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How it works

Chemical Sensors

  • Filter paper strips impregnated with anthocyanin and curcumin solutions;

  • Glycerol added to retain moisture and improve the color-change process;

  • A 3D-printed PLA frame to keep the filter paper strips with indicators in a fixed position.

 

Computer Vision Algorithm

  • ArUco markers printed on the sensor frame for automatic localization;

  • Real-time video stream analyzed in the HSV color space (Hue–Saturation–Value);

  • The algorithm extracts the average hue over a predefined area of the sensor.

 

Classification

Based on calibrated thresholds, the system assigns one of three freshness states:

  • FRESH – low pH, pigments within their initial color range

  • WARNING – intermediate pH, visible change in hue

  • SPOILED – high pH, strong color change, confirmed especially by curcumin

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The result is displayed live on the screen, transforming natural color changes into a clear digital signal.

Meat spoilage indicator system EN.jpg

Experimental Results

  • In a sealed testing chamber with controlled ammonia vapors, the sensors showed clear and repeatable color transitions.

  • Anthocyanin responded in approximately 15–30 seconds, transitioning from fresh to warning/spoiled.

  • Curcumin showed changes in about 10–20 seconds, confirming spoilage.

  • Graphs of digital hue versus time/pH showed a smooth, nearly linear trend, indicating reliable freshness tracking.

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