Advances On The Chemical Composition And Medicinal Value Of Coffee Beans Ⅰ

Abstract: Coffee is a popular dietary supplement with a unique flavor in the world. Coffee beans contain complex chemical components and extensive biological activities. The research on the chemical components of coffee beans such as alkaloids， sugars， organic acids， esters， sterols, and diterpenes had made significant progress. The effects of neuroprotection， defense against hyperglycemia and hyperlipidemia， anticancer， anti-inflammatory，anti-oxidation， and liver protection were found in coffee beans. This article reviewed the chemical components and discoveries methods in coffee beans，the biosynthesis of the main active substances and their potential medicinal value， and provides references for in-depth research and industrial development of coffee beans. 

Keywords: Coffee； Chemical composition； Pharmacological effects； Medicinal value

Coffee (Coffea sp.) is a Rubiaceae coffee plant, native to central and northern Africa, and is now widely grown in Latin America, Africa and Asia Pacific. There are many kinds of coffee, up to more than 90 kinds, which are divided into four categories: large-grain (Coffea liberica), medium-grain (Coffea robusta), small-grain (Coffea arabica) and excelsa (Coffea excelsa). The best quality of coffee beans [1].

Coffee is the most commonly used beverage plant and has great economic value. China first introduced coffee trees to Taiwan in 1884, and currently Hainan and Yunnan are the main coffee producing areas in China. Traditional Chinese medicine believes that coffee is slightly bitter, astringent, and flat; Coffee contains a variety of chemical components such as alkaloids, flavonoids, phenolic acids, terpenes, etc., which have the functions of lowering blood sugar, lowering blood lipids, anti-oxidation, and neuroprotection. It has great medicinal value and has broad development prospects. This paper expounds the chemical composition and medicinal value of coffee beans, and provides a reference for related research.

1 Chemical composition and discovery method

The chemical composition of coffee beans mainly includes two categories: non-volatile substances and volatile substances. The non-volatile components of green coffee beans are much higher than that of roasted coffee beans, and their non-volatile components mainly include nitrogen compounds, carbohydrates, acid compounds and ester compounds. Among them, nitrogen-containing compounds are mainly alkaloids and amino acids, carbohydrates are mainly polysaccharides and a small amount of oligosaccharides, acid compounds include chlorogenic acid and small molecular organic acids, and esters are mainly coffee oil, sterols and diterpenoids.

1.1 Alkaloids

Green coffee bean alkaloids are mostly caffeine, theophylline, theobromine, hypoxanthine, matrine and trigonelline, of which trigonelline is the precursor substance for generating furan, pyrazine and alkylpyridine.

Caffeine is the most important alkaloid in green coffee beans and the main source of bitterness. The representative substance in caffeine is caffeine. Andrade et al. [3] used supercritical fluid extraction to extract caffeine from green coffee beans, and found that the highest yield of caffeine was extracted with a mixed solvent of CO2 and isopropanol. The researcher [4] used high performance liquid chromatography (High perfarnance liquid chromdtograpny, HPLC) to study the changes of caffeine content in coffee beans from different producing areas and altitudes. Shao Jinliang et al. [5] studied the content of trigonelline and caffeine in green coffee beans, roasted coffee beans and coffee powder, and found that caffeine is the characteristic quality index of coffee beans. Basin is the second principal component.

Trigonelline is a derivative of pyridine, which is demethylated in the roasting process of coffee beans to generate niacin, which plays a role in promoting the production of aromatic compounds, and its content is high in Arabica varieties [6]

. Liu Hongcheng et al. [7] determined the effect of different extraction methods on the content of trigonelline by HPLC, and found that the extraction method had little effect on the content of trigonelline.

Click here to get more info about Cistanche Coffee

1.2 Amino acids

Coffee beans contain a variety of proteins and free amino acids, such as glutamic acid, aspartic acid, leucine, glycine, and alanine. Some scholars use the alkali-soluble acid precipitation method to extract the protein in coffee beans, and detect the content of essential amino acids in them. 67.02% of the protein content [6]. Dong et al. [8] conducted a semi-quantitative identification of 79 volatile compounds in coffee by using headspace solid-phase microextraction-GC-MS, and detected essential amino acids such as leucine, lysine and arginine in coffee beans. .

