Nachtigall Carsten, Surber Georg, Wefers Daniel, Vogel Cordula, Rohm Harald, Jaros Doris
Institute of Natural Materials Technology, Technische Universität Dresden, 01062 Dresden, Germany.
Institute of Chemistry, Food Chemistry-Functional Food, Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany.
Foods. 2023 Jan 31;12(3):596. doi: 10.3390/foods12030596.
is a species frequently used in the manufacture of fermented milk. Apart from acid production, some strains additionally synthesize exopolysaccharides (EPS) which contribute to texture improvement and syneresis reduction, both being attributable to the EPS's high water binding capacity. There are two different types of EPS that may be produced, namely free exopolysaccharides (fEPS) which are secreted into the medium, and capsular EPS (cEPS) which remain attached to the bacterial cell wall. This study aims to analyze their individual contribution to techno-functional properties of fermented milk by determining the moisture sorption behavior of isolated fEPS and cell-attached cEPS from two strains separately: ST-1G, a producer of non-ropy fEPS and cEPS, and ST-2E, a producer of ropy fEPS and cEPS. Differences in moisture load and sorption kinetics, determined for the first time for microbial EPS, were related to structural and macromolecular properties. The observed data are discussed by using previously published data on the physical properties of stirred fermented milk produced with these two strains. ST-1G EPS showed a higher cEPS fraction, a higher moisture load and slower moisture desorption than EPS produced by ST-2E, thus contributing to lower syneresis in fermented milk. For ST-2E, higher gel viscosity was related to a higher intrinsic viscosity and molecular mass of the ropy fEPS. Both strains produced complex EPS or EPS mixtures with clearly different molecular structures.
是一种常用于发酵乳生产的菌种。除了产酸外，一些菌株还能合成胞外多糖（EPS），这有助于改善质地和减少乳清析出，这两者都归因于EPS的高水结合能力。可能产生两种不同类型的EPS，即分泌到培养基中的游离胞外多糖（fEPS）和附着在细菌细胞壁上的荚膜EPS（cEPS）。本研究旨在通过分别测定来自两株菌（非黏性fEPS和cEPS的生产者ST-1G以及黏性fEPS和cEPS的生产者ST-2E）的分离fEPS和细胞附着cEPS的吸湿行为，分析它们对发酵乳技术功能特性的各自贡献。首次针对微生物EPS测定的水分负载和吸附动力学差异与结构和大分子特性有关。利用先前发表的关于用这两株菌生产的搅拌发酵乳物理性质的数据对观察到的数据进行了讨论。与ST-2E产生的EPS相比，ST-1G EPS显示出更高的cEPS比例、更高的水分负载和更慢的水分解吸，因此有助于降低发酵乳中的乳清析出。对于ST-2E，更高的凝胶粘度与黏性fEPS的更高特性粘度和分子量有关。两株菌都产生了具有明显不同分子结构的复杂EPS或EPS混合物。
