Alkaline dissolution of native potato starch − impact of the preparation conditions on the solution properties determined by means of SEC-MALS

Abstract

The preparation of molecularly dispersed solutions of starch for the characterization by means of size exclusion chromatography–multi angle laser light scattering (SEC-MALS) was investigated. Solutions were prepared by pasting granular native potato starch using strong alkali at 25°C, neutralization and subsequent dilution in DMSO with the objective of ideally complete dissolution and simultaneously absence of molecular degradation. Process parameters such as type of alkali (KOH and NaOH), starch concentration in the alkaline dispersion (1.25 and 2.50%), dissolution time (0.5, 2, and 24 h), high shear treatment of the neutralized paste (Ultra-Turrax at 0.625 and 1.25%; speed: 11 000 and 24 000 min−1; duration: 2 and 4 min) and applying an aftertreatment following dilution to final concentration (0.125 and 0.250%; stirring) were systematically varied and impacts on SEC recovery rate and Mw of the starch examined using two experimental designs. Besides high reproducibility of the molecular data obtained, the laboratory-scale preparation method provided basically very good solutions. Most factors were significant and detailed conditions ensure that a high degree of a dissolved amount and simultaneous minimal molecular degradation were identified. Solutions containing 0.250% starch with applied aftertreatment gave best results (Mw between 40 × 106 g/mol (KOH) and 35 × 106 g/mol (NaOH); corresponding SEC recovery rates of 85% or higher). A pasting duration of 2 h was found to be sufficient for nearly complete dissolution. Including a high shear treatment, the preparation process was characterized by a compromise on the achieved solution state and accompanied molecular degradation. The investigated procedure represents a suitable alternative to current existing methods.