Analysis of main components of cooked Coffee beans in Yunnan

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Shenyang, the birthplace of China, has many authentic delicacies. There is a melting pot of culture. the ancient city with a history of more than 5000 years, the first capital of the Qing Dynasty, was once called Xishui, Fengtian, Shengjing and so on. There are Hui communities, fresh communities, Japanese communities and so on, so the food culture is particularly developed. When I was in primary school, there were many Korean students and Japanese half-race in my class. I was a Japanese half-race. But after arriving in Hangzhou, many people can not understand, feel very fresh, but do not realize that it is a common thing in the northeast. Ever since I was a child, my parents used to take me to Xita (the territory of the Koreans in Shenyang) for barbecue. I will never forget the charming incense in my life. The barbecue is very popular in Northeast Korea, but the people of Hangzhou don't like it very much. Since I went to England at the age of 15, my parents would take me to Fuyunlong barbecue every time I went back to Shenyang. Now I know that in the process of barbecue, there is a chemical reaction called Maillard reaction.

Friends who know something about coffee roasting must know why the deeper the roasting degree of coffee beans, the darker the color. Huaxia mentioned in the speech that there are a lot of physical and chemical reactions in the process of roasting coffee. One of the most famous is the Maillard reaction (Maillard Reaction). Through our human sense of smell, we can find the charming incense in food, and the vision can see its color, because it produces a brown substance called melanin-like substance.

[Maillard reaction (Maillard reaction)], also known as Maillard reaction, Maillard reaction, Mena reaction and carbonylamine reaction, is a non-enzymatic browning reaction widely distributed in the food industry, which refers to a series of complex reactions between reducing sugars (carbohydrates) and amino acids / proteins in food at room temperature or heating, resulting in the formation of brown-black macromolecular melanins or quasi-melanins. In addition to producing melanoidin, hundreds of intermediate molecules with different odors, including reducing ketones, aldehydes and heterocyclic compounds, are produced in the reaction process, which provide delicious flavor and attractive color for food.

[Maillard reaction] was discovered by French chemist Louis Camille Maillard in 1912. In 1953, John Hodge and others officially named this reaction as Maillard reaction. In 1912, Maillard told other scientists at the French Academy of Sciences about her discovery that a mixture of amino acids and sugars produced a yellowish brown solution, but few of those present at the time realized the potential significance of the reaction. However, today, Maillard reaction has become a technology closely related to the modern food industry, which can be seen everywhere in meat processing, food storage, essence production, traditional Chinese medicine research and other fields. Current studies have also shown that it is closely related to the physiological and pathological processes of the body. When we pass by the private room or have a barbecue, we will ask about the charming incense, which is the product of Maillard reaction, and it is also very sweet in the process of roasting coffee.

Egg fried rice is also a Maillard reaction, the egg liquid and the rice surface produce caramelization reaction when heated, the rice grains will become hard and easy to separate because of crystallization, in order to fry the fried rice with distinct grains, it is not necessary to use the refrigerator to store cooked rice. In traditional Chinese cuisine, stir-fry the meat with sugar or sprinkle starch first, which will also lock up the essence of the flavor of the ingredient. The fried food has scorched fragrance but no trace of burning, looks beautiful, and collects color, fragrance and taste in one plate.

Melanoidin is a kind of brown and complex macromolecular compounds formed in the later stage of Maillard reaction, which is common in food. Food melanin is a brown substance formed in the later stage of Maillard reaction between carbohydrates (generally refers to sugars) and nitrogen-containing compounds with free amino groups (such as amino acids, peptides, proteins, etc.). It is generally believed that food melanin is a mixture of some different kinds of high molecular weight compounds. the reason for the formation of its color is not only those high molecular weight melanin-like substances, but also some low molecular weight colored compounds. sometimes it also includes some low molecular weight melanin-like substances.

Melanoidin has the function of anti-oxidation, combined with flavor substances, and has the effect of anti-cancer and preventing dental caries. Relatives who like Japanese food all know that Japanese food's Weizeng soup is very delicious. Wei Zeng soup contains quasi-black essence, which is why often drinking Wei Zeng soup has the effect of light body, which is a favorite product for Japanese women to lose weight. Melanoidin-like detoxification is healthy and has a magical ingredient to prevent the rapid rise of blood sugar. A bowl of Weizeng soup every day, super detoxification, excellent anti-cancer effect.

