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6Raman spectroscopy method for evaluation of punicic acid content in pomegranate seed oil
S.M. Kuznetsov'*, P.K. Laptinskaya1, V.S. Novikov1, M.N. Moskovskiy2, S.V. Gudkov1,
G.Yu. Nikolaeva1, E.A. Sagitova1
1- Prokhorov General Physics Institute of the Russian Academy of Sciences, 38 Vavilov St., 119991 Moscow,
Russia
2- Federal Scientific Agro-Engineering Center VIM, 1st Institutskiy Proezd 5, 109428 Moscow, Russia
Punicic acid (C18H30O2, also called pomegranate acid or omega-5) is a polyunsaturated fatty acid. This acid is the main component of pomegranate seed oil (PSO) with the content of 65 - 85%. Punicic acid is extremely useful for human health due to its antioxidant, anti-inflammatory, antiparasitic, antiangiogenic and anticarcinogenic properties; it can also suppress cellular inflammation and tumor growth [1].
Traditionally, the content of fatty acids is studied using chromatographic methods. However, punicic acid and its isomers are chemically active due to the presence of three conjugated C=C bonds in their structure that can brake during the sample preparation. Therefore, their identification needs other techniques that do not require sample preparation, such as Raman spectroscopy. It is a fast and informative method for identifying and analyzing the quality of vegetable oils, including the detection of counterfeit products.
In this work, for the first time, we provided a Raman study of punicic acid contained in 13 mixtures of PSO and sunflower oil (SO) with various component ratios using two excitation wavelengths (^exc) of 532 and 785 nm. Figure 1 represents several Raman spectra (^exc = 532 nm) of pure SO and PSO, and their mixtures.
1628 cm"1
I
= 532 nm
Punicic acid content: 60 % (PSO) 30 %
6 %
0 % (SO)
—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1
800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800
Wavenumber, cm"1
Figure 1. Raman spectra of mixtures of PSO and SO with various component ratios. The percentage in the legend refers to the content of the punicic acid in the samples.
Our results show that Raman spectra contain bands at 1160 and 1628 cm-1 that are characteristic of punicic acid in PSO and are not observed in spectra of other vegetable oils. The band at 1628 cm-1 is observable in our work even in case of the mixture with a very low punicic acid content of 0.05 mass %. This work was supported by the RSF grant № 24-22-20100, https://rscf.ru/project/24-22-20100/.
[1] M.T. Boroushaki, H. Mollazadeh, A.R. Afshari, Pomegranate seed oil: a comprehensive review on its therapeutic effects, International
Journal of Pharmaceutical Sciences and Research, vol. 7, pp. 430-442, (2016).
