Recycled UHT Milk Carton Cellulose Surface as a Novel Substrate for Dual-Lactate Sensor for Milk Spoilage Indication

Recycled cellulose substrate from UHT milk carton waste was firstly applied as a novel substrate for the colorimetric and electrochemical lactate sensor for milk quality indication. The cellulose and aluminum foil were extracted from the packaging. For preparing the recycled cellulose substrate, chemical treatment (alkali and bleach treatment) was used for the extraction. Then, the recycled cellulose substrate has done enzymatic immobilization for the colorimetric sensor to enhance the specific reaction with the lactate on its surface. For the electrochemical sensor, the recycled cellulose substrate was immersed into the extracted aluminum solution to fabricate the conductive working electrode to improve the surface roughness compared with the recycled cellulose substrate, confirmed by atomic force microscopy. Scanning electron micrograph presented a 3D fibrous network including with air space in between, and X-ray photoelectron spectroscopy showed the binding energy of Al-O at 73.256 eV, confirming the appearance of the aluminum on the recycled cellulose substrate after the surface modification with aluminum solution. For the analytical performance, the colorimetric sensor showed the increasing purpleness of color upon increasing lactate concentration. Furthermore, the aluminum-coated recycled cellulose substrate provided an increasing current response toward the increment of lactate concentration. This dual-lactate sensor can offer linearity of 0.125-2 M, covering a cut-off lactate value in cow’s milk (1.0 M) for milk spoilage indication, which can be used for lactate determination in actual milk samples. Eventually, this platform can represent a new utilization of UHT milk carton waste for the colorimetric and electrochemical sensor that can be applied in food quality control applications.