FTIR and Raman spectroscopic study of Fenugreek (Trigonella foenum graecum L.) seeds

Abstract

The composition of Fenugreek seeds in the form of powder, ash, and oil is investigated through FTIR and FT Raman spectra measurements. The results indicate that Fenugreek seeds (powder) are rich in proteins. Fats (lipids) and starch are present in small amounts in the seeds. The FTIR absorption bands of seed powder appeared at: 3365 cm⁻¹ assigned as N-H stretching vibrations (amide A of protein), 1657 cm⁻¹ (C=O, amide I), 1540 cm⁻¹ (N-H bending vibration, amide II), and 1240 cm⁻¹ (N-H bending, amide III). In the FT Raman spectra the band at 1661 cm⁻¹ is ascribed to amide I ν(C=O) of proteins while the band at 1080 cm⁻¹ indicates the starch. The fenugreek oil Fourier transform infrared absorbance ratios A(3009 cm⁻¹)/A(2924 cm⁻¹), A(3009 cm⁻¹)/A(2854 cm⁻¹), and A(3009 cm⁻¹)/A(1740 cm⁻¹) were considered for measuring the iodine values. These ratios (0.3609, 0.4916, and 0.4129) revealed that the iodine value of fenugreek oil is higher than that of other oils. On the other hand, the ash of fenugreek is very rich in phosphate compounds. The spectra showed absorption bands at frequencies 1082, 1000, 618, and 566 cm⁻¹, and the FT Raman spectrum showed a strong absorbance band at 793 cm⁻¹, which is due to phosphate compounds. It could be concluded that the inorganic part of fenugreek consists mainly of phosphate compounds. The Fenugreek seed contains proteins, fat, fiber, and ash, which is in complete harmony with AACC, 1980.