DisplayTitle

Milling—A Further Parameter Affecting the Rapid Visco Analyser (RVA) Profile

¹Division of Food Sciences, School of Biological Sciences, University of Nottingham, Loughborough LE12 5RD, UK. ²Corresponding author. Phone: 0115 95 16145. Fax: 0115 95 16142. E-mail: Sandra.Hill@nottingham.ac.uk

Rapid Visco Analyser (RVA) profiles were recorded for raw maize grits and two extruded nonexpanded pellets based on wheat and maize. Large differences were found between the profiles obtained when an impeller mill was used to prepare the samples compared with a disk mill. The differences were related to differences in particle properties of the ground products (particle-size distribution, particle shape, and protein content). Generally, milling the samples with the impeller mill resulted in greater starch conversion than with a disk mill. For raw maize grits, this was shown by X-ray diffraction, differential scanning calorimetry (DSC), and alkaline viscosity measurements. Several other laboratory mills were tested and all produced particulates with a sieve range of 125–212 μm that had substantially differing RVA profiles. Cooling the sample during milling did not nullify the milling effects. All the laboratory mills produced <20% of the particulates of the size range required for the RVA analysis. The mill used for sample preparation can exert a significant effect on the RVA for both raw and processed cereal samples, even if measurements are made on a defined sieve fraction.