Abstract
There are more and more studies on the detection method of 3-chloro-1,2-propanediol fatty acid esters (3-MCPD esters) at present. By comparing these methods for the determination of 3-MCPD esters. Indirect methods, which determine total amount of 3-MCPD after hydrolysis of the esters, have an advantage over direct methods. The existing indirect methods, however, may yield unreliable results or require long hours of alkaline methanolysis. In contrast, the Indirect enzymatic hydrolysis method has mild conditions and more accurate results. In this study, we developed a reliable and rapid indirect method for determinations of 3-MCPD esters. 3-MCPD esters was enzymatized to 3-MCPD by indirect enzymatic hydrolysis method, and the conditions of enzymatic hydrolysis were optimized, the content of 3-MCPD after enzymatic hydrolysis was detected by gas chromatography-mass spectrometry (GC-MS) and the yield was calculated. Finally, the optimum conditions for enzymatic hydrolysis of 3-MCPD esters were determined. According to the optimal enzymatic hydrolysis condition, the contents of 3-MCPD esters in four food oils were determined. The method is simple and sensitive, and can meet the requirement of 3-MCPD esters detection in general oils.
Keywords : 3-MCPD esters; 3-MCPD; Indirect enzymatic hydrolysis method; GC-MS
Introduction
The contamination of 3-MCPD esters is one of the hot issues in the field of food safety that have been disputed internationally in recent years[1].The formation of 3-MCPD esters is directly related to the chemical refining of synthetic oil products, It has been confirmed that 3-MCPD esters are found in hot processed foods derived from grains, fish and meat products, coffee, nuts, potatoes and edible oils[2-4]. 3-MCPD esters are hydrolyzed in vivo by intestinal pancreatic lipase to produce free 3-MCPD, 3-MCPD has extremely obvious renal toxicity and high genotoxicity, which has been strictly classified as 2B carcinogen by the International Cancer Organization Working Group (IARC) of the United Nations[5-6].
3-MCPD esters detection mainly has the direct determination method and the indirect determination method. By comparing these methods for the determination of 3-MCPD esters. Direct methods based on LC-MS/MS[7–9]are available in literature, however, the great complexity of 3-MCPD esters may lead to the determination of up to several tens of compounds in one sample for which a respective number of internal standards are required[10]. This contributes to make the procedure generally expensive, but the advantages of direct methods are the lack of derivatization step and the possibility to get direct information on the content of individual esters and for these reasons they found wide application in the field[11]. Indirect methods for the determination of 3-MCPD esters in samples requires a complex pretreatment process with many steps in advance, and the change of conditions in each experimental step will easily affect the accuracy of the final detection results, the methods are based on derivatization, transforming 3-MCPD esters in free 3-MCPD, and
they include several stages such as transesterification, neutralization and derivatization steps before quantification, using NaOH for transesterification, sodium bromide for neutralization and phenylboronic acid for derivatization[12]. But in the alkaline catalyzed indirect method, if the alkaline hydrolysis reaction time conditions and salting-out conditions or temperature are not well controlled, a part of 3-MCPD may be eliminated or extra produced, thus making the determination result small or large. Acid catalyzed indirect method is more stable and durable, but relatively time-consuming. In contrast, the indirect enzymatic hydrolysis method has mild conditions and more accurate results.
At present, there are more and more studies on the determination of 3-MCPD esters by indirect enzymatic hydrolysis method. However, there are no study have reported the optimal conditions for enzymatic hydrolysis of 3-MCPD esters. In this work, 3-MCPD esters was enzymolized to 3-MCPD by indirect enzymatic hydrolysis method, and the conditions of enzymatic hydrolysis were optimized, GC-MS was used for detection and calculation of yield, then the optimum enzymatic conditions were determined. Finally, the actual samples were detected by indirect enzymatic hydrolysis method. The method is simple, reliable, and rapid, and is suitable for a routine quality control of fats and oils[13].
Experimental Procedures