Precise-color-mutation designing and programmable drop-on-demand printing for intelligent package of shrimp

Biosafe colorimetric labels that can accurately evaluate food freshness have been widely investigated in recent years. The colorimetric macro-array sensor, with the composite solution of curcumin, alizarin and acetic-acid as the indicator, was prepared by means of a self-developed 2D printing device to detect shrimp freshness. The results evidenced the sensor which had high stability, uniform color distribution and great sensitivity could be drop-on-demand printed in batches under the premise of micro-printing. When the TVB-N content of shrimp exceeded 20 mg/100g at all observed temperatures, the sensor abruptly turned from yellow to reddish-brown meanwhile the ΔE value raised sharply, indicating that there was a color mutation at the critical value of shrimp freshness. The macro-array sensor could be recognized by the smartphone to obtain the correlation between the color information (RGB) and TVB-N content, by which the shrimp freshness was determined. Furthermore, the correlation was verified through the WeChat mini-program. When the R value was less than 200 or the G value was below 140, the sensor was brown, suggesting the sample was inedible. Consequently, the system can be applied in food quality control throughout the supply chain.