Thermogravimetry: Monitoring Mass Changes in Food Analysis

Understanding how food behaves when exposed to heat is fundamental to food science. Whether you’re developing new products, optimizing preservation techniques, or ensuring quality standards, knowing exactly how a food’s mass changes during heating or cooling provides invaluable insights. Thermogravimetry, also known as thermogravimetric analysis (TGA), is a powerful analytical technique that continuously monitors these mass changes under controlled temperature conditions, offering food scientists a window into moisture content, thermal stability, and decomposition patterns.

What is thermogravimetry? 🔗

Thermogravimetric analysis is a technique that measures changes in sample mass as a function of time and temperature. In food science, this method allows researchers to observe how food materials gain or lose mass when heated or cooled, providing data about moisture content, thermal stability, decomposition patterns, and component interactions. The technique is particularly useful for monitoring processes that involve mass changes such as drying, liberation of gases, and absorption of moisture.

The data generated creates a thermogravimetric curve (TG curve) that plots mass or percentage of initial mass against temperature or time. This curve reveals critical information about when and how rapidly mass changes occur. Additionally, the first derivative of the TG curve, called the DTG curve, highlights points where weight change happens most rapidly, making it easier to identify specific thermal events during heating.

Key components of a thermogravimetric analyzer 🔗

A thermogravimetric analyzer consists of several essential components working together to deliver precise measurements:

Precision balance: The balance is the heart of the TGA system. Modern instruments use microbalances capable of detecting mass changes as small as micrograms, ensuring exceptional accuracy when measuring subtle weight fluctuations in food samples.

Programmable furnace: This component provides controlled heating, typically reaching temperatures up to 1000°C or higher. The furnace can heat samples at constant rates or maintain specific temperatures for isothermal studies.

Atmosphere control system: This allows measurements under various gas environments including inert conditions (nitrogen, argon), oxidative atmospheres (air, oxygen), or even corrosive and reactive gases. This flexibility enables researchers to simulate different processing and storage conditions.

Data recording software: Connected computers with specialized software record and evaluate the collected data points, generating TG and DTG curves for analysis.

Types of thermogravimetric experiments 🔗

Researchers can conduct different types of TGA experiments depending on their analytical goals:

Isothermal thermogravimetry: In this mode, temperature remains constant while sample weight is recorded over time. This approach provides information about a substance’s stability at a given temperature, useful for studying how foods behave during storage at specific conditions.

Dynamic thermogravimetry: Here, the sample is heated in an environment where temperature changes linearly. This method tracks how much material is lost as temperature increases, revealing decomposition temperatures and volatile content.

Quasi-static thermogravimetry: This combines both approaches-temperature is raised, then held constant for a set period before being raised again. This allows samples to reach stability at each temperature step, providing detailed information about decomposition behavior at different temperature points.

Controlling experimental conditions 🔗

To accurately simulate the various processing and storage conditions that foods might experience, thermogravimetric instruments allow measurements under controlled pressures and atmospheres. The ability to carefully control temperature, pressure, and gas composition surrounding a sample is extremely valuable for food scientists because it enables modeling of processes such as drying, cooking, and moisture uptake during storage.

Sample size and heating rate are important factors affecting thermogravimetric curves. As heating rate and sample size increase, the decomposition temperature of the sample typically increases as well. For food applications, sample sizes usually range from 5 to 20 milligrams, placed in ceramic crucibles for analysis.

Applications in food analysis 🔗

Moisture content determination 🔗

Moisture analysis is critical across all areas of the food industry, from quality control to product development. TGA offers a precise method for determining moisture content by measuring weight loss as samples are heated. The initial mass loss at lower temperatures (typically below 150°C) corresponds to moisture evaporation.

What makes TGA particularly valuable is its ability to distinguish between different forms of water in food matrices. In cereal products like rice or wheat flour, thermogravimetry can differentiate between surface moisture, bound water in starch granules, and crystallization water-information essential for determining appropriate storage conditions and shelf life.

Studying drying behavior 🔗

Drying is one of the oldest and most important food preservation methods. TGA helps optimize drying processes by revealing drying rates at different temperatures, critical moisture points where transitions between drying phases occur, and energy requirements for complete drying. This information helps develop more efficient drying protocols that preserve food quality while minimizing energy consumption.

Thermal stability assessment 🔗

Understanding how food components decompose during heating is crucial for processing and storage decisions. TGA identifies decomposition temperatures and patterns, helping food scientists design appropriate processing conditions that preserve nutritional value and sensory qualities while ensuring safety.

Composition analysis 🔗

TGA reveals the composition of food materials through characteristic mass loss patterns at different temperatures. For complex food matrices, the residue remaining after heating can indicate mineral content or inorganic residues. Researchers have used TGA to estimate the contents of amylose and amylopectin in starches and to determine bound water content in grains.

Quality control applications 🔗

Moisture content influences the taste, texture, weight, appearance, and shelf life of food products. Even slight deviations from defined standards can adversely impact physical properties. Foods that are too dry might affect end product consistency, while excess moisture can cause agglomeration, clog processing equipment, or reduce shelf life by promoting microbial growth. TGA helps manufacturers maintain optimal moisture levels for consistent product quality.

Advantages of thermogravimetry in food science 🔗

TGA offers several benefits that make it indispensable for food analysis. The technique provides continuous, real-time monitoring of mass changes, offering a detailed profile rather than just endpoint measurements. It requires only small sample amounts, making it suitable for valuable or limited materials. The controlled atmosphere capability allows simulation of various processing and storage environments.

Compared to traditional moisture determination methods like oven drying, TGA is often faster and provides more detailed information about different types of water present in food materials. The automated nature of modern TGA instruments reduces operator variability and improves reproducibility of results.

Advanced techniques and future directions 🔗

Thermogravimetric analysis continues to evolve with technological advances. Coupling TGA with mass spectrometry (MS) or Fourier transform infrared spectroscopy (FTIR) enables identification of gases evolved during heating, providing insights into decomposition mechanisms and chemical reactions occurring in food samples.

High-pressure TGA systems allow evaluation of material behavior under extreme conditions, useful for understanding how foods perform during high-pressure processing. Modulated TGA applies sinusoidal temperature programs to improve kinetic analysis capabilities, determining activation energy in real time from a single experiment.

Future developments point toward miniaturization for portable field-deployable instruments, artificial intelligence integration for interpreting complex thermal patterns, and enhanced sensitivity for analyzing ever-smaller sample amounts.

What do you think? How might thermogravimetry help improve traditional food preservation methods in your region? Could this technique play a role in verifying authenticity of high-value food products?

References

1. https://en.wikipedia.org/wiki/Thermogravimetric_analysis
2. https://people.umass.edu/~mcclemen/581Thermal.html
3. https://www.tainstruments.com/what-is-thermogravimetric-analysis-blog/
4. https://www.eltra.com/knowledge/thermogravimetric-analysis/
5. https://www.xrfscientific.com/direct-moisture-determination-of-food-and-feed-using-a-tga-analyzer/
6. https://www.researchgate.net/publication/258704703_Better_Understanding_of_Food_Material_on_the_Basis_of_Water_Distribution_Using_Thermogravimetric_Analysis
7. https://www.sciencedirect.com/science/article/abs/pii/0040603189850373
8. https://www.foodqualityandsafety.com/article/determining-moisture-content/