Prebiotic Potential of Composite Flour From Green Banana Peel, Carrot Bagasse, and Orange Peel

The valorization of agro-industrial by-products as functional food ingredients represents a promising strategy for developing sustainable prebiotic sources. This study aimed to formulate and optimize composite flour derived from green banana peel, carrot bagasse, and orange peel, and to evaluate its physicochemical characteristics, inulin recovery, and probiotic growth-promoting as potential prebiotic composite flour. Sixteen formulations were generated using a D-optimal mixture design to assess proximate composition, inulin yield, resistance to simulated gastrointestinal conditions, and stimulation of probiotic bacteria. The composite flours exhibited low moisture (6.70–7.05%), high dietary fiber (12.5–13.25%), moderate protein (7.0–7.6%), and low fat (2.4–2.85%), indicating suitability for functional food applications. Inulin extraction ranged from 12.2% to 19.8%, with the highest yield obtained from a banana-dominant blend. The extracted inulin showed a molecular weight of ~6.0 kDa and a degree of polymerization (DP) of 21, consistent with a strong prebiotic profile. Mixture-design optimization predicted that a formulation containing 51.6% banana peel, 20.1% carrot bagasse, and 28.3% orange peel maximizes both inulin yield and probiotic growth. Cultivation with this formulation supported the proliferation of Lactobacillus rhamnosus GR-1 and Bifidobacterium longum BB536, reaching 9.8 × 10⁸CFU mL⁻¹. Simulated gastrointestinal assays further demonstrated enhanced survival of these probiotic strains in the presence of the composite flour. The results highlight the synergistic contribution of banana-derived fructans and citrus pectic oligosaccharides (POS) in promoting probiotic growth. Overall, this study demonstrates the potential of fruit and vegetable processing residues as sustainable substrates for the development of value-added prebiotic ingredients suitable for functional food formulations.