Investigation of nitrite pathways in sugar beet extraction

The investigations presented in this work were carried out in order to further deepen the knowledge about nitrite pathways in the area of sugar beet extraction. The article consists of two parts with different experimental set-up: the first part focuses on laboratory trials in which the fate of nitrate and nitrite was studied in a so-called mini-fermenter. These trials were carried out using juice from the hot part of the cossette mixer of an Agrana sugar factory in Austria. In the experiments, two common sugar factory disinfectants were used in order to study microbial as well as microbial-chemical effects on nitrite formation and degradation caused by bacteria present in the juice. The trials demonstrated that the direct microbial effect (denitrification) on nitrite degradation is more pronounced than the indirect microbial-chemical effect coming from pH value decrease by these bacteria and subsequent nitrite loss. The second part describes the findings from laboratory experiments and full scale factory trials using a mobile laboratory set-up based on insulated stainless steel containers and spectrophotometric detection of nitrite in various factory juices. The trials were made at two Nordzucker factories located in Finland (factory A) and Sweden (factory B). The inhibiting effect of the two common sugar factory disinfectants on nitrite formation was evaluated in laboratory trials, whereas the full scale trials focused on one disinfectant. Other trials to evaluate potential contamination sources of thermophilic nitrite producing bacteria to the extraction system, reactivation of nitrite producing bacteria in raw juice and the effect of a pH gradient on bacterial nitrite activity in cossette mixer juice are also reported.