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DOI: 10.1016/j.foodres.2016.01.012
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Food Research International 82 (2016) 44–52 Contents lists available at ScienceDirect Food Research International Factors influencing quality variation in cocoa (Theobroma cacao) bean flavour profile — A review John Edem Kongor ,, Michael Hinneh , Davy Van de Walle , Emmanuel Ohene Afoakwa ,Pascal Boeckx , Koen Dewettinck a Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Gent, Belgiumb Department of Nutrition & Food Science, University of Ghana, P. O. Box LG 134, Legon-Accra, Ghanac Isotope Bioscience Laboratory (ISOFYS), Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Gent, Belgium This review examined the factors that influence flavour volatiles of cocoa beans and the volume of work that Received 30 November 2015 needs to be done on these factors and their impact on the flavour volatiles of commercial cocoa beans. Cocoa Received in revised form 8 January 2016 bean flavour is one of the most important quality attributes as flavour is central to acceptability of cocoa beans Accepted 15 January 2016 and cocoa products such as chocolate. The complex composition of cocoa bean flavour depends on bean geno- Available online 18 January 2016 type, postharvest treatments such as pulp pre-conditioning, fermentation and drying, industrial processes suchas roasting as well as the type of soil and age of cocoa tree. The bean genotype determines the chemical compo- sition of the bean, speci fically the contents of bean storage proteins, polysaccharides, and polyphenols. This de- termines the quantities and type of precursors formed during fermentation and drying processes leading to Flavour volatiles flavour formation, hence, influencing both flavour type and intensity. Cocoa bean fermentation and drying result Sustainable production in the breakdown of the storage proteins by endogenous proteases into amino acids and short chainoligopeptides while the polysaccharides are also degraded by invertase to glucose and fructose. The aminoacids, oligopeptides, glucose and fructose react with each other during the roasting process to produce the typicalcocoa flavour volatiles. Polyphenols are also oxidized by polyphenol oxidase during fermentation and dryingwhich reduce the astringency and bitterness of the beans, thus, enhancing the flavour of cocoa beans. However,the extent to which other factors such as age of the cocoa tree and soil chemical compositions influence the for-mation of flavour precursors and their relationships with final flavour quality remains unclear. With increasingdemand for sustainable production of high quality cocoa beans, greater understanding of factors contributingto the variations in flavour character would have significant commercial implications.
2016 Elsevier Ltd. All rights reserved.
Factors affecting flavour quality of cocoa beans. . . . . . . . . . . . . . . . . . . . . . . . 452.1.
Effect of genotype and origin of cocoa tree on cocoa bean flavour quality. . . . . . . . . . . . . . . . . 45 Effect of postharvest treatment of cocoa on bean flavour quality. . . . . . . . . . . . . . . . . . . 472.2.1.
Effect of industrial processing of cocoa on bean flavour quality . . . . . . . . . . . . . . . . . . . 492.3.1.
Soil chemical composition and cocoa bean flavour quality . . . . . . . . . . . . . . . . . . . . 49 ⁎ Corresponding author at: Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Gent, Belgium.
E-mail addresses: johnedem.kongor@ugent.be, (J.E. Kongor).
0963-9969/ 2016 Elsevier Ltd. All rights reserved.
J.E. Kongor et al. / Food Research International 82 (2016) 44–52 practices, planting low-yield varieties, pests and diseases, ageing cocoatrees and loss of soil fertility due to inadequate or no use of fertilizers Cocoa (Theobroma cacao L.) is a cash crop of huge economic signifi- cance in the world and the key raw material for chocolate manufactur- The economic and health benefits ing It forms the major of cocoa depend on the sustainable production and intensification of agricultural export commodity for several producing countries in high quality cocoa beans. Also, sustaining the production of high quality West and Central Africa, such as Cote d'Ivoire, Ghana, Nigeria and cocoa beans in West Africa is crucial for the millions of smallholder fam- Cameroon (). Cocoa be- ily farmers that depend on cocoa for their livelihoods and the millions of longs to the family of Sterculiaceae and the genus Theobroma people who enjoy chocolate and other cocoa products around the ). The genus has twenty-two species of which world. In promoting sustainability, the cocoa industry wants to see T. cacao L. is commercially the most important due to the value of its growth and improvement in the quantity and quality of the cocoa seeds (). The seeds, commonly known beans produced as well as the standard of living enjoyed by growers.
