Heimdal, Hanne

Owusu, Margaret

Petersen, Mikael Agerlin

English

Copenhagen University Research Information System

u n i ve r s i t y  o f  co pe n h ag e n  Københavns UniversitetAssessment of aroma of chocolate produced from two ghanaian cocoa fermentationtypesOwusu, Margaret; Petersen, Mikael Agerlin; Heimdal, HannePublished in:Expression of multidisciplinary flavour sciencePublication date:2010Document versionEarly version, also known as pre-printCitation for published version (APA):Owusu, M., Petersen, M. A., & Heimdal, H. (2010). Assessment of aroma of chocolate produced from twoghanaian cocoa fermentation types. In I. Blank, M. Wüst, & C. Yeretzian (Eds.), Expression of multidisciplinaryflavour science: proceedings of the 12th Weurman Symposium, Switzerland, 2008 (pp. 363-366). ZurichUniversity of Applied Sciences.Download date: 02. Feb. 2020Expression of Multidisciplinary Flavour Science   363ASSESSMENT OF AROMA OF CHOCOLATE PRODUCED FROM TWO GHANAIAN COCOA FERMENTATION TYPES   M. OWUSU1, M.A. Petersen1, and H. Heimdal2  1 Department of Food Science/Quality and Technology, Faculty of Life Sciences, University of Copenhagen; Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark 2 Toms Confectionery Group, Toms Alle 1, DK-2750, Ballerup, Denmark   Abstract  Chocolates produced from two cocoa fermentation types (heap‘ and tray‘) were analysed by GC-MS and GC-O to identify and detect important odorants. The most important odour in both types of chocolate was identified as 2/3-methyl butanal with a cocoa/chocolate attribute. One odour described as grassy/lettuce and which seemed to be important for the aroma of both types of chocolates remained unidentified. Two acids, 3-methyl butanoic acid with an unpleasant blue cheese odour and acetic acid with a sharp, vinegar odour were also identified as key odorants in the two types of chocolates. Differences were identified in the types of odorants important in the two types of chocolate and these are expected to cause sensory differences between the two types of chocolate.  Introduction  The aroma of chocolate is one of its most important characteristics that determine quality. The fermentation of cocoa is critical for the formation of precursors that develops the characteristic chocolate aroma in roasted beans. The aroma and flavour of cocoa depends on the genotype of the cocoa tree that has produced the beans, the origin, and how the beans have been fermented (1, 2). Most Ghanaian farmers practise the traditional heap fermentation method (3). This is a method where upon breaking of the pod, the beans are piled on and covered by banana leaves. The heaps differ in size and may range from 20 to 1000 kg. Big heaps have to be turned once every 24-72 hours to achieve even fermentation but this is not adhered to by most Ghanaian farmers because of the tediousness involved (3). Another fermentation method developed by the Cocoa Research Institute of Ghana (CRIG) is the Tray system which involves fermenting the beans in 10 cm deep wooden trays. Eight to ten trays are stacked on top of each other and the top-most tray is covered with banana leaves. This method allows aeration of the fermenting mass without having to turn and ensures better and more even fermentation (3). Efforts are being made to encourage cocoa farmers in Ghana to adopt the tray system to improve the quality of fermented beans. This investigation aims to assess the chemical basis for differences between the aroma of chocolate produced from Ghanaian cocoa beans fermented by the above mentioned methods: heap and tray.  