Comparison of microbial communities and nitrite formation in two different beet sugar extraction systems

Abstract

This study investigated nitrite formation in beet sugar factories, crucial due to tightening European Union directives for contaminants in feed material. Comparing two extraction systems (trough and tower), the trough system exhibited dynamic nitrite formation processes resulting in an average nitrite content of 14.35 mg/kg in raw juice. In the tower system, high nitrite levels and rapid degradation occurred in hot extraction areas, leading to an average nitrite content of 30.89 mg/kg in raw juice during sampling period. Microbial diversity analysis revealed a community shift, with Firmicutes dominating in hot extraction regions. Highly abundant amplicon sequence variants (ASVs) predominantly belonged to the genera Tuberibacillus and Geobacillus in both systems (Tuberibacillus: trough: 73%, tower: 67%; Geobacillus: trough: 41%, tower: 30%). Sequences related to bacteria relevant for nitrite metabolism varied between the two systems. Limosilactobacillus fermentum was more prevalent in the trough extraction system (6% relative abundance in raw juice), than in the tower system (0.5% relative abundance in raw juice). Similarly, Parageobacillus caldoxylolyticus was more abundant in tower extraction, especially in high-temperature zones like the countercurrent mixer (7% relative abundance). These findings provide insights into microbial processes, community structure, and potential strategies for early nitrite reduction in the extraction process.