Effect of carbohydrates on the survival of Lactobacillus helveticus during vacuum drying

AIMS: To assess four carbohydrates for the protective effect against Lactobacillus helveticus cells inactivation during vacuum drying, and to study the effect of selected carbohydrate on changes of inactivation kinetics. METHODS AND RESULTS: Early stationary phase L. helveticus cells grown in MRS media were recovered from fermentation broth, washed with PBS buffer (pH 7.0), and then mixed with different concentrations of four carbohydrates, namely lactose, sorbitol, inulin, and xanthan gum. Cells were dried in a vacuum drier at 100 mbar, 43 degrees C for 12 h. Only cells with 1% sorbitol addition showed higher survival (18%) over cells without added carbohydrate (8%). Using in situ microbalance technique whereby cell weight during vacuum drying was continuously monitored via precision balances integrated into the vacuum chamber, drying and inactivation kinetics of cells and cells mixed with sorbitol were established. CONCLUSION: Survival of L. helveticus during the vacuum drying could be improved by the addition of optimal concentration of 1% sorbitol. Addition of sorbitol did not cause drastic changes in drying rate, water content and water activity of samples. The protection mechanisms of sorbitol seemed not to be due to a direct physical effect, which could be related to drying rate. SIGNIFICANCE AND IMPACT OF THE STUDY: The increase in survival of cells after vacuum drying by the addition of a protective carbohydrate may provide an alternative mean to preserve starter cultures at a higher level of activity.