Medium-chain triglyceride
Medium-chain triglycerides (MCTs) are a class of lipids consisting of a glycerol backbone esterified with three medium-chain fatty acids, typically those containing 6 to 12 carbon atoms, such as caproic acid (C6:0), caprylic acid (C8:0), capric acid (C10:0), and sometimes lauric acid (C12:0).[1] These fats are distinguished by their shorter chain length compared to long-chain triglycerides (LCTs), which results in unique metabolic properties, including rapid hydrolysis by pancreatic lipases, direct absorption into the portal vein, and transport to the liver without requiring bile salts or carnitine for processing.[2] Unlike LCTs, MCTs are liquid at room temperature and yield approximately 8.4 kcal/g of energy, making them a readily available fuel source that bypasses typical fat storage pathways.[1] MCTs occur naturally in certain foods, primarily derived from coconut oil (46–54% lauric acid), palm kernel oil (45–50% lauric acid), and to a lesser extent in bovine milk fat (2.5–4% lauric acid), though commercial MCTs are predominantly C8:0 and C10:0 to optimize purity and functionality.[1] They are produced industrially through processes like hydrolysis of coconut or palm kernel oil followed by fractionation and re-esterification, often using enzymatic methods such as lipases or chemical catalysts, achieving high yields up to 99.7%.[1] The U.S. Food and Drug Administration recognizes MCTs as generally recognized as safe (GRAS) for use in food, with specifications requiring at least 90% of fatty acids to be C8:0 or C10:0, and trace amounts of other chains like C6:0 (≤1.8%) and C12:0 (≤1.5%).[3] In applications, MCTs are widely incorporated into medical nutrition products, such as enteral formulas for patients with fat malabsorption, preterm infant formulas (up to 50% of fat content), and ketogenic diets for epilepsy management, where they promote ketone body production for brain energy.[2] They also serve as functional ingredients in foods like cooking oils, bakery items, and supplements to enhance energy expenditure, support weight management by increasing fat oxidation (up to 5–8 times faster than LCTs), and improve nutrient absorption, including calcium and amino acids.[2] Physiologically, MCTs have demonstrated benefits in clinical settings, such as elevating beta-hydroxybutyrate levels in mild cognitive impairment patients at 30 g/day doses[4] and boosting muscle strength and albumin levels in the elderly at 6 g/day,[5][6] while exhibiting antimicrobial effects against pathogens like Staphylococcus aureus.[7] Safety studies confirm no observed adverse effect levels up to 9.5–20 g/kg body weight/day in animals and humans, with only minor, transient gastrointestinal effects at high intakes.[3]Definition and Chemistry
Definition and Nomenclature
Medium-chain triglycerides (MCTs) are a subclass of triglycerides defined as esters formed by the bonding of one glycerol molecule with three medium-chain fatty acids (MCFAs), each containing 6 to 12 carbon atoms in their aliphatic tails.[8][1] This structure contrasts with short-chain triglycerides (SCTs), which incorporate fatty acids of 2 to 5 carbon atoms, and long-chain triglycerides (LCTs), featuring fatty acids with 13 or more carbon atoms. The shorter chain length of MCTs facilitates quicker enzymatic hydrolysis by pancreatic lipases and direct absorption into the portal vein, unlike LCTs that require emulsification by bile salts and transport via the lymphatic system.[1][9] The term "medium-chain" in MCT nomenclature originates from the standardized classification of fatty acids by chain length, as established in lipid chemistry guidelines, where MCFAs specifically denote saturated or unsaturated chains between 6 and 12 carbons.[10] Common abbreviations include MCT for the triglycerides and MCFA for the constituent fatty acids, with specific compounds named systematically (e.g., tricaprylin for the triester of caprylic acid).[1] This descriptive nomenclature emphasizes metabolic and physical distinctions rather than a single chemical formula, given the variability in fatty acid composition within the class.[11] MCTs were first isolated in the 1950s during the fractionation of coconut oil for industrial purposes, marking their initial recognition as a distinct lipid fraction.[2] By the 1960s, their clinical potential was explored, leading to early medical applications in managing fat malabsorption disorders due to their enhanced digestibility.[12][13]Chemical Structure
Medium-chain triglycerides (MCTs) consist of a glycerol molecule esterified with three medium-chain fatty acids, each having a chain length of 6 to 12 carbon atoms. The general formula for triglycerides, including MCTs, is \ce{(RCOO)3C3H5}, where R denotes the saturated alkyl chain derived from the fatty acid, typically comprising 5 to 11 carbon atoms for medium-chain variants.[14][1] The molecular structure features three ester linkages, formed by the condensation of the hydroxyl groups on the glycerol backbone—a three-carbon alcohol—with the carboxyl groups of the medium-chain fatty acids. These fatty acids in MCTs are predominantly saturated, meaning they lack carbon-carbon double bonds, which contributes to the overall chemical stability of the molecule. For instance, the glycerol is bonded at its sn-1, sn-2, and sn-3 positions to the acyl chains, resulting in a non-polar, hydrophobic triester.[15][11] A representative example of an MCT is tricaprylin (also known as glycerol trioctanoate), where all three fatty acid chains are caprylic acid (octanoic acid, C8:0). Its structure can be depicted as: \ce{CH2(OCO(CH2)6CH3)-CH(OCO(CH2)6CH3)-CH2(OCO(CH2)6CH3)} with a molecular formula of \ce{C27H50O6}. This symmetric molecule exemplifies the compact nature of MCTs compared to those with longer chains.[16] Commercial MCT preparations are typically refined to high purity, consisting almost entirely of triglycerides derived from caprylic (C8:0) and capric (C10:0) acids, often in ratios such as 60:40 or 70:30, with minimal presence of other fatty acids. This composition ensures uniformity and resistance to oxidative degradation due to the saturated bonds.[2][11]Medium-Chain Fatty Acids
Medium-chain fatty acids (MCFAs) are saturated fatty acids containing 6 to 12 carbon atoms, serving as the building blocks of medium-chain triglycerides (MCTs). The key MCFAs in MCTs include caproic acid, caprylic acid, capric acid, and lauric acid, each characterized by its specific chain length and chemical properties. These acids are typically straight-chain and fully saturated, contributing to the overall stability and metabolic behavior of MCT molecules. The following table summarizes the primary MCFAs, their notations, and formulas:| Common Name | Systematic Name | Notation | Molecular Formula | Structural Formula |
|---|---|---|---|---|
| Caproic acid | Hexanoic acid | C6:0 | C₆H₁₂O₂ | CH₃(CH₂)₄COOH |
| Caprylic acid | Octanoic acid | C8:0 | C₈H₁₆O₂ | CH₃(CH₂)₆COOH |
| Capric acid | Decanoic acid | C10:0 | C₁₀H₂₀O₂ | CH₃(CH₂)₈COOH |
| Lauric acid | Dodecanoic acid | C12:0 | C₁₂H₂₄O₂ | CH₃(CH₂)₁₀COOH |