(39d) Influence of Shearing As Pretreatment on the Separation Properties of Exopolysaccharides (EPS) Producing Bacterial Starter Cultures

BACKGROUND: Bacterial starter cultures such as lactic acid bacteria (LAB) are essential for the manufacture of fermented foods. The industrial production of these starter cultures takes place at specific conditions regarding, for example, temperature, pH and nutrient composition. Due to the diversity of highly specialized starter cultures, an individual adaption of the fermentation process is necessary. However, changing fermentation parameters also leads to altered separation properties that show a large influence on the subsequent separation step.

OBJECTIVE: Aim of this project is to investigate the influence of shear energy input on the sedimentation properties of different EPS producing lactic acid bacteria. Furthermore, a guideline for the determination of the optimal pretreatment and centrifugal properties of different EPS-producing starter cultures should be developed.

METHODS: Shear forces are generated either with a rotor-stator system (Ultra-Turrax) or with a high pressure homogenizer (Emulsiflex C5). Shear energy is applied to the samples by a fast stirring rotor or by pressing the samples through a cross-section constriction, respectively. Sedimentation velocity and sediment compression are measured with an analytical centrifuge (LUMisizer), and particle size is measured with a disc centrifuge.

RESULTS: In case of bacteria with cell-bound (capsulare) exopolysaccharides (EPS) that could be sheared off the cells, shearing of the cultures leads to a higher sedimentation velocity. Furthermore, a decrease of the sedimentation velocity is induced when cell chains were disrupted because of high shear forces. Hence, there exists an optimum shear treatment for each culture that depends on the type and amount of produced EPS. Shearing in a high pressure homogenizer affected sedimentation velocity in a similar manner as did shearing with the Ultra-Turrax, but at a significantly lower energy input. Shearing with both shear devices leads to decreasing sediment heights of the examined cultures.

CONCLUSIONS: It was shown that, depending on the type and amount of the strain specific EPS, shearing EPS producing bacterial starter cultures may result in an increase or in a decrease of the sedimentation velocity. An increase in sedimentation velocity is mainly the result of shearing off capsular EPS from cell surface, whereas a decreased sedimentation velocity indicates a destruction of cell-chains due to shearing. Furthermore, sediment compression could be detected after shear treatment of EPS producing (capsular and free in the medium) LAB, which is caused by shearing of capsular EPS respectively disrupting cell-chains in case of free EPS producing LAB.

This IGF Project 18605 BG of the FEI is supported via AiF within the programme for promoting the Industrial Collective Research (IGF) of the German Ministry of Economic Affairs and Energy (BMWi), based on a resolution of the German Parliament.