THE ROLE OFBACILLUSspp. IN N-NITROSAMINE FORMATION DURING WORT PRODUCTION

The relative importance of bacterial and acid catalysed formation of Apparent Total N-Nitrosocompounds (ATNC) and N-nitrosodimethylamine (NDMA) following reduction of nitrate by a strain of Bacillus coagulans was investigated. The bacterium was isolated from the brewhouse and could grow and reduce nitrate at temperatures up to 70°C. Although evidence of thermophilic denitrification was observed, the predominant end products of nitrate reduction were ammonia and nitrous oxide. Bacterial catalysis of ATNC formation in sweet wort at pH 5.3 coincided with high nitrate and nitrite reductase activities and was, at 741 μg h−1 (mg cell protein)−1, three times faster than would be expected due to acid catalysis alone. The formation of NDMA at pH 7.8 was 300–500 times faster in the presence of nitrite than in the presence of nitrate possibly implicating the involvement of nitrite reductase.