Isomerization of 9c11t/10t12c CLA in Triacylglycerols

Abstract

Isomers of conjugated linoleic acid from 7t9c through 12t14t can be induced by thermal treatment of triacylglycerol samples of 9c11t or 10t12c fatty acids in glass tubes. The formation of conjugated linoleic acids (CLAs) has been observed during thermal induction of the above-mentioned triacylglycerols at 250, 280 and 320°C. The concentrations of isomers formed in the mixture varied depending on the temperature and duration of the heating experiments. The objective of this study was to find a suitable thermal induction temperature and time that can produce most of the isomers of CLAs from the abovementioned triacylglycerols. Such a mixture would give researchers a reference standard that can be used in the identification of CLAs in GC analyses of relevant samples. Fifteen-microlitre portions of the triacylglycerol samples containing 9c11t/10t12c fatty acid were placed in microglass ampoules, sealed under nitrogen and then subjected to thermal treatment. The glass ampoules were removed at regular time intervals, cut open, and part of the samples was analysed by infrared spectroscopy using attenuated internal reflectance technique. The remainder of the samples was subjected to derivatisation into their methyl esters. The methyl esters of the isomerised fatty acids were then analysed by gas chromatography after appropriate dilution in heptane. The results show that the thermally induced glyceride samples of 9c11t/10t12c fatty acids gave CLA profiles containing isomers ranging from 7t9c to 12t14t. However, the concentrations of the isomers are different depending on the duration of the thermal induction. It appears that [1,5] sigmatropic rearrangements and positional isomerisations take place in the heated mixtures. The rearrangements and positional isomerisations are accelerated by increasing temperature. The glyceride samples heated to 325°C form isomers within 30 min and provide a mixture of CLA isomers that can be used as reference sample containing the methyl esters of CLAs.

Stability of fatty acid composition after thermal, high pressure, and microwave processing of cow milk as affected by polyunsaturated fatty acid concentration

“…Thus, previous studies found that methyl linoleate can isomerize to C18:2 t9t11 and 18:2 t10t12 after heating at 200 and 220°C for 24 h . Assays with trilinolein suggested that reactions occur in the triglyceride molecule without previous release of the FA (Christy, 2010). In food such as milk butter, heating at 225°C for 15 min leads to isomerizations of C18:1 c9 to C18:1 t9, whereas 200°C for 2 h resulted in a sigmatropic rearrangement of rumenic and C18:2 t10, c12 into trans, trans CLA compounds (Precht et al, 1999;.…”

Thermally Induced Isomerisation Kinetics of the 9c11t and 10t12c Conjugated Linoleic Acids in Triacylglycerols as Studied by FT-IR Spectrometry Aided by Gas Chromatography

“…8) that give absorption at 970 cm -1 . A recent report [15] shows that this peak is indeed from the absorption due to 9t12t isomers (and very small concentrations of 9c12t and 9t12c). The formation of 9c11t and 10t12c go through 9t12t intermediate and the presence of 9t12t in the thermally induced 9c11t isomer is not unexpected.…”

“…Christy [14] has also contributed to supplement the mechanistic aspects by demonstrating that CLA isomers could be produced by thermal induction of 9t12t LA. In a recent report Christy [15] demonstrated that the [1,5] sigmatropic transformations and positional isomerisation could be achieved by subjecting triacylglycerols of CLAs to a suitable high temperature. All these reports paved the way for the formulation of a sequential series of CLA isomers illustrating the type of CLA isomers expected to form when thermally treating a particular CLA [13,15].…”

“…In a recent report Christy [15] demonstrated that the [1,5] sigmatropic transformations and positional isomerisation could be achieved by subjecting triacylglycerols of CLAs to a suitable high temperature. All these reports paved the way for the formulation of a sequential series of CLA isomers illustrating the type of CLA isomers expected to form when thermally treating a particular CLA [13,15]. It is now clear that the formation of CLAs follows a series of [1,5] sigmatropic transformation and positional isomerisation during thermal induction.…”