Glutathione (GSH) is a non-coding tripeptide thiol with several important regulative and protective functions in eukaryotes and in most prokaryotes. The primary function of GSH is to maintain the redox potential of the cell, which is directly connected to GSH concentration, and to prevent cellular damages caused by reactive oxygen species or toxic heavy metals. Due to its antioxidant character, it is widely used in pharmaceutical, cosmetic and food industry. There have been different strategies to optimize GSH yield and productivity in bacteria and yeasts by means of metabolic and evolutionary engineering, media optimization and bioprocess engineering. The fed-batch procedure with yeasts of the genera Saccharomyces and Candida is still common method for industrial production. However, for an economic bioprocess production of GSH key factors like media costs, strain performance and process scalability are essential. Beside the extraction and purification of GSH as bulk product, GSH-enriched yeast cells are used for food and beverage applications, as well. This review outlines current applications of microbially produced GSH and illustrates current developments and strategies for its production.

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Lactic acid bacteria (LAB) are widely applied microorganisms in food, feed, and beverage applications, where they can provide essential functionality for product modification, increase product shelf life, or act as beneficial organisms after consumption. Among these, strains of the genus Lactobacillus are often used as starters, probiotics, or biopreservatives. For all these types of bacterial preparations, a transportable shelf-stable form of concentrated bacteria, preserving their intrinsic properties, is essential for commercial distribution. Former studies revealed a relationship between the culture medium, cellular morphology, and the robustness of Lactobacillus acidophilus NCFM (name derived from North Carolina Food Microbiology) cultures. Due to these insights, a multitude of Lactobacillus strains representative of the genus were screened regarding their sensitivity to thermal medium pretreatment possibly accompanied by the alteration of their chemical composition, such as the formation of Maillard reaction products (MRPs). This study reveals a quite diverse and different growth behavior of those strains in the form of altered or non-altered cell concentrations and the size distributions of the populations, whereby five strains of the L. delbrueckii group in particular showed increased cell concentrations combined with decreased mean cell volumes. The results are of both scientific and industrial relevance, as they highlight the necessity to consider and understand the effects of media sterilization for the applied production strain.

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