Molecular characterization of acid‐thinned wheat, potato and pea starches and correlation to gel properties

Abstract

Molecular parameters and gel properties of systematically prepared acid‐thinned starch products (wheat, potato, and pea) were investigated. The impacts of acid type (HCl, H2SO4), acid concentration (0.36 and 0.72 N), and hydrolysis time (4 and 24 h) were found to be statistically significant on weight‐average molar mass (Mw) of the starch as revealed by analysis of variance (ANOVA). Especially for potato starch samples, the blue value (BV) was found to increase after short‐time hydrolysis and decrease after longer modification, indicating a reduced amount of polysaccharide chains able to complex with iodine, which was found for all products. Simultaneously, the wavelength of the absorption maximum (λmax) decreased systematically with an increasing degree of modification, giving evidence for decreasing length of linear polymer chains. Enzymatic debranching of amylopectin and dextrins and molecular characterization by means of size exclusion chromatography‐multi angle laser light scattering (SEC‐MALS) enabled the detection of Mw and the amount of amylose fraction. Generally, declining Mw of amylose was accompanied by a mass‐specific loss. Starch pastes with very good solution states were prepared in general. Pastes of the acid‐thinned starches showed dominant viscous behavior, whereat storage and loss modulus decreased with increasing degradation. Additionally, a significant reduction of the sol‐to‐gel‐transition temperature was found applying oscillation measurements. Increasing gel strength of the starch samples was detected due to acid‐thinning up to a certain degree of modification and optimal molecular parameters of the starch as well as the amylose fraction were determined resulting best strength properties. The gel clarity was reduced due to acid modification in general.