Experimental  Chocolate samples. Heap- and tray-fermented cocoa beans, grown and fermented in Ghana, were used for the manufacture of dark chocolate at Toms Confectionery Expression of Multidisciplinary Flavour Science   364Group A/S, Denmark, using the same recipe. The ingredients used in the production of the dark chocolate were sugar, cocoa beans, cocoa butter and lecithin as emulsifier.  Dynamic headspace sampling and GC-MS. Dynamic headspace sampling using Tenax traps and thermal desorption is described in a lot of studies (4, 5). The technique was optimised by using 20 g of sample and purging with a nitrogen flow of 200 mL/min for 1 h at 30°C. The volatiles were analysed using GC-MS (4, 5). GC-O. GC-O analysis was performed by three trained judges who evaluated both chocolates using the method described in (4).   Results  GC-MS identified 64 volatile aroma components in ‘heap’ chocolate and 58 in ‘tray’ chocolate. These included alcohols, acids, aldehydes, esters, furans, ketones, pyrazines, a pyrrole and a sulphur compound (Table 1). Although similar compounds have been reported by earlier workers in chocolate and other cocoa products, differences exist in the reported number of aroma compounds identified in these products. Cournet et al. 2004 identified more pyrazine-type compounds, for instance, in dark chocolate than was identified in the present study. Such differences may stem from the genotype of cocoa used, the fermentation/drying method and the manufacturing process. In the case of chocolate, the most important processes being the degree of roasting of the cocoa beans and conching of the chocolate and the ingredients used. Peak areas of isoamylacetate, linalool and methyl phenyl acetate were significantly different (p<0.05) for the two types of chocolate, whilst 2-acetylcyclopentanone, furfural, furfuryl alcohol, 1-(2-hydroxyphenyl)-ethanone and o-methoxyphenol were detected in only ‘heap’ chocolate. Twenty-three odours were detected by GC-O analysis of ‘heap’ chocolates and 24 odours in ‘tray’ chocolates, three of them in each type of chocolate still unknown. Of these, 15 odours in ‘heap’ chocolate and 19 odours in ‘tray’ chocolate seemed important as they were detected by all three judges and these included one unknown with a grassy, lettuce attribute in both types of chocolates. The most important odorant, in both types of chocolate, based on the summed duration in minutes that the odorant was detected by the judges, was a peak described as having a chocolate or cocoa odour and identified as a non separable mixture of 2- and 3-methylbutanal. This has also been reported by some earlier workers (1, 2, 6). Four odorants were detected as important in ‘heap’ chocolate alone whilst 7 odorants were detected as important in ‘tray’ chocolate alone. These odorants included pyrazines and the aldehydes, most of which are derived during the chocolate production process but others such as the alcohols and acids are products of fermentation which have persisted in the chocolate (7). The acids seemed rather abundant in both types of chocolate; 3-methyl butanoic acid, with an unpleasant blue cheese odour, and acetic acid with a sharp, vinegar odour, also seemed to be major contributors to the aroma of both types of chocolates. Linalool, detected as a key odorant in ‘tray’ chocolate alone is known to give a flowery tea-like odour to cocoa and is related to the fermentation method (7).  Differences in key odorants are expected to result in sensory differences between chocolate produced from heap- and tray-fermented cocoa beans. Further work is underway to do a sensory evaluation of the chocolates using a trained sensory panel to relate sensory measurements to instrumental measurements. Expression of Multidisciplinary Flavour Science   365Table 1. Aroma components of chocolate produced from heap- and tray-fermented cocoa beans.  