Effect of mixing speed and time on some textural and physicochemical properties of wheat starch gels

• Effects of mixing speed and heating time during processing on starch gels were studied.
• Mixing speed and time both had significant effects on final physicochemical properties of starch gels.
• Effect of time on textural properties was rather minor as compared to mixing speed.
• By controlling mixing speed and time one can achieve gels of consistent characteristics.

The physicochemical and textural properties of wheat starch gels prepared at different mixing speeds, 15, 150 and 350 rpm and heating times, 10, 30, and 45 min at 95 °C were studied and compared. With increasing time and mixing speed most of the textural properties of starch gels obtained from texture profile analysis and residual modulus of Maxwell model obtained from stress relaxation data decreased. The samples prepared at 15 rpm and 10 min heating had the highest hardness, springiness, cohesiveness, chewiness and gumminess values whilst, the gels prepared at 350 rpm and 45 min had the lowest values for these textural properties. The images of starch gels taken by scanning electron microscopy indicated that with increasing the time and speed of mixing, honeycomb-like structure of the gels formed larger cells with thicker cell walls. Intrinsic viscosity of the samples decreased with increasing heating time and mixing speed indicating depolymerisation of starch biopolymers. Rapid Visco Analyzer data showed reduction in cold-water viscosity of starch gels with increasing time and mixing speed. Mixing speed and time during starch pasting are determining factors of final textural properties, therefore require through control to achieve final products of consistent characteristics.