Showing report on Non-alcoholic beverages
Coffee is a beverage prepared from the roasted beans that are present in the berries of the coffee plant. There are two main species of the coffee plant, Coffea arabica and Coffea canephora (or Coffea robusta). Robusta, which contains about 40–50% more caffeine, can be cultivated in environments where Arabica does not thrive. Compared to Arabica, Robusta tends to be bitter and differs in flavour notes. Many espresso blends are based on dark-roasted Robusta. Most Arabica coffee beans originate from one of the three growing regions: Latin America, East Africa/Arabia and Asia/Pacific.
Coffee berries are picked, defruited, dried, sorted, and sometimes also aged. After these processes, the beans are called green coffee. Then, roasting transforms the chemical and physical properties of the green coffee beans into roasted coffee. The roasting process has a considerable influence on the taste of the final product. At lighter roasts, the bean will exhibit more of its origin flavours. As the beans darken to a deep brown, the origin flavours of the bean are eclipsed by the flavours created by the roasting process. To produce caffeine-free coffee, green coffee beans are decaffeinated before roasting.
After roasting, coffee beans are usually grinded. Types of grinds are fine Turkish (also known as Greek, Arabic or Armenian) grind, meant for mixing straight with water, and coarse grinds, used in a coffee percolator (Moka pot) or a French press. Most common in home coffee brewing machines are the middle-sized grinds for paper filters. Espresso requires a fine size grind. In the espresso method hot water is forced through the ground coffee, resulting in a stronger flavor and chemical changes with more coffee bean matter in the beverage. A number of products are sold for the convenience of consumers. Instant coffee is derived from the beverage after vigorous coffee bean extraction. This coffee beverage is dehydrated into soluble powder or granules, which can be quickly dissolved in hot water for consumption. Canned coffee is a beverage that is popular in Asian countries. Liquid coffee concentrates are sometimes used when coffee needs to be produced for many people at the same moment. Furthermore, coffee surrogates exist. These are instant coffee-like substitutes made from various roasted vegetables, roots, herbs, cereals and fruits.
Filter coffee is the only coffee beverage shown in the food composition table due to the lack of sufficient data for other coffee preparations. Filter coffee of unknown variety, as well as Arabica and Robusta coffees are included. Decaffeinated filter coffee is also described, Coffee is rich in polyphenols, phenolic acids being the most abundant polyphenol class in coffee. Simple phenols, lignans and flavanols are also present in minor amounts.
Phenolic acids are the most abundant polyphenols in coffee. The most important phenolic acids in coffee are the cinnamic acids, and more precisely the chlorogenic acids (CGAs). CGAs are water-soluble polyphenols formed by the esterification of (-)-quinic acid with one or two cinnamic acids such as caffeic acid, and to a lesser extent ferulic acid (1). Coffee beans are one of the richest dietary sources of CGAs. Green coffee beans contain about 5-10% CGAs on a dry matter basis (2). A total of forty-five chlorogenic acids, differing in the nature and the number of cinnamoyl substituents and the position of esterification on quinic acid, have been detected until now in green coffee beans (3, 4, 5). Very low amounts of p-coumaric acid are also measured after hydrolysis. Benzoic acids are present in very small amounts (0.08 mg/100 ml 4-hydroxybenzoic acid and 0.04 mg/100 ml vanillic acid in filter coffee measured after hydrolysis).
CGA content for filter coffee varies from 87 to 212 mg/100mL depending on the coffee variety. 5-Caffeoylquinic acid (5-CQA) is the most abundant CGA present in coffee. 5-CQA represents about 35-50%) of the total CGAs (70 mg/100 ml in filter coffee). High amounts of 4-CQA are also found (60 mg/100 ml in filter coffee). Other chlorogenic acids reported in filter coffee are 3-CQA (52 mg/100 ml), 5-feruloylquinic acid (5-FQA; 12 mg/100 ml), 4-FQA (8.6 mg/100 ml), 3-FQA (4.2 mg/100 ml), 3,4-dicaffeoylquinic acid (3,4-diCQA; 2.7 mg/100 ml), 4,5-diCQA (2.1 mg/100 ml) and 3,5-diCQA (1.6 mg/100 ml).
Chlorogenic acid lactones (CGLs) can be formed from CGAs during the roasting of coffee, by a loss of a water molecule from the quinic acid moiety and formation of an intramolecular ester bond. CGLs identified in coffee are 3-caffeoylquinic acid lactone (3-CQL), 4-CQL, 3-coumaroylquinic acid lactone (3-CoQL), 4-CoQL, 3-feruloylquinic acid lactone (3-FQL), 4-FQL, and 3,4-dicaffeoylquinic acid lactone (3,4-diCQL). No content data are available for brewed coffee. Their content has been measured in coffee beans. 3-CQL (205 mg/100 g) and 4-CQL (94 mg/100 g) are the most abundant lactones in coffee beans. 3-CQA and 4-CQA are respectively 2 and 6 times more abundant than their lactone analogues in commercial coffee beans (6).
