In order to better utilize the melad reaction to prepare savory flavors with excellent taste, aroma and flavor, the authors [1] summarized the main factors affecting the melad reaction.

There are various factors affecting the melad reaction, and they work together to influence the process and effect of the melad reaction. By controlling these reaction conditions, the reaction can be carried out in the desired direction to further improve the flavor and its quality.

Environmental factors

1. Reaction time

The longer the reaction time, the more flavor intermediates are produced, the more thick and rich the flavor, but it is easy to produce excessive caramelization reaction and bitter taste, and even produce some unfavorable substances and carcinogens; reaction time is too short, it can not form enough flavor and color.

2.Reaction temperature

Carbon and ammonia reaction can occur at 20-25 ℃, faster than 30 ℃, greater than 80 ℃, the reaction rate is less affected by temperature and oxygen. Under the same conditions, the longer the heating time, the darker the reaction color. On average, for every 10 ℃ rise, the reaction speed difference is 3-5 times. However, if the temperature is too high, the nutrients in the food will be damaged, and some peanut coking and fat coking toxic and harmful substances may also be produced. Temperature also affects the activity of reactants and the spinning properties.

3. pH

The effect of pH on the Melad reaction is greater than that of temperature and time. When the initial pH is greater than 3, the reaction speed is accelerated with the increase of pH. pH＜7.0, the reaction is not obvious; pH＞7.0, the reaction speed is obviously accelerated; pH＞11.0, the reaction color change is obviously weakened. It was also found that under weakly alkaline or neutral conditions, better caramel flavor and roasted aroma could be obtained [2].

4. Moisture activity

Meladic reaction is faster when the water activity is in the range of 0.3-0.7. Below or above this range, the reaction is relatively slow. In the absence of water, the reaction hardly takes place.

5. Reaction pressure

The reaction pressure and the pH in the reaction system together influence the Melad reaction. At atmospheric pressure, the reaction is faster at pH=6.5, and at pH=8 and 10.1, the reaction is faster at high pressures of 6000 MPa [3].

Reactants

1.Sugars

Both the structure and type of sugar can directly affect the rate of reaction, in general: pentose > hexanalose > hexoketose > disaccharide [4]; open-cyclic ribose > cyclic ribose; galactose > fructose [5]; D-allose > D-glucose [6]. Among reducing monosaccharides, the reaction rate of five-carbon sugars: ribose > arabinose > xylose; six-carbon sugars: galactose > mannose > glucose. Reducing disaccharides have slower reaction rate with increasing molecular weight.

2.Amino acid

Amino acids can affect the reaction rate and the resulting flavor substances. Reaction speed: amino acid in ε-position or terminal position＞α-position, basic amino acid＞acidic amino acid[7]; the same sugar and different amino acid reaction will produce different flavor.

3. Concentration of reactants

Generally the increase of reactant concentration increases the rate of reaction, but because the Melad reaction is a reaction between carbonyl ammonia, there is an important connection between the reaction process and rate and the ratio of carbonyl and amino groups between the reactants.

Others

1.Sulfite

Sulfites can inhibit the reaction process to a certain extent, probably due to the fact that sulfites combine with carbonyl groups to form compounds and then condense with amino compounds, or sulfites may react with the carbonyl groups in the intermediate products.

2.Metal ions

Metal ions can also affect the speed and process of the reaction. Copper ions and iron ions can promote the Melad reaction, but trivalent iron ions have a stronger catalytic ability than divalent iron ions. Magnesium and calcium ions can inhibit the reaction.

3. Irradiation

Irradiation affects the speed of the Melad reaction. The reaction rate of sugars under irradiation and under heating is different. Under irradiation, the reaction rate of sugar is: sucrose > fructose > glucose; under heating condition, the reaction rate is: pentose > heptose > hexose > disaccharide.

4. Buffer

For example, phosphate and citrate buffer solution [8].

5. Lipids

For example, lipids such as phospholipids have a positive effect on flavor production.