In fact, the amount of black essence-like substance in coffee is much more than that in Weizeng soup. The melanoid produced by Maillard reaction when roasting coffee, we drink coffee, the melanoidin in coffee inhibits the production of oxides, fatigue, pain and other conditions in our body, and can become the king of detoxification.

Today, Professor Qiao of Shenzhen Vocational College sent me an academic report entitled "Analysis of main components and melanin-like components of roasted coffee beans in different regions of Yunnan". This report is from the Journal of Food Science. Using raw coffee beans from three main coffee producing areas in Yunnan (Pu'er, Nujiang and Dehong) as raw materials, the main components of raw coffee beans were analyzed by roasting in different degrees (light, moderate and severe). The chemical composition of coffee melanins was analyzed by pyrolysis-gas chromatography-mass spectrometry (pyrolysis-gas chromatography-mass spectrometry,Py-GC-MS). The results showed that with the deepening of roasting degree, the protein and crude fat content of coffee beans increased, and the total amino acid content decreased, of which the highest protein content was heavily roasted Pu'er coffee bean (16.3 g 100 g), the highest amino acid content was Pu'er raw coffee bean (9.41%), and the highest crude fat content was moderately roasted Dehong coffee bean (13.85 g 100 g). The higher contents of mineral elements were K, Mg, P and Ca, and the K content of Pu'er coffee beans was the highest after heavy roasting (2.2g / kg 100g). The results of Py-GC-MS analysis showed that the melanin composition of coffee beans from different producing areas and different roasting degrees were significantly different, but there were common characteristics. The relative contents of caffeine and acids were the highest, followed by amines, esters, phenols, pyrrole, furans, pyridines, aldehydes, alcohols, ketones and so on.

The following is a summary of the findings and conclusions of the report shared with you:

Through the chemical experiments of the organizers of the report, it is concluded that the ingredients of 12 kinds of coffee beans including raw coffee are studied after coffee beans from different areas in Yunnan are roasted under different conditions. the contents of mineral elements, protein, crude fat and amino acids are all different. The content of mineral elements in raw coffee beans in Pu'er and Nujiang areas from high to low is K > Mg > P > Ca > Mn > Fe > Na > Cu > Zn. The contents of mineral elements Mg, P, Ca, Mn and Zn all increase with the deepening of baking degree. The reason may be that during the roasting process of coffee beans, on the one hand, starch is converted into caramel, and water evaporates with carbon dioxide, on the other hand, some ingredients such as fiber will also be carbonized, resulting in an increase in mineral elements under the same quality conditions. After light roasting, the contents of Fe (64.8 mg/kg), Cu (20.2 mg/kg), Na (17.2 mg/kg) and Zn (9.08 mg/kg) of Pu'er coffee beans were the highest compared with those of coffee beans from other regions. After heavy roasting, the contents of K (2.20g) and Mg (0.272 g) were the highest compared with coffee beans from other regions. After heavy roasting, the contents of P (0.242 g / 100g) and Ca (0.188 g / 100g) of Dehong coffee beans were the highest compared with those of coffee beans from other regions, while the content of Mn (118g mg/kg) of Nujiang coffee beans after moderate and heavy roasting was the highest compared with that of coffee beans from other regions.

In Maillard reaction, proteins react with carboxyl-containing sugars to produce aldehydes, ketones and other substances, but the results show that the protein content increases after baking, probably because melanin-like substances mainly have three structures. one of them is the melanin-like substance produced by the cross-linking of protein with low molecular weight coloring compounds, so the overall protein content of coffee is increased after roasting. The protein content of coffee beans after heavy roasting was in the following order: Pu'er (16.3 g) > Nujiang (15.9 g) > Dehong (15.0 g). After heavy roasting, the protein content of Pu'er and Dehong coffee beans was 3.3 g more than that of raw coffee beans.

The increase in crude fat content of roasted coffee beans may be due to the production of some new oil-soluble substances during baking, which are dissolved with the formation of oil on the surface of coffee beans, resulting in an increase in crude fat content; while fat is easy to be oxidized at high temperature, the crude fat content of Nujiang and Dehong coffee beans increases at first and then decreases with the deepening of baking. After heavy roasting, the crude fat content of coffee beans from high to low was Dehong (13.77 g) > Pu'er (11.96 g) > Nujiang (11.38 g). After moderate roasting, the crude fat content of Dehong coffee beans was 8.35 g 100 g higher than that of raw coffee beans.