1.3 Carbohydrates

Green coffee beans have a high content of sugar compounds, accounting for about 50% of the dry weight, mainly oligosaccharides and polysaccharides, with very little monosaccharide content. Among them, the main polysaccharides are arabinogalactan, mannan and cellulose [10], and the polysaccharide content decreases during the baking process. Hu Shuangfang et al [9] measured 7

After testing coffee beans from different producing areas, it was found that the golden Mandheling coffee beans had the highest reducing sugar content, as high as 11.2 mg/g. The methods of extracting polysaccharides in coffee beans include continuous extraction, acid hydrolysis, hot water extraction, enzyme extraction, etc., but so far, hot water extraction is the only accepted and most feasible process, with simple process, low cost, and no additions. [11], there are also experiments on coffee grounds by ethanol soaking, concentration, deproteinization, petroleum ether extraction, etc., and successfully extracted the polysaccharides from coffee grounds [12]. Delgado et al. [13] found that the insoluble components in coffee extracts were mainly polysaccharides.

1.4 Organic acids

Chlorogenic acid is an important phenolic compound in green coffee beans. According to reports, coffee is one of the most important sources of chlorogenic acid in human diet [14]. The monomer with the highest chlorogenic acid content is 5-caffeoylquinic acid (5-CQA), which is about 70% of the total chlorogenic acid content [15]. The content of chlorogenic acid in green coffee beans is relatively high, about 6.7-12%, and the content of chlorogenic acid in roasted coffee beans is greatly reduced, and the content is about 2-3.1% [16].

Solvent extraction, supercritical fluid extraction, adsorption elution and partition chromatography are the commonly used extraction and separation techniques for chlorogenic acid. Upadhyay et al. [17] used microwave treatment, the water phase was water, and the solvent phase was 50% ethanol and 50% methanol solution to study the extraction process of chlorogenic acid and other substances in Robusta coffee green beans, and found that the optimal condition was microwave. The power was 800 W, the extraction temperature was 50 °C, and the extraction time was 5 min. The extraction rate of chlorogenic acid was 7.25%, which was significantly higher than that of a single solvent under the same conditions. Romero-González et al. [28] used separation

The separation and extraction of three chlorogenic acids, 5-CQA, 5-FQA, and 3,5-diCQA in coffee, was carried out by countercurrent partition chromatography. The stationary phase was ethyl acetate-n-hexane, and the mobile phase was chlorine with different ion gradients. The separation of the three chlorogenic acids was achieved under the conditions of lithium sulfide and ammonium sulfate-potassium nitrate. Li Shasha et al[19] used HPLC to measure the content of chlorogenic acid in coffee beans from different origins, Phenomenex Luna C18 was used as the chromatographic column, methanol-0.5% formic acid water was used as the mobile phase, and the wavelength was 285 nm. The highest content of ortho acid was 3.333 mg/g.

In addition to chlorogenic acid, coffee beans also contain quinic acid, malic acid and citric acid. Shao Jinliang et al. [20] detected 5- The content of CQA, 4-CQA, 1,3-CQA and other substances, and the content in green coffee beans is higher than that in coffee products. Some foreign scholars have found citric acid, acetic acid, acrylic acid and fumaric acid by testing commercial instant coffee in Spain [21]. In addition to the above organic acids, coffee beans also contain succinic acid, citraconic acid, erythronic acid, gluconic acid, glyceric acid, etc.

1.5 Esters

There are many kinds of ester compounds in coffee beans, most of which are generated by the conversion of crude fat in coffee beans. After coffee beans are roasted to different degrees, the composition of ester compounds is also very different, mainly including coffee oil, sterols and Diterpenoids, etc. [22].

1.5.1 Coffee Oil

Coffee oil is rich in unsaturated fatty acids and saturated fatty acids. The unsaturated fatty acids are mainly linoleic acid, and the saturated fatty acids are mainly palmitic acid. It also contains a small amount of myristic acid, stearic acid, and arachidic acid. In addition to essential fatty acids, coffee oil also contains other biologically active substances, such as tocopherol, sitosterol, stigmasterol, squalene, etc. Coffee oil is generally extracted with ether, petroleum ether or n-hexane organic solvent. Dong et al. [23] compared the effects of different extraction methods on the content of coffee oil in coffee beans, and found that the coffee oil content of ultrasonic-microwave-assisted extraction was the highest, as high as 10.58%±0.32%. Some scholars[24] tested the chemical components of 7 kinds of coffee beans in Hainan. Using chemical measurement technology, main component analysis, hierarchical cluster analysis and one-way heterogeneity analysis, the main fatty acids in coffee oil were measured as linoleic acid, linoleic acid, Palmitic acid and oleic acid. Zeng Fankui [25] used gas chromatography mass spectrometry (Gas chromatograob-mass spectrometel, GC-MS) to analyze the content of coffee oil fatty acids in Yunnan Arabica coffee beans, Xinglong Robusta coffee beans and Vietnam Robusta coffee beans, and found that Arabica coffee beans had the highest content of fatty acids. Its content from high to low is 36.77%~46.12% of linoleic acid, 29.27%~31.62% of palmitic acid, and 18.835~25.20% of oleic acid. The three kinds of fatty acids account for 95% of the total fatty acids. Behenic acid, this result is consistent with the result detected by Chen Yiping [26] from the coffee grounds of coffee products.

