Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/19/2007
Publication Date: 5/31/2007
Citation: Schober, T.J., Bean, S., Boyle, D.L. 2007. Gluten-free sorghum bread improved by sourdough fermentation: Biochemical, rheological and microstructural background. Journal of Agricultural and Food Chemistry. 55:5137-5146. Interpretive Summary: Celiac disease is a serious illness that requires life-long avoidance of the gluten-containing cereals wheat, rye, and barley, also including relatives of bread wheat like spelt wheat, durum wheat, emmer, einkorn and the wheat-rye-crossbreed triticale. Celiac disease can now be much better diagnosed than some decades ago, and people are more aware of it. Thus, while it was regarded a rare disorder in the past, its prevalence in the U.S. and worldwide is now estimated as 0.9% and 0.4% of the population, respectively. Therefore, a growing market for gluten-free bread in the U.S. and worldwide can be expected. Sorghum grain is safe for celiacs and its use for gluten-free bread would help the celiac community to enrich their diet, as well as U.S. farmers to gain a new market for high quality, food grade sorghum. However, quality of gluten-free sorghum bread and gluten-free bread in general is not satisfactory, and profound understanding of how to improve it is lacking. The present study presents a newly developed formulation and procedure for significantly improved sorghum bread, using sourdough fermentation, and also provides information for a basic scientific understanding of the gluten-free systems to further improve these breads in the future.
Technical Abstract: This study was conducted to improve quality and theoretical understanding of gluten-free sorghum bread. Addition of 2% hydroxypropyl methylcellulose improved bread based on 105% water, 70% sorghum flour, and 30% potato starch. Nevertheless, a flat top and tendency towards a hole in the crumb remained. Sourdough fermentation of the total sorghum flour eliminated these problems. Size-exclusion HPLC demonstrated that during sourdough fermentation, proteins from the dough liquid were degraded to peptides smaller than kafirin monomers (<19 kDa). Laser scanning confocal microscopy showed aggregated protein in breadcrumb without sourdough fermentation, whereas with sourdough fermentation, only small isolated patches of protein bodies embedded in matrix protein remained. In oscillatory temperature sweeps, sourdough fermentation caused a significantly higher resistance to deformation (|G*|) after gelatinization of the above batter relative to batters without sourdough. Results suggest that a strong starch gel, without interference of aggregated protein, is desirable for this type of bread.