Recent advances on intelligent food freshness indicators; an update on natural colorants and methods of preparation

Consumers’ actual demand to be informed on the quality of food items during storage and transportation drives researchers to focus on new and innovative systems with the ability to monitor any changes inside the food pack and notify the user about the quality. This can be mainly done through a type of packaging system known as food intelligent packaging. Food freshness indicators (FFI) are a cost-effective intelligent packaging approach which is applied for the real-time detection and monitoring of freshness/spoilage status of food and informing food conditions to the consumers. An appropriate FFI should have the ability to distinguish fresh, medium fresh, and spoiled food typically by the naked eyes. Some important parameters such as the type of halochromic colorants and polymer used in the FFI and method of preparation can directly affect the performance of FFI. Although the production of FFI has longstanding precedent, the use of natural dyes from various sources in the development of FFI and the application of novel methods for preparing FFI has grown due to the exceedingly research in this field. This paper presents an update review on chemical structure, pH-responsive color change mechanism as well as advantages and shortcomings of natural colorants recently used for FFI preparation. The context also aims to provide an update of recent literature on the principal and advantages of current innovative methods of FFI preparation such as layer-by-layer assembly, sol-gel, electrospinning, foam/pad development, and 3D printing.