Soybean residue， a primary by-product of soybean processing， can undergo aerobic fermentation to enhance its nutritional value and palatability. Water activity may emerge as a key determinant of the nutritional quality of soybean residue during aerobic fermentation. The aim of this experiment was to investigate the effects of aerobic fermentation on the fermentation quality of soybean residue feed under different water activities （Aw）， providing a theoretical basis for the production process of soybean residue feed. A soybean residue feed material with water activity as a single variable was constructed by recombining the raw material substrate and microorganisms through microbial transplantation technology. Three water activity treatment groups were established： low （Aw1=0.9868）， medium （Aw2=0.9880） and high （Aw3=0.9912）. Microbial quantity， nutrient composition， and fermentation quality were analyzed after fermentation for 12 h， 24 h， 36 h， 48 h， and 60 h under aerobic conditions. The results showed that the soluble carbohydrate content was higher in the Aw2 group （P<0.001）， and Enterobacter and yeast showed greater adaptability. Crude protein content， organic acid content， and lactic acid bacteria quantity were higher in the Aw3 group （P<0.001）， and the growth of mold and aerobic bacteria was significantly inhibited. Under medium and high water activity conditions， microbial metabolism was more active and utilized substrates more efficiently. In conclusion， the fermentation quality of soybean residue feed in the medium and high water activity treatment groups （Aw2 and Aw3） were superior， and the quality of aerobic fermentation could be effectively improved by reasonably adjusting water activity.

Soybean residue  /  Water activity  /  Aerobic fermentation  /  Feed  /  Fermentation characteristics