Abstract

Acetic acid bacteria (AAB) from traditional indigenous process of cocoa bean fermentation were studied at a location in Huimanguillo, Tabasco, Mexico. High counts were detected at the beginning of the fermentation (5.7+ or - 0.26 cfu/g dry matter) and were present throughout fermentation time. Six AAB strains were isolated and characterized by morphological, biochemical and molecular methods. Morphological and biochemical methods were inconclusive for final identification of bacteria. However, the amplification of16S rDNA of the strains by polymerase chain reaction (PCR) and the Blast analysis of the obtained nucleotide sequences showed homology (99 to 100%) with Acetobacter tropicalis. Because the production of acetic acid is an important factor in the development of chocolate flavour precursors we studied the capacities of the strains to produce acetic acid. A. tropicalis ITV61 reached 2.5% (v/v) acetic acid production in 9-h on potato broth medium supplemented with ethanol (4% v/v) while the others A. tropicalis strains accumulated low acetic acid concentrations (> 0.2%). A. tropicalis ITV61 strain was able to grow at 4, and 7% ethanol. Tolerance of the strain A. tropicalis ITV61 to acetic acid is not affected at concentrations of 1% from the beginning of fermentation.

Key words: Acetobacter, cocoa, fermentation, isolation, molecular characterization.