Formation and reduction of 3-monochloropropane-1,2-diol esters in peanut oil during physical refining
Introduction
3-Chloropropane-1,2-diol (3-MCPD) is a food processing contaminant most commonly occurring in acid hydrolyzed vegetable protein (HVP) and its derived products. 3-MCPD, known as a carcinogen to induce tumors on rodents in long-term studies, was classified by the European Scientific Committee on Food in 2001 as a nongenotoxin, threshold carcinogen with a tolerable daily intake (TDI) of 2 μg/kg body weight (BW) per day. Recently 3-MCPD esters were detected in a number of foodstuffs such as edible oils (Zelinková, Svejkovská, Velíšek, & Doležal, 2006), infant formula (Zelinková, Doležal, & Velíšek, 2009) and human breast milk (Zelinková et al., 2008). Since 3-MCPD esters can be metabolized to release free 3-MCPD in the human gastrointestinal system (Buhrke, Weißhaar, & Lampen, 2011), their potential risks are highly concerned by scientists, manufacturers and consumers.
A previous study indicated that refined oils, especially palm oils, contained the highest amounts of 3-MCPD esters (Zelinková et al., 2006). Therefore, minimizing the contents of 3-MCPD esters in oils is urgently required. A variety of efforts have been made to mitigate 3-MCPD esters (Bornscheuer and Hesseler, 2010, Matthäus et al., 2011, Strijowski et al., 2011). However, for the sake of the more efficient reduction, it is still necessary to understand the refining procedures on the formation of 3-MCPD esters in edible oils.
The mechanism of 3-MCPD esters formation during the refining process is not very clear so far. It is undoubted that the deodorization step of oil refining plays a pivotal role in the formation of 3-MCPD esters. Especially, the high temperature during deodorization exceeding 200 °C are considered to be the main reason for the high contents of 3-MCPD esters observed in refined oils. Sampaio et al. (2013) found that temperature had the highest effect on the increase of the formation of the 3-MCPD esters during the refining of palm oil. Franke, Strijowski, Fleck, and Pudel (2009) reported that deodorization step had a significant impact on the formation of 3-MCPD esters for all oils whereas a direct effect of the other process steps could be neglected. Zulkurnain et al. (2012) claimed that the formation of 3-MCPD esters in refined palm oil during deodorization was attributed to the intrinsic composition of crude palm oil, and 3-MCPD ester could be reduced by removing related precursors prior to the deodorization step. Palm oil was always chosen as the study material in the publications mentioned above, not only because of its high contents of 3-MCPD esters but also its high consuming amounts in the world. Different types of oil may contain different precursors (Franke et al., 2009, Hrncirik and van Duijn, 2011). And the influences of refining conditions on the formation of 3-MCPD esters are various among different oils. Therefore, other types of oil should be also concerned about. Some surveys (Li et al., 2015, Zelinková et al., 2006) have shown that peanut oil was not most highly contaminated by 3-MCPD esters, but was consumed widely in many countries (Akhtar, Khalid, Ahmed, Shahzad, & Suleria, 2014). In 2014, the peanut oil production was 5.52 million tons in the world, therein 5.50 million tons were domestically Consumed (USDA., 2015). Therefore, it is necessary to investigate the formation and find out the reduction strategy to minimize the level of 3-MCPD esters.
In the present study, crude peanut oil was refined step by step in a laboratory scale. The impact of physical refining procedures on the formation of 3-MCPD esters was investigated by monitoring the content changes of 3-MCPD esters in the oil at the end of each refining step. And attempts were carried out for the reduction of 3-MCPD ester by washing off the potential precursors and adding auxiliary materials, diacetin, before deodorization step.
Section snippets
Materials and methods
Peanuts were purchased from a local market in Nanchang, China. Peanuts were from different locations (Henan, Shandong and Jiangxi), which were labeled on the packages.
The effects of refining on the formation of 3-MCPD esters
As shown in Table 1, deodorization was a critical factor that influenced the formation of 3-MCPD esters in peanut oil among the refining steps. In order to examine if there were any differences in the contents of 3-MCPD esters between different ways of oil production, hot pressing and solvent extracting were introduced for crude oil production. The results showed that the contents of 3-MCPD esters in crude oils extracted by solvent were lower than the limit of detection (LOD = 25 μg/kg). In hot
Conclusion
3-MCPD esters was not detected in degumming and bleaching oil when crude oils were extracted by solvent. Hot squeezing generated a low level of 3-MCPD esters in crude oils. Temperature played a key role in the formation of 3-MCPD esters. 3-MCPD esters were generated with highest contents in 1–1.5 h at a certain high temperature (220–260 °C). With the increase of deodorizing time, 3-MCPD esters tended to degrade after 2 h. There was a positive correlation between precursors (DAGs, MAGs and
Conflict of interest
The authors declare that there are no conflicts of interest.
Acknowledgements
This research was supported by National Key Technology R&D Program of China (Grant no. 2014BAD04B03) and the National Basic Research Program of China (“973” Program) (Grant no. 2012CB720805) and the Natural Science Foundation of Jiangxi Province, China (Grant no. 20142BAB204002).
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