📄 agriculture

Intelligent packaging solutions for fish and meat products: volatile gas detection via GC- MS, microbial analysis and colorimetric monitoring

This study demonstrates that a pH-sensitive anthocyanin-based colorimetric indicator serves as an effective, real-time monitoring tool for fish freshness by accurately correlating visible color changes with volatile amine production (specifically TMA and NH₃) and microbial growth, as validated by GC-MS analysis and gas detection tubes.

Original authors: Maryam Ameri, Abdellah Ajji, Samuel Kessler, Marc-Antoine Vaudreuil

Published 2026-06-29

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Maryam Ameri, Abdellah Ajji, Samuel Kessler, Marc-Antoine Vaudreuil

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you have a fish fillet in your fridge. Right now, the only way to know if it's still good to eat is to open the package, take a deep sniff, and hope you don't smell anything "off." By the time you smell it, it might already be too late.

This research paper introduces a smarter solution: Intelligent Packaging. Think of it as giving your food package a "nose" and a "mood ring" that can tell you exactly how fresh the food is without you ever having to open the box.

Here is a breakdown of how the scientists at Polytechnique Montréal and their partners built this system, using simple analogies.

1. The "Mood Ring" Sensor (The Color Change)

The core of this invention is a special sticker made from anthocyanin, a natural pigment found in things like black rice, blueberries, and red cabbage.

How it works: Imagine this pigment is like a mood ring. When the fish is fresh, the sticker is red. As the fish starts to spoil, bacteria break down the meat and release gases (specifically ammonia and trimethylamine). These gases act like an acid, changing the pH level inside the package.
The Reaction: Just like how red cabbage juice turns pink in acid and green in base, this sticker changes color as the gases build up. It goes from Red (Fresh) → Pink/Purple (Okay) → Light Purple (Getting old) → Yellowish-Brown (Spoiled).
The Result: The researchers proved that this color change happens at the exact same time the bacteria start to multiply and the "bad smell" gases appear. It's a visual alarm system that matches the invisible chemical changes.

2. The "Sniffer" (GC-MS Analysis)

To make sure the "mood ring" was actually reacting to the right things, the scientists used a high-tech machine called GC-MS (Gas Chromatography-Mass Spectrometry).

The Analogy: Think of the fish in the jar as a room full of invisible guests (gases). The GC-MS is like a super-sensitive detective that enters the room, catches every single guest, and asks for their ID cards.
What it found: The machine confirmed that as the fish spoiled, it released specific gases like Ammonia (the smell of cleaning products) and Trimethylamine (the classic "fishy" smell).
The Challenge: The scientists found that fish is a "messy" room. The gases get stuck in the water inside the fish meat, making it hard for the machine to catch them all accurately. While they couldn't count the exact number of gas molecules in the real fish, they could still see the trend: the gases were definitely increasing as the days went by.

3. The "Speedometer" (Gas Detection Tubes)

Alongside the fancy machine, they also used simple gas detection tubes.

The Analogy: These are like old-school breathalyzer tubes. You pump air from the package through a glass tube, and if the bad gas is there, the tube changes color (from yellow to blue).
The Result: This confirmed that ammonia levels were rising steadily over 9 days of storage, matching the color changes seen on the "mood ring" sticker.

4. The "Party Crashers" (Microbial Analysis)

The team also counted the bacteria (the "party crashers" causing the spoilage).

The Timeline:
- Days 0–3: The bacteria count was low; the fish was fresh.
- Days 4–7: The bacteria population exploded (like a party getting out of control). This is when the fish started to truly spoil.
- Day 9: The fish was fully spoiled.
The Connection: The "mood ring" sticker changed color right in sync with this bacterial explosion.

5. The "Surprise Guests" (Other Gases)

While looking for the main "bad smell" gases, the GC-MS detective also found some unexpected guests: Methanol, Ethanol, Dimethyl Sulfide, Butane, and Pentane.

The Analogy: It's like looking for a specific thief in a crowd and realizing there are also people selling lemonade and burning rubber nearby.
The Meaning: These gases appeared because of fermentation and the breakdown of proteins. While the study didn't focus on them as the main spoilage indicators, their presence helped confirm that complex chemical changes were happening inside the package.

The Bottom Line

The paper concludes that this color-changing sticker is a reliable, low-cost way to monitor fish freshness.

It doesn't need electricity.
It doesn't need a lab to read (you can just look at it).
It reacts to the exact same gases that cause the bad smell and bacterial growth.

Important Limitation: The researchers noted that while they could see the trend of gases increasing, the complex nature of fish (it's wet and full of proteins) made it very difficult to get a precise number for how much gas was in the package using their machine. However, for the purpose of a consumer sticker that says "Fresh" or "Spoiled," the trend was perfect.

