Acid-thinned corn starch-impact of modification parameters on molecular characteristics and functional properties

Abstract

Acid-thinned corn starches were prepared systematically by varying acid concentrations (0.09–0.72 M HCl) and hydrolysis times (4 and 24 h). The relationships between modification parameters, molecular starch structure, and functional properties were investigated. The carbohydrate solubilization was significantly enhanced with increasing acid concentration only in the long-term process. SEM micrographs revealed the preservation of the granular structure and the thermal properties changed only moderately applying different hydrolysis conditions. Molecular characterization using SEC-MALS (size exclusion chromatography-multi angle laser light scattering) showed a strong degradation of amylopectin after 4 h of hydrolysis. Enzymatic debranching prior to the analysis and separation of the amylose peak using deconvolution enabled the calculation of MMD curves of the acid-thinned amylose fraction. The data gave evidence of extensive molecular degradation of the amylose with increasing acid concentration when hydrolyzed for 24 h. The hot paste viscosity decreased with decreasing Mw and the sol-to-gel-transition temperature was found to be strongly dependent on both, the Mw of the starch as well as the amylose fraction. The correlation between molecular properties and gel strength gave evidence of an optimum degree of hydrolysis. Acid-thinning of the starch to Mw of about 12 · 106–8 · 106 g · mol−1 and 3 · 105–2.5 · 105 g · mol−1 for the amylose fraction, respectively, resulted in the highest gel strength within the present study. However, differences in gel strength had only marginal impact on the gel elasticity. The peak separation permitted a comprehensive and detailed characterization of the amylose fraction. The obtained data proved the exposed role of the amylose in the gelation process of acid-thinned starches and their gel firmness. Correlations between the modification process, the molecular starch structure, and resulting functional properties were found.