Chromatographic Methods for Coffee Analysis : A Review

Coffee has been one of the most commercialized food products and most widely researched beverage in the world for decades. It is considered a functional food, primarily due to its high content of compounds that exert antioxidant and other beneficial biological properties. This review summarized the data from analysis of coffee components, both volatile constituents and non-volatile high-molecular weight compounds performed by various chromatographic methods. A list of compounds identified by gas chromatography with mass spectrometry which define the aroma of coffee is provided. Publications on the measurement of methylxanthines (caffeine, theobromine, and theophylline), chlorogenic acids, diterpenes, sugars, amino acids, gamma-aminobutyric acid, dibasic acids, anions, and other compounds by HPLC and UHPLC-MS are reviewed. An overview of publications on the determination of organic contamination in coffee (PAHs, acrylamides, mycotoxins, etc.) and ways to reduce contamination through production technology and brewing methods are presented. Finally, an overview of the literature on authentication assessment for different grades of coffee grown in different regions is provided.


Introduction
Coffee has been studied for many years and the research varied depending on the needs: pests, nutrition, pruning, harvesting, processing and quality.Recent studies have shown that the moderate intake of coffee reduces body fat and decreases oxidative damage-related diseases, such as type 2-diabets, cardiovascular, Alzheimer's and Parkinson's disease (Bakuradze et al., 2011;Freedman et al., 2012, O'Keefe et al., 2013).Erdem et al. (2016) indicated that cinnamic acid derivatives have been related with different biological effects including anti-inflammatory, antioxidant, anticarcinogenic, or neuroprotective activities.Coffee has a complex chemical composition and the compounds which include volatile and non-volatile compounds, diterpenes, sugar, amino acids and organic pollutants are important for coffee flavor, quality and health effects.This review article will focus on the chemical composition of coffee and their analytical techniques majorly by different chromatographic methods.We will also introduce some compounds found from different coffee processing procedures and their analytical techniques.

Chromatographic Methods Used to Determine the Chemical Composition of Coffee
Coffee contains over two thousand components-from volatile low-molecular weight to high-molecular weight compounds (Morton and Macleod, 1986).Various chromatographic methods have been used to separate and identify all kinds of mixtures, from gases and volatile compounds to high-molecular weight compounds, as well as mixtures of organic and inorganic ions (cations and anions).Therefore, almost all components of coffee can be detected by chromatographic methods.The components in a mixture are first separated on columns by different adsorption rates, and then the separated components are registered at the column outlet with detectors.
weights up to 500-600 can be identified by gas chromatography.Liquid chromatography has been used to separate and identify non-volatile high-molecular weight compounds at temperatures close to room temperature.Therefore, even unstable compounds can be determined by liquid chromatography.For example, six quality markers in coffee, which are caffeine, trigonelline, nicotinic acid, N-methylpyridinium, 5-caffeoylquinic acid, and 5-hydroxyfurfural were simultaneously detected for three coffee matrices-green, roasted, and soluble-with the limit of quantification 0.069-0.71µg/ml by HPLC-DAD.This technique is useful for routine determination of the thermal degradation rate during the roasting process (Gant, Leyva, Gonzalez & Maruenda, 2015).Ion chromatography and ion exchange chromatography methods utilize columns filled with ion exchangers to separate ion mixtures.In thin layer chromatography, separation occurs not on columns but on plates made of glass, metal, or polymer coated with a thin layer of adsorbent material.Capillary electrophoresis techniques employ quartz capillaries with an inner diameter of 0.1 mm, or less.Mixtures may be separated due to the electrophoretic mechanism alone (capillary zone electrophoresis), or due to electrophoretic and chromatographic mechanisms at the same time.In the latter case, a layer of adsorbent is applied on the internal walls of the capillary, or sorbent (adsorbent) is added to the mobile phase.
Gas chromatography with mass spectrometry (GC-MS) and liquid chromatography with mass spectrometry (HPLC-MS) have recently come into wide use to identify the components of the separated compounds (i.e., to conduct qualitative analysis).Table 1 provides a list of chromatography methods used to analyze coffee (based on publications).
Table 1.Chromatographic methods used for the analysis of coffee No. Methods References 1.
HPLC-MS/ MS Trugo, 1984 9. Gel-filtration chromatography Daglia et al., 2004. 10. Micellar chromatography Perez-Martinez et al., 199511. Ion chromatography Gennano and Abrigo, 1992 12. Thin layer chromatography Levi, 1975 In addition to individual chromatographic methods, coffee has been analyzed by various combinations of chromatography methods, such as HPLC and GC, capillary electrophoresis, spectrophotometric methods, and 'electronic nose' and 'electronic tongue' systems.Table 2 provides a list of compounds which were identified in coffee (except the volatile compounds).Various estimates suggest that coffee contains 2000-3000 compounds.
Table 2 shows only useful components that determine nutritional value of coffee: sugars, amino acids, fatty acids, vitamins, antioxidants, trace elements etc.

