EFFECT OF PARTICLE SIZE, BLENDING RATIO, AND FERMENTATION TIME ON PHYSICOCHEMICAL, RHEOLOGICAL PROPERTY AND QUALITY CHARACTERISTIC OF INJERA

Abstract

"Injera," a thin fermented Ethiopian flatbread, is typically made from teff, along with other cereals and low-cost alternatives like root crops. The quality of the flour (functional, pasting properties, color, and particle size distribution), the properties of the sourdough (viscosity), and the final quality of injera (firmness and the number of injera "eyes") are crucial in the manufacturing injera. These characteristics can be influenced by factors such as the particle size of the flour, the proportion of kocho flour, and fermentation time. In this study, three particle sizes (0.125, 0.1, and 0.075mm), blending ratios (10%, 20%, and 30%), and fermentation times (24, 48, and 72 hours) were selected. The study explored a significant effect of particle size, blending ratio, and fermentation period on all parameters. Results indicated that finer flour particles and 30% kocho blend flours had significantly higher functional (BD= 0.94g/ml, WAC= 2.10g/g, SP= 6.81g/g WSI= 6.33% and BD= 0.81g/ml, WAC= 2.17g/g, SP= 7.04g/g WSI= 7.23%) and pasting properties such as PV, TV, BDV, FV, and SBV (1258, 765, 494, 1751, and 987cp and 1377, 1013, 366, 2117, and 1106cp). The color values, L*, a*, and b*, showed significant variations based on particle size, with the L* value decreasing and the a* and b* values increasing respectively increasing flour particles. However, the L* value for color in both the kocho blend samples was similar. The interaction effect of particle size and fermentation time had a significant effect on the sourdough viscosity and injera quality, including the number of eyes, firmness, and sensory attributes. Blending kocho into teff slightly affected the viscosity of sourdough, but significantly altered injera texture, reducing its firmness and increasing the number of injera eyes. Furthermore, this study aimed to optimize the particle size of teff flour, fermentation period, and kocho blending ratio, using a central composite design (CCD) within a response surface methodology (RSM) module A significant quadratic model was identified for particle size and fermentation time concerning viscosity (R2 = 0.97), firmness (R2 = 0.97), and number of eyes(R2= 0.97). Similarly, blending ratio and fermentation time showed significant quadratic models for viscosity (R2 = 0.96), firmness (R2 = 0.98), and number of eyes (R2 = 0.91). The optimized parameters were identified as follows: teff flour particle size of 0.11mm, fermentation time of 53.1 hours, Koch blending ratio of 30% with teff flour at 70%, and a fermentation duration of 33 hours.