Compositional and Conformational Analysis of Yam Proteins by Near Infrared Fourier Transform Raman Spectroscopy

Abstract

Fourier transform (FT)-Raman spectroscopy was employed to study the molecular structure of yam proteins isolated from three commonly consumed yam species including Dioscorea alata L., D. alata L. var. purpurea, and Dioscorea japonica. Although D. alata L. and D. alata L. var. purpurea consisted of similar amino acid residues, they still exhibited significant differences in conformational arrangement. The secondary structure of D. alata L. was mainly an alpha-helix, while D. alata L. var. purpurea was mostly in antiparallel beta-sheets. In contrast, D. japonica, which belongs to a different species, exhibited explicit differences in amino acid compositions and molecular structures of which the conformation was a mixed form of alpha-helices and antiparallel beta-sheets. FT-Raman directly proved the existence of S-S in yam proteins, implying that oligomer formation in yam proteins might be due to disulfide linking of dioscorin (32 kDa). The microenvironment of aromatic amino acids and the state of S-S in yam proteins were also discussed.

Investigation of the susceptibility of acid‐deamidated wheat gluten to in vitro enzymatic hydrolysis using Raman spectra and free amino acid analysis

“…Cys was the amino acid which was responsible for SS and SH linkages. Raman spectroscopy is sensitive enough to detect the redox properties of sulfhydryl groups (SS and SH linkages) 26, 27. The observed stretching at 521 cm −1 , corresponding to the gauche – gauche – trans ( g – g – t ) stretching vibration of disulfide bonds, confirmed the presence of disulfide bonds in samples (Fig.…”

“…Raman bands ratio ( I 886/760 ) could be used to monitor the strength of H‐bonding and the hydrophobicity of the environment of the indole ring of Trp residues,26, 27, 38 thus indicating the degree of buried Trp residues. Larger ratio of I 886/760 indicates more Trp is exposed.…”

“…The intensity values of 644 cm −1 on Raman spectra are a reflection of Tyr side‐chain conformational changes 26, 27, 38. The larger intensity value of I 644/621 indicated that the Tyr was more susceptible to external stresses.…”

“…The intensity ratio of Raman bands at 644 to 621 cm −1 ( I 644/621 ) as well as 860 to 828 cm −1 ( I 860/828 ) was used to evaluate the micro‐environment property of tyrosine. Also, the ratio of Raman bands at 886 to 760 cm −1 ( I 886/760 ) was used for the analysis of tryptophan micro‐environment 27. Each numerical calculation of the Raman intensity ratio was based on the average of at least triplicate measurements which showed similar trends.…”

Functional, nutritional and conformational changes from deamidation of wheat gluten with succinic acid and citric acid

“…1A) and 2570-2590 cm À1 (Fig. 1B) clearly indicated the presence of disulfide bonds and sulfhydryl groups in wheat gluten deamidated with succinic acid and citric acid, respectively (Liao et al, 2004). The intensity of the Raman peaks in the area (521 cm À1 ) was much stronger for S-DWG than for C-DWG, showing that there were more disulfide bonds in S-DWG than in C-DWG.…”