Structural Formulas and Primary Compounds in Coffee
The structures of primary compounds in coffee are presented below (Fig. 1): caffeine, theobromine, theophylline; Trigonelline; caffeic, ferulic, protocatechuic acids; chlorogenic acids; gamma-isobutyric acid and diterpenes.As one of the major primary compounds, chlorogenic acid was first isolated from coffee beans in 1908, and their structure was determined in 1932.Chlorogenic acids are mono-or diesters of quinic and cinnamic acids.Coffee contains more than fifteen chlorogenic acids along with their derivatives (lactones).Recent research indicated that the chlorogenic acid profiles of whole coffee fruits were influenced by the extraction procedures (Mullen et al., 2011;Craig et al., 2016) Coffee is one of the richest sources of chlorogenic and other oxyaromatic acids.Due to its health effects, chlorogenic acid consumption rate can be up to 1 g per day (Murata, Okada & Homma, 1995).Eleven chlorogenic acids have been detected by three-dimensional HPLC.Farah et al. (2008) studied chlorogenic acids in extracts of green and decaffeinated coffee and identified 9 major and 17 minor components.Shan et al. (2016) simultaneous determined different chlorogenic acids in green coffee bean extracts with effective relative response factors.Köseoglu Yilmaz & Kolak (2017) used a new solid phase extraction method (hydrophilic-lipophilic balance cartridges) combined with HPLC analysis to perform chlorogenic acid analysis recently.According to some publications, coffee is a major nutritional source of oxyaromatic acids for its consumers (Clifford, 2000;Murata, Okada, & Homma 1995).Besides chlorogenic acid isomers (main isomer is 5-caffeoylquinic acid) and their diesters, some other hydroxycinnamic acid conjugates were also identified (Clifford, 2000) in coffee.The recognized chlorogenic acids and their derivatives, as well as their content in coffee are provided in Tables 3, 4 and 5.

Theobromine
Table 3. List of main chlorogenic acids (Clifford, 2000) No. Proper Chemical Names of Acids Simplified Chemical Names of Acids 1.

