Modification of soy protein isolate by glutaminase for nanocomplexation with curcumin

Soy protein isolate (SPI) was first treated with glutaminase to yield modified SPI (E-SPI) before its complexation with curcumin. Comparisons were made between SPI and E-SPI concerning their characteristics and effectiveness in complexing with curcumin, along with changes in physicochemical properties, 2,2-diphenyl-1-picryhydrazyl (DPPH)-scavenging capacity and storage stability of curcumin upon complexation. The action of glutaminase did not markedly change SPI structure, but modified some secondary structures, causing greater protein unfolding with more hydrophobic clusters and amino acids exposed. Glutaminase treatment increased DPPH-scavenging capacity, foaming capacity and stability of SPI. The protein concentration played a role in the changes induced by glutaminase treatment and complexation with curcumin, and 1% protein seemed beneficial (highest DPPH scavenging activity; highest loading amount 10.07%; 98% and >90% curcumin retained in 1%-E-SPI at 4 °C for 2 h and 12 h, respectively). Therefore, glutaminase treatment of SPI before complexation with curcumin appeared to be appropriate.