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.

本研究针对德氏乳杆菌保加利亚亚种（Lactobacillus delbrueckii subsp. bulgaricus，一种益生菌兼核心乳品发酵剂培养物）的培养需求，开发并优化了以多种氮源为核心的生长培养基。本研究对德氏-罗格斯-夏普（deMan, Rogosa and Sharpe, MRS）培养基的配方进行改良，以5g/L与10g/L的不同复配比例，将原培养基中的氮源替换为替代氮源X-Seed Nucleo Max、X-Seed KAT及X-Seed Carbo Max。实验结果显示，当采用氮源复配物KCMax (10/10)时，保加利亚乳杆菌的菌体生长量显著提升。KCMax (10/10)培养基中，保加利亚乳杆菌菌株的光密度值（OD610nm）显著高于MRS对照培养基。MRS培养基与KCMax (10/10)培养基的菌体活菌计数结果无统计学差异，所有样本的活菌数均约为8 Log CFU/ml。本研究还对经L-组氨酸补充的KCMax (10/10)培养基的缓冲能力进行了测定，结果表明其缓冲能力显著优于MRS对照培养基。KCMax (10/10)培养基还可有效维持保加利亚乳杆菌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，以保加利亚乳杆菌为模型菌株的实验表明，X-Seed Nucleo Max、X-Seed KAT及X-Seed Carbo Max这三种替代氮源可显著支持乳酸菌（Lactic Acid Bacteria, LAB）的生长繁殖。因此，上述替代氮源可推荐用于乳酸菌发酵及乳品发酵剂培养物的培养。