Functional Food Development from Agro-Industrial Fruit and Vegetable By-Products: Fiber-Degrading Capacities of Indigenous Lactic Acid Bacteria

Valorizing fruit and vegetable peel residues into functional, fibre-enriched foods requires microbial starters that can both degrade complex plant polysaccharides and deliver health-relevant metabolites under food-grade safety standards. Lactic acid bacteria (LAB) are an attractive candidate for this role given their long history of safe use in fermentation, yet their capacity to degrade complex dietary fibre, as opposed to simple sugars, remains under-characterized, particularly in indigenous strains adapted to non-industrial food ecosystems. We conducted a comprehensive functional and genomic analysis of 84 LAB isolates belonging to 17 different species, sourced from traditional Moroccan dairy products (eg, Lben, Jben , and Raib ). Isolates were screened for hydrolytic activity on natural fruit and vegetable fibers (apple, banana, carrot, lemon, and orange) and purified polysaccharides. Quantification of extracellular enzymatic activity was performed using the colorimetric dinitrosalicylic acid (DNS) method to measure the release of reducing sugars. Specific activities (U/mg) were determined by normalizing sugar release against protein concentrations measured via the Lowry assay. Top-performing strains underwent whole-genome sequencing (WGS) to annotate carbohydrate-active enzymes (CAZymes), identify metabolic gene clusters (MGCs) for SCFA production, and perform safety assessments according to EFSA guidelines. Initial screening revealed that 47.6% of isolates displayed fibrolytic activity on at least one natural fiber, with apple and banana being the most frequently degraded substrates. Ten high-performing strains demonstrated broad extracellular hemicellulolytic activity, including xylanase, arabinoxylanase, and lichenase, while exhibiting moderate cellulolytic capacity. DNS assays quantified a broad spectrum of specific activities, ranging from 0.45 to 16.64 U/mg, with lichenan (7.24 ± 3.73 U/mg) and galactomannan (7.01 ± 3.43 U/mg) being the most efficiently degraded substrates. Genomic analysis of seven high-performing strains revealed a diverse CAZyme repertoire (171-225 enzymes per genome) enriched in glycoside hydrolases (GH43, GH51, GH28) and carbohydrate esterases (CE1, CE4) dedicated to fiber debranching and pectin degradation. Furthermore, genome mining with gutSMASH predicted metabolic gene clusters (MGCs) for acetate production in all strains, with Enterococcus genomes additionally harboring PFOR and uric acid-to-SCFA pathway genes, indicating genome-encoded potential for SCFA biosynthesis that awaits direct experimental confirmation. Safety assessments confirmed the absence of hemolysis, biogenic amine production, and critical acquired resistance genes. These results identify Moroccan dairy-derived LAB, induced directly by real fruit-peel substrates rather than purified model fibres, as promising starter candidates for converting agro-industrial peel by-products into fibre-modified functional foods and synbiotic formulations with predicted SCFA-supporting potential. Validating fibre degradation and SCFA output of selected strains directly in food matrices, such as peel-fortified fermented dairy products, is the priority next step toward translating these strain-level capacities into a deployable food application.