Effects of Heating on Vegetable Oil's Optical and Functional Groups

Abstract

Vegetable oils (VO) are essential in both nutritional and industrial applications; however, their physicochemical properties undergo notable changes upon heating. This study examines the optical and chemical characteristics of vegetable oils (Dhara; DhVOs, Sunflower; SuVOs and Soyabean; SoVOs) by analyzing parameters such as the absorption coefficient, extinction coefficient, mass attenuation coefficient, total molecular cross-section, functional groups, and zeta potential to evaluate thermal degradation and stability. Samples were collected from the local Kathmandu market, and some were prepared in the laboratory. Analytical techniques included UV–Vis spectrometry, Fourier Transform Infrared (FTIR) spectroscopy, and zeta potential measurements. The absorption coefficient, extinction coefficient, mass attenuation coefficient, and molecular cross-section were evaluated using UV–Vis spectroscopy. Results indicated that all these parameters decreased with increasing wavelength and were affected by thermal exposure. FTIR analysis revealed the presence of key functional groups such as C–H, C–N, C = O, O–H, and N–H. Heating effect was observed to influence these functional groups by causing peak shifts and an increase in the number of peaks, attributed to enhanced molecular vibrations. Zeta (ζ) potential measurements showed a notable reduction in particle size after heating: DhVO decreased from 7.17 nm to 3.54 nm, SuVO from 4.12 nm to 1.97 nm, and SoVO from 69.41 nm to 12.57 nm, along with frequency shifts indicating thermal effects on electric field interactions. The results demonstrate that heating alters molecular structure and enhances colloidal stability. Controlling heating conditions is recommended to optimize oil quality. Future research should investigate the nutritional and health effects of these physicochemical changes.