Study the removal of MOH in refining palm oil, with a special focus on MOAH and MOAH with more than three aromatic rings.

Abstract

Mineral oil hydrocarbons (MOH) are lipophilic food contaminants that can be present in edible oils. Mineral oil aromatic hydrocarbons (MOAH) are a subdivision of MOH, and their toxicity is a cause for concern according to the European Food Safety Authority (EFSA). More specifically, MOAH with three or more rings (MOAH ≥ 3 rings) might be carcinogenic and mutagenic. Recent studies have shown that certain steps in oil refining can reduce MOH content. Deodorization, in particular, has been shown to have a significant effect on reducing MOH. More recently, a preliminary study has shown that bleaching with activated carbon (AC) as an adsorbent can reduce MOAH. However, this study did not examine MOAH subclasses (i.e., C-fraction and number of aromatic rings), and the tests were conducted in hexane rather than oil. Apart from a few studies on the reduction of MOH through refining, the scientific literature on this subject remains limited. The primary objective of this study was therefore to investigate the elimination of MOAH and MOAH subclasses through the bleaching of palm oil with AC. To this end, two palm oils were studied (one fully refined and the other only bleached) with two types of AC. These four conditions were analysed using a design of experiment (DOE) to test different temperatures (60-80-100°C) and different AC dosages (0.3-0.68-1.05-1.43-1.8%). The pressure (50 mbar) and contact time (30 min) were kept constant. The results of these experiments really demonstrated for the first time that MOAH ≥ 3 rings can be significantly and more effectively reduced by adsorption on AC than MOAH 1-2 rings. Furthermore, it was shown that a high degree of alkylation of MOAH seems to reduce their removal rate during bleaching. The properties of the AC and the degree of oil refining also influence the adsorption efficiency. Finally, this work showed that an increase in AC concentration allows for the elimination of more MOAH and that there may be an optimal temperature (specific to each type of AC) above which MOAH desorption could occur. The second objective was to test deodorization temperatures (240-260°C) and pressures (1-3 mbar) not yet analysed in the literature in order to study their effects on MOAH and MOAH subclasses. The amount of steam (1%) and time (60 min) were kept constant. The results showed that the most extreme condition (i.e., 260°C and 1 mbar) could reduce total MOAH by 68.2%: >83% of MOAH below C25 and ±82% of MOAH below C35.