Redox enhancement of lactic acid bacteria by natural betalain pigments derived from agro-industrial residues for health-oriented food solutions

Abstract

This study explores the valorization of Beta vulgaris and Opuntia ficus-indica residues as natural sources of betalains—primarily betacyanins (Btc) and betaxanthins (Btx), respectively—for application in bioactive coatings of Lactobacillus bulgaricus (L.b) and Lactococcus lactis (L.lac). To identify the most suitable green solvent for extracting the target compounds, the COSMO-SAC thermodynamic model was employed, providing a predictive and sustainable approach to solvent selection. Subsequently, the extracted betalains were incorporated into bacterial coatings. Antioxidant capacity, evaluated via DPPH and ABTS assays, showed significant enhancement in radical scavenging activity for coated strains compared to uncoated controls (10–20 %). Coatings containing Btc from B. vulgaris and the reference compound catechin achieved the highest antioxidant performance, reaching ∼85 % scavenging. Btc-based coatings consistently outperformed Btx-based ones, with IC₅₀ values approximately three times lower for L.b strains. Viability assessments demonstrated that coatings protected and supported bacterial growth. When applied to yogurt formulations, the coated bacteria maintained their antioxidant enhancement, increasing radical scavenging activity from ∼45 % (control) to ∼63 % at the highest concentration (Sx3 = 3-fold 1–2 × 10⁹ CFU/mL), also imparting increased redness. These findings highlight the potential of betalain-rich coatings from agro-industrial residues as a sustainable strategy for developing functional dairy products with improved probiotic viability, antioxidant properties, and tailored sensory appeal.