The Maillard reaction, also known as the carbonyl-ammonia reaction or non-enzymatic browning reaction, is a reaction that occurs between amino compounds and carbonyl compounds, and is one of the main sources of food flavor production.

The Maillard reaction is considered to be one of the most important chemical reactions occurring during food processing. It affects the quality characteristics of the food such as color, flavor, nutritional value, and the physical-chemical properties of the food ingredients.

Melard reaction products (mainly melanoidins, reduced ketones, and heterocyclic compounds containing N, S, and O) are the main source of flavor in meat products, and the antioxidant properties of melard reaction products (MRPs), which are used as substitutes for phenolic food antioxidants, are attracting more and more attention.

Mechanism of Maillard reaction

Maillard reaction is a non-enzymatic browning reaction, which is mainly a complex reaction between carbonyl compounds (especially reducing sugars) and amino compounds (including amines, amino acids, peptides, proteins, etc.). The food processing industry has been utilizing the Maillard reaction since humans began grilling foods.The Maillard reaction is not only relevant to the production of traditional foods, but also to the modern food industry, such as baked goods, coffee, etc.The Maillard reaction provides foods with a delicious flavor and attractive color.

According to food chemist HODGE, the Maillard reaction process can be divided into three stages: initial, intermediate and final, each of which can be subdivided into several reactions. The reaction is a complex one, including many cross-reactions and decomposition reactions, producing a series of aromatic compounds (including ketones, aldehydes, alcohols, furans and their derivatives, pyrroles, pyridines, pyrazines, thiophenes, thiazoles, umizoles, yelzolines, and sulphides) HJ. Among these are the heterocyclic compounds (S and N compounds of pyrroles, furans, thiophenes, thiazolines, and pyrazines), the thiol compounds, the reducing ketones, and the finally produced analogous black crystals.

Factors affecting the Melad reaction

The series of chemical reactions that occur between reducing sugars and amino acids during food processing and storage is known as the Maillard reaction. The main factors affecting the extent of the Maillard reaction are the temperature and time of the processing conditions, as well as the pH, water activity, and the type and proportion of the reactants.

However, the reactants may be altered depending on the food and raw material processed. Understanding the influence of these factors on the Maillard reaction helps us to control food browning and is of great practical significance to the food industry.

1) Reaction Substrate

In Maillard reaction, the sugars involved in the reaction are mainly reducing sugars, which can be disaccharides, pentoses and hexoses. The rate of reaction is pentose > hexose > hexanone > disaccharide. Disaccharides produce poor flavor, and the fastest reacting and best flavored of the Hundredth Sugar is Ribose, but it is costly and difficult to purchase.

Considering the price of raw materials, glucose and xylose are usually used.The Maillard reaction varies in flavor and concentration of the products depending on the sugars involved in the reaction. Among them, the reaction of xylose is the best.

The type and concentration of amino acids also have a very important effect on the type and merit of the flavor of the reaction product, and different kinds of amino acids can produce different flavor substances in the Maillard reaction. Among them, sulfur-containing amino acids have a very important influence on the formation of meat flavor in the melamine reaction.

In practice, because cysteine is difficult to dissolve, people usually use the salts of cysteine (mainly cysteine hydrochloride). Certain other amino acids are also indispensable for the formation of flavor in the Maillard reaction, they play a very important role in enhancing the flavor characteristics of the product, which can help the Maillard reaction to form a more perfect and softer meat flavor.

2) Temperature

Maillard reaction is greatly affected by temperature, every 10℃ change in temperature, the browning rate will be 3~5 times different, so the food that is easy to brown should be stored under low temperature. Temperature in addition to affecting the speed of the reaction, but also affect the aroma of the product, the temperature is different, the resulting aroma is also different.

Some scholars have found that as the reaction temperature rises, Maillard reaction flavor material generation increases. In the production of meat flavor flavor reaction temperature is generally not more than 180 ℃, in order to obtain more meat flavor substances, and appropriate control of the formation of sauce flavor, reaction temperature of 115 ℃ is appropriate.

3) pH and water activity

Within a certain range, Maillard browning reaction speed and water activity and pH are positively correlated. Alkaline conditions are easy to generate nitrogen-containing volatiles (such as pyrazine); generally not more than 8, because the pH greater than 8, the reaction proceeds faster and difficult to control, the amino nitrogen is also significantly reduced, and the formation of flavor is also relatively poor.

Maillard reaction color formation of pH>7.0, the production of meat flavor pH between 5.0 and 5.5, and the higher the pH, the more flavor substances produced, and with the different pH, the components of the flavor substances produced are also different.

The Maillard reaction occurs most readily in foods with moderate water activity. If the Maillard reaction is used to prepare meat flavor, the moisture activity of 0.65 to 0.75 is the most suitable, and the reaction is slow if the moisture activity is less than 0.30 or more than 0.75.

4) Reaction time

The reaction time has a significant effect on the color of the Maillard reaction product and the generation of flavor compounds. Too short a time may make the reaction is not complete, the resulting flavor is not thick, rich; too long and may make the reaction excessive, resulting in a burnt taste and some carcinogenic substances.

