Cocoa is the partially fermented and dried bean obtained from the fruit of the cacao tree (Theobroma cacao). The three main varieties of cocoa beans used in the production of chocolate are Criollo, Forastero and Trinitario. Criollo is the rarest and most expensive fine grade cocoa. Forastero is a large group of wild and cultivated cacaos which covers 70% of the world production. Trinitario is a fine grade hybrid of Criollo and Forastero. After harvest of the beans from the cacao tree, the beans are removed from their pods. They undergo a process of fermentation and drying. The polyphenols in fresh cocoa beans are stored in the pigment cells of the cotyledon. During fermentation, cell walls are broken down and polyphenols diffuse with cell liquids from their storage cells. They undergo oxidation, both non-enzymatic and enzymatic by the enzyme polyphenol oxidase, leading to changes in polyphenol contents and profiles. Fermentation of cocoa beans leads to the development of flavour and colour of the cocoa. After fermentation cocoa beans are dried in order to reduce the moisture content from about 60% to about 7.5%. After drying, the cocoa beans are ready for further processing. To transform cocoa beans into chocolate the beans are roasted. The temperature, time and degree of moisture involved in roasting can vary along the type of beans used and the sort of chocolate required. After roasting, the hulls and germs are removed from the beans to leave the cocoa nibs. The cocoa nibs sometimes undergo alkalisation (called Dutching, usually with potassium carbonate), to develop flavour and colour. Then, the nibs are milled to create cocoa liquor (cocoa particles suspended in cocoa butter). The cocoa liquor is pressed to extract the cocoa butter, leaving a solid mass. This cocoa mass is dried into cocoa powder. Cocoa liquor consists of about 50% cocoa butter and 50% cocoa solids (cocoa powder). Cocoa liquor is used to produce chocolate through the addition of cocoa butter. Other ingredients such as sugar, milk, emulsifying agents and cocoa butter equivalents are also added. The proportions of the different ingredients depend on the type of chocolate being made. Three main types of chocolate exist: dark, milk, and white chocolate. Dark chocolate differs from milk chocolate by the absence of milk as an additive. White chocolate is based on cocoa butter without the cocoa solids. A home made chocolate beverage can be made by adding hot water or milk to cocoa powder, and eventually or sugar. Pre-mixed soluble cocoa preparations exist for instant use by adding hot water. In the food composition table, not much data are available for chocolate beverages. Data often come from single sources. Content values therefore tend to be not representative, as polyphenol contents largely depend on the amount of cocoa powder used in the final beverage.
Polyphenols account for approximately 2% w/w of fresh unfermented cocoa beans (349). They are essentially found in the cocoa liquor and powder. Total polyphenol content in cocoa powder, as estimated by the Folin assay, is 5624 mg/100 g. The main polyphenols are flavanols, which include monomers (catechins) and polymers (proanthocyanidins). Phenolic acids, flavonols, some stilbenes, simple phenols and isocoumarins are also present in minor amounts. Anthocyanins have also been reported (cyanidin 3-O-arabinoside and cyanidin 3-O-galactoside), however only in unprocessed fresh beans. Proanthocyanidins are the most abundant polyphenols in cocoa. They affect the taste of chocolate. A higher polyphenol content is typically associated with a bitter and astringent flavour. Polyphenols are also positively correlated to a green note, and negatively with fruity character (350). The procyanidin dimers B1, B2, trimer C1 and cinnamtannin A2 are the major compounds (112, 72, 24 and 33 mg/100 g resp. in cocoa powder). Total procyanidin content, as measured by normal-phase HPLC is 3145 mg/100 g in cocoa powder. Other proanthocyanidins present are dimers B3, B4, B5, up to decamers. (-)-Epicatechin and (+)-catechin are the major flavanol monomers present in cocoa (respectively 158 and 108 mg/100 g in cocoa powder). Part of these catechins can be epimerized into (+)-epicatechin and (-)-catechin during processing into chocolate where they account respectively