Soybean lipophilic proteins — Origin and functional properties as affected by interaction with storage proteins

Soy protein isolate (SPI) is a typical commercial product of soybean, widely used as a food ingredient. SPI has long been thought to consist of two major storage proteins, namely, glycinin and β-conglycinin. However, the finding of new protein fractions, lipophilic proteins (LP), which occupy about 30% of SPI, requires us to reconsider the composition and functional properties of SPI. In this review, we consider the origin of LP and its interaction with the two storage proteins referring to recent results on the solubility of LP, glycinin, β-conglycinin, and SPI. The importance of the interaction between LP and the storage proteins is also highlighted by comparing our results with those previously published on the emulsifying properties of LP. The major component of LP is a complex of oleosin-phospholipids, and this complex forms a strong membrane surrounding the oil body in soybean seeds. The possibility of using the oil body as an emulsifying agent is also discussed, and the importance of the interaction between LP and storage proteins is highlighted.