Resumen de Critical water activity for the preservation of Lactobacillus bulgaricus by vacuum drying

E. Elizabeth Tymczyszyn, Rosario Díaz, Andrea Pataro, Natalia Sandonato, A. Gómez Zavaglia, E. Anibal Disalvo

• Lactobacillus delbrueckii subsp. bulgaricus was dried under vacuum at different temperatures and its preservation evaluated analyzing the evolution of three parameters throughout the process: lag time, percentage of membrane damage and ? potential.

  Microorganisms were dehydrated at 30, 45 and 70 °C in a vacuum centrifuge for different times. The aw achieved for each time of drying was correlated with the cell recovery at all the temperatures assayed. The recovery of microorganisms was evaluated by means of: a) kinetics of growth in milk after drying, as a measure of the global damage; b) quantification of the membrane damage using the fluorescent dyes SYTO 9 and PI; c) determination of changes in the superficial charges (? potential) as measured of the increase in the hydrophobic residues exposed in the bacterial surface after dehydration. These changes correlate well with the bacterial damage occurred during the dehydration process.

  The Page's equation allowed fitting of aw and time of drying, thus making possible the determination of the appropriate dehydration conditions (time-temperature ratios) for which no cell damage occurs.

  The evaluation of three parameters (lag time, percentage of membrane damage and ? potential) allowed us to conclude that at the lowest temperature of dehydration, the first target of damage is the cell membrane. However, this damage is not decisive for the bacterial recovery after rehydration, as are the increase in the lag time and the changes in the ? potential, as was observed for L. bulgaricus dehydrated at 45 and 70 °C for larger times