Bleaching

Abstract

Traditionally, bleaching refers to that process by which colored pigments are removed from fats and oils by adsorption onto bleaching earth. Of course, certain noncolored constituents are also removed as well. In fact, the removal of particular colored and noncolored constituents during bleaching is necessary if high‐quality oil is to be produced. In this chapter, the idea of bleaching as primarily an adsorptive purification process is developed. Four key aspects are addressed: (1) the use of adsorptive purification agents, (2) the adsorptive removal of targeted constituents, (3) practical means and methods for achieving optimal efficiency and efficacy from the bleaching process, and (4) approaches for dealing with spent adsorbents. The properties and preparation of the main adsorptive purification agents used in the bleaching process (activated carbon, bleaching earth, and silica hydrogel) are discussed; differences between acid‐activated and natural bleaching earths and the types of clays used in their manufacture are delineated. The effects of various trace constituents (and contaminants) on oil quality, and the nature and specificity of their interaction with surface‐active (adsorption) sites are described. In particular, the control that noncolored constituents (phospholipids, soaps, free fatty acids, peroxides) exert over the adsorption of colored pigments (carotenoids, chlorophyll, pheophytins) is elucidated. Optimal bleaching practices and filtration conditions (“press bleach effect”) as well as processes and equipment for achieving maximum efficiency from the bleaching process are described. Finally, various tactics regarding spent filter cake, including utilization/disposal, best methods to recover retained oils, and control over smoldering, are examined.

Optimization of Bleaching Parameters in Refining Process of Kenaf Seed Oil with a Central Composite Design Model

“…Percent differences of the TOTOX between the experimental values and predicted values were ranged from 0% to 10.79%, while percent differences of the color reduction between the experimental values and predicted values were ranged from 0.52% to 10.98%. Bleaching earth removes color pigments through physical adsorption while other components are removed through chemically bound to the bleaching earth via covalent or ionic bonds (Taylor ; Gibon and others ). Acid‐activated bleaching earth is more frequently used than natural bleaching earth due to its highly adsorptive and more chemically active properties (Ghazani and Marangoni ).…”

“…Acid‐activated bleaching earth is more frequently used than natural bleaching earth due to its highly adsorptive and more chemically active properties (Ghazani and Marangoni ). Neutral bleaching earth represents as an adsorptive agent only (Taylor ), whereas acid‐activated bleaching earth performs simultaneously as a solid, acidic catalyst, adsorptive agent, cation exchanger and filter aid (Zschau and Grp ). Acid treatment on the bleaching earth is expected to increase in the specific surface area and porosity to improve the adsorption capacity of color pigments, impurities and residual phospholipids and soaps (Valenzuela‐Diaz and Souza‐Santos ).…”

Accelerating Bleaching of Soybean Oil by Ultrasonic Horn and Bath Under Sparge of Helium, Air, Argon and Nitrogen Gas

“…Optimal temperature for adsorption process is 80–100C (Taylor ). The kinetics of bubble growth and collapse can determine the total energy released by cavitation.…”

Optimization of Palm Oil Physical Refining Process for Reduction of 3-Monochloropropane-1,2-diol (3-MCPD) Ester Formation

“…Most of the gums and impurities are removed during water degumming, but acid degumming resulted in further precipitation of residual gums, expected to be the nonhydratable phospholipid, which can be removed only by a strong acid wash . This shows that acid degumming is crucial for palm oil physical refining because water degumming alone is not sufficient to get rid of the nonhydratable phospholipid, the presence of which could impart undesirable flavors and colors and shortens the shelf life of refined palm oil . Subsequently, the acid-degummed oil was washed with 1% water because the acid-degumming step could lead to activation of 3-MCPD ester precursors.…”