Effects of sour soup on silage fermentation performance and bacterial community of Broussonetia papyrifera

Sour soup is a traditional fermented food, enriched with abundant organic acids, minerals and other nutrients, which contribute to human and animal health. However, due to more consumer rejection of products caused by opportunistic contamination and sulfur-containing compounds during the spontaneous fermentation of sour soups, therefore, the development and utilization of sour soup additives can be tried, such as silage improvement applications. The purpose of the current study was to evaluated the effects of sour soup as an anaerobic fermentation additive on the fermentation characteristics, microbial diversity, community composition, and alkaloids of Broussonetia papyrifera. To compare the effects of sour soup additive on Broussonetia papyrifera silage, we selected two additives, Lactobacillus acidophilus (LAB) and sour soup (S), and no additive treatment (CK). The results indicated that additives treated with L. acidophilus and sour soup exhibited higher levels of crude protein (CP), WSC, and acetic acid (AA), as well as lower levels of neutral detergent fiber (NDF) and pH compared to the control silage, sour soup treatment has the best improvement effect on fermentation quality. Additions of L. acidophilus and S increased the abundance of Lactobacillus and decreased bacterial Shannon diversity index. Alkaloid analysis indicated that L. acidophilus additives increased the betaine content (beneficial alkaloids) of the fermentation, while the impact of sour soup additive was not great. Our structural equation model (SEM) demonstrates that the reduction in pH, induced by additives, is the primary driving factor behind the increase in silage protein and betaine content, as well as the decrease in bacterial diversity. This study showed that the addition of sour soup can be used as an additive to improve the quality of Broussonetia papyrifera silage fermentation, but its regulatory effect on bioactive substances (such as alkaloids) still needs further research.