Effect of drying method on rheological, thermal, and structural properties of chestnut flour doughs

Abstract

The objective of this work was to characterize the functional, thermal and rheological properties of chestnut flour doughs produced through freeze-drying (FD) and tray-drying (TD) process. Drying method did not influence the physicochemical properties (e.g. bulk density, water holding capacity and sediment volume fraction) of chestnut flour however affected both particle mass distribution and color values (a and b) significantly. Thermal analysis of chestnut doughs showed two distinct peaks attributed by starch gelatinization and melting of starch–lipid complex, respectively. Although there were only minor differences in the total starch contents between two chestnut flour, they displayed significant variability in pasting properties and oscillatory rheology during heating. The amylograms of the chestnut dispersions showed higher maximum viscosity and heat stability for the FD sample, as well as a higher tendency to the molecular re-association during cooling than for the TD flour. Pasting properties of chestnut doughs were well described by rheometric measurement and data obtained through both measurements are comparable. The chestnut doughs exhibited predominating solid-like property (G′ > G″). The mechanical rigidity (G′) of doughs significantly influenced by the concentration and the increase in G′ with concentration was well described by a power-type relationship. The chestnut granules exhibited a range of shapes, varying from round, oval, rectangular to irregular. Average particle diameter of the tray-dried sample was larger than the freeze-dried sample. This study provides in-depth knowledge on structural/rheological properties of chestnut flour by two drying processes, which would be helpful for selection of ingredients and their application in food industries.