pH sensitive indicator film based intelligent packaging systems of perishables: Developments and challenges of last decade

[Display omitted] •Food freshness indicators (FFI) keep consumers informed on imperceptible changes in food quality.•Halochromic indicators are sustainable, effective and novel tools to evaluate dynamic shelf life.•Selective & low pH sensitivity, better thermal and color stability and high water solubility are researchable issues.•Quality monitoring, freshness indication and product tractability are primary drivers. Consumers’ demand for novel and non-destructive systems to assess food freshness in real time has led to the development of halochromic or pH-sensitive dyes based freshness indicators (FI) as affordable technique for intelligent monitoring of perishable food. However, the genuine concern regarding the toxicity and deleterious health effect of incorporating conventional synthetic dyes in commercially available halochromic freshness indicators (i.e. fresh tag, checkpoint, and sensorQ) and their sole purpose of monitoring the freshness status of muscle foods (i.e. fish, meat, beef, and shrimp) have led to the revolutionary idea of developing a non-toxic, chemical-free, and sustainable FI based on natural pH-sensitive dyes and polymer matrix. This review delves into significant advances in the chemistry, composition, production, food interaction, stabilization and broad applications of pH-sensitive dyes in the food sector. Unfortunately, the pH-sensitive dyes have reported limited applications in fresh fruit and vegetable industry due to challenges like erratic fluctuations in pH as influenced by factors i.e. high respiration, faster ripening, and environmental changes, inability to distinguish ripening from spoilage, and complex standardization process for specific commodities. These issues merit the demand for further investigations to ensure the utilization of these smart monitoring systems in the modern industry for perishables. The use of FI can potentially play a significant role in reforming food industry, enhance consumer safety, reduce the risk of foodborne illnesses, and aid in the development of a more efficient and sustainable food supply system. Exploration of new natural ingredients and high sensitivity indicators for both animal and plant food products shall drive the innovations in FI for the food industry.