Characterization of sacha inchi (Plukenetia volubilis L.) oil by FTIR spectroscopy and 1H NMR. Comparison with linseed oil

Three oil samples obtained from sacha inchi (Plukenetia volubilis L.) seeds were studied by means of FTIR and ¹H NMR. Frequency data of the most significant bands of the IR spectrum of this oil are given. These data show that sacha inchi oil has a high degree of unsaturation. The same fact is deduced from the ratio between the absorbance of the bands due to the stretching vibrations of the cis olefinic CH double bonds at 3010.5 cm⁻¹ and to the methylene symmetrical stretching vibrations at 2855.1 cm⁻¹. The proportions of monounsaturated, polyunsaturated, and saturated acyl groups were predicted from the frequency of some IR bands, and these were in satisfactory agreement with the values obtained through FAME generation and their quantification by GC. Likewise, simple observation of the ¹H NMR spectra provided a great deal of information about sacha inchi oil, with regard not only to the relative proportions of the different acyl groups but also to their nature. Thus, the presence of γ-linolenic acyl groups was discounted. Furthermore, the area of some ¹H NMR signals was used to determine the proportion of saturated and mono-, di-, and triunsaturated acyl groups, which also were in satisfactory agreement with the values obtained by classical methods. IR and ¹H NMR determinations take very little time in comparison with classical methods and do not require chemical manipulation or transformation of the sample. A comparison was also made between the compositions of sacha inchi and linseed oil. Both oils are important sources of the healthful n−3 linolenic acyl groups, and sacha inchi also contains high proportions of the n−6 linoleic acyl groups.