Composition of Volatile Components in Coffee
In the early twentieth century little was known about coffee aromatic components.Later, different compounds such as methylamine, ammonia, trimethylamine, pyrrole, pyridine, acetone, formic and valeric acids, furfural, furfuryl alcohol were identified by classic chemical methods.
In the 1920s, 29 more compounds were detected with the financial support of the Government of Switzerland (Morton and McLeod, 1986).The most typical compounds were furfuryl mercaptan, α-diketones and alkylpyrazines.
Twenty-seven extra compounds were identified between 1929and 1962. From 1963to 1982, more than 600 components were identified by gas capillary chromatography.Different classes of compounds (Table 6) which determine aroma of roasted coffee were identified by Morton & MacLeod (1986).Primary compounds which determine coffee aroma have been study by Ky et al. (2001) (Table 7).
Table 6.Identified classes of compounds which determine aroma of roasted coffee (Morton & MacLeod, 1986) No In one study (Maeztu et al., 2001), aroma of espresso coffee from different botanical varieties and types of roast were investigated.Aroma components were determined by gas chromatography with mass spectrometry, volatile components were extracted by static headspace.Seventy-seven compounds were identified in all samples (Table 8).Among them, 13 key odorants have the greatest effect on coffee aroma (Maeztu et al., 2001) (Table 9).Chromatographic analyses were comparable with the sensory flavor profile.Aldehydes were found to correlate with a fruity aroma, diones with buttery aroma, and pyrazines with earthy burnt aroma.
These investigations showed that approximately 30 volatile compounds (Table 10) were substantially responsible for the coffee aroma.Most typical volatile compounds are provided in the literature (Vitenberg & Ioffe, 1984).The study also investigated how milk added to coffee influenced coffee aroma.The aroma intensity decreased due to milk lipids, proteins, and carbohydrates, however, aroma profile remained the same.
In recent years, a combination of GC-GC-FID with solid-phase microextraction was used for analysis of volatile compounds.In one study (Ryan et al., 2004), 44 volatile compounds were identified by two-dimensional chromatography (the first column with a polar phase and the second with a non-polar phase).Coffee was also analyzed by a time-of-flight mass spectrometer in this study.The coffee aroma was found to contain various classes of chemical compounds (ketones, tyrosines, furans, phenols, pyrroles, etc.).Bressanello et al. (2017) correlated the chemical composition of the coffee volatile fraction to its sensory properties.The chemical information concerning coffee aroma and flavor obtained with HS-SPEM of the ground coffee and in-solution Table 8.Volatile compounds identified in aroma of coffee espresso (Maeztu et al., 2001) No.
2-isobutyl-2-methoxypyrazine aroma of sweet pepper SBSE/SPME sampling combined with GC-MS to evaluate their compatibility with the cupping evaluation for quality control purposes.Yang et al. (2016) found that different temperature profiles for roasting can affect volatile aroma compounds associated with roast coffee defects (light, scorched, dark, baked and underdeveloped) by GC-MS with headspace solid phase micro extraction.
Volatile thiols are among the compounds that have the greatest impact on the flavor of coffee.Due to their extremely low odor thresholds, they have a significant sensory impact even at very low concentration.Thiols are formed during coffee roasting and are the key odorants influencing the sensory characteristics of coffee.Gas chromatography coupled to mass spectrometry is most frequently used technique for the analysis of coffee thiols.
Optimum flow rate of the eluent was 0.7 mL min -1 .The detection limit achieved under these conditions was 1• 10 -11 g.Separation time was 10 min, the yield sequence was theobromine, theophylline, and caffeine.In the same study, the content of methylxanthines was determined in some beverages (coffee, tea, cocoa, and mate) and in human urine after consumption as well.Caffeine was determined to be within 0.1 pg (350 µg mL -1 ), theobromine within 0.1 pg (32 µg mL -1 ), and theophylline within 0.1 pg (47 µg mL -1 ).
Table 11 shows the values of methylxanthines contained in various drinks and urine, as determined by HPLC.
Table 11.Concentrations of methylxanthines in beverages and urine (Bispo et al., 2002) No. Analyzed medium Concentration, µg mL The International Olympic Committee (IOC) banned the use of beverages in such amounts which results in excess of the maximum permitted urinary caffeine level of 12 µg mL -1 .Caffeine at high concentrations leads to various disorders, such as increased secretion of acid gastric juice, kidney dysfunctions, nervous system disorders, arrhythmias, etc.The IOC does not restrict the use of theobromine and theophylline because these compounds have been used to treat asthma.
In one of the most recent studies (Wanyika, Gotebe, Gitu, Ngumba & Maritim, 2010), caffeine content was determined in certain instant coffee (Africafe, Nescafe and Dormans) by HPLC with a spectrophotometric detector at a wavelength of 278 nm determined.The 250×4.6 mm column with ODS sorbent was used; methanol-acetic acid-water (20:0.1:79.9)as mobile phase and flow rate was 1 mL min -1 .The results are Dormans 1.64%, Africafe 3.42% and Nescafe 3.12%.The caffeine content was also determined by the spectrophotometric method-the results were about twice as high.Demissie et al. (2016) used UV/VIS spectrometer to determine caffeine in green coffee beans from hararghe, Ethiopia, using beer-lamberts's law and integrated absorption coefficient techniques.
Caffeine is known to be a pharmacologically active compound which stimulates the central nervous system.Caffeine does not accumulate in the body and is excreted in the urine within a few hours after consumption.