as cocoa beans, are obtained from the pods. These pods are oval in Sustainable cocoa production also involves the production of high shape, measure between 12 and 30 cm long, and contain 30 to 40 quality cocoa beans. Cocoa bean quality is made up of several compo- beans embedded in a mucilaginous pulp, which comprises approxi- nents such as flavour volatiles, nutritional composition, polyphenolic mately 40% of the bean fresh weight ( content and fermentative quality. The most important components are The pulp is reported to be the flavour volatiles of the beans as these affect cocoa bean acceptability rich in fermentable sugars of about 9 to 13% w/w () such as glucose, fructose and sucrose ( These compounds which constitute the flavour quality of the beans ), high acidity (pH 3.0–3.5) conferred by the presence of di- are, however, influenced by several factors. This review discussed the verse organic acids, but mainly citric acid factors that influence cocoa bean flavour quality. The current state of , and a protein content in the range of 0.4 to 0.6% w/w knowledge in terms of research findings of these factors on the flavour volatiles of cocoa beans is presented. Research gaps in terms of the vol- Cocoa is cultivated on lands covering over 70,000 km2 worldwide ume of work that needs to be done on these factors and their impact on between 20° north and south of the equator, the flavour volatiles of commercial cocoa beans are also exposed.
in areas with suitable environment for cocoa (). About70% of the world's cocoa production takes place in the equatorial region 2. Factors affecting flavour quality of cocoa beans of West Africa, and the rest in the equatorial regions of Central andSouth America, the West Indies, and tropical areas of Asia Several indicators are used to measure the quality of cocoa beans.
. The cocoa tree is a perennial tree, 8 to 15 m in height These include the bean size and count, bean colour and acidity of the and requires hot, moist conditions to grow and will beans. However, the most important quality indicator of cocoa beans not withstand prolonged drought conditions without seriously depress- is the amount and type of volatile flavour compounds ing the tree's vegetative and reproductive functions ( ). Flavour is central to acceptability of cocoa The fruit varies among varieties in size, shape, external colour, and ap- beans and cocoa products such as chocolate ( pearance. These characters have often been used in classifying cocoa.
) and, consequently, contributes to determining According to the World Cocoa Foundation (WCF), there are 5–6 mil- the quality The characteristic flavours of cocoa beans lion farmers in developing countries across tropical Africa, Asia and are due to a very rich volatile fraction composed of a mixture of Latin America who produce around 90% of cocoa worldwide, and the hundreds of compounds (). Currently, more than 600 number of people who depend upon cocoa for their livelihoods world- flavour compounds have been identified from cocoa beans and cocoa wide is 40–50 million ). In West and products ). These compounds comprise of nitrogen Central Africa, cocoa continues to be an important source of export and oxygen heterocyclic compounds, aldehydes and ketones, esters, al- earnings contributing significantly to the Gross Domestic Product cohols, hydrocarbons, nitriles and sulphides, pyrazines, ethers, furans, (GDP) of these producing countries. Cocoa exports generate over $8 bil- thiazoles, pyrones, acids, phenols, imines, amines, oxazoles, and pyr- lion for the region's national economies and support about two million smallholder farm households in West and Central Africa. In Ghana, the industry employs about 70% of the national agricultural labour force in the country ). For these farmers, cocoa contributes about 70–100% of their annual household incomes Most of these compounds possess particular flavour characteristics.
Apart from the economic importance of cocoa, consumption of Thus, while most esters confer a fruity/flowery attribute to flavour, chocolate and other cocoa products is reported to contribute positively pyrazines usually give earthy/roasted flavour Flavour compounds in cocoa beans are formed during roasting from flavour ). Polyphenols in cocoa beans have been reported precursors generated during the fermentation and drying process. Fla- to exhibit anti-carcinogenic ( vour compounds in cocoa beans are thus influenced by factors such as , anti-atherogenic type of cocoa (genotype), bean composition, soil type, age of cocoa and vasodilatory ( tree, postharvest treatments such as pulp pre-conditioning, fermenta- ) effects and they exert them mainly as antioxidants tion and drying, industrial processes such as roasting as well as storage and transportation ( Annual global cocoa production is reported to be more than 4 million tons per season (4.4 million tons in 2013/2014 crop season) 2.1. Effect of genotype and origin of cocoa tree on cocoa bean flavour quality However, while global demand for sustainable cocoa isgrowing annually by 2 to 3%, and West Africa still contributes about Flavour quality of cocoa beans depends on the genotype and origin 70% of the global supply, this region is confronted with a 2% annual de- of the cocoa tree that has produced the beans. Cocoa beans from differ- cline in production There is low ent genotypes and origin of cocoa tree have distinct flavour characteris- cocoa productivity in West Africa due to poor farm management tics (). Currently, three broad cultivars of cocoa are commonly J.E. Kongor et al. / Food Research International 82 (2016) 44–52 Table 1Flavour profile of different cocoa beans from different origins.
