Monitoring the Antibacterial Effect of Rosin Acids in an Austrian Beet Sugar Plant by Amplicon-Based Sequencing and Flow Cytometry

Cordula K Moser,Christina Ukowitz,Wolfgang Kneifel,Florian Emerstorfer,Ulrike Zitz,Walter Hein,Konrad J Domig

doi:10.3390/app11020737

Cordula K Moser, Christina Ukowitz + Show 5 more

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https://doi.org/10.3390/app11020737

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Abstract

For decades, microorganisms in beet sugar production have been studied using culture-based methods. However, these methods are not sufficient to describe such a complex bacterial community. In this study, therefore, an amplicon-based sequencing technique (Illumina MiSeq platform) was applied to characterize the bacterial community and its dynamics in the extraction area and juice purification station of an Austrian beet sugar plant. Depending on the process conditions thermophilic bacteria, such as Geobacillus spp., Caenibacillus spp., and Thermus spp., and mesophilic bacteria, such as Leuconostoc spp. and Bacillus spp., were found. Besides these microbiological characteristics, the antimicrobial effect of a rosin acid-based product (Defostab 220) on the bacterial communities was investigated in industrial and laboratory trials. The antimicrobial effect of a given concentration of rosin acid varies from bacteriostatic to bactericidal effects on different occurring groups of bacteria.

Highlights

The extraction of sucrose from sugar beets takes place in several steps
Sequencing analyses and bacterial count based on flow cytometry measurements
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 ± 2.60 h when treated with 3.0 mg/L of the rosin acid-based product

Summary

Introduction

The extraction of sucrose from sugar beets takes place in several steps. In Austrian plants, a combination of a countercurrent mixer and an extraction tower is employed. Sugar beets are sliced into cossettes, which are treated in a solid-liquid extraction process using the countercurrent principle to extract sucrose (Figure 1) In this area of the tower extraction system, the temperatures vary from 20 ◦ C in raw juice to 72 ◦ C in the tower end of the countercurrent mixer. Due to the conditions of high pH values and high temperatures in these processing steps, the growth of microorganisms was not considered to be of any technological relevance for a long time. This assumption changed in 1930 with the observation of microorganisms influencing the storage of beets [2].

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