BLEACHING AND CLARIFYING

 

During the last century, Ca-bentonites have increasingly been used to clarify and decolorize, or “bleach,” animal, vegetable, and mineral oils. Animal and vegetable oils contain many impurities, such as gums, phosphatides, trace metals, and free fatty acids that can produce undesirable oxidation products and reduce product shelf life.

Bleaching clays remove many of these substances, as well as color-producing compounds such as chlorophyll, xanthophyll, and carotenes. Ca-bentonites are particularly effective as bleaching clays after they have been treated with acid to improve their porosity.

Na-bentonite has a long history of use as a fining agent for clarifying wine and juice. Fining is a process in which an adsorptive substance is introduced into the liquid to remove suspended proteins and other organic colloids that would otherwise precipitate or creates haze when the liquid is chilled. Because of their small size and solubility, these undesirable materials are difficult to remove by conventional filtration. The large surface area and high negative charge of montmorillonite makes bentonite ideal for adsorbing positively charged compounds, such as proteins, and removing them through flocculation.

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