Effects of six substances on the growth and freeze-drying of Lactobacillus delbrueckii subsp. bulgaricus
Background. The efficacy of Lactobacillus delbrueckii subsp. bulgaricus as starter cultures for the dairy industry depends largely on the number of viable and active cells. Freeze-drying is the most convenient and successful method to preserve the bacterial cells. However, not all strains survived during freeze-drying.
Methods. The effects of six substances including NaCl, sorbitol, mannitol, mannose, sodium glutamate, betaine added to the MRS medium on the growth and freeze-drying survival rate and viable counts of Lb. delbrueckii subsp. bulgaricus were studied through a single-factor test and Plackett-Burman design. Subsequently, the optimum freeze-drying conditions of Lb. delbrueckii subsp. bulgaricus were determined.
Results. Lb. delbrueckii subsp. bulgaricus survival rates were up to the maximum of 42.7%, 45.4%, 23.6%, while the concentrations of NaCl, sorbitol, sodium glutamate were 0.6%, 0.15%, 0.09%, respectively. In the optimum concentration, the viable counts in broth is 6.1, 6.9, 5.13 (×108 CFU/mL), respectively; the viable counts in freeze-drying power are 3.09, 5.2, 2.7 (×1010 CFU/g), respectively.
Conclusion. Three antifreeze factors including NaCl, sorbitol, sodium glutamate have a positive effect on the growth and freeze-drying of Lb. delbrueckii subsp. bulgaricus. The results are beneficial for developing Lb. delbrueckii subsp. bulgaricus.
Lactobacillus delbrueckii subsp. bulgaricus, antifreeze factors, freeze-drying, single-factor test, PB screening test
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School of Food and Biological Engineering, Shaanxi University of Science and Technology Xi?an,China
He
Chen
School of Food and Biological Engineering, Shaanxi University of Science and Technology Xi?an,China
Jie
Huang
School of Food and Biological Engineering, Shaanxi University of Science and Technology Xi?an,China
Xiaoyu
Shi
Shaanxi Heshi Dairy, China
Yichao
Li
Shaanxi Heshi Dairy, China
Yu
Liu