Determination of 18O/16O ratio of glycerol of triglyceride in fat using GC/P/IRMS after saponification

Zhong, Q. D., Wang, D. B., Li, G. H.

Abstract

Small changes in the ¹⁸O/¹⁸O ratio can provide a fingerprint that provides a unique identifier for the origin of particular compounds within a food, which has been proved be a valuable tool for fighting against fraud food. As the backbone of triglyceride in fat, glycerol contains three non-exchangeable oxygen, which could be used to reveal the biosynthetic origin of corresponding fat. However, the need for highly pure glycerol using tedious procedures for off-line IRMS methods or GC-IRMS analysis limited the researches and applications of glycerol ¹⁸O/¹⁶O ratio in edible oil authenticity control. In this paper, a new method, with time and cost-saving procedures, is introduced for reliable, rapid, and accurate determination of the ¹⁸O/¹⁶O ratio of glycerol orginated from triglyceride in fat: By saponification in 20 volumes of KOH methanol solution, the glycerides from different origin were converted to free glycerol and to fatty acid methyl esters (FAMES); 2,2,4-Trimethylpentane were added and the upper layer were removed after shook several times; molecular sieve was added to trap the microscale water; the ¹⁸O/¹⁶O ratio was measured using GC-Py-IRMS systems. Using standard correction procedures, the method above for δ¹⁸O determination was assessed, good precision that better than 0.4‰ was obtained, the reproducibility of δ¹⁸O values from triglyceride was better than ±0.7‰. The validation of the method was carried out by measuring the intimate triglyceride samples that mixed with glycerol with known δ¹⁸O value, and a very good agreement between the measured values and the predicted data. In addition, 3 animal fats and 10 edible oil were analyzed, the mean δ¹⁸O value of glycerol samples from animal fat was approximately 16.2‰ which close to the peanut oil, δ¹⁸O value of the edible oils that from crop plant were higher than animal fat but lower than that from woody plant.

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IMEKO TC

TC23 - Metrology in Food and Nutrition

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