3-MCPD Esters Derived From Edible Oil, Their Exposure Assessment, Formation Mechanism And Control During Heat Process

3-monochloropropane-1,2-diol fatty acid esters (3-MCPD esters) are a group of contaminants derived from food processing, which mostly occur with high content in edible oil and fat as well as foods contained fat.3-MCPD esters can be hydrolyzed by lipase to release free 3-MCPD.3-MCPD had been regarded as possible carcinogen. Therefore,3-MCPD esters have received great attention from food safety research area. An analysis method was developed and validated firstly in this research. Then exposure assessment of 3-MCPD esters to Chinese population was investigated. The effects of oil refining on the formation of 3-MCPD esters, the pathway and mechanism of the formation of 3-MCPD esters and the control strategies as well, were also investigated in this study. The results of this study can provide theory reference for the risk assessment, deep insight into the mechanism, establishing control strategy in the future. The main studies and results were summarized as follows:1. A gas chromatography mass spectrometry (GC-MS) method was developed and validated for the determination of the sum of 3-monochloropropane-l,2-diol (3-MCPD) esters in edible oils. Meanwhile the measurement uncertainty was estimated.Good linearity was observed with the GC-MS method for the concentration range of 0.05-5.0 mg/kg (R2=0.9994). It was proved to be an accurate and precise method for the determination of 3-MCPD esters according to the validation results. The recovery range was 89.0-104.6% and the limits of detection (LOD) and the limits of quantification (LOQ) were 25 and 50 μg/kg, respectively. Satisfactory reproducibility was achieved with lower than 15%. Repeatability was determined and expressed as relative standard deviation (RSD), with the value range of 3.9-12.0%.The contents of 3-MCPD esters were determined in twelve kinds of oils using this method. Measurement uncertainties were calculated by applying bottom-up approach. The main dominant sources were identified and quantified, which were standard solutions preparation, recovery and calibration curve. It reminds that the predominant uncertainty sources should be paid much more attention during preparing the testing samples in the future.2. The exposure assessment of 3-MCPD esters to Chinese population was performed. A total of 143 edible oil and fat samples collected from Chinese markets were determined for the concentrations of 3-MCPD esters. The concentration data together with the data of fats consumed were analyzed by the point evaluation and probabilistic assessment for the exposure assessment of 3-MCPD esters contamination. The point evaluation showed that the mean daily intake (DI) of 3-MCPD esters were lower than the value of provisional maximum tolerable daily intake of 3-MCPD (2 μg/kg.BW.d). The mean DI values in different age groups obtained from probabilistic assessment were similar to the results of the point evaluation. However, in high percentiles (95th,97.5th,99th), the DI values in all age groups were undesirably higher than the value of PMTDI. Overall, the children and adolescents exposed more to 3-MCPD esters than the adults. Uncertainty was also analyzed for the exposure assessment. Decreasing the level of 3-MCPD esters in edible oils and consuming less oil were top priority to minimize the risk of 3-MCPD esters.3. Taking peanut oil as an example, lab-scale physical refining processes were investigated for their effects on the formation of 3-monochloropropane-1,2-diol (3-MCPD) esters. The deodorization temperature and time were investigated for their effects on the formation of 3-MCPD esters in peanut oil. The results showed that the content of 3-MCPD esters increased with the increase of temperature and up to peak values when heated for 1 or 1.5 h. The potential precursors, partial acylglycerols and chlorines were determined before each refining step.3-MCPD esters were not detected in degummed and bleached oil when the crude oils were extracted by solvent. While in the hot squeezed crude oils,3-MCPD esters were detected with low amounts.3-MCPD esters were generated with maximum values in 1-1.5 h at a certain deodorizing temperature (220-260℃).The results also showed that there were a positive correlation between diglyceride and glycidol esters, and chlorine seemed to be more effective precursor than partial acylglycerol.4. Establishing reaction models with glycerides (mono-, di-and tri-) and analyzing by GC-MS, FT-IR, LC-TOF/MS, the relations among the precursors, possible intermediates and end-products were investigated. Based on the results, the possible pathway and mechanism of formation of 3-MCPD esters were speculated. The study showed that 1-monopalmitin could generate acyloxonium ion during the initial stage of heating, and afterwards the acyloxonium ion was missing in the model. 1-monopalmitin could also generate glycidol ester(intermediate), which end-product was 3-MCPD-1-palmitate ester identified by LC-TOF/MS.1,2-palmitate diester and 1,3-palmitate diester were similar both in generating intermediates and in forming end-products. Both diesters could generate acyloxonium ion and glycidol esters during heating in the models. The analysis of end-products by LC-TOF/MS showed that both diesters could generate 3-MCPD-1-palmitate ester and 3-MCPD-1,2-palmitate diester. However, tripalmitin could not form glycidol esters, and the signal tested by FT-IR was weak. Therefore, the speculations were made based on the analysis,1-monopalmitin formed 3-MCPD-1-palmitate ester through the pathway of acyloxonium ion at initial stage and through the pathway of glycidol ester at the stage afterwards; both diesters might generate 3-MCPD esters through two pathways, namely pathway of acyloxonium ion and pathway of glycidol ester; palmitin generated 3-MCPD-1,2-palmitate diesters through pathway of acyloxonium ion.5. Washing oil before deodorization, addition of diacetin during deodorization and addition of antioxidants in heating models were investigated respectively, for their effects on the formation of 3-MCPD esters. The results indicated that degumming and decoloring could remove precursors partially and washing oil before deodorization could reduce the content of 3-MCPD esters in deodorized oil. Adding 4% of diacetin could reduce 43.8% of 3-MCPD esters during deodorizing. Six antioxidants, butylated hydroxytoluene (BHT), butylated hydroxy anisole (BHA), tert-butyl hydroquinone (TBHQ), propyl gallate (PG), L-ascorbyl palmitate (AP) and a-tocopherol (VE) were found to exhibit inhibiting capacities on 3-MCPD esters formation both in chemical models and oil models. TBHQ provided the highest inhibitory capacity both in chemical models and in oil models.44% of 3-MCPD esters formation was inhibited in the presence of TBHQ (66 mg in per kg oil) after heating of rapeseed oil at 230℃ for 30 min, followed by PG and AP. BHT, BHA and VE appeared to have lower inhibitory abilities in both models.VE exhibited the lowest inhibition rate,22% of 3-MCPD esters were inhibited in the presence of VE (172 mg in per kg oil) after heating of rapeseed oil at 230℃ for 30 min. In addition, the inhibition rates of PG and VE decreased dramatically with the increase of temperature or the heating time.