An evaluation of the Bacillus content in beer

University essay from Lunds universitet/Livsmedelsteknik och nutrition (master)

Abstract: The aim of this project was to investigate how Bacillus can survive in the finished beer. This was evaluated by producing batches of beer with starter cultures that were deemed to be interesting in terms of their Bacillus content. This beer, together with beer from microbreweries and store-bought beer were plated onto Bacillus Chromoselect agar, a selective agar for Bacillus. Samples were then taken to isolate specific colonies and send them for 16S rRNA sequencing. The colony count was higher on the produced beer than in the other types. There were minor differences in CFU between the starter cultures. Since the pure cultures presented with radical differences, the similarity in finished beer would indicate that the malt contributes more to Bacillus content than the starter cultures. Bacillus cereus, or B. thuringensis, appeared to be present to a great extent in the produced beer. B. subtilis and B. smithii were dominant in the beer from microbreweries based on the 16S rRNA sequencing results. The produced beer had an average of 108.89 ±0.2 CFU/330mL, the microbreweries had an average of 104.6 ±1.23 CFU/330mL and the store-bought beer had an average of 103.8 ±0.22 CFU/330mL. Beer from larger companies was lower than those from microbreweries, this is most likely due to filtration. The amount of CFU present in these beers were close to what is used in probiotic supplements with Bacillus. Since the sequencing showed that some of the survivors were B. subtilis it is reasoned that it could have an effect on the microflora in the intestines. This is likely since B. subtilis is currently used as a probiotic supplement. There were a lot of bacteria that could not be identified below genus level. There were only two opportunistic pathogens but they were only found once.

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