Potassium permanganate-based ethylene gas indicator of kiwifruit ripeness

A kiwifruit ripeness indicator was developed using potassium permanganate (KMnO4), an ethylene gas scavenger. A total of 500 g of kiwifruit was packaged in polypropylene (PP) containers (20 × 16 × 11.5 cm) with a heat-sealed PP, polyethylene (PE), and ethylene-vinyl alcohol copolymer (EVOH) cover film (50 µm thick) with the indicator inside, and stored at 15, 20, and 25 °C. The ethylene gas permeability of the cover films, kiwifruit firmness (ripeness parameter, ≤ 8 N), ethylene gas concentration, and indicator color were measured. The indicator changed from purple to brown. When the firmness reached 7.9 N, the ethylene gas concentrations for each cover film were different due to film permeability. The indicator color index (ΔE) for each cover film was also different and ranged from 15.2 to 23.9, falling within the visually detectable change.