Adulterating products is a simple way to cut costs, so this has long been a key concern in the food industry.1 The adulteration of food can cause major health risks if allergens or other harmful cutting agents are introduced, as well as changing nutritional values and food quality.
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It can be difficult to detect food adulteration because the substitutes mimic the physical and chemical characteristics of the original product. It is imperative to identify contamination in both raw materials and final products to ensure that the food industry can guarantee high-quality products for customers. This is only possible if precise measurements are taken during the manufacturing process.
This article describes how a 2060 The NIR Analyzer from Metrohm Process Analytics was used to identify the presence of a potato starch adulterant in a wheat flour manufacturing process using near-infrared (NIR) spectroscopy. The 2060 The NIR Analyzer offers non-destructive, reagent-free, and fast potato starch analysis using a reflectance probe that was specifically designed for such uses. No chemical reagents are needed, and results are provided rapidly.
Introduction
Wheat is a key global staple crop. According to Statista, more than 778 million metric tons of wheat were produced globally from 2021 to 2022.2 From its grains, wheat flour is produced; this is the main ingredient of bread, a staple food worldwide. Starch is the key component within bread, influencing the crumb consistency, overall flavor, and shape. During baking, gelatinization occurs between the starch in the flour and the water added to the dough.
The breakdown process from wheat grains into flour involves several preparatory steps that vary depending on the type of flour to be produced (e.g., refined flour, whole wheat flour etc.). The most common process is milling, which involves grinding grains into a flour-like consistency.
Like wheat, potatoes are among the most widely produced crops in Asia, America, and Europe.3 In China specifically, the potato is used mostly as a staple food because of its nutritional value and chemical properties (such as superior water absorption and its ability to regulate blood glucose).3 Potato flour and wheat flour are chemically similar (i.e., mostly composed of starch), making them a good alternative in some situations. Crucially, it is also hard to differentiate between wheat and potato flours.4
The demand for wheat has always been high due to its wide range of uses (e.g., durum, bulgur, flour). As a result, many types of fraudulent activity have been discovered during wheat flour production, as other materials, such as potato flour, can be mixed in to increase production volumes and thereby lower production costs.
However, mixing wheat flour and potato flour can sometimes be beneficial. Many people are to some extent intolerant of gluten, a major protein found in wheat. Therefore, depending on the application (e.g., staple food production or wheat flour manufacturing), it is necessary to have an accurate and fast method for determining the specific content of both components to avoid adulteration and cross-contamination and to guarantee product quality.
Samples are typically withdrawn from the process manually (e.g., pipe or tank) during potato/wheat flour blending, and then analyzed offline in a laboratory. This delay in the analysis results becoming available to the operator can cause crucial processing decisions to be made without the most up-to-date information.
Near-infrared (NIR) spectroscopy is an analytical technique that has been widely utilized in the food and feed sector.5 Unlike legacy wet chemical methods, NIR spectroscopy requires no chemicals and very little sample preparation. Therefore, it can even be used by non-chemists. Additionally, this method is fast: results are generally available in less than one minute.
Figure 1. The 2060 The NIR Analyzer with fiber optic cable. Image Credit: Metrohm Middle East FZC
Figure 2. Raw near-infrared spectra collected during wheat flour blending as measured by the 2060 The NIR Analyzer from Metrohm Process Analytics. Image Credit: Metrohm Middle East FZC
Metrohm process NIR analyzers allow the comparison of spectral data from the process to a primary method in real time, creating a simple yet indispensable model for crucial industrial process requirements.
Regular monitoring at multiple process points aids the early detection of adulteration trends, enabling prompt intervention and the prevention of widespread contamination. This helps to maintain the integrity of the food supply chain, thus protecting customers. Manufacturers can gain more control over the production of flour using a 2060 The NIR Analyzer (Figure 1), which can monitor up to five process points with each NIR cabinet.
A probe that is specifically designed for these applications is used as a spoon, with purge vents located on the probe tip. After each NIR spectrum is collected (see Figure 2), an air purge exiting through the ports in the probe clears the spoon for a new sample.
