Rheology of potato starch chemically modified with microwave-assisted reactions

Native potato starch was sulfated, selenated, borated, silicated and zincatated by means of microwave-assisted reactions with varying doses of relevant reagents. Resulting products were characterized involving rheological behavior of pastes, their weight-average molecular weight (M-w), and radius of gyration (R-g). Most of the pastes showed shear-thinning behavior, with the flow behavior index (n) below unity. The pastes of starch sulfated and borated with boric acid exhibited n higher than native potato starch paste. They had significantly lower consistency index (K) and plastic viscosity (eta(c)) and no yield stress (sigma(oc)). M-w values of these starches were considerably reduced. The pastes of starch selenate, borate after borax, and silicate after silicic acid, with n lower than native potato starch, had similarly lower K and eta(c) but, simultaneously, they showed non-zero sigma(oc) values, and sigma(oc), M-w and R-g of starch selenate were reagent concentration dependent. Also magnitudes of n, K, eta(c), sigma(oc), M-w and R-g of pastes of starch silicate after sodium metasilicate and zincatate were reagent concentration dependent. While their n rose with concentration, K and eta(c) significantly decreased, and sigma(oc) ceased. The effect of temperature on the apparent viscosity of modified starch pastes followed Arrhenius equation. (c) 2013 Elsevier Ltd. All rights reserved.