Isolation and selection of Bacillus strains from coffee ecosystem for fresh Robusta coffee cherry fermentation

Abstract

This study aimed to isolate and evaluate indigenous Bacillus strains from the Robusta coffee ecosystem with the ability to produce polysaccharide-degrading enzymes (particularly pectinase), thereby promoting biochemical transformations during coffee fermentation. Three bacterial strains were successfully isolated, identified, and characterized, namely Bacillus siamensis (I), Bacillus velezensis (II), and Bacillus aryabhattai (III), all of which exhibited significant pectinase activity, with clear pectin hydrolysis zones ranging from 13 to 15 mm. These strains contributed to the improvement of key biochemical parameters during fermentation, notably accelerating acidification, reducing pH to 4.2-4.8, and decreasing reducing sugar content to below 1.0 g/l under fermentation conditions of a solid-to-liquid ratio of 2:1 at 37°C for 48 hours. Fermented coffee beans showed total polyphenol contents of 120-125 mg/g and antioxidant activity with IC₅₀ values of approximately 0.28-0.32 mg/ml. Furthermore, the combined starter culture demonstrated superior performance, particularly the consortium of strains II and III, which enhanced substrate conversion efficiency and increased total polyphenol content (135-137 mg/g dry weight) along with improved antioxidant activity (IC₅₀≈0.25 mg/ml). Overall, the results indicate that controlled fermentation using indigenous Bacillus consortia represents a promising approach for improving the quality of Vietnamese Robusta coffee toward higher value products.