Abstract: In this study, we investigated the effect of natural fermentation on the gel properties and molecular structure of millet starch, aiming to provide a scientific and theoretical basis for the study of the mechanism of the modification of millet starch after fermentation for mechanized and industrial production of fermented millet products. Changes in the molecular structure and gel properties of millet starch (the ‘Huangjinmiao’ variety from Inner Mongolia) were examined after 144 h of natural fermentation. The results were showed that the surface of fermented starch granules was eroded, whereas the crystalline?structure did not change and remained A-type. The position of X-ray diffraction peaks of starch granules did not change after fermentation, but the peak intensity was reduced. Moreover, the weight-average molecular?mass of both region Ⅰ (amylopectin) and Ⅱ (amylose) was decreased from 2.5 × 104–5.9 × 105 to 2.2 × 104–5.4 × 105 g/mol and the number-average molecular?mass was increased. The setback, peak viscosity of millet starch were decreased by 425 and 470 mPa·s as compared to those before fermentation, gelatinization temperature and enthalpy value were increased by 1.62 ℃ and 7.05 J/g, and gel hardness and elasticity were decreased by 60.735 g and 0.707, respectively. After fermentation for 96 h, the gel properties of starch tended to be stable. The findings revealed that both the molecular structure and gel properties of millet starch after natural fermentation were changed, being more suitable for the production of starch products with resistance to retrogradation.

Key words: natural fermentation, starch, gel properties, molecular structure