Effect of Maillard reaction on food processing

The Maillard reaction first attracted attention due to the reaction of glucose and glycine to produce brown substances, and the brown substances produced by the reaction are one of the important sources of food color.

A significant portion of the golden-yellow substance on the surface of baked goods such as bread, pastries, and coffee beans comes from the Maillard reaction. This is what we expect, but the color produced by the MailIard reaction in the food there is no need, such as in the dairy sterilization, sometimes improper sterilization, caused by the yellowing of dairy products is the Maillard reaction.

Therefore, in the process of food processing, it is necessary to control its reaction conditions, so that the reaction to the direction of people’s expectations.

(1) The effect of Maillard reaction on the flavor and color of foods

Long-term storage of food or high-temperature heating of food will produce the end product of the Maillard reaction of melanin-like brown pigment.

There are many foods containing melanoidins, such as soy sauce, soy beans, bread, grilled meat, grilled fish, grilled bread slices, fried peanuts and coffee. These foods are processed to produce a very attractive golden yellow or dark brown color, which can arouse people’s strong interest and increase the sensory value of the food.

However, since most of the prerequisite substances for the generation of flavor substances come from the nutrients in the food, such as sugars, proteins, fats, and nucleic acids, vitamins, etc., it is unfavorable from the nutritional point of view and from certain technological points of view to consider the Maillard reaction that occurs during storage and processing of food and the generation of flavor substances.

In addition, browning affects the sensory quality of some products (e.g., milk and dairy products) to a certain extent, as it causes white products to change color and light-colored products to become darker.

(2) Effect of Maillard reaction on the nutritional properties of foods

The browning of food may cause some unwanted decrease in the nutritional value of food. Firstly, it is due to the involvement of chlorogenic acid and reducing sugars in the Maillard reaction, which can cause the loss of amino acids and reducing sugars. In addition to this, it has been found that the effectiveness of the mineral elements in the food also decreases once the Maillard reaction occurs.

3) Effect of Maillard reaction on proteins in foods

The protein-monosaccharide covalent compounds generated by the condensation of proteins and sugars through carbonylammonia have better functional properties than the original proteins, such as improved emulsification, solubility and antimicrobial properties. This increases the scope for the use of proteins in food and pharmaceutical applications.

However, the Maillard reaction also reduces the nutritional quality of some proteins and inhibits trypsin activity. For grain products, Maillard reaction will undoubtedly make its protein biomass price is lower. Some scientists have confirmed that 200 ℃ baking pastry 15min, its protein PER value from 3.6 before baking down to 2.4, if continue to bake at 130 ℃ for 1h, will be further reduced to 0.8, which is due to the reduction of lysine caused by.

4) Harmful substances and effects produced by Maillard reaction

Acrylamide and AGEs are produced during food processing such as frying and baking, etc. Acrylamide is a chemical raw material used in the manufacture of plastics, which can cause nerve damage and is a known carcinogen, so the problem of acrylamide in food has attracted global attention.

Maillard reaction end-stage protein cross-linking, the generation of glycosylation end products (AGEs), is also extremely detrimental to human health, domestic and international research has confirmed that AGEs are involved in aging, atherosclerosis, nephropathy and diabetes, and other diseases occurring in the development process.

In food processing also produces pyruvic aldehyde, which is considered by the medical profession to have a possible role in inducing mutations in the organism, but pyruvic aldehyde is only an intermediate product of the reaction, which is highly reactive and reacts quickly with other substances. In general, pyruvic aldehyde is beneficial in the reaction, and it should be controlled as much as possible to proceed in a favorable direction during the reaction, to reduce its toxicity and to prevent its accumulation.

Maillard reaction

Rational control in food processing

Maillard reaction is widely found in food processing and long-term storage of food, and is one of the main sources of food flavor production. In food production, Maillard reaction should be rationally controlled according to different processing purposes and specific process conditions.

(1) Control of Maillard reaction in the production of fruit and vegetable beverages

In the processing and production of fruit and vegetable beverages, the enzyme browning often leads to the deterioration of product quality, although the browning of fruits and vegetables, in general, the main reason is the enzyme browning, but for citrus fruits and vegetables, due to the higher amount of nitrogenous substances, it is also often easy to occur the Maillard reaction and lead to the browning of the production, the production of the production of the concentration of the PH and the sugar solution should be paid attention to.

In the processing and production of fruit and vegetable beverages, under the premise of ensuring normal taste, the PH value should be reduced as much as possible to slow down the speed of the Maillard reaction. Fruit and vegetable beverage production, the concentration of the original syrup is controlled at 30% to 50%, in order to make the most appropriate Melad reaction.

(2) Control of Maillard reaction in the production of dairy products

Milk and dairy products in the processing of casein terminal amino acids due to a lysine amino and lactose (or other reducing sugars) to generate glucosamine, and then Amadori rearrangement, cleavage, dehydration and other processes to generate brown substances. Milk and milk products browning, flavor and appearance deterioration, physical properties reduced.

