Enhancing CO2-Selective Detection in Anthocyanin?Agar Hydrogel Indicators via Parafilm Encapsulation

다국어 초록 (Multilingual Abstract)

Ensuring food safety and maintaining quality are critical priorities, as contaminated or spoiled food can pose severe threats to public health. Microbial spoilage accelerates food degradation by producing volatile metabolites such as carbon dioxide (CO2) and ammonia (NH3), both of which serve as key freshness indicators. While CO2 readily dissolves in water to form bicarbonate, thereby lowering the pH and enabling indirect colorimetric detection, this process is significantly complicated by the concurrent presence of alkaline gases like NH3. NH3 increases pH upon dissolution, counteracting the CO2 induced color transitions and severely compromising detection reliability. This inherent counteracting effect poses a major limitation for pH dependent freshness indicators, thus underscoring the necessity of achieving selective gas responsiveness. Although substantial progress has been made in developing real-time sensors for nitrogenous volatile compounds, selective detection of CO2, a predominant byproduct of microbial metabolism, remains comparatively underexplored due to previous limitations in cost, stability, and safety. In this study, a natural pigment based colorimetric freshness indicator was developed for selective CO2 detection by immobilizing anthocyanins extracted from red cabbage within an agar hydrogel matrix. While the indicator exhibited strong CO2 responsiveness, its inherent rapid reversibility limited long-term chromatic stability. To circumvent this issue, we introduced a novel Parafilm encapsulation strategy. This approach effectively suppressed reversible color recovery while simultaneously enhancing CO2 selectivity by strategically blocking the diffusion of interfering alkaline gases, particularly NH3. Experimental analyses revealed an inverse correlation between agar concentration and CO2 sensitivity, with lower agar levels promoting faster gas diffusion and color transition. Crucially, the Parafilm packaging demonstrated excellent barrier properties against NH3 while preserving selective permeability to CO2. However, increased film thickness slightly retarded CO2 diffusion, resulting in a delayed chromogenic response. Overall, these findings highlight Parafilm encapsulation as a simple yet powerful means to achieve non- reversible chromatic stability and superior gas selectivity. The proposed CO2 responsive label offers a high-fidelity, natural, and cost-effective platform for monitoring microbial spoilage in smart food packaging applications.

목차 (Table of Contents)

• 1. Introduction 1
• 1.1 Research background 1
• 2. material and method 6
• 2.1 material 6
• 2.2 Red Cabbage Hydrogel manufacturing 6
• 2.3 UV-vis absorption spectra analysis 6
• 2.4 Fourier Transform Infrared Spectroscopy 7
• 2.5 Texture Profile Analysis 7
• 2.6 Field Emission-Scanning Electron Microscope (FE-SEM) 7
• 2.7 Colorimetric response testing of Carbon Dioxide vapor 8
• 2.8 Colorimetric response testing of Ammonia vapor 8
• 2.9 CIE Lab 9
• 2.10 Response Surface Methodology (RSM) 9
• 2.11 Thickness 10
• 2.12 Gas generation in food 10
• 2.13 Statistical analysis 11
• 3. Result 12
• 3.1 pH characteristics of red cabbage extract (RCE) 12
• 3.1.1 Color changes of RCE at different pH 12
• 3.1.2 UV-vis spectra of RCE at different pH 15
• 3.2 Morphology characterization of red cabbage label 17
• 3.2.1 Texture Profile Analysis of Agar Hydrogel 18
• 3.2.2 Field Emission-Scanning Electron Microscope of Parafilm 20
• 3.3 FT-IR analysis of RCH before & after CO2 reaction 22
• 3.4 Visual representation of RCH according to variables 25
• 3.4.1 Colorimetric response test for RCH 26
• 3.4.2 RSM for RCH 28
• 3.4.3 Effect of Agar Concentration on the Colorimetric Response to 5,000 ppm CO2 30
• 3.4.4 Effect of Agar Concentration on the Colorimetric Response to 30,000 ppm CO2 32
• 3.4.5 RSM Analysis of △ E at Two CO2 Concentrations 34
• 3.5 Parafilm effect 36
• 3.5.1 Colorimetric response CO2 test for Parafilm effect 36
• 3.5.2 Colorimetric response NH3 test for Parafilm effect 38
• 3.6 Gas generation in food 40
• 4. Discussion 42
• 5. Conclusion 45
• Acknowledgment 46
• References 47
• 국문초록 53
• 감사의 말 55