Abstract: In this study, the contents of chloride, 3-monochloro-1,2-propanediol ester (3-MCPD ester) and glycidyl esters (GEs) in crude, decolorized but undeodorized corn oil and refined oil from corn oil processing plants in Anhui, Hebei and Shandong provinces were detected. The crude corn oil was refined under laboratory conditions that can be definitely controlled, and the contents of chloride, 3-MCPD ester and GEs in the refining process were detected and compared with those obtained from oil processing plants. By doing so, we aimed to examine the change of chloride ion content during corn oil refining and its effect on the contents of 3-MCPD ester and GEs. The results showed that all the corn oil samples tested contained chloride ion, 3-MCPD ester and GEs, among which the highest content of chloride ion of 0.628–2.029 mg/kg was found in the crude oil. The contents of 3-MCPD ester and GEs in the crude oil were 0.547–1.083 mg/kg and 0.246–0.721 mg/kg, respectively; the content of chloride ion in the decolorized but undeodorized corn oil was 0.110– 0.374 mg/kg, which was significantly lower than that in the crude oil, and the contents of 3-MCPD ester and GEs were 0.933–1.422 mg/kg and 0.246–0.432 mg/kg, respectively, which were higher than and similar to those in the crude oil, respectively. After deodorization, the contents of 3-MCPD ester and GEs increased markedly to 3.523–4.541 and 1.501– 13.584 mg/kg, respectively, and a maximum increase of 4.5- and 33.1-fold in them was observed in one sample, as well as a maximum decrease in chloride ion content (0.287 mg/kg). The analysis of corn oil samples refined in our laboratory and in the plants consistently showed that the chloride ion content decreased during the refining process, and maximum decrease of 76.1%–81.3% occurred at the stages of hydration degumming and alkali deacidification. By contrast, the contents of 3-MCPD ester and GEs did not change much after hydration degumming, alkali deacidification and adsorption decolorization processes, while they increased greatly after deodorization, accompanied by a decrease in chloride ion content, and a larger reduction in chloride ion content led to a greater increase in 3-MCPD ester content. This study provides a useful guideline to prevent and control the risks of 3-MCPD esters and GEs during corn oil refining and even the production of other vegetable oils.

Key words: corn oil, chloride ion, 3-chloropropanol ester, glycidyl ester, refining