Fermentation of soymilk with <i>Lacticaseibacillus paracasei</i> strain Shirota reduces soluble Gly m 4 levels and allergic reactions associated with soybean-related pollen-food allergy syndrome

Soybean-related pollen-food allergy syndrome (PFAS) is a food allergy triggered by birch or alder pollen-specific immunoglobulin E, which cross-reacts with soybean proteins homologous to pollen proteins. Although soybean-related PFAS generally causes mild symptoms, some individuals develop severe symptoms, including anaphylaxis, especially after consuming soymilk. This study attempted to reduce the risk of allergy by fermenting soymilk with <i>Lacticaseibacillus paracasei</i> strain Shirota (YIT 9029, LcS). The levels of Gly m 4, which causes soybean-related PFAS, in soymilk and fermented soymilk were analyzed using enzyme-linked immunosorbent assay (ELISA) and western blotting. Reactions to soymilk and fermented soymilk were evaluated in patients with soybean-related PFAS using skin prick tests to compare allergic risks. Gly m 4 levels in the soluble fraction of fermented soymilk were significantly lower than those in soymilk. The reduction in Gly m 4 levels was associated with alterations in the fermentation process, including pH reduction. Additionally, compared with soymilk, fermented soymilk reduced skin prick test reactions in patients with soybean-related PFAS. In conclusion, fermenting soymilk with LcS reduced soluble Gly m 4 levels and alleviated allergic reactions associated with soybean-related PFAS. This study demonstrates the potential of fermented soymilk as a safe and effective alternative for individuals with soybean-related PFAS.