Sourdough Fermentation of Carob Flour and Its Application to Wheat Bread

Research background. Carob is widely cultivated Mediterranean plant, but its flour is scarcely used in bread-making. Previous studies investigated the quality of wheat bread with added carob flour showing discrepant results. This study aimed to investigate the fermentation performance, antioxidant activity, rheological behaviour, and baking application of carob sourdough. Experimental approach. Carob sourdough was fermented with Lactobacillus brevis or Lactobacillus fermentum combined with Saccharomyces cerevisiae for 24 h at 30 °C. At the end of sourdough fermentation number of viable lactic acid bacteria and yeast cells, titratable acidity, pH value, antioxidant activity, phenolics and sugar content of sourdough were determined. Carob flour (12 % of flour mass) or sourdough equivalent (22.5 % of dough mass) was applied in making composite partially baked frozen bread. Dough rheology was monitored using a farinograph. Rebaked bread samples were evaluated for nutritive value, physical properties, and sensory attributes using a hedonic test. Results and conclusions. By the end of fermentation, carob sourdough reached pH 4.2-4.5 and total acidity 9.9-12.3 mL of 0.1 M NaOH, sugar content was reduced for 8 g/100 g d.m, while total phenolics and antioxidant activity were increased up to 21 %, depending on the starter culture. Addition of carob flour or sourdough to wheat dough resulted in higher consistency, longer development time, and lower quality number. Regardless, bread with carob flour had significantly improved specific volume of bread. Compared with common wheat bread, carob breads had increased dietary fibre content (46 %), total phenolics (140-200 %) and antioxidant activity (240-300 %), higher shape, reduced crumbliness, unchanged firmness, and darker crumb colour. Consumers’ preference and overall acceptability scores of carob sour breads were comparable to those of wheat bread, falling into the category of 'liking very much'. Novelty and scientific contribution. To our knowledge, this is the first study that proved the feasibility of carob sourdough fermentation using mixed starter cultures, where L. brevis associated with S. cerevisiae was better adapted to the substrate than L. fermentum. The carob sourdough could be used as a natural ingredient for improvement of nutritive value and reduction of crumbliness of partially baked frozen bread.