酿酒酵母和旧金山乳杆菌在面团发酵中互作机制及对馒头增香机理的研究

The rapid industrialization of steamed bread in China needs more intensive and advance research on Chinese steamed breads (CSB). In order to control its fermentation process and quality traits, the key is to understand the nature of different strains involved in the fermentation system of traditional sourdough. Microbial diversity in this niche has been studied to great depth. However, to study genetic diversity within species and to correlate it with their role in fermentation is a topic of current interest. There is no study that has enlightened the role of genetically diversified strains of the same species towards affecting the flavor profile of CSB. This project is to study the genetic diversity of Saccharomyces cerevisiae and Lactobacillus sanfranciscensis each (predominant strains in sourdough) using RAPD, VNTR and MLST methods. The fermentation characteristics of all genetically diversified strains belonging to these two species will be detected to select the strains with high fermentation potential. Further, meta-transcriptomic approach will be used to explore their role in fermentation by studying the key gene expression and metabolic pathways during single and co-culture fermentation process. In order to study the flavor characteristics, we used SDE and SPME methods of extracting volatile aroma compounds, followed by the identification of compounds using GC - MS. This project will provide deeper insights into the interaction of Saccharomyces cerevisiae and Lactobacillus sanfranciscensis and the influence on the flavor of CSB. On the other hand, it will provide opportunity to utilize the potential of selected strains to improve the industrialization of CSB.

馒头工业化是传统发酵主食研究的重要方向之一，而发酵剂是实现其工业化的关键环节，传统主食发酵剂中微生物多样性及其代谢机理则为研究热点中的焦点。目前，对传统发酵剂中微生物群落多样性研究较为成熟，而对其优势菌种互作及对馒头增香机理尚未报道。本项目以分离自我国不同地区传统酸面团中优势菌种酿酒酵母和旧金山乳杆菌为研究对象，采用DNA分子序列分型技术（RAPD、VNTR及MLST技术等）对其进行种内基因多态性解析。对不同类型菌株的合理筛选，获得发酵性能和理化指标较优的酿酒酵母和旧金山乳杆菌菌株，采用转录组学比较分析单菌种及复合菌种发酵过程中代谢路径及关键基因表达调控等，采用课题组已建立的馒头风味分析方法，SDE、SPME联合GC-MS技术手段，对不同菌株制备的馒头风味指纹图谱进行解析；结合生物信息学及生物统计学原理分析方法，科学阐明酿酒酵母和旧金山乳杆菌在面团发酵过程中互作机制及对馒头风味的增香机理。

馒头作为我国的传统发酵主食，但是深受人们喜爱的老面馒头仍以作坊式加工为主，在产品稳定性和安全性方面都受到严峻的挑战。实现传统发酵主食工业化的关键前提是主食发酵剂的工业化。目前，对传统发酵剂中微生物群落多样性研究较为成熟，而对其优势菌种互作及对馒头增香机理尚未报道。本项目以分离自我国不同地区传统酸面团中优势菌种酿酒酵母和旧金山乳杆菌为研究对象，深入探讨了两者在面团发酵中的互作机制及对馒头的增香机理。通过采用DNA分子序列分型技术（RAPD、VNTR及MLST技术等）对其进行种内基因多态性解析。MLST显示的旧金山乳杆菌菌株的基因型变异似乎与地理起源无关，该菌的重要代谢产物胞外多糖主要由葡萄糖组成；利用RAPD技术则将酿酒酵母分成了5种不同的类型。合理筛选出发酵性能和理化指标较优的酿酒酵母和旧金山乳杆菌菌株后，对面团进行了混合发酵，结合转录组学分析比较得出：在混合发酵过程中除pH不断降低和TTA不断增加之外，还发现旧金山乳杆菌对酿酒酵母的糖代谢有影响；混合发酵对风味物质组成也带来一定影响，产生了新的风味物质乳酸异戊酯，并促进乙酸、2-甲基-己酸等有机酸的合成，却使2,3-戊二酮、2-甲基-1-丙醇、3-甲基-1-丁醇、苯乙醇等一些主要通过酿酒酵母代谢产生的风味物质含量显著减少；不同旧金山乳杆菌菌株均可导致酿酒酵母对葡萄糖的利用增加、精氨酸转化为鸟氨酸的过程和乙醇的合成减少等等；混合发酵具有降低馒头水分、增加比容、降低酸面团pH值和增加总酸度等效果，对活性干酵母馒头的感官品质有明显的改善。本项目有望阐明传统面食发酵过程中优势菌株酿酒酵母和旧金山乳杆菌之间的代谢机理，为传统发酵面食工业化发展提供借鉴。