1.5.2 Sterols

Coffee beans contain a large amount of sterols, with the most abundant β-sitosterol, followed by stigmasterol, campesterol, and Δ5-avenasterol. Nzekoue et al. [27] collected 14 kinds of coffee bean residues from 12 countries, and extracted four phytosterols, namely β-sitosterol.

188.5~688.5 mg/kg, campesterol 48.6~214.5 mg/kg, stigmasterol 8.9~188.5 mg/kg.

1.5.3 Diterpenoids

The diterpenoids in coffee beans are mainly pentacyclic diterpene alcohols, with the highest content of enantio-kaurane and cafestol diterpenes, among which cafestol, kahweol, 16- Represented by O-methyl cafestol, cafestol and kahweol are resistant to acid,

Light and heat are very sensitive, with certain volatility and special aroma [28]. Lima et al. [29] catalyzed the extraction of cafestol and cafestol from green coffee beans, using platinum catalysts (Pd/C, Pd/CaCO3, Pd/BaSO4, and Pd/Al2O3) and Pd catalysts, and the product purity was high.

Tsukui et al. [30] conducted microwave-assisted extraction of 13 green coffee beans to collect coffee oil, which was six times more efficient than the traditional Soxhlet method. In order to study the changes of bioactive substances in coffee oil during storage, Hong Qidi [31] extracted coffee oil from Hainan Xinglong coffee beans, and used HPLC method to study coffee in coffee beans stored at 60°C for 36 days under accelerated storage. The changes of oil biochemical indexes showed that the initial contents of cafestol and cafestol were 23.44±0.52 mg/g and 21.01±0.31 mg/g, respectively, and decreased to 8.99±0.02 mg/g and 8.21±0.10 mg/g after 24 days. The content of biologically active components decreased to varying degrees, which indicated that the coffee oil underwent oxidation reaction during storage.

1.6 Volatile substances

The content of volatile substances in green coffee beans is very small, because the complex reactions inside the coffee beans during the roasting process lead to the production of a large number of volatile aroma substances [32], including Maillard and Strecker reactions as well as protein, sugar, trigonelline and green beans. Degradation of ortho acids [33]. The volatile substances of coffee beans mainly include alcohols, aldehydes and ketones, carboxylic acids, esters, pyrazines, pyrroles, pyridines, alkalis, sulfides, furans, phenols, etc. The most abundant are furans and pyrazines, and pyrazine compounds have the greatest impact on coffee flavor [34].

1.6.1 Furans

Furan is the most abundant volatile substance in coffee beans, and the flavor of furan is most obvious in roasted coffee beans. The process of furan generation is relatively complex. There are five pathways for furan generation: (1) the thermal degradation of carbohydrates such as glucose, lactose, and fructose; (2) the Maillard reaction of specific amino acids and reducing sugars under heating; (3) ascorbic acid and its derivatives Thermal degradation reaction occurs; ④ unsaturated fatty acid oxidation reaction; ⑤ carotenoid oxidation

reaction [35]. Volatile furans exhibit malt and sweet roasted aromas.

1.6.2 Pyrazines

Pyrazine is also a rich volatile compound in coffee beans, and alkylpyrazine compounds may be formed by the condensation of amino acids generated in the Strecker reaction [35]. In general, pyrazine compounds exhibit nutty, earthy, toasty flavors. Studies have found that ethylpyrazine and vinylalkylpyrazine mainly exhibit earthy aromas [36], while 2-ethyl-3,5-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine Pyrazine is also an important pyrazine compound in coffee [37].

1.6.3 Phenols

During the roasting process, coffee beans will generate phenolic compounds, especially guaiacol, and 4-ethylguaiacol is the main carrier substance for the spicy aroma of coffee [36]. Phenolic compounds are mainly generated by the degradation of chlorogenic acid in coffee beans to form caffeic acid, quinine ferulic acid lactone, etc., and then generated by thermal degradation [35].

