Mitigation of 3-MCPD esters and glycidyl esters during the physical refining process of palm oil by micro and macro laboratory scale refining
Introduction
3-Monochloropropane-1,2-diol ester (3-MCPDE) and glycidyl esters (GE) are well known process contaminants that are found relatively abundant in refined palm oil compared to other refined vegetable oils, for instance soy, canola, and sunflower oil (Albuquerque et al., 2018, Beekman et al., 2019, Jędrkiewicz et al., 2016). These contaminants are formed during refining process of crude palm oil (CPO) whereby lipids such as triacylglycerols (TAG) and diacylglycerols (DAG) react with the chlorides at high temperatures processing.
Currently, palm oil is pervasive due to its availability, versatility and relatively low cost compare to the other vegetable oil. Palm oil and its derivatives have become common ingredients in many consumer products. Most commercial infant formulas are fortified with refined palm oil to confer a high nutritional profile. According to a recent pilot survey of 3-MCPDE and GE in infant formula in the market, there have been reductions in chloropropanol esters in comparison with earlier investigations in the literature, but there are no total elimination strategies yet (Becalski et al., 2015, Beekman et al., 2020, Nguyen and Fromberg, 2020, Wöhrlin et al., 2015). The presence of these esters in infant products can pose a very serious health issue given that many infants are solely bottle-fed with these products, which may entail considerable health risks. Furthermore, their reductions have become vital to the refineries or food industries especially when European Commission has set the maximum limit for GE at 1000 µg/kg in vegetable oils and fats for the consumer market or ingredients in food preparation and as low as 500 µg/kg when used for the production of baby food and processed cereal-based food for infants and young children (European Commission, 2018).
Although there are many existing patented solutions to reduce 3-MCPDE and GE, no one has yet devised a practical means that is widely applicable across refinery industries. Possible mitigation strategies, for instance, involve the use of ethanol, carbon dioxide or nitrogen sparge as a low-volatility and inert stripping agent during deodorization as well as the use of magnesium silicate and silica gel as adsorbents before or after the deodorization step; however, these strategies are costly and thus represent an impediment for implementation in refining processes. Furthermore, the application of a water or ethanol–water washing step for CPO or the washing of palm fruit pulp prior to oil extraction might compound water-related environmental issues; a concrete water management plan is required and must be designed with all factors taken into consideration, particularly when handling the massive quantities of CPO and palm fruit in the upstream industry (Oey et al., 2019, Sim et al., 2019). Therefore, a more multifaceted strategy should focus on and consider facets such as economic affordability, practicability and the impact of various crude oil qualities. Moreover, modifying or changing refining conditions will affect oil properties, such as the oxidative stability and sensory qualities of the oil. Thus, the aims of this investigation were to conduct a comprehensive study and gain a better understanding of the formation of 3-MCPDE and GE in the oil refining process, with the hope that effective and practical mitigation strategies will be developed for the palm oil industry to reduce or eradicate these process contaminants to minimum levels without affecting the quality of the final product.
In view of this matter, response surface methodology (RSM) was used to obtain the optimized refining conditions to produce a refined palm oil with the lowest 3-MCPDE and GE but with acceptable quality according to the trade specifications of the Palm Oil Refiners Association of Malaysia (PORAM) (refer to Table 1) without the need for additional processing steps. RSM is a powerful tool that not only enables the evaluation of the effects of several processing parameters and their interactions on the studied response variables but also simultaneously optimizes the levels of these variables to achieve the best or desired final product quality. This study also puts forward and discusses the use of laboratory-scale refining unit with different capacities, namely: micro lab-scale (0.1 kg) and macro lab-scale (1 kg and 3 kg) with respects to their impact on 3-MCPDE and GE formation as well as the final oil quality: color and FFA value which have not been investigated in any study before.
Section snippets
Materials
CPO was acquired from Sime Darby Golden Jomalina Sdn. Bhd. (Teluk Panglima Garang, Malaysia), and acid-activated bleaching earth was obtained from PT. Clariant Adsorbents Indonesia (Bogor, Indonesia). Phosphoric acid 20% was prepared by diluting phosphoric acid 85% (Merck, Darmstadt, Germany) with distilled water.
Analytical standards such as 1,2-dipalmitoyl-3-chloropropanediol (PP-3-MCPD), glycidyl palmitate (Gly-P), pentadeuterated glycidyl palmitate (Gly-P-d5), and pentadeuterated
Optimization of physical refining process for the production of RBD palm oil with reduced GE and 3-MCPDE
In the physical refining of palm oil, every stage in the processing serves its purpose to make the oil acceptable for human consumption. Although the deodorization process is well known to remove most of the FFAs, volatile odiferous and colored components to obtain a good quality oil in terms of organoleptic attributes and physiochemical quality, the degumming and bleaching process stages must be carefully monitored as well, as any failure or deficiency in the process can adversely affect the
Conclusions
In conclusion, the mitigation of the 3-MCPDE and GE was successfully achieved by the optimization of the physical refining process without the need for additional processing steps. In addition, the color and FFA contents were maintained in the acceptable range specified by PORAM. It was found that a higher phosphoric acid dosage induces the formation of 3-MCPDEs due to the inherent acidity that activates the protonation of acylglycerols in the presence of chlorides. Although acidity is widely
CRediT authorship contribution statement
Biow Ing Sim: Methodology, Data curation, Formal analysis, Investigation, Writing - original draft. Yih Phing Khor: Methodology, Data curation, Formal analysis, Investigation, Writing - original draft. Oi Ming Lai: Supervision, Writing - review & editing. Chee Beng Yeoh: Supervision, Writing - review & editing. Yong Wang: Supervision, Writing - review & editing. Yuanfa Liu: Supervision, Writing - review & editing. Imededdine Arbi Nehdi: Visualization, Software. Chin Ping Tan: Funding
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The work was supported by the Putra Grant, Universiti Putra Malaysia (Project number UPM/700-1/2/GIPP/2017/9532400). The authors would like to extend their gratitude to the King Saud University (Riyadh, Saudi Arabia) for the funding of this research through Researchers Supporting Project number (RSP-2019/80).
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