Fabrication of Electrospun Polycaprolactone Nanofibrous Mats Loaded with Purple Basil Extract (Ocimum basilicum L.) as Colorimetric pH Indicator Films

Abstract Intelligent packaging with colorimetric pH indicators revolutionizes traditional food packaging by enabling real-time food quality monitoring. This study used electrospinning to develop pH indicator films from polycaprolactone (PCL) incorporating purple basil extract (PBE). Nanofibrous films containing 0.2% PBE (PCLN_0.2PBE), 0.4% PBE (PCLN_0.4PBE), and 0.6% PBE (PCLN_0.6PBE) were fabricated using different electrospinning conditions. The PCLNs fabricated with a voltage of 20 kV and a flow rate of 1.6 mL/h exhibited the most uniform and bead-free morphology according to scanning electron microscopy. The chemical, thermal, mechanical, and wetting characterization of the films was performed by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, texture analysis, and contact angle analysis, respectively. Both PCLN_0.4PBE and PCLN_0.6PBE films displayed fast (4–5 s) and clear color transitions (Δ E > 3.5) to successive pH buffers within the range critical for food deterioration, while they exhibited excellent color changes (Δ E > 5) for pH variations of at least two units. The PCLN_0.6 PBE film displayed a Δ E of ~ 5 in only 5 min of exposure to ammonia vapor, whereas PCLN_0.4PBE showed a similar color change for over 15 min. The interaction between the films and acidic and alkaline semi-solid foods was simulated using gelatin gels at pH 2.5 and 11, respectively. Both films displayed significant color transitions (Δ E > ~ 9) within 15 min of contact with the gels, with the response from PCLN_0.6 PBE being more pronounced. The color stability in both films was maintained for up to 14 days at 4 °C, offering potential early warnings against food spoilage. PBE release was evaluated against different food simulants. The highest release occurred in 50% ethanol; the films demonstrated resistance to 3% acetic acid. The findings indicate that electrospun PCL films integrated with PBE have a promising potential to serve as colorimetric pH indicators for monitoring the freshness of food products.