添加外源稳定剂改善乳品品质、防止乳清析出是发酵乳生产中最常用的手段，然而随着生活品质的提高，消费者对无添加发酵乳需求日益增加，开发内源稳定体系的发酵乳成为当前的研究热点。申请人前期研究发现，产黏嗜热链球菌胞外多糖（EPS）能有效改善乳品稳定性，但对EPS稳定发酵乳体系的机制还不清楚。本项目在嗜热链球菌EPS结构研究的基础上，采用光散射、热力学分析、激光共聚焦等现代仪器分析技术从分子水平上研究EPS与酪蛋白（胶束）在水溶液和牛乳体系中的相互作用，通过Crispr/Cas9基因编辑技术构建高产和不产EPS嗜热链球菌株，利用不同产EPS能力的乳酸菌构建发酵乳体系，动态研究不同体系中EPS和酪蛋白胶束的微观结构和互作位点，探讨EPS对发酵乳的稳定效果，最终阐明嗜热链球菌EPS稳定发酵乳体系的内在机制。本项目通过从分子水平到食品宏观体系的研究为乳酸菌EPS的应用和无添加发酵乳的开发提供理论基础。

The fermented milk (FM) always needs additional stabilizer to improve the quality and solve the whey separation problem. However, the development of endo-stabilizer to stabilize the FM system has become a hot research topic as the increase of the demand of additive-free FM. Our previous study found that the exopolysaccharide (EPS) from Streptococcus thermophiles could improve the stability of FM effectively, but no clear stabilizing mechanism. Based on the structure analysis of EPS from S. thermophiles, the current project tries to study the interaction of EPS and casein (micelle) in aqueous and milk system by using light scattering, thermodynamic analysis and confocal laser scanning microscope (CLSM) techniques, etc. The genome-editing technique based on Crispr/Cas9 is applied on S. thermophiles to prepare non-EPS and higher EPS producing strains, respectively. The stability of FM systems prepared by different EPS-producing ability of S. thermophiles is studied to finally illustrate the stabilizing mechanism of EPS on FM system. This study will establish the theoretical basis for the application of EPS and development of additive-free FM in molecular and complex food levels.