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Microwave-Vacuum Drying of Lactic Acid Bacteria: Influence of Process Parameters on Survival and Acidification Activity

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Abstract

Freeze drying is one important step in downstream processing of probiotics and starter cultures production and requires a long duration of the drying step, which, therefore, often is the overall production bottleneck. Microwave accelerated vacuum drying already showed promising results in terms of product quality for various food products. However, poor information on drying microorganisms by microwaves is available. The aim of this work was to set up a suitable microwave-vacuum drying process for the conservation of lactic acid bacteria and to investigate the optimum process parameters to achieve dried cultures with high survival and activity. The probiotic Lactobacillus paracasei ssp. paracasei F19 was used as model strain. The influence of the process parameters chamber pressure (7–30 mbar), specific microwave power input (1–5 W/g), and maximum product temperature (30–45 °C) on the main quality parameters survival rate, metabolic activity, and water activity of the dried samples were analyzed. Continuous energy input was shown to act detrimentally to the cells due to extreme temperature rise in the second drying stage. Proper temperature regulation could be obtained by pulsed microwave input according to a maximum set temperature. Intermediate microwave power between 3 and 4 W/g, the lowest tested pressure level of 7 mbar and low product temperatures of 30–35 °C, resulted in the highest survival and activity of the bacterial cells. With these results, it could be shown that microwave-vacuum drying appears as a promising alternative drying technique for the preservation of starter and probiotic cultures.

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Acknowledgments

This research project was supported by the German Ministry of Economics and Technology (via AiF) and the FEI (Forschungskreis der Ernährungsindustrie e.V., Bonn, Project AiF 17477 N). The authors would like to thank Chr. Hansen (Hoersholm, Denmark) for the kind providing of L. paracasei cultures. Püschner Microwaves (Schwanewede, Germany) is thanked for the technical support. Regina Mayer’s technical assistance is gratefully acknowledged.

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Authors and Affiliations

  1. Chair for Food and Bioprocess Engineering, Technical University of Munich, 85354, Freising, Germany

    S. Ambros, S. A. W. Bauer, L. Shylkina & U. Kulozik

  2. Chair of Process Systems Engineering, Gregor-Mendel-Str. 4, 85354, Freising, Germany

    P. Foerst

  3. ZIEL Institute for Food and Health, Technical University of Munich, Weihenstephaner Berg 1, 85354, Freising, Germany

    U. Kulozik

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  1. S. Ambros
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  2. S. A. W. Bauer
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  3. L. Shylkina
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  4. P. Foerst
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  5. U. Kulozik
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Correspondence to S. Ambros.

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Ambros, S., Bauer, S.A.W., Shylkina, L. et al. Microwave-Vacuum Drying of Lactic Acid Bacteria: Influence of Process Parameters on Survival and Acidification Activity. Food Bioprocess Technol 9, 1901–1911 (2016). https://doi.org/10.1007/s11947-016-1768-0

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  • DOI: https://doi.org/10.1007/s11947-016-1768-0

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