Developing a sandwich-like smart label from bromcresol green-loaded maple film coated with cationic guar gum for supervising fish and yogurt quality

A smart label with sandwich structure was fabricated through a top-down approach, in which the decolored maple veneer directly absorbed bromcresol green (BCG) through Van der Waals´ forces and hydrogen bonds, and cationic guar gum (CGG) layer was coated to prevented foods from being contaminated. When the bleaching time was 4 h, the carboxyl content of the veneer increased to 0.20 mmol/g, while the adsorption capacity of BCG decreased to 15.81 mg/g, which displayed a rapid and sensitive response to pH. In 95 % alcohol solutions, the release rate of BCG was only 1.47 %. When the label color varied from yellow to green, the total volatile basic nitrogen (TVB-N) value attained 19.170 mg/100 g closer to Chinese standard threshold of 20 mg/100 g, providing timely freshness information for consumers. The color changed from blue to green when the acidity of fermented milk rose to 69.892 °T (70 °T is the threshold). Overall, this work opened up a new path in the field of smart labels for supervising the food quality in real-time and offered a novel strategy for the diversified utilization of wood.