*3.1. The Gut Microbiota Structure in the Feces from C57BL/6 Mice*

The microbiota structure in the colon was analyzed by high-throughput sequencing spanning the 16S rDNA V3-V4 hypervariable region and shown in Figure 1. At the phylum level, *Firmicutes* (55.17%) and *Bacteroidetes* (43.62%) were abundant. As for the genus level, *Lactobacillus* (14.71%) accounted for the highest abundance of recognizable conventional microorganisms, which was consistent with the microbial composition of normal C57BL/6 mice feces [24]. C57BL/6 mice were used as a suitable animal model to evaluate dietary fiber and colon health. In other studies of HPIDF, we also chose this animal model. Therefore, we selected their feces for gut microbiota isolation and fermented HPIDF in vitro.

#### *3.2. The Structural Changes of HPIDF after Being Fermented*
