A novel colorimetric indicator film based on watermelon peel pectin and anthocyanins from purple cabbage for monitoring mutton freshness

•Purple cabbage extract (PCE) was incorporated into watermelon peel pectin (WMP) to develop an intelligent film.•WMP films containing the PCE had an excellent sensitive color response to pH.•The addition of an appropriate amount of the PCE (≤1.5%) could improve the properties of the WMP film.•The WMP/PCE1.5% film could discriminate between fresh and spoiled mutton through color change (mauve → baby blue). Novel films based on watermelon peel pectin (WMP) incorporated with purple cabbage extract (PCE) were developed for monitoring the freshness of mutton. The FTIR result showed that WMP and PCE interacted through hydrogen bonds. Low PCE content (≤1.5%) could be well dispersed in the film matrix, resulting in an enhancement in light transmittance, mechanical properties, barrier properties, and thermal stability. Excessive addition of PCE destroyed the compact structure of the film and decreased the comprehensive properties. The antioxidant and antimicrobial activity of WMP/PCE films were proportional to the amount of incorporated PCE. Moreover, the color of the film deepened as the PCE content increased. The film had excellent color stability and pH response properties. The WMP/PCE1.5 film color varied from mauve to baby blue according to the quality of mutton (fresh to spoiled). Our results suggested that the WMP/PCE film might have great potential for monitoring the freshness of mutton.