In short, they created a "smart label" that turns from red to brown as your fish goes bad, giving you a clear, visual warning before you even open the package.

Technical Summary: Intelligent Packaging Solutions for Fish and Meat Products

Problem Statement
The storage of fresh fish and meat products presents significant challenges regarding the rapid assessment of freshness and shelf-life. Post-mortem microbial activity and endogenous biochemical reactions lead to quality degradation, primarily driven by the formation of volatile basic nitrogen (TVB-N) compounds such as ammonia (NH₃), trimethylamine (TMA), and dimethylamine (DMA). While traditional methods for assessing spoilage rely on sensory evaluation or chemical tests, these often lack the timeliness and accuracy required for real-time monitoring. There is a pressing need for innovative, reliable indicators that can detect spoilage markers, specifically volatile amines, to ensure food safety and quality for consumers and industry stakeholders.

Methodology
This study employed a multifaceted approach to develop and validate an intelligent packaging solution utilizing a pH-sensitive anthocyanin dye as a colorimetric freshness indicator. The research involved three primary fish types: pangasius, haddock, and beef/chicken for comparative packaging trials.

Sensor Development: A colorimetric sensor was prepared using a polyvinyl alcohol (PVOH) matrix loaded with black rice extract (anthocyanin). The films were thermally treated (TT) at 165°C to enhance stability.
Colorimetric Monitoring: Fish samples were stored at 4°C, and the sensor's color response was captured via scanning. Color changes were quantified using the total color difference ( $\Delta$ RGB) equation, correlating visual shifts with TVB-N gas concentrations.
Gas Detection: Gas detection tubes (Dräger) were utilized for rapid, cost-effective quantification of NH₃ and triethylamine (TEA) in the headspace of amber vials containing fish samples.
Microbial Analysis: Total Viable Count (TVC) and Pseudomonas spp. counts were determined to establish the biological spoilage threshold (defined as $1 \times 10^7$ CFU/ml).
GC-MS Analysis: Headspace Gas Chromatography-Mass Spectrometry (HS-GC-MS) was optimized to detect and quantify NH₃, TMA, and DMA. The study utilized both Selected Ion Monitoring (SIM) for targeted analytes and scan mode for untargeted species. Calibration curves were generated using both pure solvent standards and matrix-matched standards (spiked fish samples) to assess extraction efficiency and matrix effects.

Key Results

Sensor Sensitivity: The anthocyanin-based pH indicator demonstrated a clear, statistically significant relationship between TVB-N gas concentration and color change ( $\Delta$ RGB). The sensor was most sensitive to NH₃, followed by TMA and DMA. A four-point freshness scale (Red to Yellowish-brown) was established, effectively differentiating freshness levels across haddock, beef, and chicken over a 9-day storage period.
Gas Detection: Gas detection tubes successfully tracked NH₃ and TEA concentrations. NH₃ levels increased significantly over time, peaking around day 8-9, while TEA remained below detection limits for the first two days before rising.
Microbial Correlation: Microbial analysis showed that TVC increased from 3.69 log CFU/ml on day 0 to 7.09 log CFU/ml by day 10. The rapid spoilage phase (days 4–7) correlated with the intensification of the sensor's color change.
GC-MS Performance:
- Quantification Challenges: While linear calibration curves were achieved in pure solvent (R² > 0.99), significant matrix effects in real fish samples prevented accurate absolute quantification. Spiked fish samples exhibited signal saturation and peak broadening, limiting the linear range.
- Trend Analysis: Despite quantification limits, the method successfully tracked trends. NH₃ signal intensity increased initially then decreased, while TMA increased from day 0 to day 3 before declining. Untargeted scan mode identified methanol, ethanol, dimethyl sulfide (DMS), butane, and pentane.
- Discrepancy: A notable discrepancy was observed where GC-MS detected decreasing TMA levels in the headspace during later storage stages, while the colorimetric sensor continued to show significant color changes. This was attributed to the partitioning of volatile amines into the aqueous phase of the deteriorating fish tissue and potential evaporation during the 80°C headspace equilibration.

Significance and Claims
The paper claims that the developed anthocyanin-based pH indicator serves as a practical, efficient, and user-friendly monitoring tool for seafood freshness. The study validates the sensor's ability to correlate visual color changes with microbial growth and volatile amine production, offering a "four-point freshness scale" that surpasses simple binary (fresh/spoiled) assessments.

The research highlights that while accurate absolute quantification of specific volatile amines in complex fish matrices via GC-MS is challenging due to matrix effects and phase partitioning, the method remains valuable for trend analysis. The integration of colorimetric sensing with gas detection and microbial analysis provides a comprehensive framework for evaluating food safety. The authors conclude that this intelligent packaging approach has potential applications in ensuring food safety and quality control within the seafood and meat industries, providing consumers with a visual indication of product spoilage driven by TVB-N formation.