Hassan Ashraf N, Frank Joseph F, Qvist Karsten B
Department of Food Science and Technology, Athens, GA 30602, USA.
J Dairy Sci. 2002 Jul;85(7):1705-8. doi: 10.3168/jds.S0022-0302(02)74243-4.
The objective of this work was to develop a methodology for direct visualization of bacterial exopolysaccharides (EPS) in fully hydrated dairy products. The new method involved staining EPS with wheat germ agglutinin labeled with Alexa fluor 488 or staining with concanavalin A 488. Samples were observed using confocal scanning laser microscopy. Distribution of EPS produced by Lactococcus lactis (CHCC 3367), a combination of Streptococcus thermophilus (CHCC 3534) and Lactobacillus delbrueckii ssp. bulgaricus (CHCC 769) and Lactobacillus delbrueckii ssp. bulgaricus RR in milk was compared in stirred and unstirred fermented milk. The EPS and proteins were observed as distinct entities, with EPS present in the protein network pores. EPS was observed in greater amounts in milk fermented by the ropy L. lactis culture than in milk fermented by the less ropy strain of S. thermophilus. Stirring the fermented milk caused aggregation of EPS into more extended structures. The more ropy the culture, the longer and larger the strands formed during stirring. The method was also applied to Feta cheese made with an EPS-producing strain of S. thermophilus. EPS was observed in the cheese as thick sheets filling pores in the protein network.
这项工作的目的是开发一种直接可视化完全水合乳制品中细菌胞外多糖（EPS）的方法。新方法包括用Alexa fluor 488标记的麦胚凝集素对EPS进行染色或用伴刀豆球蛋白A 488进行染色。使用共聚焦扫描激光显微镜观察样品。比较了乳酸乳球菌（CHCC 3367）、嗜热链球菌（CHCC 3534）和德氏保加利亚乳杆菌（CHCC 769）以及德氏保加利亚乳杆菌RR在搅拌和未搅拌发酵乳中产生的EPS在牛奶中的分布。观察到EPS和蛋白质是不同的实体，EPS存在于蛋白质网络孔隙中。与由粘性较小的嗜热链球菌菌株发酵的牛奶相比，由粘性乳酸乳球菌培养物发酵的牛奶中观察到的EPS量更多。搅拌发酵乳会导致EPS聚集形成更长的结构。培养物的粘性越大，搅拌过程中形成的链就越长、越大。该方法还应用于用产EPS的嗜热链球菌菌株制作的菲达奶酪。在奶酪中观察到EPS呈厚片状填充蛋白质网络中的孔隙。
