Proof-of-concept study of chitosan-based carbon dioxide indicator for food packaging applications

A chitosan-based carbon dioxide (CO₂) indicator was developed to monitor freshness or quality of packaged foods during their storage, as elevated CO₂ levels inside a package is one of the prime indicators of microbial spoilage of food. The objective of this proof-of-concept study, therefore, was to develop a chitosan-based CO₂ indicator and to investigate its performance in different operating environments. For the enhancement of signal strength of indicator, 2-amino-2-methyl-1-propanol (AMP) was used as an additive to the chitosan solution. Aqueous chitosan–AMP suspensions were prepared by addition of chitosan (0.1%, 0.2% and 0.4%) and AMP (0%, 5%, 10% and 20%) to distilled water at pH 7.0. Thereafter, the aqueous chitosan suspensions were incubated under 100% and 20% CO₂ test atmospheres. The aqueous solubility of chitosan, which in turn impacts the degree of transparency of the suspension, was tested at different pHs and time intervals, spectrometrically. The transparency of 0.2% chitosan aqueous suspension increased dramatically below pH 6.5 under 20% or 100% CO₂ incubation. The addition of a 5% AMP concentration to the chitosan suspension was found optimal for maximum CO₂ absorption and this, therefore, increased transparency by more than 90%.