Response Surface Methodology-Based Optimization of a Synbiotic Pennisetum Glaucum-Carica Papaya Granulate: Composition and Sensory Evaluation

Background: Synbiotic formulations are increasingly recognized for their ability to support gastrointestinal health, immune resilience, and nutrient utilization, particularly in individuals exposed to travel-related physiological stress. This study aimed to develop and optimize a millet-based synbiotic granulate enriched with Carica papaya pulp and probiotic strains (Pediococcus acidilactici, Lactiplantibacillus plantarum, and Limosilactobacillus fermentum) for improved sensory quality and desirable physicochemical properties. Methods: A face-centered central composite design (CCD) within Response Surface Methodology (RSM) was employed to evaluate the combined effects of papaya pulp and probiotic blend concentrations on sensory attributes. Thirteen formulations were prepared and evaluated by 10 semi-trained panelists using a 9-point hedonic scale. Statistical analysis was performed using Design-Expert software version 13 (Stat-Ease Inc., Minneapolis, MN, USA). Regression analysis and analysis of variance (ANOVA) were used to evaluate the models and optimize the formulation. The optimized formulation was further characterized for moisture content, water activity, pH, titratable acidity, solubility, and bulk density. Results: The optimum formulation contained 30 mL of papaya pulp and 1.25 g of probiotic blend, achieving the highest sensory acceptability with an overall desirability of 0.89. The optimized granulate exhibited low moisture content (3.85 ± 0.03%), contributing to improved storage stability; low water activity (0.34 ± 0.01); pH 4.52 ± 0.01; titratable acidity of 0.79 ± 0.01% lactic acid; high solubility (93.6 ± 0.4%); and bulk density of 0.51 ± 0.01 g/cm³.These properties could represent the physicochemical quality and storage stability of the synbiotic granulate. Statistical validation confirmed the adequacy of the optimization models for predicting the sensory responses. Conclusion: The developed synbiotic granulate combined favorable sensory acceptance with desirable physicochemical characteristics, demonstrating its potential as a shelf-stable functional food. The formulation may provide a convenient nutritional option for long-distance travelers and other individuals exposed to travel-related physiological stress.