Maillard reaction definition suggests that it is a chemical reaction between reducing sugar and amino acid in the presence of heat. This reaction is a kind of non-enzymatic browning. This reaction makes the fundamental base of the flavouring industry as different types of amino acids influence the resulting flavour.
This particular reaction is a complex one which results in several flavour compounds. These compounds further break down to form more new compounds. Every kind of food contains distinct flavouring compounds that are produced during this reaction. Based on these flavouring compounds, flavour scientists have developed several artificial flavours over the years.
Following are the two essential components of reaction de Maillard.
Amino Group- This is one of the primary components needed for this reaction. An NH2 group contains one nitrogen atom and two hydrogen atoms. This group is connected with another larger molecule of amino acid that is represented by R in chemistry.
However, other atoms still can be present in them. Hence, the group is represented as R-NH2. This particular type of groups generally presents in peptides, amino acids and proteins. These amino groups in Maillard reaction come mostly from proteins. For example, milk protein transforms into butter.
Reducing Sugar- We need this component along with amino group for this reaction to take place. It is a special kind of sugar containing a certain reactive group. For a matter of fact, reducing sugars are capable of giving away electrons.
Generally, mono and disaccharides take part in Maillard reaction. They are commonly known as ketone (-C0-) and aldehyde (-COOH-) groups. Typically, all monosaccharide like fructose and glucose are reducing sugar as well as disaccharides like lactose. However, common granule sugars or sucrose is not a reducing sugar.
The first description of the mechanism of Maillard browning reaction originated at the beginning of the 20th Century. LC Maillard, a Frenchman, first discovered the chemistry of this reaction and also stated that it occurs through several complex steps. Following are the 3 major steps of it -
The first step of this reaction is a condensation reaction between an amino group (NH2) on an amino acid or protein and reducing sugars (an aldose or ketose). In this reaction, Amadori or Heyns compounds, depending on the type of sugar, participate.
For example, Amadori will form from a sugar having aldehyde group, and for ketone group, it will be Heyns compounds.
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Fig1: Amadori formation
These molecules further react to produce aromatic compounds. Also, in this step, they develop a ring in their structure. In this step of rearrangement, these two compounds, having two double-bonded oxygen atoms, are formed and initiate Strecker reaction. It is during this stage that aromatic compounds are produced.
Finally, in the concluding stage, melanoidins, complex large molecules, are formed with multiple rings. Several reactions take place in this step with different products from different reactions. Moreover, at this point, we can see the brown coloured nitrogenous polymers.
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Fig2: Coloured molecule from Maillard reaction
Maillard browning reaction can occur in room temperature but can speed up at high temperature.
This reaction involves giving colour and flavour of several foodstuffs. Following are some of them.
Caramel from sugar and milk.
The browning of toasted bread.
The colours of chocolate, beer, maple syrup and coffee.
Production of Self-tanning products.
Roast meat flavour.
The colour of condensed or dried milk.
Because of the presence of 6-acetyl-1,2,3,4-tetrahydropyridine, the baked products like tortillas, popcorns, and bread have a biscuit-like odour. However, the 2-acetyl-1-pyrroline compound has a similar smell and is available naturally in cooked rice of different varieties. Also, both these compounds are characteristic of odour threshold lower than 0.06 ng/l.
There are a few factors that determine the outcome of the reactions. These are -
Pentose sugars react the most and disaccharides react the least, whereas Hexoses react moderately.
The browning amount differs with different amino acids
An environment of high-water activity hinders Maillard reaction as it produces water anyway.
Above 140⁰ C (285⁰ F) is the favourable Maillard reaction temperature.
Lysine has two amino groups; therefore, it reacts the fastest and causes darker colours. Milk, which contains a large amount of lysine, browns readily.
Cystine has one amino group and one sulphur group and produces the least colour of amino acids.
The Maillard reaction improves the colour and flavour of food and also contains beneficial antioxidant. However, it reduces the nutritional value of foods as an amino acid as carbohydrates, and amino acids are lost.
Products of Maillard browning reaction include desirable and undesirable colours and aroma. For example, characteristic of golden-brown colour is desirable and the aroma of caramel.
Also, over accumulation of Advanced Glycation End Products or AGE in the human body can affect cell functions, especially protein cells.
Almost in all food we cook, Maillard reaction takes place. However, the flavour, colour and aroma vary with different food items. Because of this reason, friend egg does not taste the same as a poached egg. Also, the smell of boiled meat and fried meat is different.
Maillard reaction steak produces more of flavour molecules and less of aromatic ones as it contains more protein and less sugar.
This reaction to a great extent affects the quality of food. Overreactions often turn the food bitter and accumulate burnt flavour. For example, the reaction between α-dicarbonyls and α-amino group forms Strecker Aldehyde, which deteriorates the quality of Lactose-free milk.
Therefore, for controlling quality, limiting browning reaction is essential in the food industry.
Researchers have used several techniques to control Maillard browning. Aminoguanidine, a pharmaceutical drug is capable of obstructing this reaction in food. It functions by simply trapping a-dicarbonyls.
Also, in 2005, Totlani and Peterson showed that epicatechin, a compound present in plants like cocoa, grapes, green tea, can do the same thing. However, it mainly works in two ways.
Affecting reactive sites- Earlier, this process involved the elimination of any of the reactants or addition of sulphur-rich compounds like sulphur dioxide and N-acetylcysteine. However, now the process of transforming reducing sugars into non-reducing ones adds starter cultures to prevent cheese browning.
Another way is amines modification in a whey protein isolate (WPI) by acetylation or succinylation. It is capable of blocking lysine to modify further when stored at 50⁰ C.
Targeting Intermediates- Dicarbonyls, for example, methylglyoxal (MGO), deoxyosones and glyoxal (GO), are some reactive intermediates that encourage Maillard reactions. However, trapping agents like hydroxytyrosol, creatine, and pyridoxamine can inhibit the reaction.
Test Your Knowledge
1. Which of the following is the result of caramelisation of sucrose?
Fructose and glucose
2. Which one is a reducing sugar?
Glucose in an open ring
Glucose in a closed ring
None of the above
Answers: 1-c), 2-a).
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1. How Do You Control A Maillard Reaction?
You can control a Maillard reaction by reducing sugars such as fructose, glucose, lactose, etc. and amino acids availability.
2. How Is Maillard Reaction Affected By PH
Millard reaction is correlated to pH. With increased pH, it generally increases and vice versa. Moreover, temperature also affects this reaction. For example, at a higher temperature, the reaction increases.
3. How Maillard Reaction Takes Place In Milk
One of the significant components of milk is lactose which reacts with free amino acids present in milk protein, on applying heat system. This process causes several stages of Maillard reaction and produces Maillard products and finally browning compounds or melanoidins.
4. What Is The Difference Between Caramelisation And Maillard Reaction?
There is a stark difference between caramelisation and Maillard reaction. The former results from the pyrolysis of some specific sugars, and the latter one happens in the presence of amino acids.