Due to the production of large amounts of carbon dioxide in the browning process, the phenomenon of “can expansion” occurs when milk powder and condensed milk in sealed storage undergoes more serious browning.

Methods to control the browning of milk and milk products include: controlling the temperature, using sugars with low reducing sugar content, choosing appropriate stabilizers, controlling the pH of raw milk, controlling the water content of the finished product and adding inhibitors.

3) Control of Maillard reaction during cooking process

In baking, frying, sautéing and other cooking methods, high temperature and long time heating will lead to the generation of Mamard reaction products a acrylamide and AGEs.

Acrylamide mainly comes from fried or baked starchy foods, and some scholars have proved that asparagine is an important precursor for the formation of acrylamide. The extent of the Maillard reaction during cooking is influenced by the type and amount of sugars and amino acids in the raw material, and is also related to the cooking method.

This relates to the handling of the fire, the amount of stock, the placement of seasonings and the use of heat transfer media. In the cooking process to control the cooking heating temperature and heating time, regulating the content of amino compounds and carbonyl compounds, a reasonable choice of cooking methods, to prevent the production of acrylamide and AGEs, in order to promote the formation of good color and aroma of the dishes.

Application of Melad in food processing and storage

1. Antioxidant properties of MRPs

Since the 1980s, research on the antioxidant properties of MRPs has gradually attracted the attention of researchers, and has become a popular topic in the fields of food nutrition and food chemistry. The use of antioxidants such as BHA, BHT, TBHQ, etc., which are widely used in the food industry, has been banned in Europe and the United States because of their possible carcinogenicity.

MRPS is a class of substances produced during food processing and storage, which can be considered as natural and is expected to become the next generation of natural and non-toxic antioxidants.

Maillard reaction products (Maillard Reaction products, MRPs) contained in the class of black essence, reduced ketones and a series of nitrogen-containing, sulfur-containing volatile heterocyclic compounds, these substances have a certain antioxidant properties, and their antioxidant properties are used to replace phenolic food antioxidants, is gradually attracting people’s attention.

The antioxidant strength of some of these substances is even comparable to that of antioxidants commonly used in food. Large molecular weight substances at the end stage of the reaction, such as melanotropin-releasing hormone, are considered to be the main antioxidants in MRPs.

2.Application of Maillard reaction in flavor production

①Development of domestic flavor

China’s meat flavor flavor industry started late, accompanied by the emergence of the instant noodle industry. The earliest flavor production methods are rudimentary, but well absorbed the production process of China’s traditional meat cooking.

The current domestic flavor companies and research institutions are committed to the thermal reaction of meat flavor research and development and application of its main application of thermal reaction flavor raw materials such as protein nitrogen source, carbohydrate carbon source for enzymatic hydrolysis, control hydrolysis degree, in the relevant parameters through the reasonable adjustment and through the thermal reaction process in order to generate realistic, richly flavored meat flavor. These products have good taste and pure flavor, and can simplify the food processing procedures, which is conducive to reducing production costs.

In recent years, with the improvement of consumption level, China’s demand for flavors is increasing, China’s flavor and fragrance production as a whole shows a growing trend, this rapid development momentum is expected to continue for quite a long time.

② Foreign flavor development trend

Since 1960, the British MoIrton obtained the first Maillard reaction preparation of meat flavors since the patent, meat flavors have been rapid development and commercial production. Today, the annual production of thermally reacted meat flavors in the United States and Europe has exceeded 30,000 tons, and is widely used in liquid soups, solid soups, snack foods, canned foods, new protein foods, simulated meat products and other foods.

In Europe and the United States, the production of heat-processed meat flavors accounted for more than 65% of the total amount of flavors. In recent years, researchers at home and abroad also found a new amino acid raw material a yeast extract, yeast extract instead of part of the meat extract, can make the produced meat flavor flavor flavor and taste better.

Conclusion

The research and application of Maillard reaction and its products have been an important and popular topic in the fields of food chemistry and flavor chemistry at home and abroad in recent years. People’s research on Maillard products is not only limited to be the raw material of flavors, but also more and more in-depth research on its functional properties such as antioxidant, antimicrobial, antimutagenic, emulsification, improvement of flavor modification of food, and the influence of bioactives.

As the process of Maillard reaction is quite complex, with dozens, hundreds or even thousands of products, there are still many gaps to be further studied. In recent decades, with the progress of analysis, detection technology and analytical methods, such as HPLC, GC, GC ~ MS, GC-O and other advanced research means will be applied to Maillard product separation, purification and identification.

Due to the variety and complexity of Maillard products, a considerable part of the products are beneficial to the food processing industry, but of course, the harmful components cannot be excluded, therefore, the reaction conditions should be controlled as much as possible in the future research, so that the reaction can be developed in the direction of people’s expectations. It is believed that with the in-depth study of reaction mechanism and application, the application of Maillard reaction to dry food processing industry will have a broader prospect.