Functional Characteristics and Stress Tolerance of Microbiota in Botswana’s Traditional Sourdoughs

Abstract

Sourdough fermentation is a traditional biotechnological process used to improve the nutritional value, flavour profile, and textural attributes of baked goods. Sourdough principal microflora is represented by yeasts, lactic acid bacteria (LAB) and acetic acid bacteria (AAB). The yeasts are primarily responsible for leavening whereas the LABs and AABs carry out the acidification of the dough and both contribute to the flavour of the resulting bread. Our previous work explored the microbial species diversity of sourdoughs in Botswana and showed the unique microbial communities involved in sourdough production from different areas in Botswana. This study is aimed at characterizing yeasts and bacterial isolates from 9 traditional sourdoughs indigenous to Botswana. Here we report the functional characterization of 21 yeasts, 9 LAB, 4 AAB, and 11 other bacteria isolated from traditional sourdough as reported in our previous study. These isolates were characterized based on their ability to assimilate different carbon sources found in flour (maltose, glucose, sucrose, fructose, raffinose and maltotriose), capability to ferment carbon sources (maltose, glucose, sucrose and fructose) in flour and ability to withstand baking associated stresses (thermal stress, osmotic stress, oxidative stress and ethanol stress). This characterization aimed to compare them with conventional baker’s yeast used in modern bread making and to assess their potential for future commercialization. Our results show that the majority of isolated S. cerevisiae strains can utilise different carbon sources, ferment them and withstand baking associated stresses. These are key baking traits poorly expressed in the conventional baker’s yeast. In contrast, the isolated LAB and AAB exhibited limited carbon source utilization. Despite the noted poor utilization of these isolates, we noticed that L. plantarum (ME1-B1), B. cereus (GT1-B1) and B. zhangzhouensis were able to withstand baking associated stresses better than all other bacteria isolates. This study shows how isolated S. cerevisiae strains and non-conventional yeasts have comparable capability to the conventional baker’s yeast, highlighting their potential as sourdough starters and prospects for future commercialization.