Effects of temperature and NaCl on the formation of 3-MCPD esters and glycidyl esters in refined, bleached and deodorized palm olein during deep-fat frying of potato chips
Introduction
The presence of 3-monochloro-1,2-propanediol (3-MCPD) esters together with glycidyl esters (GEs) has been reported in various types of refined vegetable oils, especially in refined palm oil. The toxicity of 3-MCPD esters and GEs is concerned due to their potential transformation to free form during digestion in the gastrointestinal tract. Free 3-MCPD is carcinogenic in animal studies. In acute studies, 3-MCPD caused effects in the kidneys, blood, and sperm. In further long-term studies, it induces tumors in rats. It causes a variety of toxicological effects in the blood, kidneys, and sperm in short-term studies and induces tumors in long-term studies in rats. 3-MCPD does not have genotoxic potential in animal studies (Matthäus, Pudel, Fehling, Vosmann, & Freudenstein, 2011). Unlike 3-MCPD, glycidol-induced genotoxic effects in in vitro assays in mammalian cells. Non-genotoxic, threshold carcinogen with a tolerable daily intake (TDI) of 2 μg/kg body weight (bw) per day was set for 3-MCPD by the European Scientific Committee on Food in 2001. Besides that, The Joint FAO/WHO Expert Committee on Food Additives (JECFA) set 2 μg/kg bw of provisional maximum tolerable daily intake (PMTDI) for 3-MCPD (Bakhiya, Abraham, Gurtler, Appel, & Lampen, 2011). The International Agency for Research on Cancer (IARC) suggested that glycidol should apply ALARA (As Low As Reasonably Achievable) principle as it was classified in group 2A (probably carcinogenic to human). The formation of 3-MCPD esters is associated with high temperature during the deodorization step of oil refining.
Generally, one of the proposed formation mechanism of 3-MCPD esters involves the formation of a cyclic acyloxonium ion from triacylglycerol, with the present of chloride ions. The formation precursors of 3-MCPD esters included chloride ions, glycerol, acylglycerols, temperature and time. Deep-fat frying is a common cooking method that involves a high temperature (>160 °C) comparable to a deodorization step. During common practice of frying, the oil is continuously and repeatedly used at high temperature (160–180 °C) with expose to air, leading to hydrolytic and oxidative decomposition of the oil (Bansal, Zhou, Barlow, Lo, & Neo, 2010).
Until today, most of the research on 3-MCPD and glycidyl esters was focused on the formation during the refining process. However, the changes in the levels of 3-MCPD and glycidyl esters during the high temperature process in cooking is worth investigating, as the fluctuations of these contaminants are still unknown. In this study, potato was used as a representative high-carbohydrate food. The effect of sodium chloride (NaCl) and temperature were investigated by soaking the potato chips in different concentrations of NaCl solution prior to frying at 160 °C or 180 °C.
Section snippets
Materials and chemicals
Refined, bleached and deodorized (RBD) palm olein (Elaeis guineensis var. tenera) was purchased from Moi Foods Malaysia Sdn. Bhd. (Selangor, Malaysia). Potatoes (Russet var.) were purchased from a local supermarket. 1,2-Bis-palmitoyl-3-chloropropanediol, 1,2-bis-palmitoyl-3-chloropropanediol-d5, glycidyl palmitate and glycidyl palmitate-d5 were purchased from Toronto Research Chemicals Inc. (Toronto, Canada). Acetone and acetonitrile of HPLC grades were purchased from Merck (Darmstadt,
Results and discussion
Deep-fat frying is one of the most common food processing methods. During frying, a series of physiochemical reactions such as hydrolysis, oxidation, polymerization and isomerization takes places with the present of oxygen, moisture and trace elements during high temperature thermal process. The decomposition of frying oil leads to the rapid degradation of the oil (Serjouie, Tan, Mirhossein, & Che Man, 2010). In this study, indirect method acid transesterification was used to determine 3-MCPD
Conclusion
The results of this study showed that frying duration, frying temperature and the concentration of sodium chloride have significant effects on the formation of 3-MCPD esters and glycidyl esters in RBD palm oil during deep fat frying. The order of the effects was frying temperature > frying duration > sodium chloride. In general, the 3-MCPD ester trend was decreasing when the frying duration increased, whereas the trend was increasing when frying temperature and concentration of NaCl increased. The
Acknowledgement
The work was supported by the Putra Grant, Universiti Putra Malaysia (project number GP-IBT/2013/9419500).
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