Purpose: The aim of this study was to isolate, characterize and assess the spoilage potential of sporeforming bacteria recovered from Brazilian beers.
Methods: One hundred sixty-three samples of beer were acquired in Campinas, Brazil. The beer samples (100 ml, pale lager and 5 ml, dark lager) were previously subjected to a heat shock (80°C/30 min), filtered through 0.45 µm membranes and plated onto Tryptone Glucose Extract (TGE) agar at 37°C/48 h. The isolates were identified through 16S rRNA sequencing. PCR reactions were performed to assess the presence of horC gene in the isolates. The spoilage potential (change in optical density) of horC positive isolates was assessed through inoculation and storage of beers (with and without alcohol) from 10 - 40°C/2 months.
Results: Survey of beers for the presence of sporeforming bacteria resulted in the recovery of 260 isolates. Among these, 45.4% isolates (n = 118), 34.3% (n = 89), 15.4% (n = 40), 2.3% (n = 6) and 2.6% (n = 7) were found to belong to the genus Bacillus, Paenibacillus, Brevibacillus, Lysinibacillus, and others, respectively. The most prevalent species were B. thuringiensis, B. megaterium, P. validus, P. humicus and Br. brevis. Among all the isolates, only 2.3% (three B. thuringiensis, one B. cereus, B. pumilus and Br. Invocatus, each), presented horC gene, which is closely related to beer spoilage ability. The horC positive isolates were inoculated in pale lager beer (with and without alcohol) and their growth/spoilage potential will be reported.
Significance: The incidence of sporeforming bacteria able to spoil beer under commercialization conditions may significantly change quality control and hygienic practices in the brewery industry and represent new challenges for microbial stability of beers.