Starter cultures storage stability

The glass matrix of a protectant can improve storage stability of dried cells by raising tbe Tg of starter cultures. The high viscosity of glasses below or around their Tg is generaUy believed to retard molecular mobility and hence slow down the deteriorative reactions. 

More recently, it was even hypothesized that a structural collapse would not lead to a deleterious product quality as—unlike for pharmaceutical applications—optical appearance of the product is not a quality criterion for starter cultures (see Section 11.1). First investigations even show that the storage stability of collapsed products may be higher, probably due to the lower porosity and also drying time may be shorter (Schersch et al., 2010, 2012). This aspect including all the consequences on product quality has to be investigated further. 

The dried cell concentrate is typically produced by specialized suppliers and distributed worldwide. As the producers of fermented foods want to build up some stock, the cultures should be stable for at least one year. As the activity of the cultures after drying depends on the previous fermentation step (see Section 11.3), and the storage stability depends on the drying process as we will show in this section, the starter culture preparation process must be looked at in a holistic approach. This... 

Starter cultures and probiotics are produced and distributed world wide by specialised companies. Therefore, stabilization of the bacteria is essential. Drying is a common stabilization method as it leads to an increased storage stability and facilitated transport compared to freezing. However, drying leads to an inactivation of the cells. The dehydration damage is especially pronounced at low Water content where structural water is removed from the biomolecules such as proteins and hydrophilic surfaces of biomembranes. 

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