## 3 Results and Discussion
### Lab Scale Trials Using a Rosin Acid-Based Product  
Treatment with the rosin acid-based product had no significant influence on the total number of bacteria in the mini-fermenter trials. However, the total number of bacteria decreased significantly during the trial period (_p_ < 0.05). By dosing the rosin acid-based product, the L-lactic acid concentration was reduced significantly (_p_ < 0.05) compared to no dosing. Furthermore, the number of living cells decreased significantly immediately after dosing the rosin acid product (_p_ = 0.0220). The L-lactic acid concentration over the trial period was also significantly lower (_p_ < 0.05) in samples from the fermenter treated with rosin acid-based product compared to untreated samples at the same stage of trial. The treatment showed no significant effect on total count of viable cells over the trial period compared with untreated samples at the same stage of the trial. These observations indicate on the one hand a very specific effect of rosin acids on certain bacterial species. While the concentration is bactericidal for some species, for others, it is only inhibiting (bacteriostatic) for a certain time period. [PERSON] et al. described the bactericidal concentration for different gram-positive bacteria. Rosin acids (10-15 mg/kg) inhibited the growth of different _Clostridia_ species. For _Lactobacillus_, the concentration was considerably higher (up to 400 mg/kg) [59]. On the other hand, if only total living cells were considered, it could be misleadingly assumed that the dosing of rosin acid-based product is not necessary to combat microorganisms in the extraction process. Our study showed that the viable cells undergoing no treatment were more active and secreted L-lactic acid by sucrose assimilation during the trial, while the pH value was constant for 6.0 \(\pm\) 2.60 h (values not shown) when treated with 3.0 mg/L of the rosin acid-based product. This bacteriostatic effect was confirmed by data from large-scale studies in the Austrian beet sugar plant. The low pH value caused by lactic acid production is responsible for additional sucrose losses by hydrolytic cleavage. A typical rate is 14-44 mg per 100 g sucrose at 60 \({}^{\circ}\)C-70 \({}^{\circ}\)C and a pH of 5.4 [60]. At the end of the trial, the number of viable cells was higher in the samples of the rosin-acid-treated mini-fermenter compared to the control (see Figures 2 and 3).  
Figure 2: Bacterial count of living, dying and dead bacteria determined by means of flow cytometry investigating samples drawn from a mini-fermenter (calculated as an average of three independent trials) after different time points after treating with rosin acids (3 mg/L) or without treatment and after 24 h (end of trial period).  
Additionally, the metabolic activity of the bacteria, such as the formation of organic acids, increased (Table 5). This result indicates that these bacteria had or developed tolerance and adapted to rosin acids or that rosin acids were no longer active due to absorption into the matrix or similar processes. To prohibit bacterial growth, further dosing may be necessary, which is the case in the sampled beet sugar extraction plant.