Development of shrimp freshness monitoring labels based on betacyanins-rich red pitaya peel and cassava starch

Red pitaya peel betacyanins-based food freshness monitoring labels are emerging intelligent packaging materials. However, the extraction and purification of betacyanins from red pitaya peel are uneconomic. In this study, red pitaya peel powder was directly complexed with cassava starch in different ratios (20:80, 40:60, 60:40 and 80:20) to produce shrimp freshness monitoring labels. Results showed the labels had 0.107–0.134 mm thickness, 18.44–30.15% moisture content, reddish-violet color, 0.46–0.65 cm 3 mm m −2 day −1 atm −1 oxygen permeability, 3.11 − 3.78 × 10 −10 g m −1 s −1 Pa −1 water vapor permeability, 54.0–70.3° water contact angle, 5.97–21.61 MPa tensile strength, and 3.64–11.48% elongation at break. Meanwhile, the labels showed strong light blocking ability, antioxidant activity and antibacterial activity. The physical and functional properties of the labels were closely associated to the ratio of red pitaya peel powder and cassava starch in the labels. Notably, the labels presented obvious color changes from reddish-violet to purple and final brown when they were exposed to ammonia atmosphere and used to monitor the freshness of shrimps. In addition, the labels had good color stability when they were stored at 20 °C in the natural light for 27 days. Above results suggested the labels could be used as intelligent packaging materials in food industry. Graphical abstract