Extraction, characterization, and multi-factor stability assessment of mulberry (Morus nigra) anthocyanins for application as natural food colorants.

Anthocyanins are promising natural alternatives to synthetic food dyes because of their safety, antioxidant functionality, and consumer preference. This study optimized the extraction, enrichment, and stabilization of mulberry (Morus nigra) anthocyanins and evaluated their physicochemical properties and storage stability for potential industrial applications. Acidified ethanol (0.1% HCl) under optimized conditions (40.0 °C, 60 min, solvent-to-solid ratio 6:1, v/w) yielded the highest extraction efficiency (83.8 ± 1.5%). Total anthocyanin content, determined by the pH differential method, reached 24.6 ± 0.2 mg cyanidin-3-glucoside equivalents per 100 g fresh mulberries. Spectroscopic and HPLC analysis identified cyanidin-3-glucoside as the dominant pigment (λmax ≈ 513 nm). The extract exhibited 16.2 ± 0.7% dry matter, 15.3 ± 0.6% soluble solids, and a natural pH of 3.2 ± 0.1. Comprehensive stability studies revealed pronounced sensitivity to light, temperature, oxygen, and pH. Anthocyanin degradation followed first-order kinetics (R2 ≥ 0.98), with an activation energy of 68.5 kJ/mol. Color retention was maximal under refrigerated, dark storage (91.5 ± 0.9%) and lowest under direct light (43.8 ± 1.7%). Enzyme inactivation (82.0 °C, 3 min), nitrogen flushing, and citric acid addition significantly enhanced pigment stability, achieving up to 98.7 ± 0.6% retention while effectively inhibiting microbial growth. Acidic pH favored the flavylium cation form, resulting in superior color intensity and structural stability. The results indicate that mulberry anthocyanins exhibit high stability and are well suited for industrial application as natural, food-grade colorants in clean-label products.