Colorimetric Paper-Based Dual Indicator Label for Real-Time Monitoring of Fish Freshness

Research background. Fish freshness and quality monitoring are of high importance for consumers, retailers, and companies. Therefore, developing novel approaches that are simple, fast, non-destructive, and inexpensive to monitor fish freshness in real-time is of great value. One alternative is using Intelligent or smart packaging to monitor the freshness level or condition of packaged fish.
Experimental approach. On-package dual indicator label based on paper-based pH sensors was developed for real-time monitoring of the milkfish (Chanos chanos) freshness. The paper-based pH sensor was prepared using bromocresol purple (BCP) and bromothymol blue (BTB) that were immobilized onto filter paper via dip-coating. Herein, the fish degradation could be monitored visually by the dual indicator label, where the BCP change from yellow to pink, then finally to purple, while the BTP change from orange to green-yellow, and finally to green-blue for fresh, medium, and spoilage respectively.
Results and conclusion. The label responds sensitively to the fish freshness, in terms of its pH change due to the fish degradation as presented by the dual indicator color change to indicate the fish freshness status at room and chiller conditions. This pH change was followed by changes in the other parameters related to freshness, such as TVBN (total volatile basic amine), TVC (total viable count), texture, and odor evaluation. The threshold of fish spoilage indication was observed at 8 h in room temperature and 7 days in chiller condition as the deterioration time point was met with color changes. Thus, it can be concluded that the dual indicator label can be applied as a simple and low-cost on-package active label for fish freshness monitoring.
Novelty and scientific contribution. Increasing consumer concerns for quality and safe food worldwide has boosted the search for a novel approach to food monitoring. In this work, a simple and practical on-package dual indicators label for real-time monitoring of fish freshness was developed. The colorimetric pH sensor was fabricated simply via dip-coating of filter paper, and yet easy detection using a naked eye for accurate fish spoilage. The dual indicators label changes color in a similar tendency toward other freshness parameters, such as TVBN, TVC, texture, and odor.