A pH indicator film based on sodium alginate/gelatin and plum peel extract for monitoring the freshness of chicken

To monitor the freshness of chicken, a pH-sensitive film based on sodium alginate, gelatin, and plum peel extract (SGPE) was created. Thickness, color, water contact angle, mechanical characteristics, water content, water vapor transmission, light transmission, and pH sensitivity were used to evaluate the performance of the film sample. SEM and FTIR graphs demonstrated that adding plum peel extract made the SGPE film's internal structure more denser and increased its mechanical property, while decreasing the water contact angle, water content, and WVP value. The color of the SGPE15 film clearly changed from red to yellow-green in various buffer solutions (pH = 1–14), demonstrating more pH sensitivity than the SG, SGPE5, and SGPE10 films. On day 6, when checking the freshness of chicken kept at 4 °C, the SGPE15 film's color changed from orange-pink to yellow-green with TVB-N level beyond the allowable limit (15 mg/100 g). The result revealed that the SGPE film might be applied to monitor the freshness of chicken breast flesh.