THE IMPACT OF ALTERNATIVE NITROGEN SOURCES ON THE GROWTH AND VIABILITY OF LACTOBACILLUS DELBRUECKII SUBSP. BULGARICUS

In this study, we developed and optimized a growth medium using various nitrogen sources for the cultivation of Lactobacillus delbrueckii subsp. bulgaricus, a probiotic and essential dairy starter culture. The composition of deMan, Rogosa and Sharpe (MRS) culture medium was modified, and the nitrogen content was replaced by alternative nitrogen sources X-Seed Nucleo Max, X-Seed KAT, and X-Seed Carbo Max in various blends of 5g/L and 10g/L respectively. Results showed that bacterial growth was significantly higher when the nitrogen source blend KCMax (10/10) was used. The optical densities (OD610nm) of the Lb. bulgaricus strains were significantly higher in the KCMax (10/10) medium than in the MRS medium. There was no significance in bacterial counts for both the MRS and the KCMax (10/10) medium, and all bacterial counts were estimated at 8 Log CFU/ml. The buffering capacity of the KCMax (10/10) medium was also tested and supplemented with L-histidine and was significantly higher than that of the MRS control medium. KCMax (10/10) also supported the freeze stability and viability of the bulgaricus cells during freezing and freeze-drying operations. Our results suggest that the alternative nitrogen sources X-Seed Nucleo Max, X-Seed KAT and X-Seed Carbo Max can substantially support the growth of lactic acid bacteria as demonstrated with Lb. bulgaricus. These alternative nitrogen sources could thus be recommended for LAB fermentation and for the cultivation of dairy starter cultures.本研究以益生菌兼核心乳品发酵剂菌种德氏乳杆菌保加利亚亚种（Lactobacillus delbrueckii subsp. bulgaricus）的培养为目标，开发并优化了一款搭载多种氮源的生长培养基。本研究对德曼-罗戈萨-夏普（deMan, Rogosa and Sharpe, MRS）培养基的配方进行改性，以5g/L、10g/L的不同复配比例，采用X-Seed Nucleo Max、X-Seed KAT及X-Seed Carbo Max三种替代氮源替换原培养基中的氮源组分。实验结果表明，采用氮源复配组合KCMax(10/10)时，德氏乳杆菌保加利亚亚种的菌体生长量显著提升；该培养基中菌株的610纳米光密度（OD610nm）显著高于MRS培养基对照组。两类培养基的菌体菌落总数无统计学差异，最终均可达8对数菌落形成单位每毫升（Log CFU/ml）。本研究还检测了添加L-组氨酸后的KCMax(10/10)培养基的缓冲性能，其显著优于MRS对照培养基；此外，KCMax(10/10)培养基可有效维持保加利亚亚种菌体在冷冻及冷冻干燥过程中的冻存稳定性与活菌存活率。本研究结果证实，X-Seed Nucleo Max、X-Seed KAT及X-Seed Carbo Max这三种替代氮源可显著支撑乳酸菌（lactic acid bacteria, LAB）的生长，该结论在德氏乳杆菌保加利亚亚种的培养中得到验证。因此，上述替代氮源可推荐用于乳酸菌发酵及乳品发酵剂菌种的培养。