Assessing the capacity of some New Zealand clays for decolourizing vegetable oil and butter

Some naturally acid New Zealand clays, of soil and hydrothermal origin, have been evaluated for their ability to decolourize a wheatgerm oil and a clarified butter. Samples rich in allophane, halloysite, kaolinite, and montmorillonite were investigated. Decolourizing capacity decreased in the order halloysite > kaolinite > montmorillonite > allophane. This observation reflects the natural pH and surface properties of the samples. Clays that had been severely leached by acids during their formation showed a relatively high propensity for decolourizing oil and butterfat. These materials required only minor treatment with HCl to optimize performance. The decolourizing capacity of an acid pedogenic halloysite-rich clay from the Bay of Islands, which had been further acidified to pH 1.5, closely matched that of Tonsil Optimum FF, a standard acid-activated clay based on montmorillonite.