Process Optimisation of Antioxidant Shuidouchi and Its Protective Effects against DSS-Induced Colitis in Mice

Intestinal health plays an important role in maintaining a high quality of life. Digestive absorption, metabolism, and mucosal immunity can decline with age, and the number of probiotics in the digestive system can rapidly decrease. Shuidouchi, a traditional Chinese fermented soybean product, involves multistep production processes that have not yet been standardised. By optimising fermentation parameters and enhancing the content of bioactive components, it can be developed into high-quality products with improved health-beneficial properties. In this study, single-factor experiments were conducted to establish different processing conditions, aiming to identify those yielding the highest levels of active ingredients and the strongest in vitro antioxidant activity. Additionally, the preventive effect of Shuidouchi against dextran sulfate sodium (DSS)‑induced colitis in mice was investigated. The results demonstrated that the optimal process conditions consisted of 12 h of soaking, fermentation in a glass container at 35 °C for 48 h. Shuidouchi produced under these conditions exhibited the highest concentration of soybean isoflavones and displayed superior antioxidant capacity compared to other fermentation conditions. The extract prepared from Shuidouchi obtained via the optimised process (soaked in twice the volume of water for 12 h, placed in a glass container, and fermented at 35 °C for 48 h) prevented colitis-associated shortening of the colon and increased the colon weight‑to‑length ratio in mice. Furthermore, Shuidouchi extract significantly reduced the disease activity index and decreased serum levels of endothelin (ET), substance P (SP), and interleukin‑10 (IL‑10), while elevating levels of somatostatin (SS), vasoactive intestinal peptide (VIP), and interleukin‑2 (IL‑2) in colitic mice. It also increased colon tissue levels of glutathione (GSH) and superoxide dismutase (SOD), whereas it reduced myeloperoxidase (MPO) and malondialdehyde (MDA) levels. Gene expression analysis in colon tissues revealed that Shuidouchi extract upregulated the mRNA expression of neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS), c‑Kit, and stem cell factor (SCF). Moreover, Shuidouchi treatment downregulated the protein expression of interleukin‑6 (IL‑6), IL-12, and tumour necrosis factor‑α (TNF‑α) in mice with colitis. In conclusion, the optimised Shuidouchi processing method effectively alleviates experimental colitis, an effect closely associated with its elevated soybean isoflavone content. The results of this study can confirm the effect of Shuidouchi on colitis only to a certain extent. Therefore, it is necessary to further verify the effect of Shuidouchi on the human body. At the same time, the mechanism of Shuidouchi in the human body also requires comprehensive and in-depth experiments. As basic research, this study has played a specific theoretical role.