Encapsulation of probiotics in freeze-dried calcium alginate and κ-carrageenan beads using definitive screening design: A comprehensive characterisation and in vitro digestion study

This research aimed to evaluate the encapsulation of the probiotic strain, Streptococcus thermophilus, in hydrogels employing sodium alginate (SA) with κ-carrageenan (κC) in gelation baths with varying salt concentrations (CaCl₂ and KCl) followed by freeze-drying. The experimentation was conducted at varying levels of κC (0-0.5 % w/v) and SA (2-4 %). Freeze-dried hydrogels were evaluated based on encapsulation efficiency and loss of viability and further characterised. The study could successfully establish an encapsulation efficiency of 87.814 % and a viability loss of 1.201 log CFU·g^-1 for the optimised samples. The SEM micrographs of the optimised Ca-alginate/κC hydrogels exhibited a much denser network with fewer pores. The influence of SA/κC in the beads was confirmed by FTIR and DSC, where distinct peak shifts were observed, which indicated the presence of κC and SA polymers. The probiotic survival under simulated gastrointestinal tract (GIT) conditions, performed in accordance with the INFOGEST protocol, indicated that the optimised Ca-alginate/κC beads had a lower rate of release in the gastric phase and a much higher rate of survival and release in the intestinal phase than the control sample. The swelling behaviour of beads varied due to varying pH in both gastric and intestinal phases, and the κC in the optimised beads affected the swelling ratio significantly.