Source: Adopted from Good cocoa impact, low bitterness, low acid, fruity, nutty Forastero hybrids Strong chocolate flavour Forastero hybrids Medium cacao, occasional off-notes São Tomé & Principe Good cocoa flavour, bitter, spicy, fruity, earthy Winey, putrid, citrus Criollo "Porcelana" Mild chocolate, slightly bitter, distinct fruity notes (plum and cherry) Cocoa impact, bitter, acid, astringent (sometimes rubber, hammy, smoky),some fruitiness, no nutty notes Trinitario and Criollo Fruity, bitter, cacao Slightly bitter and fruity Ecuador (home of Arriba) Forastero (Nacional) Balanced profile, low chocolate, floral, fruity, grass, earthy notes Low chocolate, strong acid, low fruitiness Moderate chocolate, acidic, fruit and nut notes Dominican Republic (Sanchez) Low cacao, flavourless, bitter Dominican Republic (Hispaniola) Winey, earthy, can have tobacco notes Fruity, balanced cocoa flavour Trinidad & Tobago Trinitario (birthplace) High cacao, nutty and winey notes, aromatic Chocolate, fruity, floral, grassy, woody Low chocolate, acidic, fruity High bitter, low sour, low cacao, astringent Mild, bland profile, acid, low cacao, light colour Hybrids/pure Criollo and Forastero Variable strong acid, floral, mild, nutty Forastero hybrids Low to medium cacao, medium to high acidity, astringent (due to fermentation level) phenolic recognized: Forastero, Criollo, Trinitario and a fourth variety grown in considered to be moderately resistant to pests and diseases Ecuador, called Nacional The cultivars exhibit differences Forastero beans have a higher pH after fermentation and drying when in the appearance of pods, yields of beans, flavour characteristics and compared with Criollo beans. Thus, chocolate produced from the in resistance to pests and diseases ( Forastero beans are less bitter, less astringent and less acidic than choc- olate produced from either Criollo beans or Trinitario beans cocoa type has a unique potential flavour character ( ). These differences in flavour can be attributed to inherent genetic Criollo is the original cultivated cocoa, indigenous to Northern, composition of the bean, botanical origin, location of growth but grow- South, and Central America. The beans are white to ivory or have a ing conditions such as climate, the amount and time of sunshine and very pale purple colour, due to an anthocyanin inhibitor gene ( rainfall, soil conditions, ripening, time of harvesting, and the time be- ). Their low yields and susceptibility to many dis- tween harvesting and bean fermentation all contribute to variations in eases make them rare to cultivate. Nowadays, its cultivation is limited the final flavour formation. (See .) to Central America and a few regions in Asia ( Forastero, native to the Amazon basin ), comprises Criollo cocoa is reported to of 95% of the world production of cocoa contain high amount of pyrazines and is commonly referred to as "bulk cocoa" in trade. Forastero and exhibit low pH which easily affect the flavour profile ( cocoa is predominantly cultivated in West Africa particularly Côte d'Ivoire, Ghana, Nigeria and Cameroon. The seeds are flat, astringent, The Trinitario type originated in Trinidad and covers all the products and purple in colour (more rarely ivory or pale) due to the presence of natural hybridization and recombination of the Criollo and Forastero of anthocyanins. Forastero cocoa trees are very productive and are populations ). The beans are variable in Table 2Summary of factors and their impact on cocoa bean flavour.
Impact on cocoa bean flavour Influences the type and quantity of bean storage proteins, carbohydrates and polyphenols which are degraded duringfermentation and drying to form flavour precursors Removes portion of the pulp prior to fermentation hence, reduces fermentable sugars during fermentation leading tothe production of less acids Reduces pulp volume per seed due to water evaporation and inversion of sucrose; reduces total sugar content and increasesmicro-aeration within the pulp and eventually reduces alcohol fermentation and acetic acid formation Generates flavour precursors, namely free amino acids, peptides and reducing sugars from which flavour volatiles are formed.
Polyphenols are oxidized and polymerized to insoluble high molecular-weight compounds (tannins) leading to a significantreduction of its concentration and, thus, reducing the bitterness and astringency of the beans Physical loss of acidity through outward migration of volatile acids as well as biochemical oxidation of acetic acid from thebeans leading to less acids in the beans. Oxidization and polymerization of polyphenols resulting in reduction of its concentration.
Non-enzymatic reactions, that is the Maillard reactions to form volatile fractions like pyrazines Evaporation of volatile acids from the beans causing a reduction in acidity, hence, reducing sourness. Flavour precursors namelyfree amino acids, short-chain peptides, and reducing sugars undergo the Maillard reaction and Strecker degradation to producethe desirable flavour compounds NB: impact of other factors such as soil chemical composition and age of cocoa tree on cocoa bean flavour quality is not yet known. A research gap which needs to be filled.
