Formation and physical characterization of soy protein-isoflavone dispersions and emulsions

Authors: PEREIRA, GARINN - University Of Hawaii; JUN, SOOJIN - University Of Hawaii; LI, QING - University Of Hawaii; Wall, Marisa; HO, KACIE K.H.Y - University Of Hawaii

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2023
Publication Date: 1/26/2023
Citation: Pereira, G.M., Jun, S., Li, Q.X., Wall, M.M., Ho, K. 2023. Formation and physical characterization of soy protein-isoflavone dispersions and emulsions. LWT - Food Science and Technology. 176. Article 114513. https://doi.org/10.1016/j.lwt.2023.114513.
DOI: https://doi.org/10.1016/j.lwt.2023.114513

Interpretive Summary: Isoflavones are flavonoids that are commonly found in soy food products. This class of secondary phytometabolites is known to be a part of the phytoestrogen class with a range of beneficial effects. Research was conducted to determine the effect of isoflavones on protein-stabilized oil-in-water emulsions. Results showed that isoflavone addition improved emulsion stability compared to the control without isoflavones and that they can contribute to colloidal stability of food products. This potential usage may be implemented with byproducts known to carry large concentrations of isoflavones such as okara (byproduct of soy milk and tofu production). The novel use of soy protein-isoflavone complexes to stabilize emulsions is useful for expanding the use of plant-based alternative stabilizers and contributes to understanding complex food colloids.

Technical Abstract: Proteins stabilize emulsions by adsorbing at the interface to prevent the natural tendency of droplets coalescence. Polyphenols (plant-derived secondary metabolites) are capable of complexing with proteins through structural interactions. Certain polyphenols have shown influence on interfacial properties of proteins, yet isoflavones specifically have not been widely investigated. Thus, the objective of this research was to study the effect of isoflavones on protein-stabilized oil-in-water emulsions. Soy protein fractions, assessed via SDS-PAGE and bicinchoninic acid assay contained primarily ß-conglycinin (7S) and glycinin (11S). Notable isoflavones identified from HPLC analysis were daidzin, genistin, and glycitin. Physical characteristics (size, zeta potential, polydispersity index, and wettability) of soy protein isolate-isoflavone (SPI-I) dispersions and emulsion droplets (10% oil fraction) were measured with a Zetasizer Nano ZS and goniometer. Isoflavone addition significantly increased the contact angle of sessile drops towards a neutral wettability state. Heating appeared to significantly improve colloidal stability and emulsion droplets formed with heated SPI-I dispersions sustained size and zeta potential over 7 days, with higher concentrations of isoflavones being generally correlated with smaller emulsion droplets. Collectively, these findings indicate that isoflavone addition improved emulsion stability compared to the control without isoflavones and that they can contribute to colloidal stability of food products.