Viscous gel-forming gums (VGUMS) of cereal grains: Rheology and viscosity-based enzyme activity quantification
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The rheology of viscous-gel forming gums (VGUMS) extracted from cereal grains (barley, oat, wheat) by using alkaline or acid solutions was investigated in this study. Molecular weight (Mw), viscosity average molecular weight (Mv), overlap concentration (C*) and intrinsic viscosity [η] of VGUMS were predicted by viscosity calibration assays using a reference sample with known Mw. The Mw, Mv, C* and [η] were significantly (P < 0.05) affected by temperature, solvent type, dilution rate and grain type, but all the values were within acceptable limits of previously reported values. The use of Mark-Houwink equation was very powerful and successful to predict Mw(s) of VGUMS from viscosity measurements. The present results indicated that the C* should be considered in the viscosity based enzyme activity quantification in order to avoid a systematic error in the measurement caused by the effect of volumetrically diluted substrate concentration in the solvent. Furthermore, the cellulase activity of a reference enzyme and unknown enzyme sample was well predicted by this viscosity-based quantification method, with acceptable precision and recovery rate. It can be concluded that the rheology of both acidic and alkaline VGUMS provide important information on grain quality and quantification of enzyme activity, which are useful for the industry. © 2016 Elsevier Ltd.