Some volatile polyphenols, generated upon thermal degradation during bean roasting, are important for coffee aroma (7). In filter coffee, 4-ethylguaiacol (0.64 mg/100 ml), 4-vinylguaiacol (0.46 mg/100 ml), pyrogallol (0.55 mg/100 ml) and catechol (0.41 mg/100 ml) have been detected. 3-Methylcatechol, 4-methylcatechol, 4-ethylcatechol, guaiacol and phenol have been found in lower amounts. Secoisolarirecinol is the only lignan that is reported in coffee beans (0.53 mg/100 g DW) (8) Matairesinol was not detected. Flavanols were only detected in percolator coffee and present in very minor amounts, with contents of 0.06 mg/100 ml (-)-epicatechin and 0.05 mg/100 ml (-)-epigallocatechin (9).
There are several factors of variability for polyphenol contents in coffee, like variety, roasting process, maturity, storage, and brewing method. Arabica and Robusta coffees differ in their contents of polyphenols. In green coffee, CGA contents are higher in Robusta than in Arabica coffee (10, 11, 12, 13).
Decaffeinated coffee makes up about 10% of the coffee market. Decaffeinating is performed prior to the roasting process. Organic solvents, and to a lesser extent water, are used to extract the caffeine. Chlorogenic acid contents were found to be 3-9% lower in decaffeinated coffee beans compared to regular coffee beans (14). In this study, the decaffeinating was performed with water. In the food composition table, CQA's in decaffeinated filter coffee appear to be somewhat higher than in regular filter coffee. Coffee bean variety and roasting methods may influence final CGA contents reported, since different samples were used for the comparison between regular and decaffeinated coffees (15, 16).
Roasting has a major influence on the content of polyphenols in coffee. CGA content in coffee is reduced respectively by 67% and 90% upon medium and dark roast as compared to light. The initial humidity of the beans influences the final total polyphenol concentration in roasted beans (17). Green beans dried to 5% moisture content gave lower total polyphenol contents in the final roasted coffee than undried beans. Microwave roasting caused a smaller decrease of polyphenols than convective roasting. During roasting there is a progressive destruction and transformation of CGAs (1). A longer roasting time enhances the decomposition of CGAs. Increased levels of 5-CQA were found after very light roasting (5 minutes at 230°C), while levels of 4-CQA and 3-CQA were doubled (10). Total CGA contents increased at 5 minutes roast, but decreased at longer periods of roasting.
CGAs are partly transformed during roasting into CGLs (10), caffeic acid and quinic acid. The highest amounts of CGLs are formed with light-medium roast. Less then 10% of the total CGAs in green coffee are converted into lactones (10, 18). Simple phenols such as catechol and 4-ethylcatechol are formed by further degradation of caffeic acid and quinic acid (19).
Finally, the preparation method is of great importance on the amount of polyphenols present in the coffee beverage. Factors of influence are the type of coffee grind, the brewing method (e.g. espresso, filter coffee), the proportion of coffee grind to water, the temperature of the water and the length of the contact with water. The type of coffee consumed and the various factors characterizing the brewing recipes vary greatly between countries and cultures. A recommended dosage for filter coffee preparation and for percolator coffee is 5.5 grams of ground coffee per 100 ml of water, with a brewing time of 4.5-5 minutes. Espresso, concentrated coffee served in small dosages, is preferably made from 8 g of ground coffee per serving of 30 ml (www.coffeeresearch.com). Instant coffee, strongly depending on individual preferences, is usually made from 2 g per cup or 150 ml hot water (1.33 g/100 ml water), according to producer instructions. Any deviation from these figures will affect the polyphenol content in the coffee brew. It is therefore not an easy task to determine the amount of polyphenols in a coffee serving.
Few authors have compared the polyphenol contents in various coffee brews prepared by the most common recipes. Total polyphenol content as estimated by the Folin assay has been estimated in different brews (20). Although these values are not directly comparable to the chlorogenic acid contents as determined by chromatography, they give an idea of the relative amounts of polyphenols according to the mode of brewing and serving size. Polyphenol content per serving was 43.6 for percolator coffee (serving size, 55 ml), 27.9 for espresso coffee (serving size, 45 ml) and 91.4 for filter coffee (serving size, 133 ml)(20). Higher brewing temperatures result in greater extraction of CGAs from the coffee grounds into the beverage. When coffee is heated for a longer time after brewing, the amounts of 3-CQA and 4-CQA increase, and 5-CQA decreases. There is a loss of total CQAs, as well as a reduction of 60 % of CQLs (6).