for 5% of total epicatechin and 89% of total catechin (351). Their estimation requires chiral HPLC columns and few authors have estimated them in chocolate. Usually these enantiomers are overlooked and quantified together with their respective enantiomers as appears in the present food composition table. Other catechins present are epicatechin gallate, epigallocatechin, epigallocatechin gallate (12, 3.3 and 51 mg/100 g respectively in dark chocolate). Some rare glycosylated flavanols have been identified in cocoa, all derived from (+)-catechin and (-)-epicatechin molecules bound to glucose or galactose moieties (352, 353, 354). No quantitative data however are available. Low amounts of the stilbene resveratrol and its glucoside have also been found in dark chocolate (0.04 and 0.10 mg/100 g resp.). Cocoa contains phenolic acids, most notably gallic acid (65 mg/100 g in dark chocolate). More phenolic acids have been detected after hydrolysis of cocoa powder: protocatechuic acid, (40 mg/100 g) together with minor amounts of syringic and vanillic acid. A series of N-phenylpropenoylamino acids have been found in cocoa (355, 356). N-Caffeoyl-3-hydroxytyrosine (clovamide) and N-p-coumaroyltyrosine (deoxyclovamide) contents in liquor are about 30 and 4.3 mg/100 g respectively. Cocoa is the only known dietary source of these two compounds besides red clover. Furthermore, N-caffeoylaspartic acid (48 mg/100 g), N-p-coumaroylaspartic acid (16 mg/100g), N-caffeoyltyrosine (1.4 mg/100g) and N-p-coumaroyl-3-hydroxytyrosine (0.9 mg/100g) have been reported in cocoa liquor (352). Content data in other cocoa products are not available. Flavonols are also present in cocoa, mainly as quercetin glycosides. Quercetin-3-O-arabinoside contents are 21.6 mg/100 g, and quercetin-3-O-glucoside contents are 4.7 mg/100 g, both in cocoa liquor. Small amounts of quercetin 3-O-galactoside were also found (1.6 mg/100 g). The flavone luteolin-7-O-glucopyranoside was also present, but only in small amounts (352). Finally, small amounts of the simple phenols 3-O-methylcatechol, 4-O-methylcatechol, pyrocatechol and pyrogallol have been measured in coca powder (0.01; 0.01; 0.13 and 0.19 mg/100 g respectively).
The content of procyanidins or total polyphenol contents in chocolate products is dependent on the percentage of non-fat cocoa solids (NFCS) in the product (357). Dark chocolates with a high content of cocoa solids will therefore have higher polyphenol contents. Products with less cocoa solids and more other ingredients such as milk in milk chocolate contain less polyphenols.
The origin of cocoa bean also plays an important role in the variability of polyphenol contents of cocoa products. A 3-fold difference in the range of total polyphenol contents between fermented cocoa beans from six different countries of origin (Ivory Coast, Ecuador, Jamaica, Venezuela, Nigeria, Papau New Guinea) has been reported. The relative polyphenol composition was similar among the samples (358, 359). A 6-fold variation in epicatechin content of fermented cocoa beans originating from different regions has also been described (360). The fermentation of cocoa beans has a major impact on polyphenol content. Polyphenols are partly degraded both by the polyphenol oxidase and by non-enzymatic reactions (361). Fermentation and drying result in a loss of flavonoids (7). During fermentation anthocyanins are also degraded the bean colour changes from purple to brown. A longer fermentation and drying time results in a bigger loss of polyphenols. High roasting temperatures and longer roasting times also reduce polyphenol contents in cocoa (362). High-polyphenol chocolate and chocolate milk beverages have been developed by some companies: high-polyphenol-varieties and underfermented beans can be used, and the roasting time and/or temperature can be reduced. Alkalisation also reduces flavanol and procyanidin contents (357, 363). Alkalized cocoa powder contains almost 80% less procyanidins than non-alkalized cocoa powder (364).
Cocoa products may significantly contribute to the dietary intake of polyphenols. A chocolate beverage prepared with 5 g cocoa powder would provide about 298 mg polyphenols (Folin) and 110 mg procyanidins, and a 30 g serving of dark chocolate 622 mg polyphenols (Folin) and 128 mg procyanidins.