Physicochemical properties and volatile formation mechanism of medium-chain triacylglycerols during heating.

Medium-chain triacylglycerols (MCTs), including caprylic acid (C8), a mixture of caprylic acid and capric acid (C8+C10), and high-MCT coconut oil (HMCO), were heated at 180°C. Their volatile profiles were analyzed to determine the MCT degradation mechanisms. As heating time increased to 10 h, secondary oxidation products and acid value of all samples increased continuously. Ketones, alkanes, fatty acid anions, fatty acid esters, and lactones were found in all heated MCTs. 2-Hexanone and heptane were detected in C8 after 2 h of heating, and 2-heptanone, heptanal, methyl octanoate, γ-octalactone, and δ-octalactone were detected after 4 h. For the C8+C10, ketones, alkanes, and aldehydes were first observed. Hydrolysis and decarboxylation seem to occur first for ketone and alkane formation. Cracking and cyclization may occur later for fatty acid esters and lactones in heated MCTs. This result can help to understand thermal decomposition mechanisms of saturated fatty acids like MCTs. PRACTICAL APPLICATION: Medium-chain triacylglycerols (MCTs) have been used in cosmetic and fragrance industries due to their high oxidative stability, relatively high polarity, and smooth textures. In addition, MCTs have gained popularity among consumers for their health beneficial effects. MCTs could be used as major continuous phases for many food ingredients receiving high thermal energy for cooking. The results of this study can provide basic and useful information on the physicochemical properties and thermally decomposed volatile profiles from MCTs, which can help to produce stable processed products with lengthy shelf-lives in the food industry.