Determination of Diterpenes (Kahweol and Cafestol) in Coffee
Many studies related to the effects of coffee consumption on human health are aimed at investigating its lipid composition such as coffee oil (Boekschotem, Engberink & Katan, 2003).Coffee oil contains pentacyclic diterpene alcohols.Coffee diterpenes are primarily esterified by various fatty acids.Fourteen cafestol derivatives and twelve kahweol derivatives were detected (Kurzrock & Speer, 2001).These compounds are partially preserved during the roasting process (Roos, Van Der Weg & Urgert, 1997).But they are also dehydrated which results in the formation of dehydrated derivatives along with other decomposition products, such as kahweol, cafestol, isokahweol, and dihydroisokahweol.Cafestol was found in both coffee Arabica and in coffee Robusta whereas kahweol was found only in coffee Arabica (Roos, Van Der Weg & Urgert, 1997).These diterpenes may contribute to the decomposition of toxic substances and provide a protective effect, particularly against aflatoxin B1 (Cavin, Holzhaeuser & Scharf, 2002).Moreover, they were noted to have anticarcinogenic, antioxidant, anti-inflammatory, and hepatoprotective properties (Kim, Hwang & Jeong, 2007;Lee, Choi & Jeong, 2007;Lee & Jeong, 2007).These beneficial effects of coffee oil create great opportunities for its use in the food and cosmetics industries.The use of coffee oil as a sunscreen agent in cosmetics has already been patented (Grollier & Plessis, 1998).However, the diterpenes, mainly cafestol, were also reported to have an undesired effect which tends to increase cholesterol levels (Kurzrock & Speer, 2001;Kim Hwang & Jeong, 2009;Urgert, Van Der Weg & Kosmeijer-Schuil, 1995).A reliable analytical method is necessary for the determination of synthetic metabolic pathways of these diterpenes.In addition, the determination of diterpene content can be used for classification of coffee mixtures, in particular as a means of establishing the difference between Arabica and Robusta.

Determination of Sugars in Coffee
The content of low molecular weight sugars was investigated in green Arabica coffee beans which were obtained after flesh of the berries was separated from the seeds by wet or dry methods (Knopp, Bytof & Selmar, 2006).
Low content of fructose and glucose was noted in washed coffee beans (wet method).The content of these sugars was higher when coffee beans were dry processed.Laboratory models of these processing methods have confirmed the above results.Table 13 shows the content of monosaccharides in coffee samples of several manufactures from various countries.As can be seen from these data, saccharose typically has the highest content level.
Table 13.Concentration of the most common sugars in commercial green coffee samples (Knopp, Bytof & Selmar, 2006)  Saccharose content is significantly lower in the Robusta than the Arabica.In the Arabica coffee, the saccharose content remains basically the same and does not depend either on the processing method or location where it was grown.A similar conclusion can be drawn with respect to glucose.However, the fructose content does depend both on the processing method and the location where it was grown.The fructose content in the Robusta coffee is higher compared with the Arabica, yet the glucose content is approximately the same in both grades.Typical content of sugars is provided in Table 14.Coffee processing technology can be ascertained by the content of fructose and glucose.The content of sugars was determined by ion exchange chromatography on the Dionex PA20 column with amperometric detector at gold electrodes; NaOH solution as eluent and the flow rate was 0.5 mL min -1 .

