GC-MS and GC-O Tracks Soybean Off-Flavor Compounds

Researchers set out to identify the specific compounds responsible for unwanted flavors in regular soybean flour, then tracked how these compounds changed across different soybean-based products made from both regular soybeans and a high-oleic-acid variety. Using headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), they detected 55 different volatile compounds in regular soybean flour. Of these, 18 were identified as actually contributing to the smell, using gas chromatography-olfactometry (GC-O). A paper based on this work was published in the journal Frontiers in Nutrition.¹

What Causes the Unwanted Flavors in Soybean Products, and Why Is This an Important Problem to Solve?

Soybeans are one of the world's most important legume crops, packed with nutrients and containing about 40% protein which is just as high-quality as what one would expect from meat or other animal sources.² Because soybean protein is reliable, affordable, and works well in food products, it's widely used to make soy-based foods. The problem is that soybean processing often creates off-putting flavors, and this remains one of the biggest reasons consumers avoid these products, which in turn makes it harder for manufacturers to improve quality and win over more customers.³

Much of this bad flavor comes from fat breakdown during processing.⁴ Regular soybeans contain fairly high levels of certain fats (like linoleic and linolenic acid)⁵ that break down easily when exposed to oxygen during processing, and this breakdown produces well-known culprits behind soy's off-flavors, including hexanal, 2-pentylfuran, and 1-octen-3-ol.^6,7

How Do Key Off-Flavor Compounds in Soybean Products Differ Across Soybean Varieties and Processing Methods?

Researchers identified 18 compounds responsible for off-putting smells and narrowed these down to 13 that were strong enough to matter, then measured them precisely, which led them to pinpoint 10 key compounds that were the main culprits behind the bad odors. To confirm this, they ran tests where they added these compounds back into odor-free samples and removed them one at a time. In both cases, the results clearly showed these compounds were driving the unwanted smell.¹

Next, the team precisely measured these odor compounds across eight different soybean products made from two soybean varieties, then used statistical analysis to spot patterns. They found that, with a few exceptions (three specific compounds), the high-oleic acid soybean samples generally had lower levels of these off-putting compounds compared to regular soybean samples. They also found that soybean meal and soy protein isolate typically had lower levels of these compounds than soybean flour, aside from two exceptions. Meanwhile, textured soy protein, which goes through an extrusion process, showed levels that went up and down inconsistently rather than following a clear pattern.¹

“The results,” write the authors of the paper,¹“showed that off-flavor formation in soybean-based products is mainly associated with the coordinated changes of lipid oxidation-derived aldehydes, alcohols, and furans. The lower levels of several key odorants in high oleic acid products further suggest the potential of controlling off-flavor through the regulation of fatty acid composition, such as editing oleate desaturase genes.”

“These findings,” the authors continue,¹ “provide a more comprehensive understanding of the off-flavor profile and its evolution in soybean-based products, and offer useful guidance for raw material selection, process optimization, and flavor quality improvement.”

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References

1. Zhou, J.; Huang, D.; Xu, S. et al. Characterization of Key Off-Flavor Compounds in Soybean and their Dynamic Changes During Progressive Processing. Front Nutr. 2026, 13, 1866732. DOI: 10.3389/fnut.2026.1866732
2. Schmidt, M. A.; Barbazuk, W. B.; Sandford, M. et al. Silencing of Soybean Seed Storage Proteins Results in a Rebalanced Protein Composition Preserving Seed Protein Content Without Major Collateral Changes in the Metabolome and Transcriptome. Plant Physiol. 2011, 156 (1), 330-345. DOI: 10.1104/pp.111.173807
3. Starowicz, M.; Kubara Poznar, K.; Zieliński, H. What Are the Main Sensory Attributes That Determine the Acceptance of Meat Alternatives? Curr. Opin. Food Sci. 2022, 48, 100924. DOI: 10.1016/j.cofs.2022.100924
4. Zhang, Y.; Guo, S.; Liu, Z. et al. Off-Flavor Related Volatiles in Soymilk as Affected by Soybean Variety, Grinding, and Heat-Processing Methods. J Agric Food Chem. 2012, 60 (30), 7457-7462. DOI: 10.1021/jf3016199
5. Yeom, W. W.; Kim, H. J.; Lee, K. R. et al. Increased Production of α-Linolenic Acid in Soybean Seeds by Overexpression of Lesquerella FAD3-1. Front Plant Sci. 2020, 10, 1812. DOI: 10.3389/fpls.2019.01812
6. Yang, L.; Zhang, T.; Li, H. et al. Control of Beany Flavor from Soybean Protein Raw Material in Plant-Based Meat Analog Processing. Foods 2023, 12 (5), 923. DOI: 10.3390/foods12050923
7. Kong, Y.; Wu, Z.; Li, Y. et al. Analyzing Changes in Volatile Flavor Compounds of Soy Protein Isolate During Ultrasonic-Thermal Synergistic Treatments Using Electronic Nose and HS-SPME-GC-MS Combined with Chemometrics. Food Chem. 2024, 445, 138795. DOI: 10.1016/j.foodchem.2024.138795