The preservation of lactic acid starter cultures by alternative drying processes has attracted increasing attention due to the high costs and energy consumption of freezing and freeze drying. This review thus aims to provide a survey regarding the state of knowledge of starter culture production at high levels of viability. The results from numerous studies on various drying processes and lactic acid bacteria are summarized. The alternative drying processes considered, such as spray drying, fluidized bed drying, and vacuum drying, are mainly of industrial interest. The features, advantages, and disadvantages of these drying processes are described. In conclusion, the important factors that need to be considered, standardized, or optimized to achieve high levels of viability include intrinsic tolerance of cultures, growth media and conditions, stress induction, cell harvesting conditions, protective agents, rehydration conditions, enumeration of cells, and storage conditions.

Summary The preservation of lactic acid starter cultures by drying are of increased interest. A further improvement of cell viability is, however, still needed, and the insight into inactivation mechanisms of the cells is a prerequisite. In this present work, we review the inactivation mechanisms of lactic acid starter cultures during drying which are not yet completely understood. Inactivation is not only induced by dehydration inactivation but also by thermal‐ and cryo‐injuries depending on the drying processes employed. The cell membrane has been reported as a major site of damage during drying or rehydration where transitions of membrane phases occur. Some drying processes, such as freeze drying or spray drying, involve subzero or very high temperatures. These physical conditions pose additional stresses to cells during the drying processes. Injuries of cells subjected to freezing temperatures may be due to the high electrolyte concentration (solution effect) or intracellular ice formation, depending on the cooling rate. High temperatures affect most essential cellular components. It is difficult to identify a critical component, although ribosomal functionality is speculated as the primary reason. The activation during storage is mainly due to membrane lipid oxidation, while the storage conditions such as temperature moisture content of the dried starter cultures are important factors.

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The addition of microencapsulated probiotic cells to food products is a relatively new functional food concept. Most of the published scientific research in this field is not older than ten years. However, the technological background reaches back to the 1980s, where lactic acid bacteria were microencapsulated within the concept of the so-called immobilized cell technology (ICT). Target applications of ICT were continuous fermentation processes and improved biomass production. The methods adopted from immobilized cell technology were applied for the microencapsulation of probiotics, often optimized towards specific requirements associated with the protection of probiotic cells in food applications. However, there are still significant hurdles with respect to currently available methods for probiotic cell microencapsulation. This is mainly due to the fact that important characteristics of microcapsules based on ICT appear to be in conflict with the requirements arising from an application of probiotic microcapsules in food products, with particle size and inappropriate matrix characteristics being the most prominent ones. Based on this situation the aim of this review is to give a critical overview of the current approaches regarding the microencapsulation of probiotic cells for food applications and to report on emerging developments.

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Reversible and irreversible states of pressure-dissociated casein micelles were studied by in situ light scattering techniques and ex situ atomic force microscopy. AFM experiments performed at ambient pressure reveal heterogeneities across the micelle, suggesting a sub-structure on a 20 nm scale. At pressures between 50 and 250 MPa, the native micelles disintegrate into small fragments on the scale of the observed sub-structure. At pressures above 300 MPa the micelles fully decompose into their monomeric constituents. After pressure release two discrete populations of casein aggregates are observed, depending on the applied initial pressure: Between 160 and 240 MPa stable micelles with diameters near 100 nm without detectable sub-structures are formed. Casein micelles exposed to pressures above 280 MPa re-associate at ambient pressure yielding mini-micelles with diameters near 25 nm. The implications concerning structural models are discussed.