Fitness Factors and Microbial Behavior in Guarana Beverages

Although recent studies have reported the presence of a variety of bacteria in guarana products, particularly in beverages from soda fountain machines, investigations into microbial behavior in the guarana production chain remain limited. This study evaluated the fitness and microbial growth of bacterial isolates from guarana-based products and by-products. The behavior of seventeen isolates (Enterococcus hirae LMQA-PG1 and LMQA-PG2, Klebsiella pneumoniae LMQA-PG4, Klebsiella variicola LMQA-PG4.2, Cronobacter sp LMQA-PG3.2, LMQA-PG4.1, and LMQA-PG4.2, Bacillus cereus LMQA-PG9.1, LMQA-PG2.1, and LMQA-PG3.1, Enterobacter cloacae LMQA-PG3.3, LMQA-PG3.1, and LMQA-PG4.1, Pseudomonas aeruginosa LMQA-PG1.2, and LMQA-PG1.3, Escherichia hermannii LMQA-PG4.3, and Salmonella sp. LMQA-AF3) were assessed under different pH (3 to 7), temperature (2-55°C), and water activity (a_w) (0.500 to 0.919). Most isolates showed high growth performance when cultivated at 25-42°C and pH 6-7, but were inhibited under extreme conditions, including temperatures of 2, 10, and 55°C, acidic pH values of 3-3.5, and all a_w tested. Several isolates exhibited enzymatic activities with proteolytic and lipolytic spoilage potential, particularly Bacillus cereus, and resistance to more than two antimicrobial agents. Based on fitness performance, eight representative isolates (from Enterococcus, Klebsiella, Cronobacter, Bacillus cereus, Enterobacter, Pseudomonas, Escherichia hermannii, and Salmonella) were then tested in six guarana beverage matrices, three reconstituted guarana-flavored powdered refreshments, and three ready-to-drink guarana refreshments. None of the beverages stored at 30 or 37°C for microbial growth supported bacterial growth, with reductions up to 6 log UFC/mL observed in reconstituted formulations (pH 3.01-3.29). PRACTICAL APPLICATIONS: This study demonstrated that all brands of reconstituted guarana-flavored powdered (pH 3.12) and ready-to-drink guarana refreshment (pH 3.31) beverages investigated inhibited the microbial growth of bacteria isolated from guarana products and production residues.