Study on the Modification of Dietary Fiber and Degradation of Zearalenone in Corn Germ Meal by Solid-State Fermentation with Bacillus subtilis K6

Abstract

Although corn germ meal is a rich source of dietary fiber, it contains a relatively low proportion of soluble dietary fiber (SDF) and is frequently contaminated with high levels of zearalenone (ZEN). Solid-state fermentation has the dual effects of modifying dietary fiber (DF) and degrading mycotoxins. This study optimized the solid-state fermentation process of corn germ meal using Bacillus subtilis K6 through response surface methodology (RSM) to enhance SDF yield while efficiently degrading ZEN. Results indicated that fermentation solid-to-liquid ratio and time had greater impacts on SDF yield and ZEN degradation rate than fermentation temperature. The optimal conditions were determined as temperature 36.5 °C, time 65 h, and solid-to-liquid ratio 1:0.82 (w/v). Under these conditions, the ZEN degradation rate reached 96.27 ± 0.53%, while the SDF yield increased from 9.47 ± 0.68% to 20.11 ± 1.87% (optimizing the SDF/DF ratio from 1:7 to 1:3). Scanning electron microscopy (SEM) and confocal laser scanning microscope (CLSM) revealed the structural transformation of dietary fiber from smooth to loose and porous forms. This structural modification resulted in a significant improvement in the physicochemical properties of dietary fiber, with water-holding capacity (WHC), oil-holding capacity (OHC), and water-swelling capacity (WSC) increasing by 34.8%, 16.4%, and 15.2%, respectively. Additionally, the protein and total phenolic contents increased by 23.0% and 82.61%, respectively. This research has achieved efficient detoxification and dietary fiber modification of corn germ meal, significantly enhancing the resource utilization rate of corn by-products and providing technical and theoretical support for industrial production applications.

Keywords: corn germ meal; microstructural characterization; physicochemical properties; solid-state fermentation; soluble dietary fiber; zearalenone degradation.

Figure 1

Effect of filling amount and amount of NaHCO₃ added on total bacterial count. (A) The influence of filling amount on total bacterial count and moisture content. (B) The influence of NaHCO₃ on total bacterial count. Note: Different lowercase letters indicate significant differences (p < 0.05).

Figure 2

Influence of different factors on SDF yield and ZEN degradation rate. (A) Fermentation time, (B) fermentation temperature, (C) solid-to-liquid ratio. Note: Different lowercase letters indicate significant differences (p < 0.05).

Figure 3

Response surface curve graph of fermented corn germ meal. (A1) Influence of time and solid-to-liquid ratio on degradation rate of ZEN, (B1) influence of time and temperature on degradation rate of ZEN, (C1) influence of temperature and solid-to-liquid ratio on degradation rate of ZEN (A2) influence of time and solid-to-liquid ratio on yield of SDF, (B2) influence of time and temperature on yield of SDF, (C2) influence of temperature and solid-to-liquid ratio on yield of SDF.

Figure 4

CLSM microstructure observation of IDF and SDF before and after fermentation. (A₁) IDF fiber staining, (A₂) FIDF fiber staining, (A₃) SDF fiber staining, (A₄) FSDF fiber staining, (B₁) IDF protein staining, (B₂) FIDF protein staining, (B₃) SDF protein staining, (B₄) FSDF protein staining, (C₁) IDF combination diagram, (C₂) FIDF combination diagram, (C₃) SDF combination diagram, (C₄) FSDF combination diagram (50 µm).

Figure 5

SEM microstructure observation of IDF and SDF before and after fermentation. (A) IDF (3000×), (B) FIDF (3000×), (C) SDF (1000×), (D) FSDF (1000×).