UHPLC–QTOF-MS Tracks Fats Behind Soymilk's Odor

Changes in the fats inside soybeans are closely tied to the "beany" smell of soymilk, so understanding these changes could help manufacturers better shape and control how soymilk tastes and smells. Pinpointing which fats give rise to the beany odor, and which steps in the process cause them to change, would let producers adjust those steps to cut down on the smell. With that goal in mind, a team of researchers set out to track how the fats in soybeans change during soaking and cooking. They used two types of nuclear magnetic resonance (NMR) analysis along with ultrahigh-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UHPLC–QTOF-MS), with the aim of providing a reference for how fats behave during soymilk production. A paper based on their work was published in the journal Food Chemistry.¹

How is Soymilk Made, and Why Does It Often Smell Beany?

Soymilk is a popular drink that looks and tastes a lot like cow's milk and has a similar nutritional makeup. Soymilk is made by soaking and grinding soybeans in water, though, so it's completely plant-based and suitable for vegans.²Making soymilk usually involves a few basic steps: choosing the soybeans, soaking them, grinding them, straining out the solids, cooking the liquid, adding any extra ingredients, and packaging the finished product.³Unfortunately, soymilk often has an unpleasant "beany" smell that's hard to avoid. Soybeans are rich in fats, including a type called polyunsaturated fats, and when soymilk is heated during production, these fats break down and form the compounds responsible for that beany odor.⁴

How Do Soaking and Cooking Change the Fats in Soybeans During Soymilk Production?

The results of the study showed that soaking lowered the amount of one type of fat, called phospholipids (PLs), as these broke down into smaller pieces. Cooking, on the other hand, lowered the amount of a different type, called neutral lipids (NLs), which also broke down into smaller pieces. A more detailed look at the individual fat molecules confirmed these trends. Soaking increased the levels of most triglycerides, the most common type of fat, while cooking reduced them. Both soaking and cooking reduced the levels of most PLs.¹

“These findings,” write the authors of the paper,¹ “indicated that both PL and NL may be the key lipid precursors for beany odorant formation during soymilk processing, providing a reference for controlling beany odor development in soymilk. In particular, these results point to specific lipid classes and processing stages as potential targets for optimizing soymilk processing and minimizing beany odor in industrial production. More broadly, they may also contribute to the understanding of flavor chemistry in soy products by linking specific lipid classes and molecules, along with their hydrolysis behaviors, to beany odor generation.”

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References

1. Zhang, Q.; Wei, Y.; Tang, B. et al. Using Lipidomics to Reveal the Changes in Lipid Composition During Soymilk Processing. Food Chem. 2026, 532 (Pt 1), 151396. DOI: 10.1016/j.foodchem.2026.151396
2. Rizzo, G.; Baroni, L. Soy, Soy Foods and Their Role in Vegetarian Diets. Nutrients 2018, 10 (1), 43. DOI: 10.3390/nu10010043
3. Giri, S. K.; Mangaraj, S. Processing Influences on Composition and Quality Attributes of Soymilk and its Powder. Food Eng. Rev.2012, 4 (3), 149-164. DOI: 10.1007/s12393-012-9053-0
4. Wang, B.; Zhang, Q.; Zhang, N. et al. Insights into Formation, Detection and Removal of the Beany Flavor in Soybean Protein. Trends Food Sci. Tech. 2021, 112, 336-347. DOI: 10.1016/j.tifs.2021.04.018