The role of microwave absorption capacity and water mobility in the microwave treatment of grain vs. flour: Impact on the treated flour characteristics

Abstract

Four alternative crops (amaranth, buckwheat, quinoa, and sorghum) were subjected to microwave-assisted heat-moisture treatment (MWT) under identical conditions (100 °C for 30 min at 25% moisture content) in two different forms (grain and flour). The effects of MWT on the microstructure, thermal properties, and techno-functional properties of the resulting flours were evaluated. The microwave absorption capacity and water mobility in flours and grains during heating were also determined to explain the different impacts of MWT depending on the matrix and its form. The results revealed that the microwave absorption capacity was comparable for all the samples, with water being the primary microwave-absorbing component. However, a different mobility and distribution of water during heating were observed for grains and flour and among matrices, leading to variations in the properties measured. The matrix, the form of treatment, and their interaction significantly influenced most of the analysed properties. MWT resulted in disruption of the native structure with partial fusion and loss of integrity of constituents, reduction in gelatinisation enthalpy, increase in the extent of amylopectin retrogradation, increase in water absorption capacity, and decrease in emulsifying capacity. The water absorption index and water solubility index showed increments or decrements depending on the matrix and the form of treatment. Moreover, the MWT of grain proved effective in limiting the colour change observed in the MWT of flour while enhancing the water absorption capacity. These findings highlight the importance of controlling not only the MWT conditions, but also the form of the matrix, as this influences the mobility of water and the final flour properties.