# Comparison Between Emerging and Conventional Methods for Edible Oils Bleaching

## TL;DR

This paper reviews traditional and new methods for bleaching edible oils, highlighting the drawbacks of acid-activated clay and the potential benefits of emerging technologies like ultrasound and microwave.

## Contribution

The paper compares conventional acid-activated clay bleaching with novel technologies like ultrasound and membrane-assisted methods for edible oil purification.

## Key findings

- Traditional acid-activated clay bleaching causes oil degradation, environmental issues, and byproduct formation.
- Emerging methods like ultrasound and microwave improve adsorption efficiency and reduce processing time and temperature.
- Adsorption processes follow Freundlich and Langmuir isotherms and are endothermic and spontaneous.

## Abstract

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.

The use of acid‐activated clay in industrial oil bleaching presents several drawbacks: prolonged filtration times, substantial oil loss, increased environmental concerns, landfill costs, degradation of triacylglycerols, increasing oil acidity, and formation of undesirable byproducts such as conjugated dienes and trienes. Utilizing novel technologies to replace industrial approaches is of interest. Recently, ultrasound, microwave, high‐voltage electric field, and membrane‐assisted bleaching have attracted much attention. These innovative methods could enhance the adsorbents' sorption capacity and reduce the adsorbent, time, and temperature.