Comparison Between Emerging and Conventional Methods for Edible Oils Bleaching

The activated bleaching clay is used at high temperatures and for extended periods to eliminate pigments and remove impurities from oils through physical and chemical interactions. However, the use of acid-activated clay in industrial oil bleaching (IB) presents several drawbacks: prolonged filtration times due to the clay's fine particle size and compact structure; substantial oil loss and the generation of significant acid and acidic salts requiring specialized disposal; increased environmental concerns and landfill costs due to excessive clay use; degradation of triacylglycerols into free fatty acids (FFAs); rising oil acidity; formation of undesirable byproducts such as conjugated dienes and trienes; and generation of oxidation byproducts during bleaching due to high acid-activated clay usage. Therefore, utilizing novel technologies to replace industrial approaches is of interest. Recently, ultrasound (US), microwave (MW), high-voltage electric field (HVEF), and membrane (MB) assisted bleaching have attracted much attention. These innovative methods can enhance the adsorbents' sorption capacity, reduce the quantity of adsorbent required, and decrease the time and temperature needed, making them likely to be cost-effective. In this review, the function of the industrial bleaching method for removing pigments, tocopherols, sterols, heavy metals, and primary and secondary oxidative products was investigated and compared with the emerging approaches. Adsorption isotherms favor the Freundlich and Langmuir models, reflecting heterogeneous multilayer adsorption. Kinetic studies often follow pseudo-first-order models for physisorption or pseudo-second-order for chemisorption, with intraparticle diffusion as a rate-limiting step. Thermodynamic analyses indicate that these processes are endothermic and spontaneous, driven by entropy gains.