The total amount of amino acids decreases with the deepening of baking degree, because amino acids participate in the synthesis of melanin-like substances in Maillard reaction and decompose into furan, pyridine and other substances in the heating process. The total amount of amino acid in raw coffee beans from high to low was Pu'er (9.41%) > Dehong (8.49%) > Nujiang (6.90%). The content of glutamic acid was the highest, followed by aspartic acid and leucine, and methionine was the lowest. The contents of lysine and arginine changed greatly, and the roasted coffee beans were significantly lower than those of raw coffee beans. Proline was not detected in Pu'er coffee beans. The change of amino acid content of Nujiang coffee bean was not obvious, but the change of amino acid content of Pu'er coffee bean and Dehong coffee bean decreased.

In [lightly roasted coffee melanin], 115 kinds of pyrolysis products were detected in Pu'er coffee melanin, and 19 with a matching degree of not less than 50%. Among them, the relatively high contents were caffeine (47.01%), palmitic acid (6.99%), oleic acid amide (5.11%), 3-isobutyl-2 pyrrole-hexahydropyrrole [1-ray 2a] pyrazine-1-4-Dione (1.8%). A total of 159 kinds of pyrolysis products were detected in Nujiang coffee melanin, of which 30 with a matching degree of not less than 50% were caffeine (23.77%), palmitic acid (22.85%), stearic acid (6.09%), oleic acid amide (1.09%), (S)-5-hydroxymethyl dihydrofuran-2-one (1.03%). A total of 78 kinds of pyrolysis products were detected in Dehong coffee melanin, and 10 with a matching degree of not less than 50%, of which caffeine (27.94%), palmitic acid (19.00%) and oleic acid amide (2.04%) were relatively high.

Among the pyrolysis products of moderate roasted coffee melanin, 168 kinds of pyrolysis products were detected in Pu'er coffee melanin, and 26 kinds of products with a matching degree of not less than 50% were detected. Among them, the relatively high contents are caffeine (37.57%), palmitic acid (8.86%), oleic acid amide (2.45%), stearic acid (2.11%), 3-isobutyl-2pyrrole [1hydropyrrole] pyrazine-1-diketone (2.08%), (S)-5-hydroxymethyl dihydrofuran-2-one (1.14%), pyrrolide (2pyrrol-F)-pyrazine-1-dione (1.05%). A total of 102 kinds of pyrolysis products were detected in Nujiang coffee melanin, and 19 species with a matching degree of more than 50% were detected. The relatively high contents were caffeine (39.36%), palmitic acid (15.02%), stearic acid (2.80%), 3-isobutyl-2pyrrole (3pyrrole), 7pyrrole (8a), pyrazine-1 (1.89%), 2-methyl-3-hydroxy-4-pyranone (1.18%) and 3-hydroxypyridine (1.14%). A total of 112 kinds of pyrolysis products were detected in Dehong coffee melanin, and 17 kinds of pyrolysis products with a matching degree of not less than 50% were detected, of which caffeine (36.25%), palmitic acid (16.46%) and stearic acid (4.54%) were relatively high.

Among the pyrolysis products of [heavy roasted coffee melanin], 174 kinds of pyrolysis products were detected in Pu'er coffee melanin, and 32 kinds of pyrolysis products with a matching degree of more than 50% were detected. The ones with higher relative contents were caffeine (37.24%), palmitic acid (9.14%), 3-isobutyl-2 pyrrole (6pyrrole), 8a-hexahydropyrrole [1mia2lica] pyrazine-1pyrrolidine (6.50%), (2-aminoethyl) benzyl benzyl carbamate tert-butyl ester (2.45%), pyrrolido (2mem1MIF) pyrazine-1dione. (s)-5-methylol dihydrofuran-2-one (1.70%), 3-cyano-4-oxopyrrolidine-1-tert-butyl formate (1.18%), hexahydropyrrolido [1mae 2mai A] pyrazine-1je 4-Dione (1.00%). A total of 83 kinds of pyrolysis products were detected in Nujiang coffee melanin, of which 14 with a matching degree of not less than 50% were caffeine (22.25%), palmitic acid (21.89%) and stearic acid (5.04%). A total of 93 kinds of pyrolysis products were detected in Dehong coffee melanin, and 35 ones with a matching degree of not less than 50%. Among them, the relatively high contents were caffeine (26.52%), palmitic acid (14.23%), stearic acid (3.30%), 3-isobutyl-2pyrrole-hexahydropyrrole [1pyrrol 2a] pyrazine-1benzodione (1.97%).