Coffee surrogates exist as an alternative to coffee. Main surrogates are chicory roots, barley, rye, figs, dandelion and oak seeds. Like instant coffee, the surrogates are prepared by pouring on hot water. They usually contain no caffeine. Coffee surrogates have low contents of polyphenols, when compared to coffee. Contents of 10 mg 5-CQA per 100 g DW in a roasted malted barley and chicory-based surrogate have been measured. Unroasted chicory root-based surrogates contain more polyphenols, with levels of 160 mg 5-CQA per 100 g (DW)(21). In roasted chicory root mixtures polyphenol contents are lower. Chicory and dandelion both contain chicoric acid (22). However quantitative data are missing. Roasted dandelion root contains no CGAs. Polyphenol contents in coffee surrogates can vary according to the type and proportion of substitutes, and processing methods. More data on coffee surrogates are needed to make valid comparisons between polyphenols in surrogate and coffee beverages.
The polyphenolic fraction of tea brewed (Camellia sinensis) accounts for 30 to 40% wt/wt of infusion solids (23, 24). Polyphenols provide astringency, colour and flavour to the tea beverage. There are three main types of manufactured tea, differing in the degree of enzymatic oxidation or ‘fermentation’: green (unfermented), oolong (partially fermented) and black (fully fermented).
In tea, catechins predominate (74% total polyphenols in green tea), followed by phenolic acids, flavonols and proanthocyanidins. Tea contains eight major catechins: (-)-epicatechin (EC), (-)-epicatechin 3-O-gallate (ECG), (+)-catechin (C), (-)-epigallocatechin (EGC), (-)-epigallocatechin 3-O-gallate (ECGC), (+)-catechin gallate (CG), (+)-gallocatechin (GC) and (+)-gallocatechin 3-O-gallate (GCG). Specific compounds of black tea are thearubigins and theaflavins, formed during the fermentation by oxidation of catechins and other phenolic compounds present in tea leaves. Catechin content is therefore lower in black tea than in green tea.
As catechins are non-glycosylated, polyphenols in tea infusions are more often quantified by HPLC without hydrolysis. Glycosylated flavonols have also been estimated as aglycones by HPLC after hydrolysis. Chloroform is sometimes used to remove caffeine and chlorophylls. Because of their high molecular weight, polymeric nature and lack of available standards, thearubigins are difficult to estimate. Spectrophotometric methods have nevertheless been developed (25, 26). But samples were taken at the time of manufacture and were therefore not commercially available. So, corresponding content values have not been included in the database. Moreover, these methods overestimate thearubigins contents and data need to be revised with further chromatographic knowledge (27). Other authors estimate thearubigins by subtracting the sum of individual phenolics quantified by HPLC from total phenol values obtained by the Folin assay (24, 28, 29). This method is not reliable due to uncertainties linked to the choice of the standard used for the Folin assay. The total phenol content estimated by the Folin assay appears to be lower than the sum of the contents of individual compounds. This clearly shows that the Folin assay underestimates the true phenol content in tea. For this reason, thearubigin values obtained by this method have not been aggregated.
The choice of tea and mode of preparation of tea infusion differs between countries and depends on individual preferences. Several parameters influence polyphenol content in tea. Variety, growing environment, manufacturing conditions, and particle size of the leaves influence the final infusion composition (30, 31). Stirring during brewing, increasing leaf concentration, beverage temperature or brewing time lead to higher polyphenol concentrations in the infusion (32, 33, 34, 35, 36). A two-min infusion solubilizes only 50% of the polyphenols contained in tea leaves (28). The catechin concentration is increased by 44% when the infusion is extended from 2 to 5 min (30). It also increases in proportion to the amount of tea leaves used in the infusion which vary from country to country (3.1 g in UK tea bags and 2.0 g in Europe tea bags) (28).
In green tea, average contents of polyphenols obtained after aggregation are 65.7 mg/100 ml for catechins, 12.5 mg/100 ml for phenolic acids, 5.3 mg/100 ml for flavonols and 5.5 mg/100 ml for proanthocyanidins. In black tea, mean content values are 49.5 mg/100 ml for catechins, 12.4 mg/100 ml for theaflavins, 18.9 mg/100 ml for phenolic acids, 9.4 mg/100 ml for flavonols, and 11.4 mg/100 ml for proanthocyanidins. In the semi-fermented oolong tea, mean content values are 35.7 mg/100 ml for catechins and 5.03 mg/100 ml for phenolic acids. Because of a lack of data, the total polyphenols in bottled tea appears much smaller than in infusions.
EGCG is the most abundant polyphenol in tea and is often considered as the most representative polyphenol in tea. It accounts for 41% of total catechins and 31% of the total polyphenols in green tea. It is difficult to evaluate the contribution of EGCG to the total polyphenol content in black tea due the lack of reliable content values for thearubigins, and the too limited number of samples analysed for oolong or bottled tea.
The amounts of polyphenols consumed with a tea serving can be calculated from the present aggregated values. The size of tea servings varies from one country to the other (28). A cup of black tea consumed in UK (235 ml) provides a total of 239 mg polyphenols (thearubigins excluded) with 49% of catechins, 12% of theaflavins, 9% of flavonols, 19% of phenolic acids and 11% of proanthocyanidins. A cup of green tea (235 ml) provides a total of 209 mg polyphenols with 74% of catechins, 6% of flavonols, 14% of phenolic acids and 6% of proanthocyanidins.