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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Food Quality Laboratory » Research » Publications at this Location » Publication #333535
Research Project: Enhancing Fruit and Vegetable Nutritional Quality with Improved Phenolics Contents

Location: Food Quality Laboratory

Title: Optimization of a cryoprotective medium to increase the viability of freeze-dried Streptococcus thermophilus by response surface methodology

Author
item LU, YINGJIAN - University Of Maryland
item HUANG, LIJIN - Nanjing Agricultural University
item Yang, Tianbao
item LV, FENGXIA - Nanjing Agricultural University
item LU, ZHAOXIN - Nanjing Agricultural University

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2017
Publication Date: 1/18/2017
Citation: Lu, Y., Huang, L., Yang, T., Lv, F., Lu, Z. 2017. Optimization of a cryoprotective medium to increase the viability of freeze-dried Streptococcus thermophilus by response surface methodology. LWT - Food Science and Technology. 80:92-97. doi: 10.1016/j.lwt.2017.01.044.

Interpretive Summary: Streptococcus sativarius subsp. thermophilus is one of the most widespread bacterial species used in the production of yogurt and other dairy products. Streptococcus thermophilus normally exhibits different survival rates in different bacterial medium during freeze-drying. The aim of the present work was to identify the optimum levels of three important protective agents (glycerol, sodium glutamate and skim milk) in medium for S. thermophilus strain STX2 in order to maximize the viability after freeze-drying. Results showed that the most significant factor influencing the resistance of S. thermophilus STX2 to freeze-drying was skim milk, followed by sodium glutamate, and then glycerol. These three factors may have interactive effects and produce synergistic protective effects on the growth of S. thermophilus STX2. Our analysis indicated the optimal concentrations of glycerol, sodium glutamate, and skim milk. S. thermophilus STX2 freeze-dried in a medium with the optimal formulation obtained a best cell viability up to 93.58 %.

Technical Abstract: Streptococcus thermophilus normally exhibits different survival rates in different bacteria medium during freeze-drying. In this study, response surface methodology (RSM) was applied on the design of experiments for optimizing the cryoprotective medium. Results showed that the most significant factor influencing the resistance of S. thermophilus STX2 to freeze-drying was skim milk, followed by sodium glutamate, and then glycerol. These three factors may have interactive effects and produce synergistic protective effects on the growth of S. thermophilus STX2. Regression analysis indicated that the optimal concentrations of these variables were determined as: glycerol 79.60 g/L, sodium glutamate 77.40 g/L, and skim milk 116.40 g/L. S. thermophilus STX2 freeze-dried in a medium with the optimal formulation obtained a best cell viability up to 93.58 %.