Department of Food Science, Food Microbiology, University of Copenhagen, Rolighedsvej 26, DK-1958 Frederiksberg C, Denmark.
Department of Food Science, Food Microbiology, University of Copenhagen, Rolighedsvej 26, DK-1958 Frederiksberg C, Denmark.
Int J Food Microbiol. 2016 Jun 2;226:5-12. doi: 10.1016/j.ijfoodmicro.2016.03.002. Epub 2016 Mar 5.
Performance of Lactococcus lactis as a starter culture in dairy fermentations depends on the levels of dissolved oxygen and the redox state of milk. In this study the microarray analysis was used to investigate the global gene expression of L. lactis subsp. lactis DSM20481(T) during milk acidification as affected by oxygen depletion and the decrease of redox potential. Fermentations were carried out at different initial levels of dissolved oxygen (dO2) obtained by milk sparging with oxygen (high dO2, 63%) or nitrogen (low dO2, 6%). Bacterial exposure to high initial oxygen resulted in overexpression of genes involved in detoxification of reactive oxygen species (ROS), oxidation-reduction processes, biosynthesis of trehalose and down-regulation of genes involved in purine nucleotide biosynthesis, indicating that several factors, among them trehalose and GTP, were implicated in bacterial adaptation to oxidative stress. Generally, transcriptional changes were more pronounced during fermentation of oxygen sparged milk. Genes up-regulated in response to oxygen depletion were implicated in biosynthesis and transport of pyrimidine nucleotides, branched chain amino acids and in arginine catabolic pathways; whereas genes involved in salvage of nucleotides and cysteine pathways were repressed. Expression pattern of genes involved in pyruvate metabolism indicated shifts towards mixed acid fermentation after oxygen depletion with production of specific end-products, depending on milk treatment. Differential expression of genes, involved in amino acid and pyruvate pathways, suggested that initial oxygen might influence the release of flavor compounds and, thereby, flavor development in dairy fermentations. The knowledge of molecular responses involved in adaptation of L. lactis to the shifts of redox state and pH during milk fermentations is important for the dairy industry to ensure better control of cheese production.
乳球菌作为乳制品发酵中的起始培养物的性能取决于溶解氧水平和牛奶的氧化还原状态。在这项研究中，使用微阵列分析来研究乳球菌亚种乳球菌 DSM20481（T）在牛奶酸化过程中的全基因表达，该过程受氧气耗尽和氧化还原电位降低的影响。发酵在不同的初始溶解氧（dO2）水平下进行，通过牛奶吹入氧气（高 dO2，63%）或氮气（低 dO2，6%）获得。细菌暴露于高初始氧气导致与活性氧（ROS）解毒、氧化还原过程、海藻糖生物合成相关的基因过度表达，以及与嘌呤核苷酸生物合成相关的基因下调，表明有几个因素，包括海藻糖和 GTP，与细菌对氧化应激的适应有关。一般来说，在充氧牛奶发酵过程中，转录变化更为明显。对氧气耗尽的响应而上调的基因参与嘧啶核苷酸、支链氨基酸的生物合成和运输，以及精氨酸分解代谢途径；而涉及核苷酸和半胱氨酸途径挽救的基因则受到抑制。参与丙酮酸代谢的基因表达模式表明，在氧气耗尽后，随着特定终产物的产生，代谢向混合酸发酵转变，这取决于牛奶处理方式。参与氨基酸和丙酮酸途径的基因的差异表达表明，初始氧气可能会影响风味化合物的释放，从而影响乳制品发酵中的风味发展。了解乳球菌适应牛奶发酵过程中氧化还原状态和 pH 变化的分子反应对于乳制品行业确保更好地控制奶酪生产非常重要。
