Abstract
Sourdough fermentation as one of the most ancient and traditional biotechnologies, has profound effects on rheology, sensory and shelf life attributes of leavened baked goods. Thirty years of knowledge on sourdough has been accumulated providing deeper insights into the process technology along with enhancing the nutritional features of sourdough bread. While some aspects such as the potential to lower glycemic index, increase mineral bioavailability and decrease the gluten content have been proven almost definitively, other potentialities are emerging, which deserve novel insights. This thesis focuses on the effects of the sourdough biotechnology on the exploitation of new cereals like ‘Tritordeum’ (Triticum durum (durum wheat) х Hordeum chilense (wild barley)) and conventional and organic wheat and rye flours. Tritordeum, a novel hybrid cereal, is sustainable by nature and well-documented for combining the nutritional benefits of durum wheat and wild barley. The preparation and propagation of Tritordeum sourdough by traditional type I sourdough fermentation were investigated to study the microbiota dynamics and the changes of biochemical and nutritional features. Under controlled conditions, Tritordeum sourdough reached maturity by day 5 with Lactiplantibacillus plantarum and Saccharomyces cerevisiae as the dominant lactic acid bacteria and yeast species, respectively. The acidification of sourdough reflected positively on the fermentation quotient (FQ) (molar ratio of lactic acid and acetic acid), which was close to the optimal values. Moreover, utilization of glucose, fructose and sucrose was found from fourth day onwards which in turn determined a progressive increase in mannitol concentrations. The sourdough fermentation positively afftected the profile of nutritional features (total phenol content, antioxidant activity, dietary fiber content and total free amino acids) and that of antinutritional factors (phytic acid and raffinose). In addition, Tritordeum sourdough bread (SDB) showed better rheology and texture as compared to the bread made with baker’s yeast (BYB). Furthermore, both Tritordeum breads (SDB and BYB) were investigated for their effects on the human gut microbiota and immunomodulatory properties. Breads were subjected to in vitro digestion (INFOGEST protocol) followed by 24 hours faecal fermentation of digested breads to simulate the human digestion. Changes in gut microbiota and release of microbial metabolites were determined at 0, 5, 10 and 24 h. The faecal fermentation with SDB and BYB substrates indicated substrate-dependent changes in the gut microbiota with the increased relative abundances of Bifidobacterium, Megasphaera, Mitsuokella, and Phascolarctobacterium. While minimal differences were found between 3 the two substrates in the gut microbiota structure, the microbial metabolites showed significant (P<0.05) differences between the substrates. Short chain fatty acid (SCFA) concentrations, specifically acetic and butyric acids, were significantly increased after 24 h with SDB as compared to BYB, while most of the amino acids, their derivatives and sugars were depleted by the end of batch culture faecal fermentation. Additionally, the fecal fermentation supernatants were analyzed for their immunomodulatory effects through in vitro cell culture models. The integrity of intestinal barrier was investigated under exposure to SDB and BYB substrates by determining transepithelial electrical resistance (TEER) measurements across Caco-2 cell monolayer. Additionally, the release of pro- (IL 1β, IL-6, TNF-α) and anti- (IL-10) inflammatory cytokines was assessed during the in vitro Caco-2/PBMC co-culture experiment. The membrane integrity was significantly enhanced with SDB whereas the cytokine release did not differentiate between the immune function of the test breads. While our findings give insights into the functional potential of sourdough baked goods, further studies should be conducted using laboratory animals and human intervention trials to get better insights into the human gut physiology. Nevertheless, this thesis highlights the role of sourdough in improving the functional and nutritional features of leavened baked goods and encourages the use of sourdough in the commercial baking industry.