has a significant retarding effect on lipolysis and may be used for controlled-release formulations. However, the high temperature (above 150°C) used during the gel-forming process becomes an obvious limitation that hinders the application of EC oleogels to temperature-sensitive active ingredients. A cold-mixing procedure that could allow for an encapsulation at a temperature of around 40°C is proposed in this study. A warm solution of EC in oil is allowed to cool down, and just before the gelation, the solution is mixed with a cool oil dispersion of the heat-sensitive ingredient. The temperature drops, and the gel is solidifying within a few minutes. The evaluation shows that the oleogels formed have a lower hardness and oil entrapment than the hot-mixed EC oleogels. However, the gel character remains, displaying a comparable digestion resistance. There is a limited loss of viability of the probiotics when encapsulated in the oleogels, about 50%. The loss of viability when released from a cold-mixed oleogel under digestive conditions becomes about 90% due to the detrimental digestive environment. This observation can be compared to 99% loss when released from oil under digestive conditions. Thus, the in vitro evaluation of an EC oleogel suggests that systems formed after cold-mixing can provide prolonged delivery of oxygen and bile-sensitive bioactive ingredients without exposing them to detrimental temperatures during the formulation. • Ethylcellulose (EC) oleogels can be applied to encapsulate thermolabile ingredients. • EC oleogels accept dilution during the gelation with a limited loss of strength. • EC oleogels can protect probiotics from bile, according to in vitro results. • Cold-mixed EC oleogels provide prolonged release towards ileum and/or colon.