Peak areab x103 Compound Identificationa Description of odour ‘heap’  ‘tray’  2/3-Methylbutanal MS, GC-O, S cocoa, chocolate 438 512 2,3-Butanedione MS, GC-O, S caramel, sweet 327 201 Hexanal MS, S  59 86 Isoamylacetate MS  388* 95* 2-Pentanol MS, S  107 79 2-Heptanone MS, S  88 64 Heptanal MS, S  17 18 2/3-Methyl butanol MS, S  45 26 2-Pentyl furan MS, S  82 95 1-Pentanol MS, S  94 53 Methylpyrazine MS  48 35 3-Hydroxy-2-butanone MS, GC-O fruity 365 220 2-Octanone MS  60 58 Octanal MS, GC-O, S orange, soapy 30 22 2,5-Dimethylpyrazined MS, GC-O, S earthy, mushroom 104 76 2,6-Dimethylpyrazine MS  64 54 2-Decanol MS  51 24 Ethylpyrazined MS, GC-O  popcorn 22 16 2-Acetylcyclopentanone MS  43 - 2,3-Dimethylpyrazinec MS, GC-O  popcorn, potato 61 37 Dimethyl trisulphide MS, GC-O, S  unpleasant, sharp 12 10 2-Ethyl-6-methylpyrazine MS  37 25 2-Nonanone MS, GC-O, S alcohol 72 43 Nonanal MS, GC-O, S fresh, fruity 120 113 2,3,5-Trimethylpyrazine MS, GC-O earthy, grass 388 166 Unknown 1 GC-O sharp, liquorice n.d. n.d. Unknown 2 GC-O grass, lettuce n.d. n.d. Ethyl octanoate MS, S  29 26 Acetic acid MS, GC-O, S vinegar, sharp 3596 4686 Furfural MS, S  37 - 2,5(or 6)-Dimethyl-3-ethylpyrazine MS, GC-O, S potato, earthy 35 21 Linalool oxide MS, S   34 20 Tetramethylpyrazine MS, GC-O potato, earthy  2393 1042 2-Acetylfuran 2-Decanone MS, GC-O, S MS sharp, rubber  26 9 14 23 Benzaldehyded MS, GC-O, S vegetable, grass 359 267 2,3,5-Trimethyl-6-ethylpyrazinec MS, GC-O grass, paprika 39 14 Propanoic acid MS, S  31 21 Linaloold MS, GC-O flowery, fruity 16*  47*  Table 1.  cont’d.  Compound Identificationa Description odour Peak areab x 103    ‘heap’  ‘tray’ 2-Methyl propanoic acid MS  1135 518 1,3/2,3-Butanediol MS  1945 1746 Dihydro-2(3H)-furanone MS  79 55 Butanoic acid MS, S  68 47 Phenylacetaldehyded MS, GC-O cocoa 132 121 1-Phenyl ethanone MS, GC-O flowery, sweet 137 70 Furfuryl alcoholc MS, GC-O, S oat 14 - 3-Methyl butanoic acid MS, GC-O, S unpleasant, blue cheese 1453 912 3-Methyl-2-heptanone MS  - 10 Benzyl acetated MS, GC-O, S liquorice 14 9 Methyl phenylacetate MS  29* 8* Epoxylinalol MS, GC-O sweet, flowery 34 18 Ethyl phenylacetate MS, GC-O, S flowery, rose 133 255 1-(2-Hydroxyphenyl)-ethanone MS  16 - 1-Phenylethanol MS  44 19 Phenethyl acetate MS, GC-O, S  775 667 1-Butanol-3-methyl benzoate MS  214 93 Hexanoic acidd MS, GC-O, S sharp, spicy 131 108 Butoxyethoxy ethylacetate MS  31 32 o-Methoxyphenol MS, S  53 - Benzyl alcoholc MS  61 214 Unknown 3 GC-O sweet, vanilla n.d. n.d. 2-Phenethyl alcohol MS, GC-O, S flowery, rose 881 324 2-Phenyl-2-butenal MS  30 16 Heptanoic acid MS, S  131 108 2-Acetylpyrrole MS  63 59 Phenol MS  71 28 a Identification by (MS) mass spectra, (GC-O) Gas Chromatography-Olfactometry and S, standard compound; b mean of five replicates; c key odorant in ‘heap’ chocolate alone;. d key odorant in ‘tray’ chocolate alone; * significant difference at p<0.05; n.d., not determined; -, not detected.  References  1. Counet C., Ouwerx C., Rosoux D., Collin S. (2004) J. Agric. Food Chem. 52: 6243-6249. 2. Bonvehi J. S. (2005) Eur Food Res Technol 221: 19-29. 3. Baker D.M., Tomlins K.I., Gay C. (1994) Food Chemistry 51: 425-431. 4. Nielsen G.S., Poll L. (2004).J. Agric. Food Chem. 52: 1642-1646. 5. Varming C., Petersen M.A., Poll, L. (2004) J. Agric. Food Chem. 52: 1647-1652. 6. Frauendorfer F., Schieberle P. (2006) J. Agric. Food Chem. 54. 5521-5529. 7. Gill M.S., Macleod A.J., Moreau M. (1984) Phytochemistry 23: 1937-1942. 

Assessment of aroma of chocolate produced from two ghanaian cocoa fermentation types

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Assessment of aroma of chocolate produced from two ghanaian cocoa fermentation types

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