Sensitive label-free detection of adulteration in sesame oil using mode-mismatched dual-beam thermal lens technique

The growing demand and high economic value of vegetable oils (VOs), particularly sesame oil (SO), have made them increasingly vulnerable to adulteration with lower-cost alternatives such as sunflower and coconut oils. The work presents a laser-assisted, label-free method for the detection and characterization of adulteration in SO, aligning with the broader goals of food quality assurance and authenticity. This study explores the impact of adulterant volume concentration (10 %-50 %) on the thermal diffusivity (D) of SO using a highly sensitive mode-mismatched dual-beam thermal lens (MMDBTL) technique. Adulteration-induced changes are examined using Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopy. While FTIR spectra initially appear similar, detailed analysis reveals intensity shifts in characteristic absorption modes. PL spectra show a clear decrease in emission intensity with increasing adulteration, further confirmed through analysis using the International Commission on Illumination coordinates and power spectra. The inverse relationship between PL intensity and TL signal amplitude demonstrates a complementary nature between radiative and nonradiative emissions. Crucially, the MMDBTL measurements indicate a consistent reduction in D values with higher adulterant percentages, signifying increased thermal inertia and heat retention due to added resistance to heat flow. This work advances food traceability and authenticity detection by introducing a non-destructive technique for monitoring oil quality, with potential implications for both regulatory enforcement and the development of thermally functional food ingredients.