Through analysis, it is found that there are obvious differences and common characteristics in the pyrolysis products of black essence of coffee beans in different regions and different roasting degrees. Caffeine is the substance with the highest content in melanin. It turns out that caffeine belongs to melanin. Caffeine has strong thermal stability and its content is stable in the process of baking. The relative content of caffeine in Pu'er coffee melanin is relatively high, the relative content of coffee melanin after light roasting is 47.01%, and the lowest is Nujiang coffee melanin after heavy baking, which is 22.25%.

Acid compounds mainly affect the sour taste of coffee, the relative content of Nujiang coffee black essence is relatively high, after heavy roasting, the relative content is 56.93%; the lowest relative content is Pu'er coffee black essence, which is 6.99%; palmitic acid and stearic acid are the highest in all black essence.

Amines are the basic aroma substances of coffee, and the highest relative content is Dehong coffee melanin after heavy roasting, which is 7.04%, followed by Pu'er coffee melanin after light baking, which is 5.11%. Moderate roasting Nujiang coffee melanin does not contain; the highest relative content of amines in all melanin is oleic acid amide.

The relative content of esters in lightly roasted Nujiang coffee melanin was 5.66%, followed by heavily roasted Pu'er coffee melanin (4.78%) and Dehong coffee melanin (2.85%).

Phenolic compounds are mainly characterized by pleasant clove flavor, and the highest relative content is Pu'er coffee black essence after moderate roasting, in which the relative content of 4-vinyl-2-methoxyphenol is the highest (0.25%). It is also the main phenolic compound in melanin-like compounds.

The relative content of ketones in heavily roasted Pu'er coffee melanin is 0.36%; only in Dehong coffee melanin after heavy baking is 0.10%, and is not found in light and moderate roasted coffee melanin.

The relative content of alcohols in Nujiang coffee melanin is the highest, and the relative content after heavy baking is 0.51%. The lowest relative content is moderate roasted Pu'er coffee melanin, which is 0.04%. However, it is not found in Pu'er coffee melanin after light and heavy roasting.

Aldehydes make a great contribution to the taste of coffee cream. Only lightly roasted Pu'er coffee melanin and Nujiang coffee melanin contain 0.30% and 0.06% respectively, and only one aldehyde compound is 5-hydroxymethylfurfural (0.30%) and nonaldehyde (0.06%).

Furan, pyrrole and pyridine compounds in coffee are mainly scorched and caramelized. After heavy roasting, the relative content of black essence in Pu'er coffee is the highest, which is 11.42%, while that in Nujiang coffee is the lowest, which is 0.32%.

There are also coexisting components in coffee melanin in different regions and different baking temperatures, and caffeine and palmitic acid have the highest relative content. The results show that different roasting degrees have great effects on the composition of coffee and its melanin-like composition, and there are significant differences in coffee from different areas, which provides theoretical guidance and basis for the baking process of coffee beans from different areas.

In this experiment, coffee beans from three main producing areas in Yunnan were used as raw materials. After roasting in different degrees, the main components of coffee beans were analyzed, and melanin-like compounds were selected. Py-GC-MS technology was used to analyze the components and differences of melanin-like beans. Due to the difference of planting area, environment and soil conditions, the total content of mineral elements and protein in Pu'er coffee was higher, the content of crude fat in Dehong coffee bean was the highest, and the total amount of amino acid decreased with the deepening of roasting degree. The highest is Pu'er coffee beans. Among the melanin-like components, caffeine was the highest in Pu'er and Dehong coffee, while acid was the highest in Nujiang coffee, in which palmitic acid and stearic acid were the highest. There are amines, esters, phenols, pyrrolites, furans, pyridines, aldehydes, alcohols, ketones and so on.

NB: the above experimental data and results are from the academic report "Analysis of main components and melanin-like components of roasted coffee beans in different regions of Yunnan". Journal of Food Science 2017, Vol.38, No.02176 p. 183.