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Freeze-drying, bacterial cell, Streptococcus thermophilus, FTIR, hydrophobicity

Abstract

Streptococcus thermophilus (ST) is a key acidifying bacteria used by dairy industry as starter culture. Freeze drying has been widely used in biotechnology industry for producing frozen bacterial cells including STs. It is well-known that the freeze-drying profile and process parameters can have significant impact on the functionality of the final product. However, the underlying principle behind it has not been yet thoroughly investigated. In this work, we have applied different freeze-drying profiles on a formulated ST-4458, and stored the freeze-dried products for one month at high temperature  of 37°C. The acidification performance of the stored samples was evaluated by CINAC milk acidification activity test. We primarily showed how different drying profiles result in variation in acidification performance during the storage of the products. Further, at a more profound level, we examined the  freeze dried granulates during their storage using hydrophobicity measurement and FTIR analysis. The results demonstrated that there is a strong correlation between surface- driven properties such as hydrophobicity of bacterial cells and chemical composition of cell membrane with the acidification  performance of those samples.

Acknowledgement

We thank the members of Process Design Department, Fermentation Lab, and Biochemical Assays Department of Novonsis A/S for their technical support.

References

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