Influence of chemical refining process and oil type on bound 3-chloro-1,2-propanediol contents in palm oil and rapeseed oil

Abstract

The formation of bound 3-chloro-1,2-propanediol (3-MCPD-ester) in oils during chemical refining process was investigated for two palm oils and one rapeseed oil. Additionally, contents of mono- and diglycerides as well as total chlorine and chloride were determined. For all oils the deodorisation step representing one part of the refining process had the main impact on formation of 3-MCPD-esters whereas a direct effect of the other process steps could be neglected. 3-MCPD values in the range of 4–5 ppm for palm oil and 1 ppm for rapeseed oil were found. The chloride content was below detection limit. However, measurable amounts of total chlorine were found in palm oil with the highest 3-MCPD-ester contents. A considerable part of this total chlorine in the refined palm oil was embedded in the 3-MCPD-esters. On the other hand, content of diglycerides as the other potential pre-cursor was between 1% and 10% exceeding the 3-MCPD-ester contents by up to five magnitudes.

Introduction

Free 3-chloro-1,2-propanediol (3-MCPD) is known as a substance which exhibits genotoxic effects in in-vitro tests but not in in-vivo studies. JECFA recommended a maximum tolerable daily intake of 2 μg/kg BW (Opinion, 2001). So far, soy products especially hydrolyzed soy proteins in sauces were found with higher amounts of free 3-MCPD and for these products a provisional maximum level of 0.02 mg/kg on a liquid basis was fixed by the European Commission (Commission regulation 466/2001).

During the last few years the occurrence of 3-MCPD bound in 3-MCPD fatty acid esters (3-MCPD-ester) containing one or two fatty acids at the sn-1 and sn-2 position of the glycerol backbone was reported for refined fats and oils by several groups (Svejkovska et al., 2004; Weißhaar, 2008, Zelinková et al., 2006). Up to 1.5 mg/kg 3-MCPD liberated from the ester-bound form was found in refined olive oil (Weißhaar, 2008) and about 2.5 mg/kg were found in fat mixes containing palm olein (Seefelder et al., 2008).

So far, recommendations for daily intake of 3-MCPD-esters do not exist. However, the current toxicological risk evaluation of 3-MCPD-ester of German authorities and EFSA is based on the assumption that all bound 3-MCPD is released in the body during digestion (BfR, 2007, EFSA, 2008). Considering such a worst case scenario, the application of refined oils and fats can lead to a significant excess of the recommended daily intake of free 3-MCPD, especially in infant foods that contain vegetable oils.

Therefore, a short-term minimization of 3-MCPD-ester contents in oils is required.

So far, limited and contradictory knowledge is available about the influences of the raw materials and refining procedures on the formation of 3-MCPD-esters in oils. The highest ester contents were found in refined oils whereas virgin or non-refined oils have low contents which are often below detection limits. A heat pre-treatment of the seed (or fruit), e.g. roasting, can contribute to detectable contents in non-refined oils.

Refined olive oils and palm oils seem to generate higher levels of 3-MCPD-esters compared to seed oils like rapeseed oil or maize oil (Zelinková et al., 2006). With respect to processing conditions, Zelinková et al. (2006) found a decrease in the contents during longer heating at 230 °C for olive oils and an increase for rapeseed oil. On the other hand, they found a decrease of 3-MCPD-esters in rapeseed oil during the refining process including deodorisation. Therefore, the influence of single refining steps on contents of bound 3-MCPD in different type of oils is ambiguous so far. To get more insight into the influences of oil type and refining processes, own investigations were carried out for palm oil and rapeseed oil. Additionally, the contents of potential pre-cursors for the formation of 3-MCPD-ester, especially mono- and diglycerides as well as total chlorine and chlorides, were determined in the oils.