Determination of degree of unsaturation in edible oils using coherent anti‐Stokes Raman scattering spectroscopy

Abstract

We demonstrate the use of coherent anti-Stokes Raman scattering (CARS) spectroscopy for determination of degree of unsaturation in edible oils. To this end, we have measured CARS spectra of six kinds of commercial edible oils having different degree of unsaturation, and it was found that the spectral intensity ratio (I ¼C-H /I C-H ) of two specific bands in C-H stretch region depends on the degree of unsaturation of sample. Based on this relation, the mass unsaturation (N ¼C-H /N C-H ) of six oils was estimated through the results of CARS spectroscopy in five fatty acids (FA), which are major component of edible oils. In addition, we obtained the calibration curve for determining iodine value (IV), and the result of our work was well matched with referred IV.

Authentication of adulterated edible oil using coherent anti‐Stokes Raman scattering spectroscopy

“…PA and SA have carbon–carbon single bonds with 16 carbons and 18 carbons within the fatty acid chain, respectively. However, OA, LA, and LNA having 18 carbons contain one, two, and three double bonds within the fatty acid chain, respectively …”

“…In the previous study of our group, the relation between mass unsaturation and CARS intensity ratio of six edible oils and fatty acids was observed. And we demonstrated that CARS spectroscopy can determine the degree of unsaturation in edible oils and obtained the calibration curve for determining iodine value that can be an alternative method of existing chemical methods . This method can be applied to only pure edible oils.…”

“…It was reported that concentrated samples with large Raman cross section can be regarded as the limiting case that the resonant term is large enough in comparison with the nonresonant term. [16,17,20] Then only the first term is effective, and other terms are neglected in the right side of Equation 1. The resonant term is given by [21] 3χ res ¼ 2Nc 4 ℏω 4 s dσ dΩ ω 0 Δj…”

“…However, OA, LA, and LNA having 18 carbons contain one, two, and three double bonds within the fatty acid chain, respectively. [17] Figure 1(a) represents CARS spectra of edible oils in C─H stretching region. CARS spectra were recorded five times per sample and then were averaged.…”

“…And we demonstrated that CARS spectroscopy can determine the degree of unsaturation in edible oils and obtained the calibration curve for determining iodine value that can be an alternative method of existing chemical methods. [17] This method can be applied to only pure edible oils. If oil is not pure, it is impossible to identify the type and amount of impurities or adulterants with only the iodine value.…”