The Effect of Fermentation and Extrusion on the Microbiological Composition of Millet and Defatted Soybean Blends

Aims: To evaluate the effect of fermentation and extrusion on the microbiological properties of Millet and defatted soybean blends and to determine the storage stability of the plant product.

Methodology: Flour blends were prepared from millet and defatted soybean and at different proportions (100, 90:10, 80:20, and 70:30). A portion of the blends was extruded, and the other portion was preconditioned (using solid state fermentation method) and then extruded in a laboratory single screw extruder.

Results: The pH of the raw flour blends during fermentation, recorded a decrease from a range of 9.2-9.3 at day 1 (0 hour) to a range of 6.6 - 6.8 at day 4 (72 hours). Bacillus cereus, Bacillus subtillis, Enterococcus sp., Micrococcus sp. and Lactobacillus sp were isolated during fermentation. Also in the fermenting flour were some microorganisms which may not have played any part in the fermentation process such as Pseudomonas sp., Proteus sp., and coliforms (Enterobacter sp. and Klebsiella sp.). The microbiological load as measured by the total plate count per gram of the extrudates was generally low in all the extrudates stored at room temperature (35+2°C). The total plate count at room temperature steadily increased (0-20 days). The total plate count of the extrudates at day 0 showed an initial total plate count of 2.06×104-2.72×104CFU/g in the extruded (E) blends and 1.48×104-3.68×104CFU/g in the fermented-extruded (FE) blends. Highest count was observed in both extrudates in E3 and FE3 with 2.72×104CFU/g and 3.68×104CFU/g respectively.

Conclusion: The extrudates were stable under the storage condition investigated in this study.