Observation of bacterial exopolysaccharide in dairy products using cryo-scanning electron microscopy |
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| Affiliation: | 1. Department of Food Science and Technology, The University of Georgia, Athens, GA 30602, USA;2. Department of Dairy Science and Technology, Alexandria University, Egypt;1. College of Food Science and Engineering, Northwest A & F University, 28 Xinong Road, Yangling, Shaanxi Province 712100, China;2. Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, 127 Youyi Xilu, Xi''an, Shaanxi Province 710072, China;3. Tibetan Plateau Laboratory of Agric-Product Processing, Qinghai Academy of Agriculture and Forestry, 253 Ningda Road, Xining, Qinghai Province 810016, China;4. Educational Ministry Key Laboratory of Resource Biology and Biotechnology in Western China, Life Science College, Northwest University, Xi''an 710069, China;1. Department of Chemical Engineering, National Cheng Kung University, Tainan 70101, Taiwan;2. Department of Chemical and Biochemical Engineering, Xiamen University, Xiamen 361005, China;3. Department of Biotechnology, Southern Taiwan University of Science Technology, Tainan 71005, Taiwan |
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| Abstract: | Cryo-scanning electron microscopy was used to visualize the microstructure of two types of cheese (Karish and Feta) and milk fermented with different ropy and non-ropy strains of lactic acid bacteria. Specimen frozen in liquid nitrogen slush were transferred in a frozen state and under vacuum into the preparation chamber where they were fractured, etched and coated with gold. Specimen were then transferred under vacuum onto the cold stage and imaged using scanning electron microscopy (SEM). Milk fat and exopolysaccharide (EPS) were visible in pores within the protein network. Cheese and fermented milk made with EPS-producing cultures exhibited a porous structure in which the largest pores were associated with visible EPS. A compact structure with small pores was seen in cheese and milk fermented with EPS non-producing cultures. EPS and protein appeared to be segregated in both cheese and fermented milk. EPS formed a network-like structure. Differences were observed in the microstructure of EPS between moderately ropy and highly ropy strains. A relatively long etching (sublimation) time caused EPS to appear as thin filaments similar to those seen with conventional SEM. |
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