J.E. Kongor et al. / Food Research International 82 (2016) 44–52 colour, although rarely white, and the trees show a susceptibility to ). Three groups of polyphenols can be pests and diseases intermediate to Forastero and Criollo populations distinguished in cocoa beans and these are: catechins or flavan-3-ols The Trinitario cultivar is (ca. 37%), anthocyanins (ca. 4%) and proanthocyanidins (ca. 58%) known to have strong basic chocolate characters and some typical win- ). The main catechin in ery type of aroma that are not found in other varieties the cocoa bean is (−)-epicatechin with up to 35% of polyphenol con- ). Both Trinitario and Criollo varieties produce the "fine" cocoas, tent. Other catechins found in smaller amounts are (+)-catechin whose share in the total world production is below 5% ().
as well as traces of (+)-gallocatechin and (−)-epigallocatechin These cocoas are used to make high quality dark chocolate ( The anthocyanin fraction ). Nacional cacao is viewed as a fine variety producing the well- consists mainly of cyanidin-3-α-L-arabinoside and cyanidin-3-β-D- known Arriba beans with distinctive floral and spicy flavour notes galactoside ), while proanthocyanidins are mostly flavan-3,4-diols, that are 4 → 8 or 4 → 6 bound to condensed dimers, trimers or oligomers with epicatechin as the main extension Work by noted consistent differences in overall cocoa flavour intensity, acidity, sourness, bitterness and astrin- Other polyphenols found in cocoa beans are the flavonol glycosides gency among West African Amelonado variety (AML), four Upper Ama- such as quercetin-3-O-α-D-arabinoside and quercetin-3-O-β-D- zon clones [Iquitos Mixed Calabacillo 67 (IMC67), Nanay 33 (NA33), glucopyranoside ). Again, up to 17 phe- Parinari 7 (PA7), and Scavina 12 (SCA12)], and unidentified Trinitario nolic acids and esters have also been reported and the total amount (UIT1) grown in Sabah, Malaysia. Work by also sug- of seven of them comprises not more than 23 ppm of the seed gested that monoterpenes such as linalool are part of the components dry weight (phloroglucinol, protocatechuic acid, vanillic acid, o- or molecules responsible for fine flavour in cocoa and concluded that hydroxyphenylacetic acid, p-coumaric acid, caffeic acid, ferulic acid) fine flavour cocoas contain higher amounts of linalool than bulk cocoa.
). reported that epicatechin Cocoa bean genotype influences the type and quantity of bean stor- and the smaller procyanidins up to three subunits are soluble and, age proteins, carbohydrates and polyphenols ().
therefore, cause the astringent taste sensation of cocoa but molecules This determines the quantities and type of precursors formed during built up of more than three subunits are insoluble and cause no fermentation and drying processes leading to flavour formation thus in- fluences both type of flavour of the beans and intensity found four predominant fractions of protein in cocoa beans representing 95% (w/w) of total seed proteins, bean is made up of two main parts namely, the testa (seed coat or the and these are albumins (water-soluble), globulins (salt-soluble), prola- shell) and the embryo ). Attached to mins (alcohol-soluble) and glutelins (soluble in dilute acids and alkali).
the testa is the sugary, white mucilaginous pulp that surrounds it, Albumin is a major polypeptide accounting for about 52% of total bean while the embryo is contained within the seed coat or testa. The main protein and has a molecular weight of 21 kDa ( parts of the embryo are two folded cotyledons connected by a small em- bryonic axis (The dry weight of cocoa bean varies considerably, but is approximately 1.0–1.2 g ( min is not degraded during fermentation ().
The chemical composition of cocoa beans has been studied ex- Work done by showed that incubating the puri- fied cocoa albumin with cocoa proteases did not produce any specific cocoa aroma upon roasting. The globulin fraction accounts for 43% of cocoa bean has an approximate composition of 32–39% water, 30–32% total protein in cocoa beans and it consists of three polypeptide subunits fat, 10–15% proteins, 5–6% polyphenols, 4–6% starch, 4–6% pentosans, with apparent molecular weights of 47, 31 and 16 kDa ( 2–3% cellulose, 2–3% sucrose, 1–2% theobromine, 1% acids and 1% caf- ) and it is almost insol- feine The predominant uble at pH b 5.0 (). These are subunits of the sugars in cocoa beans are sucrose, fructose and glucose ( vicilin-type (7S) globulin (VCG), a glycoprotein, each of them consisting ) with sucrose being the major component (about 90% of of multiple pI-forms total sugars), followed by fructose and glucose (about 6%) ( The vicilin-class globulins are quantitatively de- graded during fermentation (88–90% of the initial content) into flavour Cocoa fat contains about 95% triacylglycerols, 2% diacylglycerols, b1% precursors such as peptides and amino acids, which are important pre- monoacylglycerols, 1% polar lipids, and 1% free fatty acids (as percent- cursors for the formation of cocoa flavour through Maillard reactions ages of lipids) (). The predominant fatty acids during drying and roasting in cocoa butter are saturated (stearic; 18:0, 35% and palmitic; 16:0, 25%) and monounsaturated (oleic; 18:1, 35%), with the remaining fatbeing primarily polyunsaturated linoleic (3%) The coty- 2.2. Effect of postharvest treatment of cocoa on bean flavour quality ledon is composed of two types of parenchyma storage cells The first storage cell is the polyphenolic cells (14–20% dry bean Postharvest treatment of cocoa involves all the primary process har- weight) which contain a single large vacuole filled with polyphenols vested cocoa pods goes through before the final dried beans is obtained.
