Curcumin-based colourimetric CO2 indicators for low-range headspace screening

Carbon dioxide (CO 2 ) is central to modified atmosphere packaging (MAP), but its concentration can change during filling, storage and distribution. This study developed a camera-readable CO 2 indicator using a curcumin-β-cyclodextrin (Cur-β-CD) preparation in a hydroxypropyl methylcellulose (HPMC) matrix containing sodium bicarbonate. The poor aqueous solubility and tendency of free curcumin to aggregate make uniform deposition from water-based formulations difficult. Thus, the addition of β-CD assisted curcumin dispersion, HPMC provided coherent deposition on paper and polypropylene (PP), and bicarbonate established the alkaline state required for the response to CO 2 -derived carbonic acid. Patches containing black and white references were exposed to 0-30% CO 2 in N 2 at 10°C under a high-humidity condition generated with wetted tissues. Four independently deposited spots were distributed between two sealed glass cylinders, with two spots per cylinder, and followed through the same exposure sequence. Corrected red intensity and chroma are reported as mean ± SD for the four spot measurements. The largest change occurred below approximately 10% CO 2 , followed by a plateau at 20-30% and partial colour return. One-hour readings were operational endpoints. O 2 and temperature produced smaller changes under separate protocols, whereas pH-conditioned exposure caused marked drift. The results support semi-quantitative low-range CO 2 screening under the tested conditions.