pH-responsive chitosan/PVA-based fiber films with enhanced antioxidant and colorimetric response via pomegranate anthocyanin enrichment.

Pomegranate juice (PJ), rich in anthocyanins (ACNs), was efficiently concentrated using a nonionic acrylic polymeric adsorbent resin to develop ACNs-rich fraction aim to develop natural pH-sensitive indicators for real-time food deterioration detection. The ACNs-rich fraction was incorporated into fiber films made from two hydrocolloid matrices composed of polyvinyl alcohol, chitosan, and starch. Optimal adsorption conditions (94.0 %) were achieved at pH 2.5, with a 40-minute contact time and a PJ-to-resin ratio of 30 ml/0.7 g. Desorption reached 93.3 % using a 6-bed volume solvent and 8-minute contact time. HPLC analysis showed an 82-fold increase in anthocyanin content and a 6.2-fold rise in antioxidant activity compared to raw PJ. Isotherm and kinetic studies showed good fits with the Freundlich (R = 0.96) and pseudo-second-order (R = 0.99) models, respectively. FTIR-ATR and molecular docking analyses revealed hydrogen bonding between ACNs and the polymer matrix. The developed fiber films based on chitosan and polyvinyl alcohol exhibited ultrafine average diameters, pronounced color changes in response to ammonia exposure, and antioxidant activities that were 51.0 and 72.5 times higher than those of the unloaded control. This study introduces a novel natural indicator for real-time food deterioration and proposes optimized, scalable preparation methods with commercial potential for food packaging.