保加利亚乳杆菌胞外多糖合成条件的优化及其在发酵乳中的应用研究

Optimized production and application of EPS by Lactobacillus delbrueckii subsp.bulgaricus Y5 in fermented milks

研究了不同碳源、氮源、碳氮比及发酵条件等因素对保加利亚乳杆菌Y5菌株产胞外多糖的影响。结果表明,以果糖为碳源时,胞外多糖的产量是55.46 mg/L,显著高于用半乳糖作为碳源时的产量(29.59 mg/L);以鱼蛋白胨作为氮源为时,胞外多糖产量可达到46.89 mg/L,明显高于用胰蛋白胨作为氮源时的产量(P<0.01);当碳氮比为2︰1时,Y5菌株产生的胞外多糖最多,可达50.10 g/L,显著高于碳氮比为1︰2时的产量(P<0.01)。培养温度为40℃,发酵时间为16h,初始pH值为6.0,葡萄糖添加量为2%的发酵条件是Y-5菌株产胞外多糖的最佳工艺条件,其胞外多糖水平可达105.36 g/L。与采用ST和LB菌株的发酵乳相比,应用Y5菌株生产的发酵乳,其乳清析出量仅为7 mL(P<0.01);冷藏30 d后,Y5菌株制备的发酵乳仍能维持107 mL-1以上的活菌数,明显高于对照菌株的存活数量(P<0.01)。

The factors, including carbon and nitrogen sources, the ratio of C to N, temperature, incubation time and initial pH in medium affecting the level of exopolysaccharides （EPS） produced by Lactobacillus delbrueckii subsp, bulgaricus Y5 were studied. Strain Y5 preferred fructose to galactose as carbon source in producing EPS （P〈0.01）. In the presence of fructose, EPS formed by strain Y5 reached 55.46mg/L; whereas in the presence of galactose, EPS was 29.59 mg/L. EPS production by strain Y5 was higher in the presence of fish peptone than in the presence of tryptone, and reached 46.89 mg/L. Clearly, a 2：1 of C to N was better than a 1：2 of C to N in improving strain Y5 to produce EPS with 50.10 mg/mL. The combinations of temperature at 40℃, 16h of fermentation time, initial pH in 6.0 and supplemented glucose of 2% significantly improved EPS production, up to 105.36 g/L. Use of strain Y5 to manufacture fermented milk produced significantly lower whey separation than strains ST and LB did （their fermented milks used as the control）, and the amount of whey separated was only 7 mL. The live cell counts of strain Y5 decreased slowly during a 30 d refrigerated storage at 4 ℃, but were higher than 10^7 mL^-1 and were significantly improved compared to those of the controlled samples.