Role of Ascophyllum nodosum and Fucus vesiculosus in Improving the Stress Resistance of Lactiplantibacillus plantarum

The survival and efficacy of probiotic bacteria depend on their ability to grow under optimal conditions and withstand environmental stresses, and marine macroalgae are emerging as promising prebiotic sources that may enhance their viability. In this study the effect of <i>Ascophyllum nodosum</i> and <i>Fucus vesiculosus</i> supplementation (0.5% <i>w</i>/<i>v</i>) on <i>Lactiplantibacillus plantarum</i> was evaluated by assessing growth performance and stress resistance under different conditions, including temperatures (15, 25, 30, 37, 42 °C), pH levels (2.5, 3.5, 4.5, 6.5, 8.5), and enzymatic challenges (pepsin, trypsin, bile). Both algal supplements promoted faster initial growth between 25 and 42 °C, particularly at 37 °C, by reducing the lag phase and increasing the growth rate. Under acidic stress, survival exceeded 80% after 3 h, with significant improvements at pH 2.5 and 3.5 in the presence of seaweeds, while enzymatic assays demonstrated enhanced tolerance against pepsin, trypsin, and bile salts. Overall, supplementation with brown algal biomass provided modest but consistent benefits to <i>L. plantarum</i> growth and stress resistance, supporting the use of whole macroalgae as functional additives in probiotic formulations for both human and animal nutrition.