Determination of Amino Acids in Coffee
Amino acids in coffee have been determined by a classic ion exchange chromatography in the form of derivatives as well as by a direct method with amperometric detection (Nakhmedov, 1984).Amino acids were also separated by HPLC and ion-pair chromatography in the form of derivatives with ortho-phthalic dialdehyde by other researchers (Bytof et al., 2005).The following amino acids were identified in green coffee: glutamic acid, aspartic acid, serine, histidine, glycine, arginine, alanine, tyrosine, methionine, valine, norvaline, tryptophan, phenylalanine, isoleucine, leucine, lysine, etc with concentration range 4.4-1075 mg per 100g of coffee dry powder.The content of protein amino acids from different process methods are different.It is higher in dry processed coffee than wet processed coffee.
As a non-protein amino acid, Gamma-aminobutyric acid (-aminobutyric acid, GABA) is an inhibitory neurotransmitter which reduces brain activity, especially during sleep, and reduces depression.The World Health Organization believes that by 2020 depression will be the second most common disease after cardiovascular diseases.-aminobutyric acid (GABA) is contained in the Gabaron tea grade which was specially cultivated in Japan.GABA is also contained in coffee.
Drinks containing GABA are considered to be medicinal, they have the following basic biological properties:  Help cure stress-related insomnia and improve sleep quality;  Reduce risk of cardiovascular diseases;  Have anti-hypertensive properties;  Help cure alcoholism (alcoholics have decreased GABA content in the blood);  Help in treatment of diabetes, Alzheimer's disease and Parkinson's disease;  Retard the aging process.
In one study, the impact of coffee technological processing on the GABA content was investigated (Bytof, Knopp & Schieberle, 2005).Significant amounts of GABA were found in green coffee obtained by dry method.Coffee beans produced by the wet method had significantly less GABA.

Determination of Heavy Metals
As for heavy metals, in accordance with the Regulation of Health Food, coffee may contain only trace amounts.In one study, less than 0.1 µg kg -1 of lead and less than 0.05 µg kg -1 of arsenic was detected by atomic absorption spectrophotometry (Rajkovic, Vukovic & Demin, 2004).Maximum permissible concentration of these elements is below 1μg kg -1 .

Determination of Organic Pollutants in Coffee
There are some compounds undesirable for flavor and bioactivity of the brew which occur due to inappropriate harvesting, weather conditions during processing or improper storage of coffee.Most of these compounds are microbial by products such as ochratoxin and specific biogenic amines.Acrylamide and polycyclic aromatic hydrocarbons could be formed by high roasting temperature.
The concentrations of PAHs in different grades of coffee are different, with lower content in green coffee.Benzo(a)pyrene was not found in green coffee at all.The most amount of benzo(a)pyrene was determined in instant coffee and in roasted coffee.It was shown that the content of benzo(a)pyrene depends on the roasting degree (Kayali-Sayadi et al., 1999;Badolato, et al., 2006).Typically, benzo(a)pyrene served as an indicator of the overall contamination of coffee with PAHs.

Determination of Acrylamide in Coffee
Acrylamide exerts a carcinogenic effect (Tarcke, Rydberg, Karlsson & Tomnqvist, 2002).Acrylamide is synthesized when carbohydrate-rich foods are heated (Taeymans et al., 2004).One of the possibilities is that acrylamide synthesis occurs via Maillard reaction when amino acids react with carbonyl compounds during heating.Significant amounts of acrylamide can be formed during coffee roasting process, therefore coffee may become a source of acrylamide in people's every day diet.Reliable and quick method to measure acrylamide level in coffee is needed to optimize the technology of making coffee with minimal acrylamide level.As is well-known, some compounds which are formed in the roasting process give coffee unmatched aroma and pleasant taste.At the same time, some undesirable and even harmful compounds could also be formed in the roasting process.
The effect of temperature and roasting time on the acrylamide content in coffee was also studied (Senyuva & Gökmen, 2005).The same sample was roasted at 150º C, 200º C, and 225º C for 30 min.At 150º C, the acrylamide content was increasing during all roasting period, whereas at 200º C and 225º C, the acrylamide content was increasing only during the first 10 minutes, after that, the acrylamide content was continuously decreasing during the remaining roasting time (up to 30 min).The level of acrylamide cut down to 5%.
Coffee also changed its color during roasting process.Nonlinear correlation between the color of coffee, as measured by Minolta's CM-3600d spectrophotometer, and acrylamide content in it was noted for 9 types of coffee.The highest acrylamide level, 338 ng g -1 , was noted in Jacobs Monarch coffee.
Prior to the analysis, samples were extracted with methanol and purified.

