Effect of fermentation time on the functional, thermal, pasting and microstructural properties of starch extracted from finger millet (Eleusine coracana) grains

Abstract

This study investigated the effect of natural fermentation time, specifically 0, 12, 24, and 36 hours at 30°C, on the functional, thermal, pasting, and microstructural properties of starch extracted from finger millet grains. The experimental design utilised a completely randomised approach to systematically evaluate these specific variables across different time intervals. Starch was isolated using an alkaline steeping method and subsequently subjected to a series of comprehensive physicochemical, thermal, and structural analyses. Results indicated that natural fermentation significantly enhanced water and oil absorption capacities, while swelling power and solubility progressively declined. Furthermore, the lightness of the extracted starch increased significantly, while redness and yellowness decreased, thereby improving its overall colour profile for commercial food applications. Textural analysis revealed that fermentation softened the starch gel, reducing hardness but significantly improving springiness and chewiness. Biochemically, total starch content decreased due to microbial metabolism, whereas amylose content increased significantly after 24 and 36 hours of natural fermentation. Pasting profiles demonstrated substantial reductions in peak, final, breakdown, and setback viscosities, indicating a marked decrease in retrogradation tendency. Differential scanning calorimetry showed a gradual increase in gelatinisation temperatures, with gelatinisation enthalpy peaking at 12 hours before steadily declining. Microstructural evaluations via scanning electron microscopy revealed progressive surface erosion, distinct dents, and pore formation on the granules. X-ray diffraction confirmed the retention of the native A-type crystalline pattern, though relative crystallinity marginally increased at 12 hours before steadily declining. Fourier transform infrared spectroscopy confirmed structural alterations in hydrogen bonding within amorphous regions without forming any novel functional groups. In conclusion, fermentation induces profound structural modifications primarily driven by enzymatic and acid hydrolysis. Ultimately, a fermentation period of up to 24 hours is optimal for enhancing functional attributes, improving gel elasticity, and mitigating retrogradation, thereby providing a highly viable bioprocessing strategy for diverse industrial applications.