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.

Properties of heated aqueous starch dispersions dependent on the preparation conditions

“…Since the starch polymers commonly exist in the form of semicrystalline granules, which are not soluble and restricted and reversibly swellable in cold water , an aqueous suspension has to be heated to gelatinize and disintegrate . However, a complete dissolution of a native starch without molecular degradation, as discussed for example for DMSO as solvent or alkaline conditions elsewhere , is not possible. Different molecular structure and size, distribution and participation within the semicrystalline granule structure as well as different availability for water are reasons for the incremental release of the starch fractions AM and AP from the granule during the heating phase of the aqueous dispersion .…”

Molecular Dispersion of Starch as a Crucial Parameter during Size-Exclusion Chromatography

“…When DMSO/water solution (90:10, v/v) was used to obtain starch dispersion prior to aqueous SEC the recovery was also not improved (41% recovery for corn starch) [53]. Dispersion of potato starch for 2 h in 1 M alkali aqueous solution at 25 • C yielded recovery rates of 85% during organic (DMSO) SEC [46].…”

“…Starch samples of 30 mg were allowed to disperse in 4.5 mL of urea (2.3 M)/NaOH (1 M) aqueous solution [31] at 0 • C for 24 h and then were neutralized with 0.5 M H 3 PO 4 and diluted with the mobile phase used for SEC separation. Results for corn starch were compared with other alkaline dispersion methods which employed 0.5 or 1 M NaOH [45] or 2 M KOH [46,47] at 65 • C and stirring with a magnetic bar at 400 rpm. Briefly, 30 mg of starch were wetted by 50 µL of ethanol to prevent lumping.…”

Microstructural Changes and In Vitro Digestibility of Maize Starch Treated with Different Calcium Compounds Used in Nixtamalization Processes

“…Starch treated with Ca(OH) 2 showed faster hydrolysis than starch treated with CaCl 2 and CaCO 3 . Previous results by Ulbrich et al [11] indicated that alkali treatment induces starch dissolution under mild temperature and concentration conditions, an effect that was reflected as significant reductions of the molecular weight of starch chains via the breaking of intermolecular hydrogen bonds. Similarly, Lobato-Calleros et al [10] showed that alkali treatment of starch chains led to reduced starch molecular weight.…”

“…This effect was reported for lime treatment of maize starch. [10] Ulbrich et al [11] showed that alkali (e.g., KOH and NaOH) treatment was able to dissolve potato starch within 2 h under mild temperature and concentration conditions. It was shown that alkali treatment led to significant reductions of the molecular weight of starch chains via the breaking of intermolecular hydrogen bonds.…”