Microbial Succession in Arabica Coffee Fermented Using a Carbonic Maceration-based Ohmic Technology Fermenter

Abstract

Coffee fermentation under carbonic-maceration-based closed conditions with self-induced anaerobiosis is sensitive to temperature. This study evaluated physicochemical trajectories and culturable bacterial succession during 24–240 h of whole-cherry Arabica fermentation at 31 and 36 °C in an ohmic-controlled sealed fermenter. Fermentation liquid was analysed for pH, °Brix, total dissolved solids (TDS), culturable bacterial counts, Gram characteristics, presumptive genus-level identification, and MALDI-TOF MS identification of selected isolates. pH decreased rapidly from 24 to 48 h at both temperatures and then remained relatively stable. TDS remained stable at 31 °C (2.41–2.60%) but increased at 36 °C to 3.26 ± 0.10% at 240 h, whereas °Brix increased over time and was higher overall at 36 °C. Descriptive culture-dependent observations showed persistent Gram-negative dominance at 31 °C, with presumptive shifts from Klebsiella to Acinetobacter and subsequently to Pseudomonas and Alcaligenes. At 36 °C, Gram-positive bacteria contributed more during early to mid-fermentation, with presumptive Lactobacillus at 24–48 h and Bacillus at 72–120 h. MALDI-TOF MS identified selected isolates obtained at 72 h as Bacillus subtilis, B. amyloliquefaciens, B. vallismortis, and B. idriensis. The results indicate distinct temperature-associated physicochemical and culturable bacterial trajectories, with 72–96 h at 36 °C representing a potential transition period. Key words: Arabica coffee; carbonic maceration; culturable bacteria; fermentation temperature; ohmic heating; self-induced anaerobiosis.

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