Coffee and cacao byproducts as sustainable carbon sources for baker's yeast growth

Coffee and cacao bean production in Colombia generates around 80% of residual biomass from both liquid and solid residues. This study aims to explore the feasibility of using these residues as carbon sources for the growth of commercial baker's yeast, a domesticated strain of Saccharomyces cerevisiae that shares genomic ancestry with strains used in European grape wine and Asian rice wine production.
Liquid effluents from coffee grain fermentation (Geisha, Caturra, and Castillo varieties) and fermented mucilage/placenta extracts from cacao (FEC2 and CCN51 varieties) were investigated as carbon sources for formulating growth media for S. cerevisiae cultures. We evaluated the influence of media composition (% of coffee, mucilage or placenta extracts) and pH on baker’s yeast biomass production.
Our findings demonstrate that culture media containing 25% v/v of coffee effluents, without pH adjustment, support S. cerevisiae growth similarly to a standard YPD culture medium. Similarly, fermented mucilage (25% v/v) and placenta extract (50% w/v) from the CCN51 cocoa variety showed significant substrate potential for S. cerevisiae growth. Compositional analysis revealed that coffee effluents from Geisha, Caturra, and Castillo varieties contain 5.97%, 4.93%, and 2.40% of total carbohydrate content, respectively. Fermented cacao mucilage from CCN51 and FEC2 varieties yielded 10.68% and 10.42% total carbohydrates, respectively, while the placenta extract had 2.88% (CCN51) and 4.51% (FEC2). The monosaccharide composition in effluents and extracts was dominated by fructose and glucose except in the Castillo variety, which only contained fructose.
The pH values of the initial effluents/extracts ranged from 3.13 to 3.90. Interestingly, we observed that regulating the pH to 5.5 did not affect the growth rates of S. cerevisiae compared to cultures grown at the original pH level. This indicates the possibility of cultivating S. cerevisiae over a wide working range of pH values.
Our results highlight the viability of coffee effluents (Geisha and Caturra), fermented mucilage, and cacao placenta extract (CCN51) as carbon sources for S. cerevisiae culture growth. These sources could facilitate the manufacture of commercial bioproducts, such as baker’s yeast and alcoholic beverages.