Effect of the drying process on the color change, fissure development, and morphology of fortified rice kernels

Abstract

AbstractFortified rice kernels (FRK) were manufactured using extrusion technology and dried in a hot air tray dryer. The present study was aimed to find the effect of air temperature (40, 50, 60, and 70°C) and the drying time (0–160 min) at 1.0 m/s air velocity on color attributes of FRK. The increase in temperature and time decreased the L* and WI and increased the a*, b*, and ΔE values of FRK. The kinetic modeling suggested a fairly good fitting of the quadratic model for ΔE and WI. The Page model (R2 ≥ 0.9512, RMSE ≤ 0.0556, and χ2 ≤ 0.0037), as an alternate approach, showed the best fitting to predict the color change ratio of FRK. For fissure and morphological analysis, the FRK were dried to a final moisture content of 12–13 %wb at each drying temperature. The results revealed that the drying at 50–70°C formed fissure inside the FRK and was confirmed by the X‐ray CT scan images. However, the scanning electron microscope (SEM) image analysis did not show any fissure at the surface of FRK. Thus, the lower temperature (40°C and 120 min) drying resulted in better color attributes with no fissure inside the FRK.Practical applicationsFRK are being used to blend in the normal rice in the 1:100 ratio to prepare micronutrient fortified rice. It is expected that the FRK should be indistinguishable in normal rice after blending. Color is an important parameter that could make easy detection of FRK in normal rice. This makes it necessary to match the characteristics of FRK with normal rice in terms of color, physical dimensions, and density. Moreover, fissure formation in FRK leads to disintegration during cooking. Therefore, the study's findings will help to get an idea about the color change during the commercial drying of FRK and decide the drying conditions that will not develop fissure inside the FRK.