The colour of crude vegetable oil comes mainly from two pigment families: chlorophyll, which gives a green cast, and carotenoids, which give yellow to red hues. Activated bleaching earth removes these pigments by different mechanisms, and understanding the difference helps refiners hit colour targets efficiently. This guide explains.
Two Different Pigment Families
Chlorophyll is a magnesium-centred porphyrin pigment that is strongly polar and adsorbs readily onto the acid sites of activated bleaching earth. Carotenoids (carotene, xanthophylls) are non-polar conjugated hydrocarbons that are partly adsorbed and partly removed thermally during bleaching and deodorisation.
Why Chlorophyll Is the Bleaching Priority
Because chlorophyll is not significantly removed by heat alone, adsorption onto bleaching earth is the primary route for green-colour reduction. This makes the earth's surface area and acidity especially important for oils with high chlorophyll, such as sunflower, soybean and rapeseed oil.
Carotenoids and Heat Bleaching
Carotenoids in oils such as palm are partly adsorbed by the earth and partly destroyed by heat during high-temperature deodorisation. This is why palm oil refining combines earth bleaching with thermal carotene reduction.
Implications for Dosage
Oils dominated by chlorophyll typically respond strongly to higher-surface-area, acidic bleaching earth. Oils dominated by carotenoids may rely more on the thermal step, with bleaching earth handling the remaining pigments and oxidation products.
Matching Earth to the Pigment Load
Bleach Master's high surface area (290–310 m²/g) and controlled acidity make it effective against the polar chlorophyll pigments that are hardest to remove, helping refiners hit Lovibond targets reliably.
Frequently Asked Questions
Does bleaching earth remove chlorophyll or carotenoids better?
Bleaching earth is especially effective at adsorbing chlorophyll, which is polar and binds to its acid sites. Carotenoids are partly adsorbed and partly removed by heat during deodorisation.
Why does chlorophyll matter most in bleaching?
Chlorophyll is not removed by heat alone, so adsorption onto bleaching earth is the main route to reduce green colour. Surface area and acidity of the earth are therefore critical.
How are carotenoids removed in palm oil?
Through a combination of adsorption on bleaching earth and thermal destruction at high deodorisation temperatures, which is why palm refining pairs the two steps.
Which oils have the most chlorophyll?
Sunflower, soybean and rapeseed/canola oils often carry significant chlorophyll, making bleaching earth quality particularly important for hitting their colour specifications.
Need Activated Bleaching Earth for Your Refinery?
Contact Umiya Minerals for product samples, technical data sheets, and bulk pricing. We supply pan-India from Bhuj, Gujarat.