Freeze-Drying Conditions of Starter Cultures for Sourdoughs

Studies were conducted on the viability of Lactobacillus reuteri, a starter culture for sourdough, using some natural substances such as bran, flour, bran-flour, and skimmed milk. The suspending media were employed alone or in combination with cryoprotectants (glutamate, glucose, or maltose). The drying conditions were controlled to obtain an optimal residual moisture of 0.30-0.35%. The number of survivors was determined by pour plates immediately after drying and during 12 months of storage at -20.5 and 25°C (room temperature). The stability of the freeze-dried cultures during long-term conservation was predicted by means of an accelerated storage test. The best suspending medium was found to be 20% bran in water supplemented with 5% monosodium glutamate because of important economic advantages: a short time of drying and high survival rate of the freeze-dried samples, even after storage at room temperature.