Maillard Reaction
The Maillard reaction is a chemical process that takes place when food is heated, involving the interaction between amino acids (as amino acid itself, peptide, or protein) and reducing sugars. This aminocarbonyl non-enzymatic reaction leads to the browning of food and the formation of a diverse range of flavor compounds, contributing to the development of a complex taste. While the Maillard reaction occurs rapidly when food is heated, it can also occur at room temperature, albeit at a slower pace, requiring an extended period of time.
Mechanism of Maillard Reaction
The Maillard reaction is a complex process comprised of numerous elementary reactions, and its complete mechanism has not been fully understood or elucidated thus far.
The series of reactions starts as the carbonyl group of the sugar reacts with the amino group of the amino acid, peptide, or protein. The result glycosylamine through amadori rearrangement turns into amadori product. Those intermediate products undergo further reactions to form even more products, including various melanoidins and aroma compounds. The latter part of Maillard reaction is rather complex and depends on the acidity condition.
Aromas from Maillard Reaction
The Maillard reaction during cooking produces a variety of aromatic compounds, adding rich flavors and enticing aromas to cooked foods. Some examples of the aromas resulting from the Maillard reaction include the roasted or toasted scent found in coffee, bread, and nuts. The Maillard reaction also contributes to the nutty or biscuity aroma found in almonds, cookies, and cereals. Additionally, the savory and smoky grilled aroma associated with barbecued meats and seared steaks is a product of this reaction. Finally, the complex and indulgent chocolatey aroma in cocoa beans and chocolate owes its existence to the Maillard reaction. These are just a few examples of the diverse range of aromas that arise from the Maillard reaction, enhancing the sensory experience of cooked foods.
The aroma produced through the Maillard reaction is influenced by the specific combination of amino acids and sugars involved, as well as the reaction conditions. For instance, when Glucose (sugar) and Valin (amino acid) undergo the Maillard reaction, it yields the smell of rye bread at lower temperatures (100 °C, or 212 °F), while at higher temperatures (180 °C, or 356 °F), it produces a spicy chocolate aroma. Similarly, the combination of Glucose and Leucine (amino acid) results in a sweet chocolate smell at lower temperatures and a toasted cheese aroma at higher temperatures. Another example is the Maillard reaction between Glucose and Phenylalanine (amino acid), which can create floral scents like violet (at lower temperatures) or lilac (at higher temperatures). By carefully controlling factors such as temperature and the choice of sugar and amino acid, the Maillard reaction offers a means to achieve a wide array of aromas in food, allowing for the creation of complex, multi-layered flavor profiles.
Melanoidin
Melanoidins are high molecular weight brown polymers that can be formed as potential end products of the Maillard reaction, while their chemical structure has not been fully elucidated. Melanoidins are the source of the brown and dark colors of food after the reaction and have biological activity, including antioxidant, antimicrobial, and anti-inflammatory properties.
Melanoidin as Antioxidant
Melanoidins possess antioxidant properties that aid in safeguarding cells against oxidative stress and damage induced by free radicals. A comparative study on Japanese Miso found a correlation between high melanoidin (shown as zone M contribution in chromatogram) and relative radical scavenging (RS) activity. Samples with highest RS activity were made from soybeans and indicated darker colors (lower Y.)
Takeuchi, T. (2004). Studies on the DPPH radical scavenging capacity of miso. Miso no Kagaku to Gijutsu, 52, 23–31.
There have been similar studies on the property of Melanoidins in different food, and a few of the examples are listed below.
Alves, G., Xavier, P., Limoeiro, R., & Perrone, D. (2020). Contribution of melanoidins from heat-processed foods to the phenolic compound intake and antioxidant capacity of the Brazilian diet. Journal of Food Science and Technology, 57, 3119–3131.
Pastoriza, S., & Rufián-Henares, J. A. (2014). Contribution of melanoidins to the antioxidant capacity of the Spanish diet. Food chemistry, 164, 438–445.
Xu, Q., Tao, W., & Ao, Z. (2007). Antioxidant activity of vinegar melanoidins. Food Chemistry, 102(3), 841–849.
Other Links to Maillard Reaction
Maillard Reaction and Diabetes
The end products of Maillard reaction are also called advanced glycation end products, or AGEs, which include melanoidin. The formation of AGEs contributes to the development of diabetes as these compounds are generated when proteins or lipids react with reducing sugars within the body; diabetes are associated with high concentration of sugar in the body, thus accelerate Maillard reaction. The accumulation of AGEs in tissues can contribute to the development of diabetic complications, including neuropathy, nephropathy, and retinopathy.
As discussed, AGEs are produced through the Maillard reaction during food processing, and they are present in significant amounts in certain processed and fried foods. The consumption of a diet rich in AGEs has been associated with an elevated risk of diabetes and various chronic diseases.
Maillard Reaction and Aging
The Maillard reaction plays certain roles in the aging process. With aging, there is a buildup of fructose-lysine (FL) as a initial product of the Maillard reaction as well as various AGEs including structurally characterized adducts (e.g. N(ε) -(carboxymethyl)lysine, or CML, and N(ε) -(carboxyethyl) lysine, or CEL) and fluorescent cross-links (e.g. pentosidine formed between lysine and arginine residues) resulting from the Maillard reaction in the collagen of cartilage. It is believed that glycation plays a role in making cartilage stiffer and more prone to brittleness as we get older.
Verzijl, N., DeGroot, J., Oldehinkel, E., Bank, R. A., Thorpe, S. R., Baynes, J. W., Bayliss, MT, Bijlsma, JW, Lafeber, FP, & TeKoppele, J. M. (2000). Age-related accumulation of Maillard reaction products in human articular cartilage collagen. Biochemical Journal, 350(2), 381–387.
