378 Bulletin UASVM Agriculture, 68(2)/2011 Print ISSN 1843-5246; Electronic ISSN 1843-5386 Rheological Evaluation of Some Commercial Xylanases Mihai OGNEAN, Claudia-Felicia OGNEAN, Neli DARIE “Lucian Blaga” University from Sibiu, The Faculty of Agricultural Sciences, Food Industry and Environmental Protection, Sibiu, Romania, 5-7, Ion Raiu Street, Sibiu, 550012, Romania, mihai.ognean@ulbsibiu.ro Abstract. The arabinoxylans play and the xylanases play an important role breadmaking. For a better selection of xylanases, it is necessary to understand how they work in breadmaking. At the same activity, the xylanases have different effect on dough rheology. The xylanases activity measured through birch xylan hydrolysis it is not correlated with extensographic effects. Weak but better correlations were observed when the xylanase activity was measured as the ability to decrease the viscosity of soluble wheat arabinoxylans solution. Keywords: arabinoxylans, Extensograph, breadmaking, wheat flour, dough. INTRODUCTION Arabinoxylans (AX) are polysaccharides with a complex structure and their sources is cell wall. They represent the main nonstarch polysaccharides of wheat and wheat flours, 1.4 to 2.1 (Izydorczyk et al, 1991). AX have complex structures which determine their different properties. One of the most important properties is their solubility / extractability, Delcour and Courtin (2002) classify the AX according to their extractability and the main important categories are water extractable arabinoxylans (WEAX) and water unextractable arabinoxylans (WUAX). Despite they represent only a minor fraction of flour weight AX play an important role in breadmaking. The most important properties of AX is the ability to bind large amount of water (Bushuk , 1966)(Autio, 2006) (Maeda and Morita, 2003) and to increase de viscosity of solution (Udy, 1956)(Autio, 2006)(Rybka, 1993)( Izydorczyk et al, 2001). Also they present surface activity (Izydorczyk et al, 1991) and are implicated in oxidative gelation due the small amount of ferulic aacid contained (Geissman and Neukom, 1973) (Carvajal-Millan et al, 2005) (Ciacco and D’Appolonia, 1982). Despite their very similar structure the AX have opposite impact on breadmaking according their solubility / extractability in water. WEAX have positive effect on bread (Redgwell et al, 2001) (Graybosch et al, 1993) (Hoseney, 1994), (Gan et al, 1995) (Jelaca and Hlynka, 1971) (McClearly et al, 1986). The WUAX have negative impact on bread properties (Gan et al, 1995), (Courtin et al, 1999), they stimulate the pore coalescence and reduce the gas retention in dough. The positive role of AX in human nutrition was demonstrated. The AX and especially the oligosaccharides obtain by hydrolysis of AX present prebiotic properties (Grootaert et al, 2007) (Crittenden et al, 2002) (Madhukumar and Muralikrishna , 2010). Because of nutritional benefits of fibres it is recommended to consume whole or black bread with a larger content of AX than white bread. The consumer are reticent about these breads because their poor consuming quality. The higher amount of WUAX from whole and black wheat flours lead to poor quality of breads so it is necessary to convert the WUAX with bad effect in WEAX with a good effect on bread quality. This conversion it is possible by enzymatic