and alkaloids including caffeine, theobromine and theophylline These processes include pulp pre-conditioning, fermentation, and dry- ). argued that the ing. These processes are usually carried out in the country of origin pigmented polyphenols, when undisturbed, confer deep purple colour and they play a critical role in the flavour profile of the dried cocoa to fresh Forastero cotyledons. The other storage cells, the lipid–protein beans ). While the complex composition of cocoa cells, on the other hand, have cytoplasms tightly packed with multiple bean flavour depends on the bean genotype, specifically on contents small protein and lipid vacuoles and other components such as starch of bean storage proteins, polysaccharides and polyphenols, it is possible granules — all of which play roles in defining cocoa flavour and aroma and easier to produce cocoa beans with poor flavour profile with bad Polyphenols in cocoa beans are stored in the pigment cells of the cot- 2.2.1. Pulp pre-conditioning yledons and depending on the amount of anthocyanins, those pigment Pulp pre-conditioning involves changing the properties of the cells, also called polyphenol-storage cells, are white to deep purple pulp prior to the development of microorganisms in fermentation J.E. Kongor et al. / Food Research International 82 (2016) 44–52 (). The pulp is the reported that pulp preconditioning by post-harvest storage of substrate metabolized by a sequence of microorganisms during fermen- Malaysian cocoa pods led to the reduction of nib acidification during tation and since the properties of the sub- subsequent fermentation, reduction of acid note and an increase in strate determine microbial development and metabolism, changes in cocoa flavour in the resulting cocoa beans. also the pulp may affect the production of alcohols by yeasts and subsequent noted that increasing pod storage (PS) consistently decreased the production of acids by lactic acid bacteria and acetic acid bacteria. These non-volatile acidity with concomitant increase in pH during fermenta- changes may be in the form of altering the moisture content of the pulp, tion of Ghanaian cocoa beans. reported that sugar content, and volume of pulp per seed as well as pH and acidity of pulp pre-conditioning of cocoa prior to fermentation was significant in the pulp. Removing portions of cocoa bean pulp or reducing the fer- affecting the changes in acidity, causing a significant reduction in the mentable sugar content has been shown to contribute to less acid pro- content of polyphenol compounds especially (−)-epicatechin and duction during fermentation, leading to less acid beans (+)-catechin during fermentation, hereby reducing the astringency ). Studies have shown that pre- and bitterness in cocoa and cocoa products ( fermentation treatments have significant effects in changing the acidityand polyphenol content of the cocoa beans and thus, flavour of the 2.2.2. Fermentation Fermentation of cocoa beans is very crucial as it promotes dramatic Pulp pre-conditioning can biochemical changes in the type and concentration of flavour precursors be done in three basic ways prior to fermentation and these are pod storage, depulping (mechanical or enzymatic depulping) and bean beans have an astringent and unpleasant taste and have to be fermented . Cocoa pulp can be pre- and dried to obtain the characteristic cocoa taste and flavour. The cor- conditioned either inside the pods (pod storage) before the bean–pulp rect fermentation and drying of cocoa beans, which are carried out in mass is brought out for fermentation or outside the pods (mechanical the countries of origin are essential to the development of suitable fla- or enzymatic depulping and bean spreading).
