Abstract
Discarded bleaching earth was used after its reactivation for the bleaching of sunflower, soybean and corn oils. The efficiency of reactivated bleaching earth was compared to the efficiency of virgin activated bleaching earth. Acid reactivated earth (pH 2.5-3) had a slightly higher content in silicone than virgin activated or neutralized reactivated earths. The best results in the color of sunflower and corn oils were obtained when neutralized earth (pH 6–7) was used at 1 and 2 % levels. Acid reactivated earth used at 2 % achieved a higher reduction in soybean oil color than virgin earth (pH 3) at the same dosage. Both reactivated earths reduced peroxide value, iron, conjugated dienes and soap, while they increased acidity and conjugated trienes. Furthermore, these reactivated earths determined higher decrements in the oil induction period than virgin earth. Reactivated earth could be used for 5 cycles for the bleaching of soybean or corn oils and for more than 6 cycles for sunflower oil.
Highlights
Bleaching is recognized as one of the most important steps in edible oil processing (Mag, 1990; Micheal et al, 1992)
Bleaching clay is a general term for a clay-like substance, water containing aluminosilicates containing various proportions of magnesium, calcium and iron (Waldmann and Eggers, 1991)
The results showed that silicone was the main mineral present, followed by aluminum for virgin activated and reactivated bleaching earths but at different levels
Summary
Bleaching is recognized as one of the most important steps in edible oil processing (Mag, 1990; Micheal et al, 1992). According to Brimberg (1982), Young (1987), Abul Kalam and Joshi (1988), and Topallar (1998), bleaching is used daily in refining practices and aims at the removal of coloring bodies, pigments, etc., and at the removal of residual amounts of phospholipids, mucilage, oxidized tri – or partial acyl – glycerols, metal traces in ionizable and non – ionizable (complexed) forms, and soap traces which survived the washing of the neutralized oil. Waldmann and Eggers (1991) reported that montmorillonite is the starting material for all activated bleaching clays. Waldmann and Eggers (1991) mentioned that to make clay suitable for bleaching purposes, montmorillonite is subject to acid treatment, which replaces cations by protons and partially dissolves the original crystal structure. Many other processes for the regeneration of bleaching earth have been patented (Abul Kalam and Joshi, 1988). In Egypt, spent bleaching earth is not used in any manufacturing, so this discard causes some problems for the environment
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