Exopolysaccharides (EPS) produced by Arthrospira platensis (A. platensis) has been widely applied in industry and commerce for its various activities but the accumulation of EPS in culture medium may influence the growth of A. platensis reversely. This work aims to explore the impacts of initial pH, nitrogen source and concentration, phosphate concentration and recycle times of the culture medium on the growth of A. platensis and the secretion of its EPS. The results showed that EPS accumulated with the increase in recycle times of culture medium. The optimal initial pH for the growth of A. platensis was 8.50, and high pH of 11.5 inhibited the growth of biomass while resulting in highest EPS content of 92.87 mg/g DW. Excessive and limited nitrogen (NaNO₃ of 25.00 g/L and NaNO₃ < 2.50 g/L) and phosphate (K₂HPO₄ of 5.00 g/L and K₂HPO₄ < 0.50 g/L) inhibited the biomass production of A. platensis by 1.28–30.77% and 14.29–45.05%, respectively. EPS yield of 97.57 mg/g DW and 40.90 mg/g DW were obtained under NaNO₃ of 25.00 g/L and K₂HPO₄ of 5.00 g/L due to salt stress. These findings are beneficial in providing a theoretical basis for high yield EPS from A. platensis without affecting biomass yield.

The objective of this study was to optimize the process parameters of the anaerobic co-digestion of pig manure and rice straw to maximize methane production and system stability. In this study, batch experiments were conducted with different mixing ratios of pig manure and rice straw (1:0, 1:1, 1:5, 1:10, and 0:1), total solid concentrations (6%, 8%, 10%, 12%, and 14%), and inoculum accounts (5%, 10%, 15%, 20%, and 25%). The results show that a 1:5 mixing ratio of pig manure to rice straw, a 12% total solid content, and a 15% inoculum account yielded biogas up to 553.79 mL/g VS, which was a result of co-digestion increasing the cooperative index (CPI > 1). Likewise, the evolution of the pH and VFAs indicated that the co-digestion system was well-buffered and not easily inhibited by acidification or ammonia nitrogen. Moreover, the results of the Gompertz model’s fitting showed that the cumulative methane production, delay period, effective methane production time, and methane production rate under optimal conditions were significantly superior compared to the other groups employed.

Butyrate is a key short-chain fatty acid (SCFA) essential for maintaining colon health, immune homeostasis, and metabolic balance. Its synthesis primarily depends on the fermentation of dietary substrates by the gut microbiota. In a healthy state, carbohydrate fermentation sustains the stability of the gut microbiota; however, in chronic diseases, the diversity of the microbiota decreases, and the metabolic pathway shifts from carbohydrate fermentation to protein fermentation, thereby inhibiting butyrate production. Polysaccharides and proteins play key roles in regulating butyrate synthesis. As fermentable carbon sources, polysaccharides promote the proliferation of probiotics, lower colonic pH, and inhibit anaerobic fermentation of proteins. However, excessive protein fermentation produces branched-chain fatty acid (BCFA), ammonia, phenols, and other metabolites that inhibit butyrate production. The structural characteristics of polysaccharides and the digestibility of proteins can determine the substrate selection of gut microbiota. This review systematically elucidates the biosynthetic pathways of butyrate in the gut and the host metabolic signaling pathways in which it participates, focusing on the interactions between dietary proteins and polysaccharides and their key regulatory mechanisms affecting butyrate production by the gut microbiota.

Improper cultivation can easily cause excessive nitrate accumulation in leafy vegetables, and the cooking processes used to prepare them can upset their nitrate/antioxidant balance, affecting their potential nitrite safety risk (PNSR). We investigated the impacts stir-frying, steaming, microwaving, and boiling on the nitrate, nitrite, and antioxidant capacity in water spinach and cabbage, and observed the impacts of storage duration on the PNSR. The antioxidant/in vivo nitrite ratio (A/N) was used to evaluate the nitrite risks in the cooked vegetables. Boiling achieved the highest A/N ratio (1.57) for water spinach, reducing the nitrate content by 25% without significantly affecting the antioxidant capacity. Stir-frying achieved the highest A/N ratio (6.55) for cabbage, increasing the antioxidant capacity by 140% without significantly affecting the nitrate content. Furthermore, it was found that the storage periods for boiled water spinach and stir-fried cabbage should not exceed 12 h and 24 h, respectively. Appropriate cooking methods and limited storage times are thus required for leafy vegetable to prevent adverse health effects.