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In this study, the utilization of 16 nitrogen sources of Lactobacillus delbrueckii subsp. bulgaricus B61-3 were determined, and the types and amounts of nitrogen sources that can improve the freeze-drying tolerance of the strain were screened out. More importantly, the effects of nitrogen source modification on the fermentation performance, cell morphology and enzyme activities of freeze-dried powder of the strain were investigated. The results showed that 30 g/L of bovine bone peptone improved the freeze-drying survival rate from 9.68% to 18.90%, and increased fermentation activity by 22.15% compared with the control group. Changed cell size and morphology of the cultured cells of bovine bone peptone were also observed by electron microscope. Cell cultured in bovine bone peptone medium represented a short rod with smooth surface, and the ratio of length to diameter or area to volume decreased significantly (P

The acid-producing, viscosity-increasing, and aroma-producing capacities and laboratory storage stabilities of ten strains of Lactobacillus delbrueckii subsp. bulgaricus were measured. The probiotic characteristics of the strains were also explored by monitoring their antibiotic resistance, antibacterial activities, and β-galactosidase (β-gal), α-galactosidase (α-gal), and lactate dehydrogenase (LDH) activities. Single-strain fermentation experiments show that the strain KSDB-1 had a short coagulation time (approximately 6.3 h), a lactic acid degree of 76.02ºT upon coagulation, and good acid-producing ability. The viscosity and water holding capacity (1305.67 mPa-s and 50.55%, respectively) were significantly higher than those of other strains (p<0.05). Aroma production of strains HDS-13, DDB14, and KSDB-1 was superior. Strain HDS-13 displayed a diacetyl content of 2.88 mg/L and an acetaldehyde content of up to 30.08 mg/L. These attributes could effectively improve the flavor of the yoghurt product. Probiotic tests show that all the ten tested strains were sensitive to most antibiotics and thus would be relatively safe to use. Strains HDS-13, DDB-14, HDB-1, HDS-18, and KSDB-1 could inhibit six pathogenic bacteria and effectively inhibited the growth of pathogenic intestinal bacteria. The LDH activities of strains HDS-12 and KSDB-1 were relatively high. The β-gal activities of strains HDS-12 and HDB-17 were relatively greater than that of the other strains. The α-gal activity of strain DDS-15 was significantly higher than those of other strains (p< 0.05), reaching 1.3263 U/mg. The collective data indicate that strain KSDB-1 has excellent fermentation properties and, to a certain degree, satisfactory probiotic properties. DDS-15 has potential in industrial application for yogurt fermentation. [ABSTRACT FROM AUTHOR]

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