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 (Mw), and radius of gyration (Rg). 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 (ηc) and no yield stress (σoc). Mw 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 ηc but, simultaneously, they showed non-zero σoc values, and σoc, Mw and Rg of starch selenate were reagent concentration dependent. Also magnitudes of n, K, ηc, σoc, Mw and Rg of pastes of starch silicate after sodium metasilicate and zincatate were reagent concentration dependent. While their n rose with concentration, K and ηc significantly decreased, and σoc ceased. The effect of temperature on the apparent viscosity of modified starch pastes followed Arrhenius equation.

► The rheological properties of potato starch chemically modified were characterized. ► Sulfation and boration with boric acid lead to acidic decomposition of starch. ► The viscosity and K, ηc and σoc values of these modifications decrease. ► Silication, selenation, zincatation lead to alkaline decomposition and crosslinking of starch. ► The viscosity and K and ηc of these products decrease but their σoc increases.