Although studies indicate chemical changes during bleaching such as carotene and unsaturated fatty acids oxidation, which are probably responsible for the color fixation of palm oil, this process is not very clear. The objective of this study was to investigate the effect of type and amount of bleaching earth (BE) on the final quality of refined palm oils, especially on the oxidative state and color. Two types of bleaching earth were tested, one natural (NBE) and one acid-activated (ABE) (0.5-3.0% w/w). Crude palm oils were bleached at 105°C, during 30min at 50mmHg pressure. Afterwards, a deodorization step was performed at 260°C, 3mbar, 1.5% steam during 60min. These refining procedures were evaluated after each step by measuring β-carotene, color, peroxide (PV) and p-anisidine (pAV) values. It was observed that both BE can decompose peroxides. However, a maximum pAV followed by a decrease was observed for ABE while the pAV remains approximately constant at a maximum for NBE, suggesting only ABE catalytically decomposes secondary oxidation products. The color after deodorization was inversely proportional to pAV when bleaching was performed with ABE, even though the oil has a lighter color after deodorization. © 2014 Elsevier Ltd.592P212581264Ahmad, A.L., Chan, C.Y., Shukor, S.R.A., Mashitah, M.D., Adsorption kinetics and thermodynamics of beta-carotene on silica-based adsorbent (2009) Chemical Engineering Journal, 148 (2-3), pp. 378-384(1998) Methods and recommended practices of the American Oil Chemists' Society, , Champaign, AOCSBenevides, C.M.D., Veloso, M.C.D., Pereira, P.A.D., de Andrade, J.B., Achemical study of beta-carotene oxidation by ozone in an organic model system and the identification of the resulting products (2011) Food Chemistry, 126 (3), pp. 927-934Boki, K., Kubo, M., Wada, T., Tamura, T., Bleaching of alkali-refined vegetable-oils with clay-minerals (1992) Journal of the American Oil Chemists Society, 69 (3), pp. 232-236Bonnie, T.Y.P., Choo, Y.M., Oxidation and thermal degradation of carotenoids (1999) Journal of Oil Palm Research, 2 (1), pp. 62-78Bosser, A., Paplorey, E., Belin, J.M., Asimple way to (+/-)-dihydroactinidiolide from beta-ionone related to the enzymatic cooxidation of beta-carotene in aqueous-solution (1995) Biotechnology Progress, 11 (6), pp. 689-692Burton, G.W., Ingold, K.U., Beta-carotene - an unusual type of lipid antioxidant (1984) Science, 224 (4649), pp. 569-573Dijkstra, A.J., Enzymatic degumming (2010) European Journal of Lipid Science and Technology, 112 (11), pp. 1178-1189Dijkstra, A., Segers, J., Production and refining of oils and fats (2007) The lipid handbook with CD-ROM, pp. 143-262. , CRC PressEl-Agamey, A., McGarvey, D.J., Evidence for a lack of reactivity of carotenoid addition radicals towards oxygen: a laser flash photolysis study of the reactions of carotenoids with acylperoxyl radicals in polar and non-polar solvents (2003) Journal of the American Chemical Society, 125 (11), pp. 3330-3340Fraser, M.S., Frankl, G., Colored components of processed palm oil (1981) Journal of the American Oil Chemists Society, 58 (10), pp. 926-931Gee, P.T., Analytical characteristics of crude and refined palm oil and fractions (2007) European Journal of Lipid Science and Technology, 109 (4), pp. 373-379Gibon, V., De Greyt, W., Kellens, M., Palm oil refining (2007) European Journal of Lipid Science and Technology, 109 (4), pp. 315-335. , (This paper presents a complete review on palm oil refining procedures, including its main problems such as the color fixation discussed in our work. In fact, this work highlights about the problem of color fixation for the palm oil refiners.)Kamal-Eldin, A., (2003) Lipid oxidation pathways, , AOCS Press, Chaimpaing, IL, (This book presents three possible pathways for β-carotene oxidation and how different environments can affect it. It was important to the authors to conclude that the environment modification made by the bleaching earth could affect the oxidation pathway.)Kent, K., Adsorption (2008) Albright's chemical engineering handbook, pp. 1119-1171. , CRC PressKhoo, L.E., Morsingh, F., Liew, K.Y., Adsorption of beta-carotene-1 by bleaching earths (1979) Journal of the American Oil Chemists