A pH-Responsive Biobased Indicator Film from Red Cabbage for Application in Intelligent Packaging

Abstract

This study investigates the development of a pH-responsive indicator film from red cabbage using biobased materials for application as intelligent packaging to monitor the quality of agricultural products through pH-dependent color changes. The research was divided into two parts: (1) preparation and evaluation of biobased films using starch, focusing on the effects of starch type and glycerol content on film properties, and (2) preparation and evaluation of indicator films from red cabbage in both powder and aqueous extract forms. The results revealed that the film with the best physical properties was obtained from mung bean starch with the addition of 5 mL of glycerol. The film was transparent, colorless, and had a non-sticky surface, with an average thickness of 0.22±0.01 mm. It exhibited good film-forming ability, low water absorption and solubility, as well as higher tensile strength compared to other formulations. When this formulation was further developed into indicator films incorporating red cabbage, the resulting films appeared translucent brown with non-sticky surfaces, and had average thicknesses of 0.23±0.01 mm and 0.24±0.01 mm for the red cabbage powder- and aqueous extract-based films, respectively. The powder-based film showed slightly lower water absorption and solubility than the aqueous extract-based film. Nevertheless, both indicator films exhibited reduced mechanical properties compared to the original mung bean starch film. In terms of application, the indicator film prepared from red cabbage aqueous extract demonstrated a clear and wide color response across the pH range of 1–14, whereas the powder-based film showed distinct color changes primarily in the alkaline range (pH 12–14). In conclusion, the developed red cabbage-based indicator film shows interesting potential for use in intelligent packaging to monitor food quality, enhancing safety while remaining environmentally friendly.