Article

Oat Bran Fermentation by Rye Sourdough

Cereal Chemistry - CEREAL CHEM 01/2002; 79(3):345-348. DOI: 10.1094/CCHEM.2002.79.3.345

ABSTRACT Cereal Chem. 79(3):345-348 Hydration of oat bran including fermentation by rye sourdough was studied. Three types of oat bran suspensions were prepared (a control, one with whole meal rye flour added, and one with rye starter added). The suspensions were incubated for 1, 2, 3 and 4 hr. β-Glucan content and solubilities of protein and β-glucan were analyzed. Viscosity of the super- natants of oat bran suspensions was determined. Neither the rye sour- dough nor the rye flour alone had a significant effect on the total β- glucan content of oat bran suspensions. However, the addition of rye, either as whole meal rye flour or as sourdough starter, markedly increased the solubility of β-glucan and proteins and simultaneously decreased the viscosity of the water-soluble fraction of oat bran suspension. This sug- gests that a hydrolysis of β-glucan had occurred that could change the rheological properties of oat bran in baking and the physiological potential of oat bran in nutrition. Bread rich in oat bran is a potential daily source of soluble fiber which in oat bran is mainly (1→3)(1→4)-β-D-glucan, referred to as β-glucan. However, when using bran in baking, the rigid fiber particles of bran disturb the formation of the gluten-protein matrix (Gan et al 1989). To reduce this disturbing effect, the bran particles can be softened by hydration, thus enabling enzymatic function. Oat bran itself should be enzymatically inactive because of the kiln- drying treatment performed in the milling process. Nevertheless, hy- drating might risk activating micro-organisms and hydrolysis of β- glucan. In baking, micro-organisms such as bacilli and molds can be controlled by lowering the pH level (adding acids or by lactic acid fermentation). In oat bran baking, lactic acid fermentation would prevent harmful microbial growth and would also provide flavor to the bread. Sourdough starter could be used in oat bran hydration, especially in countries where sour rye bread is pro- duced and bakeries keep their own rye sourdough starter on hand. However, the rye sourdough starter also contains enzymes such as the endogenous hydrolytic enzymes of rye flour. These could affect the properties of the oat polysaccharides and protein. In rye baking, rye flour components in the sourdough undergo considerable change involving swelling, solubilization, and partial hydrolysis, and the breakdown products have an important role as flavor compo- nents. The aim of this study was twofold: 1) to determine the effect of oat bran fermentation by rye starter on the soluble β-glucan and protein contents in oat bran suspensions and on the viscosity prop- erties of the solubles; and 2) to evaluate the potential for β-glucan hydrolysis by the rye flour and by rye sourdough. MATERIALS AND METHODS Commercial oat bran (Melia Ltd, Raisio) was used in this study. The oat bran was ground with a laboratory pin-mill KT-30 (Koneteol- lisuus Oy, Helsinki). The particle size distribution was obtained by sieving the milled oat bran (50 g) through sieves (1.6, 1, 0.71, 0.4, 0.2) for 10 min on a laboratory Bühler-Miag sieve (Braunschweig 1977). Most of the oat bran particles (85%) were retained on apertures of 1.6 to 0.4 mm. Amounts retained by sieves 1.0, 0.71, and 0.4 were 27.4, 26.8, and 30.5%, respectively. Only 1% of oat bran particles were >1.6 mm. The remaining two fractions retained by the 0.2-mm sieve and passed through the sieve were 8.5 and 6.7%, respectively.

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