Optical Characterization of Shea Butter Oil Used for Frying by SLIPI-1p at 450 nm

Shea butter oil (Vitellaria paradoxa) is widely used in West Africa as a frying medium, particularly for cooking plantain bananas. During repeated frying cycles, this oil undergoes significant physicochemical transformations that alter its optical properties. In this study, the optical behavior of shea butter oil subjected to successive frying operations was investigated using the single-phase Structured Laser Illumination Planar Imaging technique (SLIPI-1p). Ten oil samples, labeled E₁ to E₁₀, were collected at successive frying stages under controlled and identical conditions, with E1 corresponding to the oil after the first two frying cycles and E10 after twenty cycles. The samples were analyzed at a wavelength of 450 nm. The SLIPI-1p technique enabled the reduction of multiple scattering effects, while a dedicated image-processing workflow was applied to extract the extinction coefficient reliably from the transmitted laser sheet. The results show that the extinction coefficient increases progressively from 0.3475 to 0.4854, reflecting the accumulation of absorbing and scattering species generated during thermal degradation. This evolution indicates a cumulative degradation mechanism in which optically active species increase with each frying cycle. These findings demonstrate that SLIPI-1p is a powerful, non-destructive tool for characterizing dense edible oils. The method shows strong potential for real-time monitoring of frying oil degradation, although further validation against standard chemical indicators, such as peroxide value and total polar compounds, is required. Future work will include correlation with these chemical indicators to strengthen the interpretation of optical measurements.