vour and/or flavour precursors (). During fermentation, microbial successions occur as the 2.2.1.1. Depulping of cocoa beans. Excessive pulp on the cocoa beans leads micro-environment (temperature, pH, oxygen availability) changes to high acid production during fermentation which is detrimental to bean flavour quality as it makes it excessively sour ( ). The flavour quality of cocoa beans depends By removing a portion of the pulp, or reducing the fer- on complex chemical and biochemical changes which occur in the mentable sugar content of the beans, it has been shown that less acid is beans during fermentation and drying. Fermentation generates flavour produced during fermentation, leading to less acid beans precursors, namely free amino acids and peptides from enzymatic deg- radation of cocoa proteins and reducing sugars from enzymatic degra- Removal of up to 20% of the cocoa pulp dation of sucrose from fresh Brazilian cocoa beans significantly improved the flavour quality of the beans produced (). Depulping which the typical cocoa aroma is generated during the subsequent can be done in two ways, namely mechanically and enzymatically roasting process ). Besides the forma- tion of the flavour precursors, there is also a significant increase in vol- Methods for mechanical depulping of fresh cocoa beans include atile compounds, such as alcohols, organic acids, esters and aldehydes presses (), centrifuges after fermentation ( or simply spreading beans onto a flat surface for several hours ). Again, phenolic compounds are oxidized and polymerized to in- prior to fermentation, causing a significant increase in the sweating pro- soluble high molecular-weight compounds (tannins) leading to a signif- duced in the first 24 h of fermentation. Mechanical depulping is done to icant reduction of its concentration and, thus, reducing the bitterness remove some of the pulp of the fresh cocoa beans so as to reduce sub- and astringency of the final product to acceptable levels ( strates and therefore acids produced during fermentation with a subse- quent decrease in sourness. The process causes bruising of the beans Cotyledon protein degradation into peptides and free amino acids and its cell structures leading to the activation of enzyme, which appears central to flavour formation and reported might influence various biochemical processes during fermentation. In that the combined action of aspartic endopeptidase and serine addition to reducing acidity, benefits of de-pulping include shorter fer- carboxy-(exo) peptidase on vicilin (7S)-class globulin (VCG) storage mentations and increased efficiency and the ability to use the excess polypeptide yields cocoa-specific precursors. Proteolysis in the seeds pulp in the manufacture of jams, marmalades, pulp juices, wines or mainly takes place within 24 h after destruction of the cells and acidifi- cocoa soft drinks ( cation by acetic acid (The aspartic endopeptidase hy- ). By using a mechanical depulper, drolyses peptide bonds in VCG at hydrophobic amino acid residues, the pulp is removed substantially uniformly from the beans and the forming hydrophobic oligopeptides which then become substrates for amount of pulp removed from the fresh cocoa beans in the depulper the serine carboxy-(exo) peptidase which removes carboxyl terminal may be from 10 to 30%, preferably from 20 to 25% by weight based on hydrophobic amino acid residues the original total combined weight of the beans and pulp.
). Carboxypeptidase plays an impor- Enzymatic depulping involves the addition of pectin degrading en- tant role in converting hydrophobic oligopeptides to cocoa specific zymes to the cocoa bean–pulp mass prior to the fermentation process aroma precursors, namely hydrophilic oligopeptides and hydrophobic to breakdown the pectin in the pulp. The breakdown of the pectin in free amino acids (especially leucine, valine, alanine, isoleucine, phenyl- the pulp leads to a reduction in pulp volume which in turn increases alanine), which are required for the formation of the typical cocoa the aeration of the fermenting mass during fermentation.
aroma components in the presence of reducing sugar upon roasting( 2.2.1.2. Pod storage. Pod storage is basically storing harvested cocoa pods The duration and method of fermentation are crucial to the forma- for a period of time before opening the pods and fermenting the beans.
tion of flavour compounds and flavour precursors. Pod storage as observed by appears to have noted an increased level of organic acids such as propanoic acid, 2- highly beneficial effect on the chemical composition of cocoa beans methylpropanoic acid, 3-methylbutanoic acid and acetic acid after and subsequent development of chocolate flavour. 72 h of cocoa fermentation. The increased levels of organic acids are a J.E. Kongor et al. / Food Research International 82 (2016) 44–52 result of the breakdown of sugars from the pulp surrounding the cocoa beans ). Propanoic acid, 2-methylpropanoic acid, 3- ). The less volatile acids, such as oxalic, methylbutanoic acid and acetic acid are all reported to be important citric, tartaric, succinic and lactic acids remain largely unchanged by odour-active compounds in cocoa the roasting process ).
). Unfermented cocoa beans are reported to develop little Again, flavour precursors namely free amino acids, short-chain pep- cocoa and chocolate flavour when roasted while over-fermented beans tides, and reducing sugars produced during fermentation and drying produce unwanted hammy and putrid flavours ( process undergo the Maillard reaction and Strecker degradation during Important flavour-active components produced during roasting to produce the desirable flavour compounds such as pyrazines, fermentation include ethyl-2-methylbutanoate, tetramethylpyrazine alcohols, esters, aldehydes, ketones, furans, thiazoles, pyrones, acids, and certain other pyrazines ).
