pH-Sensitive Cassava Starch/Onion Peel Powder Films as Colorimetric Indicators for Minced Beef Freshness Monitoring

Abstract

pH-sensitive intelligent films offer a novel strategy for real-time monitoring of food freshness via visible color changes. This study valorizes onion peel powder (OPP), a polyphenol-rich agro-industrial by-product, by incorporating it into cassava starch-based films at three concentrations (1O, 2O, 3O). Increasing OPP content led to significantly higher total phenolic and flavonoid levels, enhancing the films' antioxidant properties (<i>p</i> < 0.0001). While the films exhibited selective antibacterial effects, pronounced inhibition zones were observed against <i>Pseudomonas aeruginosa</i> and <i>Escherichia coli</i>, two relevant meat spoilage and pathogenic bacteria. The films displayed clear and gradual color shifts from light to dark brown across a wide pH range (1-13), confirming their suitability as pH indicators. When applied as labels in minced beef packaging stored at 4 °C, the films successfully tracked freshness over 13 days. Film color changes were strongly correlated with microbial load and pH variations, accurately flagging spoilage onset. These findings support the potential of cassava starch/OPP films as biodegradable, cost-effective intelligent packaging tools, contributing to food safety, waste reduction, and circular bioeconomy principles. The system provides a practical, non-invasive solution for meat freshness monitoring without requiring instrumentation.