Enzymatic time-temperature indicator with cysteine-loaded chitosan microspheres/silver nanoparticles.

A time-temperature indicator (TTI) based on acid-base reaction was developed by applying a new pH dye composed of cysteine-loaded chitosan (Cys-CS) microspheres and silver nanoparticles (AgNPs). It was hypothesized that cysteine released by the disintegration of Cys-CS microspheres at a critical pH would cause AgNPs to aggregate, leading to color change. Cys-CS microspheres were produced as water-in-oil (paraffin oil, MCT oil, soybean oil) emulsions according to the KOH addition method. An enzymatic TTI was made using glucose oxidase, glucose, and catalase. Only paraffin oil produced Cys-CS microspheres (average diameter, 335 ± 100 µm), whereas the others did not, probably due to saponification with KOH. FTIR analysis confirmed that cysteine was encapsulated in the microspheres. The microspheres disintegrated at pH 6.18 in a titration test. The TTI pH gradually decreased and showed a sudden color change at pH 6.10, which was similar to the critical pH of microsphere disintegration.

Polycaprolactone/Anthocyanin-Based Electrospun Volatile Amines Gas Indicator with Improved Visibility by Varying Bi-Solvent Ratio: A Case of Intelligent Packaging of Mackerel.

Electrospun nanofibers have been applied as a new technology for gas indicators in food intelligent packaging. A poly(ε-caprolactone) (PCL)/red cabbage anthocyanin (RCA)-based nanofiber volatile amines gas indicator was developed by applying a bi-solvent of acetic acid (AA) and formic acid (FA) in electrospinning. The visibility of color change was improved from pink to blue, compared to blue to yellow-green, when using a single solvent of AA. The solutes of PCL (12.5, 15, 17.5, and 20%) and RCA (10, 20, 30, and 40%) and the solvents of AA/FA (9:1, 7:3, 5:5, 3:7, and 1:9) were applied in electrospinning under the condition of 12.5 cm, 1.0 mL/h, and 20 kV. The optimal microstructure with the thinnest fiber diameter and constant arrangement without forming NF beads appeared under the 7:3 FA/AA, 15% PCL, and 20% RCA condition. The indicator changed from pink to blue with the values of total color change (ΔE) of 10, 14, and 18 when exposed to the saturated gas of ammonia solutions of 8, 80, and 800 mM, respectively. The indicator was stable and unchanged in color for 28 days when exposed to light at room temperature. In the application to mackerel packaging, the built-in indicator changed from pink to purple regardless of storage temperature when the spoilage point was reached.