Baking basic science, browning reaction non-enzymatic browning

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Non-enzymatic browning reaction is different from enzymatic browning reaction. Non-enzymatic browning reactions do not require enzymes, but their reactions require heat, sugars and amino acids. There are two kinds of non-enzymatic browning reactions related to coffee roasting: caramelization (caramelization recation) and Maillard reaction (Mailard reaction).

Caramelization reaction (caramelization reaction)

The caramelization reaction is easier to explain. Caramelization is a process of oxidation, dehydration and degradation of sugar, which affects the flavor and color of coffee. The sugar we refer to here is mainly sucrose (sucrose). The sugar we use in cooking belongs to sucrose. When the sugar cup is added to 160 degrees C, it begins to slowly dehydrate and dissolve into a translucent liquid. When heated to 200 degrees, the compounds in the sugar begin to recombine to produce brown caramel (toffee) with a certain burnt smell and bitter taste, which is completely different from the caramel taste in the sweet caramel cake. Caramel is usually eaten with sugar, milk, or other flavor agents.

Depending on the purpose of use, the manufacturer can choose the flavor and color caused by caramelization, for example, the caramel pigment produced by ammonia method is used in coloring cola drinks.

In addition to producing odors and colors, caramelization produces organic acids (organic acids). For example, in the process of making crisp sugar, baking soda powder (baking soda) is added to react with organic acids to release carbon dioxide to form a unique taste.

A similar reaction occurs during coffee roasting. Sugar degradation also produces carbon dioxide, which increases the pressure on the fibrous tissue inside the coffee bean, which eventually causes the fiber tissue to break, forming the popping sound of the "second explosion" in the coffee roasting process. The cause of the "first explosion" phenomenon in the coffee process is different from the "second explosion". The "first explosion" is mainly caused by the pressure caused by the evaporation of water in coffee beans.

About 90% of sucrose is degraded during baking to form a variety of products, including formic acid (formic acids) and acetic acid (acetic acids).

Some experiments show that the content of acetic acid can increase by about 20 times in the early stage of baking and decrease rapidly in the later stage of baking. Although acetic acid is a weak acid, it can affect the flavor of coffee. Arabica coffee contains about twice as much sucrose as robusta coffee so we can experience obvious aroma and acidity in Arabica coffee.

In short, caramelization produces aromas, acidity, carbon dioxide, and color during baking. Caramel reaction and Maillard reaction together have an effect on the formation of the final flavor of coffee.

Maillard reaction The Maillard Reaction

Maillard reaction should be the most complex of all browning reactions. Although it is closely related to food, in fact it was first discovered in the pharmaceutical industry. In 1900 Dr Louis Camille Maillard was engaged in the most complex study of his life: the mechanism by which the human body produces proteins. When he heated the mixture of reducing sugar and specific amino acids, the solvent gradually changed from a transparent liquid to a brown liquid with the aroma of baked nuts and toast, marking the official discovery of the Maillard reaction. Then a large number of companies began to study Maillard reaction. During World War II, soldiers complained about the discoloration of powdered eggs in their supplies, which attracted the attention of the military and began to investigate. Until now, people do not fully understand the whole process of Maillard reaction. Maillard reaction is an important research topic in the modern food industry, and it involves the research on the aging process in the pharmaceutical industry.

The core issue of Maillard reaction is the effect of the combination of different amino acids and sugars on the flavor and taste of the final product (toast, beef, coffee, etc.) during the hot processing of organic food. In view of the complexity of Maillard reaction, the discussion in this paper can only be regarded as a basic introduction, and more in-depth research is beyond the scope of this paper.

Maillard reaction can be summarized into four main steps:

In the first step, sugars and amino acids combine to form glucosamine (N-glucosamine) compounds during baking, which are unstable and usually undergo a second reaction (glucamine rearrangement reaction Amadori Rearrangements) to form other intermediates. So far all the compounds produced have no color, no smell or taste. In the third step of strecker degradation, glucosamine reacts with specific amino acids to form new aromatic compounds, which are directly related to the aroma of coffee, such as pyrazine, pyridine with the smell of roasted corn / roasted nuts / bitter. The protein melanin compound produced in step 4 determines the color of the coffee.

Some factors can affect Maillard reaction including water content, pH value and temperature. Water is produced during the combination of amino acids and sugars, and the high water activity of the baking substance (the active part of the water content or free water) will hinder the Maillard reaction. For those substances with low water activity, such as bread and milk powder, browning will occur faster. Maillard reaction is accelerated under alkaline conditions, which is conducive to the formation of Amadori rearrangement products to form 1-deoxysome (deoxyglucuronone), which is the precursor of many food flavors. Temperature is a factor we can control, and every 10 degrees C in temperature doubles the speed of Maillard's reaction. This phenomenon is more obvious after the "second explosion".

With the deepening of the baking degree, more and more water disappears from the coffee beans, resulting in an increase in the proportion of potential reactants (more like the proportion of evaporated salts in seawater), and Maillard reaction will also accelerate with the increase of the specific gravity of reactants. With the increase of temperature and the acceleration of reaction, the flavor trend of coffee also changed. the content of phenol, pyrazine and pyridine increased, and the content of acetic acid decreased rapidly after reaching the peak at the initial stage. To put it simply, the deepening of the roasting degree of coffee will result in an increase in aroma, alcohol thickness, irritation and a gradual decrease in acidity.

Caramelization and Maillard reaction are both similar and different:

1. The caramelization reaction does not require nitrogen sources (elements), it is only the decomposition of sugar. Maillard reaction requires sugars and amino acids (nitrogen sources).

two。 The temperature of caramelization reaction is higher than that of Maillard reaction. Maillard reaction can be carried out slowly at room temperature, while caramelization reaction is usually carried out above 150 ℃.

3. Both reactions result in the formation of protein melanin and flavor compounds: color and flavor.