Determination of ochratoxin in coffee
Ochratoxin is one of the carcinogenic mycotoxins which may develop in foods and beverages under inadequate production processes and storage conditions.In many countries, the maximum allowable levels of ochratoxin are set within 2-50 ng g -1 .
The EU Commission plans to establish standards for ochratoxin levels in green and roasted coffee.AOAC current method for the determination of ochratoxin in coffee was first published in 1975 (Levi, 1975).This method is based on the thin-layer chromatography with an insufficiently sensitive detection (maximum permissible concentration 20 ng g -1 ).
It has been planned to develop a new method for the determination of ochratoxin in coffee.In recent years, dozens of articles were published on this subject.In one study, it was suggested to use reversed-phase HPLC with fluorimetric detection.The presence of ochratoxin in coffee was confirmed by mass spectrometry.The detection limit was 0.1 ng g -1 .Twenty samples of coffee from different countries, such as Brazil, Colombia, Zimbabwe, India, and Indonesia, were analyzed.Extraction was carried out with 1% NaHCO 3 .A polymer-based column (Oasis MAX) which employs both reversed-phase and ion-exchange mechanisms of retention was used in this study.Using such a state-of-the-art technique, ochratoxin in the amounts exceeding the MPC was not detected either in green or in roasted coffee.
Another publication describes a method for measuring an ochratoxin level in green coffee by immunoaffinity column cleanup followed by HPLC separation and analysis (Vorgas, Dos Santos & Pittet, 2005).This technique was tested in 8 countries as part of preparation for establishing it as the EU official method.
A new HPLC-MS-MS method was developed for simultaneous determination of 21 mycotoxins in coffee beverages.Mycotoxins were detected at the µg kg -1 level.Ochratoxin-a mycotoxin regulated in coffee in Europe-was measured in two samples at the maximum allowable level (Garcí a-Moraleja, Font, Mañes & Ferrer, 2015).
Eight types of aflatoxins (B 1 , B 2 , G 1 , G 2 , M 1 , M 2 , GM, GM 2 ) could be formed out of the three structural variants of aflatoxins.Determining aflatoxin B 1 is the most important goal since it is the precursor of all types of aflatoxins (Rajkovic, Vukovic & Demin, 2004).
Aflatoxins were determined by HPLC with fluorimetric detection at the detection limit of 2.5 µg kg -1 , excitation wavelength of 366 nm and emission wavelength 460nm.In all samples of Grand and Don coffee varieties (Golex Product), the total amount of B 1 and G 1 aflatoxins was less than 2.5 µg kg -1 whereas the maximum permissible concentration is 5.0 µg kg -1 (Regulation of Health Food).
The harmful substances in coffee can be eliminated or reduced to a minimum (below MPC) by adherence to the adequate technology for gathering and processing green coffee beans, and proper storage conditions of the finished product.It is worth to mention people should avoid to consume coffee or tea along with foods containing significant amount of nitrates since hydrogen cyanide may be formed (Seto et al., 2008).
Coffee Arabica has richer aroma than coffee Robusta.Arabica coffee tastes slightly sour whereas Robusta coffee has a more bitter taste.Experts can organoleptically-by taste and aroma-distinguish natural roasted Arabica and Robusta coffee.
Less than 3 mg Less than 3 mg 15 Mineral substances (Nа, Mg, K, Fe, Mn, Zn, etc.) 3-4.5% 3-4.5% Note: Coffee contains polyamines and gamma-aminobutyric acid.The table shows average values-the actual values depend on coffee variety and growing area.
Recently the elemental detection of green bean of arabica and robusta coffee from Gayo Highland, Aceh-Indonesia, has been identified by using fundamental Nd-YAG Laser for distinguishing the characteristics of both coffees.It is noticed that the order of elements concentration from highest to lowest are Ca>K>CN>Na>C for arabica and K>Ca>CN>Na>N for robusta.The ratio of intensities of these elements to C intensity could be used as a marker to discriminate kind of coffee for the purpose of authentication (Abdulmadjid, Meilina, Hedwig & Kurniawan, 2017).
