Yeast cocoa bean fermentations

Although the cocoa bean fermentation process is a spontaneous process, it is characterised by a fairly strict microbial ecosystem (De Vuyst et al. 2010 Schwan and Wheals 2004), which dominates this fermentation process at different stages (Fig. 3.2). In general, a specific succession of yeasts, LAB, and AAB results in well-fermented, high-quality cocoa beans, albeit other bacteria might also be involved (De Vuyst et al. 2010 Papalexandratou et al. 2013 Schwan and Wheals 2004). 

During the later stage of the cocoa bean fermentation process (36-112 h Fig. 3.2), conditions become favourable for the growth of AAB, namely, a temperature increase above 37 °C, aeration caused by further breakdown of the cocoa pulp, and the availability of substrates such as ethanol (produced by the yeasts) and lactic acid, acetic acid, and mannitol (produced by the LAB) (Camu et al. 2007, 2008). The main activity of AAB is the (incomplete) oxidation of ethanol into acetic acid, an enzymatic two-step reaction carried out in the periplasm by membrane-bound pyrroloquinoUne quinone (PQQ)-dependent dehydrogenases, enabling energy... 

Hermann S (1928) Uber die sogenannte Kombucha. . I Biochem Z 192 176-187 Ho VTT, Zhao J, Fleet G (2013) Yeasts are essential for cocoa bean fermentation. Int J Food Microbiol 174 72-87... 

Papalexandratou Z, De Vuyst L (2011) Assessment of the yeast species composition of cocoa bean fermentations in differem cocoa-producing legimis using denaturing gradient gel electrophoresis. FEMS Yeast Res 11 564—574... 

Cocoa bean fermentation is a mixed-culture process, consisting initially of fermentations by yeast and lactic acid bacteria followed by oxidation of the fermentation products ethanol and lactic acid into acetic acid and acetoin by several Acetohacter strains, of which /I. pasteurianus is the prominent one (Moens et al. 2014). A C-based carbon flux analysis of Acetohacter during cocoa pulp fermentation-simulating conditions revealed a functionally separated metabolism during co-consumption of ethanol and lactate. Acetate was almost exclusively derived from ethanol, whereas lactate served for formation of acetoin and biomass building blocks. This switch was attributed to the lack of phosphoenolpyruvate carboxykinase and malic enzyme activities, which prevents conversion of oxalo-acetate and malate formed by acetate metabolism in the TCA cycle to PEP and pyruvate and subsequently to acetoin (Adler et al. 2014). Lactate, on the other hand, can be converted to pyruvate, which is then used for acetoin formation or, after conversion to PEP by pymvate phosphate dikinase, for gluconeogenesis. The inability of conversion of TCA cycle intermediates to PEP resembles the situation in G. oxydans, where in addition no enzyme for conversion of pyruvate to PEP is present. 

During the first 24-48 h of cocoa bean fermentation (phase 1), yeasts convert saccharides (sucrose, glucose and/or fructose) into alcohol (ethanol) under conditions of high carbohydrate concentrations (characteristic for the fresh cocoa pulp-bean mass), limited oxygen availability (due to tight packing... 

Ravelomanana, R., Guiraud, J.-R, Vincent, J.C., and Galzy, P. (1985) The yeast flora of cocoa bean fermentation in the Ivory Coast. MIRCENJl, 319- 326. 

Loew says, the process of fermentation depends especially on yeast cells which increase rapidly in the syrup of the cocoa bean, with the formation of alcohol and C02. Also bacteria take part in the fermentation, oxidizing the alcohol to AcOH. A rise in temperature takes place and the slimy tissue surrounding the seeds comes off and collects on the bottom of the vat. The removal of this tissue is the chief end of the fermentation. It causes the seeds to be more easily dried. An oxidation of the tannin takes place which causes the brown color of the bean. The taste and the aroma depend on the fermentation as well as on the roasting. ... 

Daniel H-M, Vrancken G, Takrama JF, Camu N, De Vos P, De Vuyst L (2009) Yeast diversity of Ghanaian cocoa bean heap fermentations. FEMS Yeast Res 9 774—783 De Keersmaecker J (1996) The mystery of lambic beer. Sci Am 275 74—81 de Melo Pereira GV, Miguel MGCP, Ramos CL, Schwan RF (2012) Microbiological and physicochemical characterization of small-scale cocoa fermentations and screening of yeast... 

Jespersen L, Nielsen DS, Hpnholt S, Jakobsen M (2005) Occurrence and diversity of yeasts involved in fermentation of West African cocoa beans. FEMS Yeast Res 5 441-453 Jung JY, Lee SH, Kim JM, Park MS, Bae J-W, Hahn Y, Madsen EL, Jeon CO (2011) Metagenomic analysis of kimchi, a traditional Korean fermented food. Appl Environ Microbiol 77 2264-2274... 

Candida Anamorphic yeast devoid of pigments, some species are pathogenic Used for fermentation of cocoa beans and is used in Kefir grains C. lipolytica C. albicans (pathogenic)... 

Daniel et al. 2009 Papalexandratou and De Vuyst 2011 Papalexandratou et al. 201 Ic, 2013 Pereira et al. 2012 Crafack et al. 2013). As the variation of yeast species is much larger than that of bacterial species, the presence of the former may have profound effects on the fermentation efficiency and fermented cocoa bean quality, either directly or indirectly (Meersman et al. 2013). 

K. marxianus, as pectinase producer, and the naturally vigorous yeast, 5. cerevisiae, as ethanol producer, might he a better yeast choice for future defined inocula. Moreover, inoculation of fresh cocoa pulp-hean mass with a K. marxianus hybrid yeast strain with increased pectinolytic activity has shown that it affects the microbial community structure during fermentation, increases by one third the volume of sweatings (and hence naturally increasing aeration), stimulates faster and improved cocoa bean protein degradation, results in reduced cocoa bean cotyledon acidity, and hence positively influences the fermented cocoa bean quality as well as the sensory quality of the chocolates produced thereof (Leal et al. 2008). The enhanced pectinolytic activity of K. marxianus has been confirmed during cocoa bean tray fermentation processes inoculated with a culture of this yeast species (Crafack et al. 2013). 

Buamah, R., Dzogbefia, V.P., and Oldham, J.H. (1997) Pure yeasts culture fermentation of cocoa (Theobroma cacao L.) Effect on yield of sweatings and cocoa bean quaUty. World J Microbiol Biotechnol 13, 457 462. 

Sanchez, J., Daguenet, G., Guiraud, J.-R, et al. (1985) A smdy of the yeast flora and the effect of pure culture seeding during the fermentation of cocoa beans. Lehemmitt Wiss Technol 18, 69-76. 

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