Agarose-based freeze-dried capsules prepared by the oil-induced biphasic hydrogel particle formation approach for the protection of sensitive probiotic bacteria

This work reports on a simple, fast and food-grade encapsulation approach with potential for probiotic protection, which consists on the formation of agarose-based hydrogel particles. These were generated by the supramolecular self-assembly of the probiotic-containing carbohydrate solutions by dripping them into a biphasic bath with an upper oil layer, which acted as the particle-forming antisolvent, and a lower aqueous layer, where the hydrogel particles were collected. This technique, which we have named “oil-induced biphasic hydrogel particle formation”, has been used to encapsulate the sensitive strain Bifidobacterium pseudocatenulatum CECT 7765. In order to avoid agarose gelling at 40 °C before the encapsulation process, this seaweed-derived carbohydrate was combined with other hydrocolloids (alginate, whey protein concentrate, and gelatin), and the obtained probiotic-containing hydrogel particles were subsequently freeze-dried. The protection ability of this method versus directly freeze-drying the probiotic-containing solutions was demonstrated during storage and simulated in-vitro digestion. Both the formation of a continuous layer surrounding the bacteria and the optimal combination of materials (agarose providing suitable oxygen barrier and WPC with proven probiotic affinity) rendered encapsulation systems keeping viability levels required for commercial applications.