Configuration
The 2060 The NIR Analyzer is part of the next generation of process spectroscopy instruments from Metrohm Process Analytics. With its proven and unique design from the inside out, it delivers accurate results every 10 seconds. It provides non-destructive analysis of solids and liquids directly in the process line, or in a reaction vessel by using contact probes and fiber optics. Its design enables the connection of up to five probes and/or flow-cells. The five channels can be configured independently from each other using the versatile embedded proprietary software.
As part of the 2060 Platform, the 2060 The NIR Analyzer has a modular concept and is available in three other versions: the 2060 The NIR-Ex Analyzer, 2060 The NIR-R Analyzer, and 2060 The NIR-REx Analyzer.
Image Credit: Metrohm Middle East FZC
Application
The spectra shown in Figure 2 cover concentrations from 0 to 100 % for both types of flour (potato and wheat). A spectrum cannot be assigned to a type of flour merely by visual inspection: advanced mathematics (chemometrics) must therefore be used.
The wavelength range used is 1100–2000 nm, which corresponds to the region where the compounds of interest respond, in this case: fat, sugar, protein, water (moisture), and starch. Inline analysis can be performed using a micro-interaction reflectance probe with purge on the collection tip directly in a feeder/hopper or in a blender.
Typical Ranges
Table 1. Parameters to monitor inline during the wheat flour blending process. Source: Metrohm Middle East FZC
| Analyte |
Concentration (%) |
Precision |
| Wheat flour content |
0–100 % |
2.5 % |
| Potato flour content |
0–100 % |
2.5 % |
Remarks
An appropriate range of samples that cover the process variability should be analyzed using both methods (primary and NIRS) to build an accurate NIRS model. Correlations are made in accordance with process specifications. The correct NIRS probe must be placed in situ in a way that provides enough sample contact with the probe tip window. Correct probe design and proper placement in process equipment are very important.
Conclusion
Using NIR spectroscopy for the inline detection of wheat flour adulteration offers a reagent-free, rapid, and non-destructive solution to ensure the quality and safety of products in the food industry. Adulterating wheat flour using substances such as potato starch may compromise nutritional values and carry health risks.
Legacy methods for detecting such adulteration often involve offline analysis and manual sampling, which cause delays and mean processing decisions could be based on outdated information. However, NIR spectroscopy, exemplified by the 2060 The NIR Analyzer from Metrohm Process Analytics, allows the manufacturing process to be monitored in real time, providing fast and accurate results. By using NIR spectroscopy, manufacturers can uphold product integrity, make informed decisions, and prevent cross-contamination to meet consumer demands for safe and authentic food products.
References
- Rohman, A. and Che Man, Y.B. (2011). The use of Fourier transform mid infrared (FT-MIR) spectroscopy for detection and quantification of adulteration in virgin coconut oil. Food Chemistry, 129(2), pp.583–588. DOI: 10.1016/j.foodchem.2011.04.070. https://www.sciencedirect.com/science/article/abs/pii/S0308814611006364.
- Statista. (2025). Topic: Wheat worldwide. (online) Available at: https://www.statista.com/topics/1668/wheat/?srsltid=AfmBOorm_yF_2zncSSuT21877D4DqLd8UYrUZGqdU7XMFOMWOk2KEqlt.
- Tao, C., et al. (2020). Effects of potato starch on the properties of wheat dough and the quality of fresh noodles. CyTA - Journal of Food, 18(1), pp.427–434. doi: 10.1080/19476337.2020.1768152. https://www.tandfonline.com/doi/full/10.1080/19476337.2020.1768152.
- YÁNEZ, E., et al. (2007). Potato flour as partial replacement of wheat flour in bread: baking studies and nutritional value of bread containing graded levels of potato flour*. International Journal of Food Science & Technology, 16(3), pp.291–298. DOI: 10.1111/j.1365-2621.1981.tb01017.x. https://academic.oup.com/ijfst/article/16/3/291/7910631.
- Rady, A.M. and Guyer, D.E. (2015). Rapid and/or nondestructive quality evaluation methods for potatoes: A review. Computers and Electronics in Agriculture, 117, pp.31–48. DOI: 10.1016/j.compag.2015.07.002. https://www.sciencedirect.com/science/article/abs/pii/S0168169915001970?via%3Dihub.
This information has been sourced, reviewed and adapted from materials provided by Metrohm Middle East FZC.
For more information on this source, please visit Metrohm Middle East FZC.