Effects of different fermentation treatments on the processing characteristics of maize flour and starch granules structure

Abstract: Maize is one of the most important crops in the world. However, only 5% of the total production can be used as food rich in nutrients after processing. This study aims to determine the effect of fermentation treatments on the processing characteristics and starch granules of maize flour, in order to improve the application of maize in the food industry. Specifically, an emphasis was focused on the effects of fermentation starters and treatments on the hydration characteristics, gel properties, and appearance of the product. The thermal properties, size distribution, and microstructure of starch were further analyzed with the differential scanning calorimeter (DSC), laser size detector, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectrum. A mixed fermentative agent was selected to combine the Lactobacillus plantarum, rice leaven, and Lactobacillus plantarum in the treatment. The results showed that there were some significant effects of fermentation conditions on the processing characteristics of maize flour. The 24 h Lactobacillus plantarum fermentation treatment significantly reduced the water binding capacity, water absorption index, and water solubility index, where the swelling power of maize flour was reduced by 9.87%, 10.7%, 35.2%, and 13.0%, respectively. The yellowness of samples decreased, as the fermentation time increased. The overall color of maize flour was much whiter than that of the raw material after fermentation treatment. There was also more beneficial for the application of maize flour in food with higher color requirements. Along with the progression of fermentation up to 36 h, the brightness was increased by 7.41% when inoculated with Lactobacillus plantarum and rice leaven, and then inoculated with the Lactobacillus plantarum. Mixed fermentation of maize flour resulted in an increase in the water absorption index and swelling power relative to Lactobacillus plantarum fermentation alone, indicating an important effect on the paste-forming properties and the sticky-tooth feel of maize foods. The 24 h fermentation of maize flour with the Lactobacillus plantarum resulted in a 25.8% decrease in enthalpy value. Specifically, there was a much more increase in the enthalpy of the raw material than the single strain fermentation, with the inoculation of rice leaven for 12 h, followed by the inoculation of Lactobacillus plantarum for the mixed fermentation treatment. The highest enthalpy was obtained for the maize flour with a total fermentation time of 36 h. The volume average particle size of maize flour was significantly reduced when the total time was 36 h. There was no change in the position of functional groups of maize starch during fermentation treatment, but the changes were observed in the intensity of some absorption peaks. Therefore, the fermentation treatment posed a great influence on the degrees of order and double helix, particularly with a greater effect of mixed strains fermentation. The SEM images showed that the fermentation treatments destroyed the structural integrity of starch grains in the appearance of holes and cracks on the surface of particles. Specifically, the fermentation of a mixture of rice leaven and Lactobacillus plantarum also damaged the structure of maize starch to a greater extent than that of Lactobacillus plantarum alone, indicating the outstanding influence on the hydration properties and other processing characteristics of the maize flour. The mixed fermentation of Lactobacillus plantarum and rice leaven provided a new idea to improve the processing properties of maize flour. The changes in the fermentation treatment were closely related to those in the starch, indicating the processing characteristics of maize flour. Consequently, the fermentation technology can be expected to treat the maize flour for optimal hydration properties. The fermentation-treated maize flour can also perform better in baked goods, noodles, Jiaotuan, maize paste, and other food products. Anyway, the finding can offer a strong reference to further broaden the more rational application of maize flour in the food field.