Dry-heat treatment vs. heat-moisture treatment assisted by microwave radiation: Techno-functional and rheological modifications of rice flour

Abstract

The capacity of microwave (MW)-assisted dry-heat and heat-moisture treatments to modify techno-functional properties and gel viscoelasticity of rice flour was studied. Flour samples at 30%, 20%, 15%, 13%, 8%, and 3% of moisture content (MC) were microwaved for 480 s at 18W/g. The 3% MC sample was unmodified by treatment. However, the 8% MC sample was one of the most affected, along with the 20% and 30% samples, indicating that a small amount of water can plasticize rice flour enough to rearrange its biopolymers molecules (mainly starch) responsible for the modifications. The lowest peak and breakdown viscosities and the highest pasting temperature were found in the 30% MC sample, which varied -58%, -89%, and +8ºC respectively, from native flour. DSC revealed partial pre-gelatinization in the 20% and 30% MC samples. Swelling power increased in all samples after treatment, while water solubility only increased in the 8% and 30% MC samples. Treatments promoted gel stability and enhanced viscoelastic moduli, particularly in the 8% and 20% MC samples. Flour MC in MW-assisted treatment allowed the modulation of techno-functional properties of rice flour and rheological and thermal characteristics of their gels.