Abstract: The natural fermentation of millet is difficult to control. This study aimed to compare the physicochemical properties of naturally fermented millet starch and those fermented by the dominant microbes lactic acid bacteria and yeasts isolated from naturally fermented millet for the purpose of better understanding the mechanism of the natural fermentation of millet and providing a theoretical guideline for controlling the process. Starches were extracted from three different fermented millet samples with 0.2 g/100 mL NaOH and measured for solubility, swelling power, transparency, thermal properties and viscosity characteristics. The results demonstrated that, the solubility, swelling power and transparency of all three millet starches were decreased with fermentation time, and the transparency of millet starch fermented by lactic acid bacteria and yeasts were decreased by 1.4% and 1.0% compared with natural fermentation. The gelatinization temperature of millet starch subjected to lactic acid bacterial fermentation and yeast fermentation for 96 h were decreased by 1.84 ℃ and 1.13 ℃, respectively compared with natural fermentation, the peak temperatures were decreased by 1.04 ℃ and 0.43 ℃, respectively, the final temperatures were reduced by 3.69 ℃ and 2.85 ℃, respectively, and the enthalpies were increased by 1.00 J/g and 0.78 J/g. respectively. In addition, lactic acid bacterial fermentation and yeast fermentation resulted in a decrease in breakdown viscosity of millet starch of 978 and 743 mPa·s and a decrease in setback of 400 and 471 mPa·s as well as an increase in peak viscosity of 185 and 103 mPa·s, respectively in comparison with natural fermentation. In conclusion, fermentation with the dominant microorganisms of lactic acid bacteria and yeasts isolated from naturally fermented millet could significantly modify the physicochemical properties of millet starch compared with natural fermentation.

Key words: millet starch, fermentation, lactic acid bacteria, yeast, physicochemical properties