Microbial diversity during maturation and natural processing of coffee cherries of Coffea arabica in Brazil

The magnitude and diversity of the microbial population associated with dry (natural) processing of coffee (Coffea arabica) has been assessed during a 2-year period on 15 different farms in the Sul de Minas region of Brazil. Peptone water-washed samples were taken of maturing cherries on trees (cher ries, raisins and dried cherries) and from ground fermentations. The microb ial load varied from 3 x 10(4) to 2.2 x 10(9) cfu/cherry with a median valu e of 1.6 x 10(7) cfu/cherry. The microbial load increased after heavy rainf all on cherries that were drying on the ground. At all stages, bacteria wer e usually the most abundant group, followed by filamentous fungi and finall y yeasts. Counts of bacteria, yeasts and fungi varied considerably between farms and at different stages of maturation and processing and no consisten t pattern could be seen. Yeasts showed an increase during the fermentation process. Median counts were not significantly different for fungi, yeasts a nd bacteria between the 2 years although Gram-negative bacteria dominated i n the wet year and Gram-positive bacteria dominated in the dry year. Of a t otal of 754 isolates, 626 were identified to at least genus level comprisin g 44 genera and 64 different species. The 164 isolates of Gram-negative bac teria included 17 genera and 26 species, the most common of which were memb ers of the genera Aeromonas, Pseudomonas, Enterobacter and Serratia. Of 191 isolates of Gram-positive bacteria, 23 were spore-forming and included six Bacillus species, and 118 were non-spore-formers of which over half were C ellulomonas with lesser numbers of Arthrobacter, Microbacterium, Brochothri x, Dermabacter and Lactobacillus. Of the 107 yeast isolates, 90 were identi fied into 12 genera and 24 different species and almost all were fermentati ve. The most common genera, in decreasing frequency, were Pichia, Candida, Arxula and Saccharomycopsis. There were many rarely described yeasts includ ing Pichia lynferdii and Arxula adeninivorans. Almost all 292 fungal isolat es were identified to genus level and 52 were identified to species level. Cladosporium, Fusarium and Penicillium each comprised about one third of th e isolates and were found on all farms. Only 3% of the isolates were Asperg illus. Beauvaria, Monilia, Rhizoctonia and Arthrobotrys species were also o ccasionally found. The microbial flora is much more varied and complex than found in wet fermentations. The genera and species identified include memb ers known to have all types of pectinase and cellulase activities. (C) 2000 Elsevier Science B.V. All rights reserved.