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

Abstract

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.