Department of Food and Nutrition, University of Helsinki, 00014, Helsinki, Finland.
Helsinki Institute of Sustainability Science, Helsinki, Finland.
Microb Cell Fact. 2021 Jan 22;20(1):23. doi: 10.1186/s12934-021-01515-4.
Lactic acid bacteria can synthesize dextran and oligosaccharides with different functionality, depending on the strain and fermentation conditions. As natural structure-forming agent, dextran has proven useful as food additive, improving the properties of several raw materials with poor technological quality, such as cereal by-products, fiber-and protein-rich matrices, enabling their use in food applications. In this study, we assessed dextran biosynthesis in situ during fermentation of brewers´ spent grain (BSG), the main by-product of beer brewing industry, with Leuconostoc pseudomesenteroides DSM20193 and Weissella confusa A16. The starters performance and the primary metabolites formed during 24 h of fermentation with and without 4% sucrose (w/w) were followed.
The starters showed similar growth and acidification kinetics, but different sugar utilization, especially in presence of sucrose. Viscosity increase in fermented BSG containing sucrose occurred first after 10 h, and it kept increasing until 24 h concomitantly with dextran formation. Dextran content after 24 h was approximately 1% on the total weight of the BSG. Oligosaccharides with different degree of polymerization were formed together with dextran from 10 to 24 h. Three dextransucrase genes were identified in L. pseudomesenteroides DSM20193, one of which was significantly upregulated and remained active throughout the fermentation time. One dextransucrase gene was identified in W. confusa A16 also showing a typical induction profile, with highest upregulation at 10 h.
Selected lactic acid bacteria starters produced significant amount of dextran in brewers' spent grain while forming oligosaccharides with different degree of polymerization. Putative dextransucrase genes identified in the starters showed a typical induction profile. Formation of dextran and oligosaccharides in BSG during lactic acid bacteria fermentation can be tailored to achieve specific technological properties of this raw material, contributing to its reintegration into the food chain.
根据菌株和发酵条件的不同，乳酸菌可以合成具有不同功能的葡聚糖和低聚糖。葡聚糖作为一种天然结构形成剂，已被证明可作为食品添加剂，改善技术质量较差的几种原料的特性，如谷物副产物、富含纤维和蛋白质的基质，使其能够应用于食品中。在这项研究中，我们评估了在啤酒酿造工业的主要副产物——啤酒糟（BSG）发酵过程中，葡聚糖的原位生物合成，使用了肠膜明串珠菌 DSM20193 和魏斯氏菌 A16。研究了在 24 小时发酵过程中，有无 4%蔗糖（w/w）时，发酵剂的性能和形成的主要代谢物。
发酵剂表现出相似的生长和酸化动力学，但糖的利用不同，特别是在存在蔗糖的情况下。含有蔗糖的发酵 BSG 中的粘度增加首先在 10 小时后发生，并在 24 小时内与葡聚糖的形成一起持续增加。24 小时后，葡聚糖在 BSG 总重量中的含量约为 1%。10 至 24 小时期间，与葡聚糖一起形成具有不同聚合度的低聚糖。在肠膜明串珠菌 DSM20193 中鉴定出 3 个葡聚糖蔗糖酶基因，其中一个在整个发酵过程中显著上调并保持活性。在魏斯氏菌 A16 中也鉴定出 1 个葡聚糖蔗糖酶基因，其诱导模式也很典型，在 10 小时时上调最高。
所选的乳酸菌发酵剂在啤酒糟中产生了大量的葡聚糖，同时形成了不同聚合度的低聚糖。发酵剂中鉴定出的潜在葡聚糖蔗糖酶基因表现出典型的诱导模式。在乳酸菌发酵过程中，BSG 中葡聚糖和低聚糖的形成可以根据特定的技术特性进行定制，有助于该原料重新融入食物链。
