APPLICATION OF FLUORESCENCE EXCITATION–EMISSION SPECTROSCOPY FOR WALNUT OIL AUTHENTICATION

Abstract

Walnut oil is a high-value edible oil appreciated for its nutritional, sensory, and health-promoting properties. Due to its premium market value, it is particularly vulnerable to adulteration with lower-cost vegetable oils, creating the need for rapid and reliable authentication methods. In this study, a methodology based on three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy was investigated for the detection of walnut oil adulteration. Fluorescence excitation–emission data were acquired using a Shimadzu RF-6000 spectrofluorophotometer from authentic walnut oil samples and adulterated samples prepared with sunflower, rapeseed, and soybean oils at different concentration levels (5%, 10%, 20%, 30%, 40%, and 50%). The obtained EEM spectra revealed distinct fluorescence fingerprints for each oil type, reflecting differences in their chemical composition and fluorophore distribution. Authentic walnut oil exhibited characteristic fluorescence regions associated with natural pigments and antioxidant compounds, whereas adulterated samples showed notable changes in fluorescence intensity and peak distribution. The most pronounced spectral modifications were observed in the 470–550 nm region, indicating the influence of adulterant oils on the fluorescence profile of walnut oil. These results demonstrate that EEM fluorescence spectroscopy is a rapid, non-destructive, and sensitive technique for distinguishing authentic walnut oil from adulterated samples. The method shows strong potential for food authentication applications and could support quality control and fraud prevention in the edible oil industry.