Kinetic-Modelled Synbiotic and Postbiotic Microbeads from L. plantarum DHCU 70 Fermented Pearl Millet Show Gastrointestinal Resilience and Colonic Viability

Pearl millet (Pennisetum glaucum) was fermented with Lactiplantibacillus plantarum DHCU 70 to develop a cereal-based matrix for microbial encapsulation. A re-parameterized modified logistic model was fitted to viable cell growth data to identify a fermentation harvest interval associated with high cell density and fermentation-metabolite accumulation. Based on the composite desirability analysis, desirability was maximal at 17.5 h and remained on a plateau (D ≥ 0.97) from 17 to 22 h; a harvest interval of 18.0 to 20.5 h within its plateau was selected, during which viable counts reached 9.15 to 9.25 log CFU mL−1 and total measured organic acids were 27.9 to 28.7 g L−1 (maximum 29.9 g L−1 at 17.5 h). The selected fermented matrix, containing viable cells, residual soluble carbohydrate fractions and constituents derived from fermentation was incorporated into calcium-alginate–gelatin microbeads with 0.8 to 1.2 mm diameters. The bead formulation showed high retention of viable cells and measured fermentation-derived constituents during encapsulation. Under sequential simulated oral, gastric and intestinal conditions, the Ca-alginate–millet–gelatin formulation retained 6.45 log CFU mL−1, compared with 3.45 log CFU mL−1 for free cells, corresponding to a lower viability loss for encapsulated cells. FTIR analysis showed retention of characteristic hydroxyl, carboxylate and spectral bands associated with carbohydrates following encapsulation. Relative to the non-encapsulated fermented matrix, microbeads showed reduced amylolysis during the applied in vitro assays. Lyophilised microbeads exhibited a water activity of 0.40 ± 0.02, hygroscopicity of 56 ± 2.26% and 71.66 ± 26.30% rehydration after 10 min. The selection of the harvest time for encapsulation was guided by fermentation kinetics and metabolite profiles of the fermented matrix. The resulting alginate–gelatin microbeads improved the survival of Lpb. plantarum DHCU 70 relative to free cells under simulated gastrointestinal conditions tested. The formulation provides a cereal-based platform for further development of fermented functional food delivery systems.