Effect of Concentration and Extraction Conditions on Wheat Water Extracts Viscosity

Abstract

SUMMARY In wheat grain, arabinoxylans are the major polymer s of cell walls, approximately 88% of wheat endosperm cell wall polysaccharides, of which one third to one half is soluble in water (Lineback and Rasper, 1988). They are formed of a linear backbone of (1-4)-linked β-D-xylopyranosyl units. The xylose generally repres ents more than 50% of the constitutive sugars and a great diversity of side chains are pre sent on the main chain on the O-2 or O-3 positions or both. In addition, acetic acid, feruli c acid and hydroxycinnamic acids, are found as esters (Saulnier et al., 2007). Arabinoxylans ex hibit different physico-chemical characteristics such as water solubility, viscosity , gelling and hydration properties, which are the basis of their functional properties in differe nt processes and food systems. Since the viscosity of a polymer solution is directly related to the fundamental molecular properties (molecular conformation, molecular weight, and molecular weight distribution) and concentration of the polymer, the study had in view the effect of the extraction conditions and the soluble arabinoxylans concentration of wheat wa ter extracts on the specific viscosity (ηsp), The water-soluble fraction was obtained using a single extraction at a ratio 1:2 (w/v), with (WE1) and without (WE2) endogenous enzyme inactivation. Dynamic viscosity measurements were made using a cone/plate viscometer (Brookfield Model DVIII Cone CP40) at 100 rpm and 25°C. Relative viscosity ( ηrel) and specific viscosity ( ηsp = ηrel‐1) were calculated. The ηsp increased with wheat concentration: from 1.08 (0 % wheat) to 1.78 (20% wheat) for WE1 and from 0.42 (0% wheat) to 0.63 (20% wheat) for WE2. The lower values suggest that soluble arabinoxylans were hydrolyzed and consequently their molecular mass reduced. The specific viscosity increased with the time the flour and water remained in contact prior to centrifugation on average with 0.4 35±0.023 for WE1 and with 0.342±0.018 for WE2 when time increased from 60 to 120 minutes. Acknowledgements : This work was supported by CNCSIS ‐UEFISCSU, project number 1055/2009 PNII ‐ IDEI code 898/2008.