Ultrasound Pretreatment of Oat and Barley Bran Contributes to the β-Glucans Content and Technological Properties of Flatbread with or Without Sourdough

Sourdough fermentation of bran can overcome the technological problems encountered in bread making but favors the activity of endogenous β-glucanase leading to a degradation of β-glucans. This study investigated the effects of high-intensity ultrasound (US) pretreatment of oat bran (OB) and barley bran (BB) on its β-glucans content, properties, and preservation in processing, as well as on the acidification kinetics of bran sourdough fermentation and on its application in flatbread. To reduce β-glucanase activity, OB and BB (15% water suspensions) were US-pretreated prior to sourdough fermentation. The acidification kinetics, the microbial viable cell count, and the total titratable acidity (TTA) of the sourdough were determined. The total β-glucans content of bran, sourdough, and bread, as well as water solubility and the molecular weight (Mw) of untreated and US-pretreated bran, were investigated. The physical properties of control wheat and composite flatbreads were compared. The US-pretreatment increased the acidification rate (30%) and TTA (51%) of OB sourdough, however, decreased the acidification rate of BB (18%). After the US-pretreatment of OB and BB, the total (11.5–12.3%) and water-soluble β-glucans (31–40%) increased while their Mw decreased (7–21.7%). In sourdough and flatbread prepared with US-pretreated OB/BB, 93–95% and 90–98% of β-glucans were retained, respectively, compared to 64–72% and 82–92% in control samples. The US-pretreatment and/or sourdough fermentation of OB and BB resulted in flatbreads of higher specific volume (8–22%) and cohesiveness (11–20%) while reduced hardness (40–55%) and chewiness (51–73%) compared to their control bread.