Comparison of microbial community structure and metabolic nitrite formation level in two different sugar beet extraction systems
Nitrite is formed from nitrate in beet sugar factories and finally remains in molasses. Since molasses is used as an additive to animal feed and nitrite in feed material from the sugar industry is currently only exempted from EU directives with the addition "for the time being", the formation of nitrite in sugar factories is of particular interest. To investigate the influence of the extraction system on the nitrite formation potential, two sugar factories with different extraction systems (trough and tower extraction) were compared regarding nitrite formation and degradation. Samples from different process stages were analyzed for nitrate, nitrite, pH-value, lactic acid, acetic acid, and microbial diversity using metagenomic sequencing. Results revealed differences between the extraction systems. The trough extraction system showed complete nitrate and nitrite degradation and high lactic acid levels in the upper trough chambers, likely due to active microbial and chemical processes. In the cossette mixer/tower extraction system, high nitrite levels and rapid degradation were observed in the hot extraction areas. pH-values reflected microbial activity and chemical nitrite degradation, particularly in the upper chambers of the trough extraction. Microbial diversity analysis revealed a shift in community composition along the production line, with Firmicutes as the predominant bacterial phyla in the hot parts of the extraction. Specific bacterial species, such as Limosilactobacillus fermentum and Parageobacillus caldoxylolyticus, correlated with nitrate and nitrite levels, suggesting their involvement in nitrite metabolism. Notably, P. caldoxylolyticus demonstrated efficient degradation of nitrate and nitrite, making it a promising bacterium for nitrite management. These findings provide insights into microbial processes, community structure, and potential strategies for reducing nitrite early in the extraction process.