Repurposing of Blackcurrant Pomace via Microwave-Assisted Hydrothermal Fractionation into pH-Sensitive Films

The valorization of unavoidable food waste and repurposing through the adoption of circular, zero-waste principles is an important driver to combat global grand challenges of food security, responsible consumption and production, and, ultimately, climate change. Herein, the microwave-assisted hydrothermal valorization of blackcurrant pomace into anthocyanin (ACN), blackcurrant pectin (BCP), and defibrillated cellulose (DFC) fractions and their repurposing into pH-sensitive sodium alginate (NaAlg) films is reported. The inclusion of BCP, DFC, and ACN fractions into NaAlg matrices positively affected the antioxidant activity. The inclusion of BCP primarily influenced the mechanical properties and hydrophilicity of films. NaAlg–BCP films were able to detect ammonia, with NaAlg–BCP50 showing the most distinct color change. Moreover, NaAlg–BCP50 showed reversible color changes upon sequential exposure to NH3 and CH3COOH. Differential scanning calorimetry (DSC) showed that the films are suitable for relatively high-temperature food applications (up to 187 °C). In addition, the films demonstrated antifogging properties due to their high water vapor permeability (WVP), supporting their use in packaging for highly perishable produce. This work demonstrates the potential for reducing unavoidable food waste and repurposing it into intelligent food spoilage indicator films.