Hassan Ashraf N, Corredig Milena, Frank Joseph F, Elsoda Morsi
Department of Food Science and Technology, The University of Georgia, Athens, GA 30602, USA.
J Dairy Res. 2004 Feb;71(1):116-20. doi: 10.1017/s0022029903006605.
The objective of this research was to determine the effect of exopolysaccharide (EPS) production by lactic acid bacteria on the microstructure and rheology of Karish cheese, a soft acid coagulated cheese made using skim milk. An EPS-producing strain of Streptococcus thermophilus, and its EPS non-producing genetic variant were used to make comparable batches of the cheese. EPS in cheese was visualized by cryo-SEM as a large, dense, filamentous mass. Cheese made with the EPS non-producing culture was characterized by a dense protein network with smaller pores compared to that prepared with the EPS-producing culture. High elastic and viscous moduli measured by dynamic rheology were observed for EPS negative cheese and was attributed to its dense protein network. Creep test experiments demonstrated that cheese prepared with the EPS non-producing strain was more rigid and recovered its deformation, while cheese made using the EPS producing culture was more deformable. These results indicate that EPS-producing cultures can improve the physical properties of Karish cheese by reducing undesirable rigidity.
本研究的目的是确定乳酸菌产生的胞外多糖（EPS）对卡瑞什奶酪微观结构和流变学的影响，卡瑞什奶酪是一种用脱脂牛奶制成的软质酸凝奶酪。使用嗜热链球菌的一个产EPS菌株及其不产EPS的基因变体制作了可比批次的奶酪。通过低温扫描电子显微镜观察到奶酪中的EPS为大的、致密的丝状团块。与用产EPS培养物制备的奶酪相比，用不产EPS培养物制作的奶酪具有致密的蛋白质网络，孔隙较小。通过动态流变学测量发现，不产EPS的奶酪具有较高的弹性和粘性模量，这归因于其致密的蛋白质网络。蠕变试验表明，用不产EPS菌株制备的奶酪更坚硬，能恢复其变形，而用产EPS培养物制作的奶酪更易变形。这些结果表明，产EPS的培养物可以通过降低不良硬度来改善卡瑞什奶酪的物理性质。
