A Polydiacetylene-Based Colorimetric Sensor as an Active Use-By Date for Plant-Based Milk Alternatives

Existing date marking tools, such as use-by and sell-by dates, fail to inform decision-making throughout food distribution because they do not adapt to storage conditions such as temperature. Polymer-based sensors can be incorporated into food packaging to provide an indication of food quality in real time, which can greatly reduce waste. This work identifies free fatty acid (FFA) as a marker for the quality of plant-based milk and demonstrates the first detection tool for the freshness of almond milk using phospholipid-doped polydiacetylene (PDA) vesicles. The sensor discriminates between triglycerides and FFA by a visible color change and can therefore be used to track fat metabolism during food spoilage. The interaction between FFA and PDA is investigated by electron microscopy and dynamic-light-scattering studies. PDA vesicles are then fabricated in agarose and used to discriminate between fresh and spoiled almond milk. Upon exposure of the PDA/agarose sensor to spoiled almond milk, a visible blue-to-red color change is induced in the film, which is correlated with FFA concentration in the samples. Incorporation of this technology into food packaging can be used to indicate food quality in real time, surpassing the efficacy of current date marking tools to reduce food waste.