1.6.4 Furanones

The main flavor of furanone is caramel aroma[35], mainly including 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 4-hydroxy-2-ethyl-5-methyl v3 (2H)-furanone and 4-hydroxy-5-methyl-3(2H)-furanone, etc. [38]. Furanones are formed from monosaccharides and free amino acids through Maillard reaction after enolization, degradation, isomerization, cyclization, and dehydration [35].

1.6.5 Sulfur-containing compounds

The content of sulfur-containing compounds is relatively low, but the strong roasted smell of sulfur is also one of the key aromas of coffee beans. Cysteine, acetaldehyde, methyl mercaptan, etc. in coffee beans undergo Strecker reaction with hydrogen sulfide to form sulfur-containing compounds [35], including 2-methyl-3-furanthiol, 3-methyl-2-butane alkene-1-thiol, 2,4-dimethyl-5-ethylthiazole, etc. [38].

1.6.6 Extraction and determination of volatile components in coffee beans. Coffee beans are rich in volatile components. Zhan Jiafen et al. [39] used ultrasonic extraction and distillation extraction to analyze the volatile components in Lao coffee beans. A total of 77 volatile components were identified by GC-MS, including 25 nitrogen oxides, 12 ketones, 12 esters, 10 phenols, 6 acids, 6 hydrocarbons, and aldehydes. 3 types, 2 types of ethers, 2 types of alcohols. Wu et al. [40] used extraction methods such as direct solvent extraction and assisted flavor evaporation to process coffee beans. Using gas chromatography-olfactory method, aroma extraction dilution analysis method and gas chromatography-mass spectrometry method, a total of 46 volatile compounds, including 3-hydroxy-4,5-dimethyl-2(5H)-fulanone, 2-methylpropane, 3-methylbutane, etc. Dong et al. [41]

The coffee beans were dried in five different ways: room temperature drying, solar drying, heat pump drying, hot air drying and freeze drying, and 62 volatile substances were detected. Among them, the hot air drying method obtained the most volatile components, and the freeze drying method obtained the most volatile components. the highest volatile components.

2 Biosynthesis of the main active substances in coffee beans

There are many chemical components in coffee beans, and the metabolic process in plants and coffee beans is extremely complex. There are few research reports. In particular, there are few chemical reactions and material changes in coffee beans during processing, and only caffeine has a clear biosynthetic pathway. , Trigonelline and Chlorogenic Acid.

2.1 Biosynthesis of caffeine

Caffeine is one of the most important active ingredients in coffee beans and belongs to the methamphetamine alkaloids. The biosynthetic pathway of caffeine in coffee beans mainly consists of four steps: xanthine methylation to 7-methylxanthine, N-methyl nucleotide synthase to form 7-methylxanthine, and then to 7-methylxanthine. Theobromine synthase reacts to form theobromine, which finally reacts with caffeine synthase to form caffeine. Although researchers have discovered other synthetic pathways for caffeine in the later period, this pathway is still the main pathway for caffeine biosynthesis [42].

2.2 Trigonelline

In coffee, trigonelline accounts for 2% of its dry weight. The current study shows that there are two synthetic pathways for trigonelline in coffee beans: the first is the de novo synthesis pathway starting from aspartic acid and phosphotrisaccharide: aspartic acid-quinolinic acid-nicotinate mono Nucleotide - nicotinic acid adenine nucleotide - nicotine adenine dinucleotide - nicotinamide mononucleotide - nicotinamide riboside - nicotinamide - nicotinic acid - trigonelline [43].

In this synthesis process, nicotinic acid can regenerate nicotinate mononucleotide under the action of nicotinic acid phosphoribosyltransferase, thus forming the amphetamine nucleotide cycle [44]; the second synthesis pathway is the middle of de novo synthesis pathway The product nicotinate mononucleotide directly generates nicotinic acid riboside to produce nicotinic acid, the precursor of trigonelline [45].

2.3 Biosynthesis of chlorogenic acid

Chlorogenic acid is a phenylpropanoid compound, which is produced in coffee beans from cinnamic acid and quinic acid through the shikimic acid pathway: phenylalanine-cinnamic acid-p-coumaroylquinic acid-coumaroyl-CoA- p-Coumaroylquinic acid—5-CQA, 4-CQA, 3-CQA—5-FQA, 4-FOA, 3-FQA, and p-coumaroylquinic acid can also interact with catechol-O-methyl The base transferase reaction generates caffeic acid and ferulic acid, and then reacts with coenzyme A ligase to generate 5-CQA, 4-CQA, 3-FQA, etc. [46].

Support:wallence.suen@wecistanche.com   0015292862950