Effects of ginseng stem and leaf extract fermented by Lactobacillus casei on growth, immunity and antioxidant function of Carassius auratus

As a major ginseng cultivator, China is among the top countries in the world in terms of total ginseng production each year. In order to diversify the use of ginseng resources, scholars have begun to study the pharmacological effects and active ingredients of ginseng stems and leaves. Studies have confirmed that probiotic fermentation of Chinese herbal medicine can significantly improve its efficacy, and the efficacy of fermented ginseng is better than feeding ginseng alone, and it has been concluded that ginseng can be fermented to improve its biological activity and enhance its efficacy after fermentation. However, not all microorganisms are suitable for fermentation of Chinese medicine, and the degree of suitability of microorganisms and Chinese medicine needs to be further explored. The application of fermented ginseng stems and leaves to aquatic animals has not been reported, and the research on the aptamer used for fermenting ginseng stems and leaves still needs to be studied. In order to study the effect of ginseng stem and leaf extract fermented by Lactobacillus casei on the immune and antioxidant function of Carassius auratus, the stem and leaf extract of ginseng was fermented with L. casei liquid of 3%, 4%, 5% and 6% (recorded as L3, L4, L5 ,L6), and then added to the basic feed (recorded as L0). The C. auratus with an initial average weight of (25.00±0.05) g was fed for five weeks. Periodic samples were collected from the serum, hepatopancreas, middle kidney, spleen and whole intestine of the C. auratus to detect the changes of relevant immune indexes. A protective test for Aeromonas hydrophila attack was performed at the end of the feeding trial. The results showed that alkaline phosphatase (AKP), immunoglobulin M (IgM), lysozyme (LZM), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities were significantly higher in the group with L. casei seed inoculation of 5% (L5 group) compared with the control group, and malondialdehyde (MDA) activity was significantly lower in the L5 group than in the L0 group. The gene expression levels of IL-10, TNF-α, TGF-β, IFN-γ, and IL-1β were elevated to different degrees in all tissues, showing spatial and temporal differences, with the elevated gene level expression of IL-10 being more sensitive.In the protective attack test, the L5 group had a survival rate of 30%, the highest survival rate compared to the other groups.Under the present experimental conditions, when the inoculum of L. casei was 5%, the fermentation of ginseng stem and leaf extract was the most effective for the application to C. auratus , which could improve the antioxidant capacity and the expression of immune-related genes, and had a better preventive effect on reducing the infection of A. hydrophila. This experiment adheres to the concept of turning waste into treasure and green safety, which provides a theoretical basis for the application of probiotic fermentation of traditional Chinese medicine in practical production.