ABSTRACT
The Ghanaian cocoa bean heap fermentation process was studied through a
multiphasic approach, encompassing both microbiological and metabolite
target analyses. A culture-dependent (plating and incubation, followed
by repetitive-sequence-based PCR analyses of picked-up
colonies) and culture-independent (denaturing gradient gel
electrophoresis [DGGE] of 16S rRNA gene amplicons, PCR-DGGE) approach
revealed a limited biodiversity and targeted population dynamics of
both lactic acid bacteria (LAB) and acetic acid bacteria (AAB) during
fermentation. Four main clusters were identified among the LAB
isolated: Lactobacillus plantarum, Lactobacillus
fermentum, Leuconostoc pseudomesenteroides, and
Enterococcus casseliflavus. Other taxa encompassed, for
instance, Weissella. Only four clusters were found
among the AAB identified: Acetobacter pasteurianus,
Acetobacter syzygii-like bacteria, and two small clusters of
Acetobacter tropicalis-like bacteria. Particular strains of
L. plantarum, L. fermentum, and A.
pasteurianus, originating from the environment, were well adapted
to the environmental conditions prevailing during Ghanaian cocoa bean
heap fermentation and apparently played a significant role in the cocoa
bean fermentation process. Yeasts produced ethanol from
sugars, and LAB produced lactic acid, acetic acid, ethanol, and
mannitol from sugars and/or citrate. Whereas L. plantarum
strains were abundant in the beginning of the fermentation, L.
fermentum strains converted fructose into mannitol upon prolonged
fermentation. A. pasteurianus grew on ethanol, mannitol, and
lactate and converted ethanol into acetic acid. A newly proposed
Weissella sp., referred to as “Weissella
ghanaensis,” was detected through PCR-DGGE analysis in
some of the fermentations and was only occasionally picked up through
culture-based isolation. Two new species of Acetobacter were
found as well, namely, the species tentatively named“
Acetobacter senegalensis” (A.
tropicalis-like) and “Acetobacter
ghanaensis” (A.
syzygii-like).
Brewers’ spent grain as substrate for dextran biosynthesis by Leuconostoc pseudomesenteroides DSM20193 and Weissella confusa A16
