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AEM
Vol. xx, No.
xx, 2014; Pages: xxxx

OXIDATION OF METABOLITES HIGHLIGHTS THE MICROBIAL INTERACTIONS AND ROLE OF ACETOBACTER PASTEURIANUS DURING COCOA BEAN FERMENTATION

Frédéric Moens, Timothy Lefeber and Luc De Vuyst

Research Group of Industrial Microbiology and Food Biotechnology, Faculty of Sciences and Bioengineering Sciences, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium.

Abstract

Four cocoa-specific acetic acid bacteria (AAB) strains, namely Acetobacter pasteurianus 386B, Acetobacter ghanensis LMG 23848T, Acetobacter fabarumLMG 24244T, and Acetobacter senegalensis 108B, were analyzed kinetically and metabolically during monoculture laboratory fermentations. A cocoa pulp simulation medium (CPSM) for AAB, containing ethanol, lactic acid, and mannitol was used. All AAB strains differed in their ethanol and lactic acid oxidation kinetics, whereby only A. pasteurianus 386B performed a fast oxidation of ethanol and lactic acid into acetic acid and acetoin, respectively. Only A. pasteurianus386B and A. ghanensis LMG 23848T oxidised mannitol into fructose. Co-culture fermentations with A. pasteurianus 386B or A. ghanensis LMG 23848T andLactobacillus fermentum 222 in CPSM for lactic acid bacteria (LAB), containing glucose, fructose, and citric acid revealed oxidation of lactic acid produced by the LAB strain into acetic acid and acetoin, which was faster in the case of A. pasteurianus 386B. A tri-culture fermentation with Saccharomyces cerevisiaeH5S5K23, Lb. fermentum 222, and A. pasteurianus 386B, using CPSM for LAB, showed oxidation of ethanol and lactic acid produced by the yeast and LAB strain, respectively, into acetic acid and acetoin. Hence, acetic acid and acetoin are the major end-metabolites of cocoa bean fermentation. All data highlight that A. pasteurianus 386B displayed beneficial functional roles to be used as a starter culture, namely a fast oxidation of ethanol and lactic acid, and that these metabolites play a key role as substrates for A. pasteurianus in its indispensable cross-feeding interactions with yeast and LAB during cocoa bean fermentation.

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