The state-of-the-art equipment, namely, multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) and isotope ratio mass spectrometer (IRMS), were used to determine coffee authenticity and its origin (Bertrand, Etienne, Lashermes, Guyot & Dovrieux, 2005).Sixty samples from twenty different geographical areas were analyzed.The 87 Sr/ 86 Sr isotope ratio and average value of the 18 О 2 isotope were determined in the samples.The measurement results showed a high degree authenticity of coffee origin, especially for countries in South America.
Different compounds from coffee have been used to assess the grade of coffee and its origin.Samples of coffee (fruit, beans, husks) from China, India, and Mexico were analyzed with regards to the content of chlorogenic acids, caffeine, and total polyphenols (Mullen et al., 2013).Among chlorogenic acids (69 chlorogenic acids are currently identified in green coffee beans), 5-О-caffeoylquinic acid was prevalent.The analysis was performed by UHPLC coupled with a QE Orbitrap MS.The samples' antioxidant capacity was also determined.The content of chlorogenic acids in coffee from India and Mexico was similar (18.8 and 22.9 mg g -1 in Arabica coffee beans; 27.3 and 27.4 mg g -1 in Robusta coffee beans, respectively), while it was significantly lower in coffee beans from China (1.7 and 7.2 mg g -1 ).Also, coffee from China contained a third to a half of the amount of polyphenols in coffee from India and Mexico, although the total content of flavonoids was about the same.Antioxidant activity measured by FRAP was 2-2.5 times lower in coffee from China than in coffee from India and Mexico (112, 227 and 267 μmol g -1 , respectively, for Arabica coffee).Coffee husk turned out to be a rather rich source of procyanidins, flavanols, and flavonols-about 115-130, 18-30, 260+ µg g -1 , respectively.Mehari et al., (2015) simultaneously determined the alkaloids in green coffee beans from Ethiopia using chemometric method to evaluate the geographical origin of coffee.High performance liquid chromatography was applied and the limits of detection for the method were established.Study showed that the application of linear discriminant analysis provided 75% correct classification of samples into the respective production regions, with a 74% prediction success rate.The moderate classification efficiency obtained when using alkaloid data demonstrated the potential of using this class of compounds in discriminant models for determination of the geographical origin of green coffee beans from Ethiopia.

Conclusion
Coffee is one the most popular beverage and consumed by millions of people all over the world.Numerous factors throughout the coffee production chain, from plant to cup, have been shown to have effects on the color, aroma, and flavor of coffee.This article reviews publications on qualitative and quantitative determination of volatile and non-volatile compounds in green and roasted coffee which determine its aroma, taste and quality, majorly by chromatographic methods.
Using these methods, the following antioxidants and nutrients were identified in coffee: oxyaromatic acids, chlorogenic acids, vitamins, amino acids, sugars, diterpene glycosides, trace minerals, etc. Knowing the chemical composition of coffee will facilitate the study of coffee impact on human health and disease prevention.
It has been reliably proven by now that moderate consumption of coffee reduces cardiovascular risk, prevents the development of type 2 diabetes, protects the liver and even helps combat liver cirrhosis, reduces the risk of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases, and protects against asthma.In general, coffee intake decreases oxidative stress which precedes many dangerous diseases.

Figure 1 .
Figure 1.The structures of primary compounds in coffee

Table 15 .
Overall typical chemical composition of Arabica and Robusta coffee