Synergistic Impact of Lactobacillus plantarum and Bacillus coagulans on Solid-State Fermentation of Astragalus and Effects of Fermentation Products on Disease Resistance of Crucian Carp (Carassius auratus)

Abstract

Dietary supplementation with fermentation products of Astragalus can enhance the immune function of aquaculture animals. We explored the synergistic effects of Lactobacillus plantarum and Bacillus coagulans on the solid-state fermentation of Astragalus to investigate whether feeding fermentation products to crucian carp can improve disease resistance. The optimal ratio of Astragalus + (L. plantarum + B. coagulans) (ALB), temperature, and number was 3 : 3, 37°C, and 1.0 × 108 CFU/g, respectively. After 48 h mixed fermentation, the number of probiotics increased to 2.2 × 109 CFU/g, pH decreased to 3.2, and high molecular weight proteins disintegrated into small molecular weight or soluble proteins. In addition, several holes appeared on the Astragalus surface. Compared with unfermented Astragalus, the content of Astragalus polysaccharide and calycosin increased by 3.82- and 1.31-fold, respectively, on fermentation and that of total Astragalus saponins decreased by 0.77-fold. Furthermore, on Cyprinid herpesvirus 2 (CyHV-2) and Aeromonas veronii (A. veronii) challenges, the cumulative survival rates of crucian carp fed common feed and ALB were 80.00% and 65.00%, respectively. Overall, feeding mixed fermentation products to crucian carp positively impacted their health and disease resistance. We believe that our results provide theoretical guidance for developing effective plant-based agents to prevent diseases in crucian carp.