Energy-size relationship and starch modification in planetary ball milling of quinoa

Abstract

The effects of speed (250–450 rpm) and time (10–50 min) on milling energy (E), particle size distribution (PSD), crystallinity degree (CD), damaged starch (DS), microstructure, hydration and pasting properties of flours obtained in a planetary ball mill (PBM) were investigated. As increasing milling severity quinoa flours showed polydispersed PSD (peaks at 417, 40 and 2 μm) with a shift towards smaller size and greater dispersion (Span: 3.0–5.2) as well as particles with rounded edges and polished surfaces (SEM images). The relationship E − D50 were satisfactorily predicted by the Walker's equation. The hydration tests as function of temperature and milling conditions revealed a complex flour behavior due to differences in PSD, composition, and DS content. The increasing milling energy caused a decrease in peak viscosity (PV), trough viscosity (TV) and final viscosity (FV) of up to 36%, 29%, and 25%, respectively. Significant correlations between flour attributes were found (DS-CD, r = −0.83, p < 0.01; PV-D50, r = 0.92, p < 0.01; TV-D50, r = 0.94, p < 0.01; FV-D50, r = 0.90, p < 0.01) denoted the increase of starch degradation as milling severity rises. These results can be used to improve the manufacture and the selection criteria of quinoa flour with specific functional attributes.