Water binding properties of acid-thinned wheat, potato, and pea starches

Acid-thinned wheat, potato, and pea starches prepared by variation of acid type (HCl and H2SO4), concentration (0.36 and 0.72 N in a 40% w/w suspension), and hydrolysis time (4 and 24 h) were characterized in terms of water binding properties. Hydrolysis decreased the water content bound by sorption at water activity (a(W)) 1.0, at which the water was detected to be non-freezable (w(nf)) using differential scanning calorimetry (DSC). The decrease of w(nf) due to hydrolysis was in the order potato > wheat > pea starch. The modification changed the ability to certain granule swelling as well as porosity and void volume of the starch ballast affecting the water uptake based on capillary suction properties (WHCCS) and the water hydration capacity (WHCC). Decreasing WHCC was found systematically by enhancing the hydrolysis time for wheat and potato starches. Incremental molecular degradation including partial debranching in the threshold area between amorphous and crystalline regions promotes re-organization of helices near the crystallite surface reducing granule swelling.