Novel Probiotic Candidate with in vitro Antidepressant-Like Activity: Its Isolation, Identification, and Microencapsulation

We report for the first time the usage of in vitro double indicators (ability to secrete L-tryptophan and dopamine, anti-inflammatory effect) for the isolation of probiotic candidates with potential antidepressant activity. Six strains of lactic acid bacteria (LAB) and four LAB with great ability to produce dopamine (84.4–320.4 μmol/L) or L-tryptophan (389.6–707.2 μmol/L) were sourced from human feces and traditional fermented vegetables, respectively. Therein, five LAB from human feces were found to either possess the virulent efaA and gelE genes or exhibit the hemolytic activity, thus cannot be regarded as safe candidates for food application. The four safe LAB from fermented vegetables belonged to L. paraplantarum and L. plantarum (LP) species, and the last LAB from human feces was identified as Weissella confusa. In comparison, the LP-B2 strain exhibited a higher anti-inflammatory function by significantly decreasing the levels of IL-1β and IL-6 and downregulating TLR-2 expression in RAW 264.7 macrophages induced by lipopolysaccharide. Furthermore, this strain exhibited the highest adhesion ability to the Caco-2 cell line (29.2 ± 7.2 %). However, a notable decline in its viable counts from 7.7 ± 0.6 to 5.6 ± 0.1 log₁₀ cfu/mL under simulated gastrointestinal conditions underscores the importance of encapsulation technology against the adverse factors during digestion. Therefore, the pH-responsive hydrogels fabricated from Millettia speciosa Champ cellulose were employed to encapsulate the LP-B2 strain, which finally showed the protective effects, with the viability of encapsulated LP-B2 surpassing the minimum effective count in the intestine. Overall, the LP-B2 strain could be regarded as a probiotic candidate with great potential application against depression. This work provides an available reference for the initial isolation of probiotics with the function of anti-depression.