Thermal degradation in edible oils by surface enhanced Raman spectroscopy calibrated with iodine values

Ho Ying Lam, Pradip Kumar Roy, Surojit Chattopadhyay*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

We present a facile surface enhanced Raman scattering (SERS) based methodology to study the thermal degradation of edible oils using a special gold sputtered SERS tattoo. The methodology is calibrated with Iodine values, which is an industrial standard. This analytical study aims to compare the safety of 7 edible oils rich in monounsaturated (MU), polyunsaturated (PU), and saturated (S) fatty acids (FA) against high temperature re-cooking as done in most restaurants, and street food joints. The changes in the SERS signal intensity (I) ratio of the saturated (@1440 cm-1), and unsaturated (@ 1265 cm−1) FA, I1265/I1440, was studied as a function of heating time, and temperature (T), around the ‘smoke point’. The SERS marker for thermal degradation, I1265/I1440, measuring the normalized unsaturated FA content in the oils decreased consistently, and significantly for the PUFA, and MUFA oils when heated above the ‘smoke point’, following the changes in the industrial standard ‘Iodine value’. Olive (MUFA), and Coconut (SFA) oil showed marginal, and no decrease, respectively, of the SERS marker over the temperature range studied. Based on the SERS marker, a parameter ζ, -the decrease of (I1265/I1440) value of the heated oil with respect to the as-purchased value, is defined that can compare the degradation of the edible oils under different thermal stressing. The Arrhenius fit of the SERS marker yielded similar activation energy of the thermal degradation to that obtained independently from Iodine value, and demonstrates the correctness of the presented methodology.

Original languageEnglish
Article number103018
JournalVibrational Spectroscopy
Volume106
DOIs
StatePublished - Jan 2020

Keywords

  • Edible oil
  • Gold film
  • Iodine value
  • SERS
  • SERS tattoo

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