imines, amines, oxazoles, pyrroles and ethers ( Bitter notes are evoked by theobromine and caffeine, together with diketopiperazines formed from roasting through thermal decompositions ). The ideal conditions for the Maillard re- of proteins (). Other flavour precursor compounds action to occur are high temperatures and low moisture content and derived from amino acids released during fermentations include 3- these conditions can be found in roasting . The carbon- yl derivative from the Maillard reaction reacts with free amino acids 2-ethyl-3,5-dimethyl- and 2,3-diethyl-5-methylpyrazine ( during Strecker degradation. This causes degradation of amino acids to aldehydes which contribute to the aroma. Strecker degradation ofeach specific amino acid produces a unique aldehyde with a unique After fermentation, the beans are dried to reduce the moisture con- The choice of roasting parameters determines the character of the tent from about 60% to between 6 and 8% ) to chemical and physical processes that occur inside the beans, and thus prevent mould infestation during storage and also allow some of the the quality of the end products chemical changes which occurred during fermentation to continue Several studies revealed that the tem- and improve flavour development (). The drying process perature and duration of roasting substantially affect the chemical and of fermented cocoa beans initiates major polyphenol oxidizing reactions physical changes occurring in cocoa beans catalysed by polyphenol oxidase, giving rise to new flavour components ). Cocoa bean roasting conditions generally range from and loss of membrane integrity, inducing brown colour formation. This 15 to 45 min with temperatures from 130 to 150 °C helps to reduce bitterness and astringency and also the development of the chocolate brown colour of well fermented cocoa beans. The bio- ). Time and temperature of the roasting process depend on several chemical oxidation of acetic acid from the beans continues during dry- factors, such as cocoa material (beans, nibs or liquor roasting), final cocoa product (dark or milk chocolates) and type of cocoa (Criollo or and have both suggested that during the drying of fermented cocoa beans, reducing sugars participate reported that "fine" cocoa varieties in the thermal treatment of non-enzymatic browning reactions, that such as Criollo require lower temperatures than the "bulk" ones, while is the Maillard reactions to form volatile fractions of pyrazines.
indicated that low temperature roasts are have confirmed earlier findings by employed for milk and some dark chocolates.
and by identify-ing Amadori compounds, the first intermediates of Maillard reaction in 2.4. Soil chemical composition and cocoa bean flavour quality dried, unroasted cocoa beans. These Amadori compounds are the firstintermediates of the reaction of free amino acid and glucose.
Cocoa trees are extremely selective about where they grow, includ- Drying rate during the drying process is of crucial importance for the ing the type of soil they prefer. Cocoa tree needs a soil containing coarse final quality of the cocoa beans. The drying process must not be too particles and with a reasonable quantity of nutrients, to a depth of 1.5 m rapid otherwise the beans tend to retain an excessive amount of acetic to allow the development of a good root system ). Cocoa acid, and this is deleterious to flavour trees are more sensitive to moisture stress than other tropical crops.
The cocoa tree is sensitive to a lack of water, so the soil must have ). Rapid drying of the beans results in case hard- both water retention properties and good drainage. The chemical prop- ening which prevents outward migration of acetic acid from the beans, erties of the topsoil are most important, as the plant has a large number thus, leading to a build-up of acidity in the beans ( of roots for absorbing nutrients. Cocoa can grow in soils with a pH in the ). On the other hand, too slow drying rate would range of 5.0–7.5. It can therefore cope with both acid and alkaline soil, result in low acidity, poorer colour and high presence of moulds but excessive acidity (pH 4.0 and below) or alkalinity (pH 8.0 and above) must be avoided (). The influence of soil pH is critical on the solubility of minerals and nutrients and it is thus regarded as auseful indicator of other soil parameters 2.3. Effect of industrial processing of cocoa on bean flavour quality Soil pH provides useful information about the availabilities of ex- changeable cations (e.g. Ca2+, Mg2+ and K+) in soils ( Roasting is one of the important steps which affects the quality char- ). The soil should also have a high content of organic matter of acteristic of cocoa beans during industrial processing about 3.5% in the top 15 cm of soil. The organic matter of soils includes Roasting determines the character of the remains of plants, animals and microorganisms in all stages of de- the chemical and physical processes that occur inside the beans, as composition. The level of organic matters in soils influences a number well as the quality of the final products ( of soil chemical and physical properties (). Soils for ). During roasting, there is evaporation of volatile acids from the cocoa must have certain anionic and cationic balances. Exchangeable beans causing a reduction in acidity, hence, reducing sourness and bit- bases in the soil should amount to at least 35% of the total cation terness of the cocoa beans (). The high roasting tem- exchange capacity (CEC) otherwise nutritional problems are likely perature reduces the acidity, specifically the volatile acids with low ). The CEC is a measure of the soil's ability to adsorb (and boiling point such as acetic acid, making the cocoa beans less acidic release) cations (It is highly needed for the J.E. Kongor et al. / Food Research International 82 (2016) 44–52 estimation of contaminant transport potential and sorption capacity for Sustainable cocoa production, however, depends largely on the quantity any soil location, i.e., the total number of cations it can retain on its cocoa beans produced annually as well as the quality of the beans.
