Starter cultures for sourdough production: rational selection, mixed-strain starter cultures, and strain monitoring

Sourdough is a flour-water mixture fermented by lactic acid bacteria (LAB) and yeasts. The addition of starter culture strains allows steering the fermentation process toward sourdoughs with tailored properties. However, the rational selection of candidate starter culture strains for sourdough production is of crucial importance, yet challenging. This review aimed to (i) describe the microbial diversity of non-starter culture-inoculated sourdoughs as source for starter culture strains for future use, (ii) examine LAB and yeast metabolism (carbohydrate, amino acid, and ester metabolism) and sourdough bread characteristics (flavor, rheology, nutritional and other health properties) as a target to screen and select strains, (iii) explore the interactions between LAB and yeasts and their implications for the use of starter cultures, and (iv) discuss how the different process parameters (raw material, oxygen, fermentation and storage duration and temperature) should be adapted for different starter culture strains. Furthermore, the techniques available for strain selection and starter culture strain monitoring are summarized, highlighting their current use, their challenges, and perspectives. Overall, a successful starter culture-initiated sourdough production process requires rational strain selection encompassing multiple complementary techniques and optimized process conditions. In addition, mixed-strain starter cultures, composed of LAB and yeast strains, show potential for enhancing sourdough quality.