Low D, Ahlgren J A, Horne D, McMahon D J, Oberg C J, Broadbent J R
Department of Nutrition and Food Sciences, Utah State University, Logan, Utah 84322-8700, USA.
Appl Environ Microbiol. 1998 Jun;64(6):2147-51. doi: 10.1128/AEM.64.6.2147-2151.1998.
Recent work by our group has shown that an exopolysaccharide (EPS)-producing starter pair, Streptococcus thermophilus MR-1C and Lactobacillus delbrueckii subsp. bulgaricus MR-1R, can significantly increase moisture retention in low-fat mozzarella (D. B. Perry, D. J. McMahon, and C. J. Oberg, J. Dairy Sci. 80:799-805, 1997). The objectives of this study were to determine whether MR-1C, MR-1R, or both of these strains are required for enhanced moisture retention and to establish the role of EPS in this phenomenon. Analysis of low-fat mozzarella made with different combinations of MR-1C, MR-1R, and the non-EPS-producing starter culture strains S. thermophilus TA061 and Lactobacillus helveticus LH100 showed that S. thermophilus MR-1C was responsible for the increased cheese moisture level. To investigate the role of the S. thermophilus MR-1C EPS in cheese moisture retention, the epsE gene in this bacterium was inactivated by gene replacement. Low-fat mozzarella made with L. helveticus LH100 plus the non-EPS-producing mutant S. thermophilus DM10 had a significantly lower moisture content than did cheese made with strains LH100 and MR-1C, which confirmed that the MR-1C capsular EPS was responsible for the water-binding properties of this bacterium in cheese. Chemical analysis of the S. thermophilus MR-1C EPS indicated that the polymer has a novel basic repeating unit composed of D-galactose, L-rhamnose, and L-fucose in a ratio of 5:2:1.
我们团队最近的研究表明，产胞外多糖（EPS）的发酵剂组合嗜热链球菌MR-1C和德氏乳杆菌保加利亚亚种MR-1R，能显著提高低脂马苏里拉奶酪的保水性（D. B. 佩里、D. J. 麦克马洪和C. J. 奥伯格，《乳品科学杂志》80:799 - 805，1997）。本研究的目的是确定增强保水性是否需要MR-1C、MR-1R这两种菌株中的一种或两种，并确定EPS在此现象中的作用。对用MR-1C、MR-1R以及不产EPS的发酵剂培养菌株嗜热链球菌TA061和瑞士乳杆菌LH100的不同组合制作的低脂马苏里拉奶酪进行分析，结果表明嗜热链球菌MR-1C是奶酪水分含量增加的原因。为了研究嗜热链球菌MR-1C的EPS在奶酪保水性中的作用，通过基因置换使该细菌中的epsE基因失活。用瑞士乳杆菌LH100加不产EPS的突变体嗜热链球菌DM10制作的低脂马苏里拉奶酪的水分含量明显低于用菌株LH100和MR-1C制作的奶酪，这证实了MR-1C的荚膜EPS是该细菌在奶酪中具有水结合特性的原因。对嗜热链球菌MR-1C的EPS进行化学分析表明，该聚合物具有一种新型的基本重复单元，由D-半乳糖、L-鼠李糖和L-岩藻糖以5:2:1的比例组成。
