Starch and Agar-Based Color-Indicator Films Integrated with Shikonin for Smart Packaging Application of Shrimp

Shikonin extracted from Lithospermum erythrorhizon was employed to develop pH-indicating biodegradable starch- and agar-based films using a solution casting method. The Fourier-transform infrared spectroscopy results confirmed shikonin was incorporated successfully into the biopolymers. The addition of shikonin increased the film properties such as UV-light barrier, mechanical strength (7 and 3%), and water vapor permeability (25 and 18%) of the starch/agar-based film. In addition, the shikonin-added composite film showed potent antioxidant activity and some antibacterial activity (Listeria monocytogenes). The composite film displayed excellent color change properties from red to blue in buffered or gaseous environments at various pH values. In addition, the indicator film exhibited a sensitive and rapid color change when exposed to ammonia vapor. When used in shrimp packaging, the film shows a distinctive color change from reddish-pink to blue-violet, indicating the onset of shrimp spoilage. This study provides a way to design a commercial intelligent pH indicator that can meet the reference aspect according to the standards and requirements of the food industry.