Society, 56 (7), pp. 672-675Krinsky, N.I., Yeum, K.J., Carotenoid-radical interactions (2003) Biochemical and Biophysical Research Communications, 305 (3), pp. 754-760. , (This reference shows that β-carotene can react through cation, forming an alkyl radical. This is the mechanism we ascribe to oxidation when using acid activated bleaching earth.)Liebler, D.C., Antioxidant reactions of carotenoids (1993) Carotenoids in Human Health, 691, pp. 20-31Liebler, D.C., McClure, T.D., Antioxidant reactions of beta-carotene: identification of carotenoid-radical adducts (1996) Chemical Research in Toxicology, 9 (1), pp. 8-11Maclellan, M., Palm oil (1983) Journal of the American Oil Chemists Society, 60 (2), pp. 368-373Martinez, A., Vargas, R., Galano, A., Theoretical study on the chemical fate of adducts formed through free radical addition reactions to carotenoids (2010) Theoretical Chemistry Accounts, 127 (5-6), pp. 595-603Marty, C., Berset, C., Factors affecting the thermal-degradation of all-trans-beta-carotene (1990) Journal of Agricultural and Food Chemistry, 38 (4), pp. 1063-1067Mordi, R.C., Walton, J.C., Burton, G.W., Hughes, L., Ingold, K.U., Lindsay, D.A., Oxidative-degradation of beta-carotene and beta-apo-8'-carotenal (1993) Tetrahedron, 49 (4), pp. 911-928. , (This reference presents the main stable products of β-carotene, such as high molecular weight components (epoxy-β-carotenes, apo-carotenals and apo-carotenones).)Petrauskaite, V., De Greyt, W.F., Kellens, M.J., Physical refining of coconut oil: effect of crude oil quality and deodorization conditions on neutral oil loss (2000) Journal of the American Oil Chemists Society, 77 (6), pp. 581-586(1990) Test methods carotene content, , PORIMRodriguez, E.B., Rodriguez-Amaya, D.B., Formation of apocarotenals and epoxycarotenoids from beta-carotene by chemical reactions and by autoxidation in model systems and processed foods (2007) Food Chemistry, 101 (2), pp. 563-572Rossi, M., Gianazza, M., Alamprese, C., Stanga, F., The effect of bleaching and physical refining on color and minor components of palm oil (2001) Journal of the American Oil Chemists Society, 78 (10), pp. 1051-1055Sabah, E., Cinar, M., Celik, M.S., Decolorization of vegetable oils: adsorption mechanism of beta-carotene on acid-activated sepiolite (2007) Food Chemistry, 100 (4), pp. 1661-1668Sampaio, K.A., Ceriani, R., Silva, S.M., Taham, T., Meirelles, A.J.A., Steam deacidification of palm oil (2011) Food and Bioproducts Processing, 89 (C4), pp. 383-390Sarier, N., Guler, C., Beta-carotene adsorption on acid-activated montmorillonite (1988) Journal of the American Oil Chemists Society, 65 (5), pp. 776-779. , (This paper presents a study on β-carotene adsorption on acid activated montmorillonite. On this work, it was observed that carotenes remaining in solution after adsorption process was oxidized, giving us the clue to our hypothesis.)Silva, S.M., Sampaio, K.A., Ceriani, R., Verhé, R., Stevens, C., De Greyt, W., Adsorption of carotenes and phosphorus from palm oil onto acid activated bleaching earth: equilibrium, kinetics and thermodynamics (2013) Journal of Food Engineering, 118 (4), pp. 341-349Taylor, D.R., Bleaching (2005) Bailey's industrial oil & fat products, 5, pp. 285-340. , John Wiley & Son, New YorkWache, Y., Bosser-DeRatuld, A., Lhuguenot, J.C., Belin, J.M., Effect of cis/trans isomerism of beta-carotene on the ratios of volatile compounds produced during oxidative degradation (2003) Journal of Agricultural and Food Chemistry, 51 (7), pp. 1984-1987Zeb, A., Oxidation and formation of oxidation products of beta-carotene at boiling temperature (2012) Chemistry and Physics of Lipids, 165 (3), pp. 277-281Zeb, A., Murkovic, M., Determination of thermal oxidation and oxidation products of beta-carotene in corn oil triacylglycerols (2013) Food Research International, 50 (2), pp. 534-544Zeb, A., Murkovic, M., Pro-oxidant effects of beta-carotene during thermal oxidation of edible oils (2013) Journal of the American Oil Chemists Society, 90 (6), pp. 881-889Zschau, W., Bleaching of edible fats and oils - cooperative work of the German Society for Fat Science (DGF) (2001) European Journal of Lipid Science and Technology, 103 (8), pp. 505-550. , Grp G.S.F.S.S