Abstract:

Purple sweet potato anthocyanins-protein complexes were extracted with hot water and precipitated by adding
ammonium sulfate to 60% saturation. Purple sweet potato protein (PSPP) was further purified from the complexes by DEAE-52
ion exchange chromatography and Sephadex G-75 gel filtration chromatography. The molecular weights of PSPP and the
complexes were determined by SDS-PAGE. A series of spectroscopic methods were used to characterize their structures.
Results showed that there was no difference between PSPP and its complexes with anthocyanins in molecular weight.
SDS-PAGE analysis exhibited four bands with molecular weights of 58, 24, 18 and 14 kD, respectively. The UV absorption
spectra of both PSPP and the complexes showed a peak at 200 nm, but additional peaks and red-shift phenomenon of the
complexes were observed when compared to PSPP. The maximum fluorescence emission wavelength of PSPP was 340 nm,
and the intensity for the complexes was almost entirely quenched. FTIR spectra of PSPP had characteristic amide bands, and
the shape and intensity of the complexes revealed a significant change. Circular dichroism (CD) revealed that PSPP had a
secondary structure characterized by β-sheets (43.6%) and random coils (45.7%), β-turns (10.6%), while the complexes had
higher content of β-sheets (72.2%) and decreased content of random coils (27.8%), and showed the disappearance of β-turns.

Key words: purple sweet potato, anthocyanins-protein complexes, purple sweet potato protein, structure characterization