adsorbent complex at a given pH. The optimum total nitrogen/total Cocoa bean flavour is an important quality attribute which determines ac- phosphorus ratio should be around 1.5 ceptability of cocoa beans and cocoa products such as chocolate. The com- Several works have been done on soil type, soil chemical composition plex composition of cocoa bean flavour depends on the bean genotype and nutrient requirements for cocoa production ( specifically on contents of bean storage proteins, polysaccharides and polyphenols. Pulp pre-conditioning, fermentation and drying enhance However, all research works the formation of the flavour precursors which undergo the Maillard reac- on soil effects on cocoa are focused on yield with little or no work on tion during roasting to produce the typical cocoa flavours. Research works the effect of soil on the flavour quality of cocoa beans. There is, therefore, on age of cocoa tree and the soil chemical compositions are focused on a big gap in terms of research work on the effect of soil chemical compo- yield with little or no work on flavour quality. More works need to be sition on the flavour quality of cocoa beans.
done on the impact of age of cocoa tree and soil chemical compositionson the development of flavour precursors during fermentation and drying 2.5. Age of cocoa tree and flavour quality and their subsequent formation of flavour volatile compounds duringcocoa bean roasting.
Like any living organism, the cocoa tree goes through different stages in its entire life cycle. According to production life cycle of cocoa occurs in four stages whichincludes: (1) an early period of no yield which normally occurs in the This review was conducted as part of a project funded by the first 3 years, (2) a period of increasing yield at an increasing rate, (3) a Belgium Government (ZEIN2013PR394) under the VLIR TEAM Cocoa period of increasing yield at a decreasing rate, and (4) a period of de- Project. The sponsor is gratefully acknowledged for the Research creasing yields. The last stage is associated with trees that are past their yield prime. also reportedthat after four years from the time of planting, the cocoa tree becomesproductive and the yield rate increases annually until approximately 18 years of age. Then, the yields begin to decline due to exhaustion of Abekoe, M. K., Obeng-Ofori, D., & Egyir, I. S. (2002). Technography of cocoa in the forest soil nutrients, erosion, and increasing occurrence of pests and plant dis- zone of Ghana. Unpublished technical report, Convergence of Sciences Project.
University of Ghana, Legon, Pp. 51.
Age is therefore an important factor in the life of cocoa trees due to biological lags inherent to the crop (). Several studies have reported on the impact of ageing cocoa farms or trees in Ghana Adewole, E., Ogunmodede, O. T., Talabi, J., Ajayi, O. O., Oso, O. A., & Lajide, L. (2011).
and other West African cocoa producing countries on yield ( little or no work on flavour quality. There is therefore a big research gap that needs to be filled. The influence of cocoa tree age on the forma- tion of flavour precursors during cocoa bean fermentation as well as the formation of flavour volatiles needs to be studied.
Afoakwa, E. O. (2015). Afoakwa, E. O., & Paterson, A. (2010). 2.6. Research gaps Cocoa is a crop of huge economic significance especially in develop- ing countries. The crop is also enjoyed by millions of people around the world in the form of chocolate and other cocoa related products. As a result, several researchers have taken keen interest in developing and improving on the quality characteristics of cocoa beans as well as the wellbeing of cocoa farmers so as to ensure a sustainable production. Ex- tensive works have been done on cocoa fermentation, drying and roasting and their impact on the polyphenolic and flavour characteris- Afoakwa, E. O., Quao, J., Takrama, J., Budu, A. S., & Saalia, F. K. (2011b). tics of cocoa beans. Other factors such as pod storage and mechanical depulping which influence the flavour profile of cocoa beans during fer- mentation, drying and subsequent roasting have also received fair at- Afoakwa, E. O., Quao, J., Takrama, J., Budu, A. S., & Saalia, F. K. (2012). tention by some researchers.
However, works done on age of cocoa tree and soil characteristics have concentrated on the impact on yield with little or no work on the fla- vour quality characteristics of the beans. Therefore, works need to be done on the influence of age of cocoa tree on the formation of flavour pre- cursors during cocoa bean fermentation, drying as well as the flavour vol- atiles produced during subsequent roasting. The nutrients and chemical composition of soils need to be studied and ascertain their influence on Amusan, O. A., Amusan, F. O., Braimoh, A., & Oguntunde, P. (2005). the flavour quality of cocoa beans.
Sustainable production of cocoa is crucial to both the small holder Andújar, I., Recio, M. C., Giner, R. M., & Ríos, J. L. (2012). Cocoa polyphenols and their farmers and their families that depend on cocoa for income and also the potential benefits for human health — Review article. Oxidative Medicine and millions of people who enjoy chocolate and other cocoa related products.
Cellular Longevity, 906252. http://dx.doi.or(23 pp.).
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