Effect of κ-carrageenan with different molecular weights and its acetylated derivatives on the structure and metabolites of the intestinal flora

The digestive fermentation characteristics of κ-carrageenan with different molecular weights and its acetylated derivatives were investigated by analyzing the variation patterns of the intestinal flora and metabolites. The results showed that κ-carrageenan with different molecular weights and its acetylated derivatives were not digested in the oral-gastric-small intestinal digestion process but could be fermented by the colonic flora and were mainly degraded in the ascending colon stage. The lower molecular weight κ-carrageenan was more likely to increase the abundance of <i>Proteobacteria</i> and <i>Enterobacteriaceae</i> and decreased colonic acetic acid production at the transverse-descending colon, which could be reversed by the acetylation modification of κ-carrageenan. Meanwhile, the acetylation modification of κ-carrageenan increased the abundance of beneficial bacteria such as <i>Lactobacillus</i> and <i>Bifidobacterium</i>, and greatly increased the content of acetic acid. Moreover, the increased acetic acid from acetylated κ-carrageenan fermentation was produced by the Wood-Ljungdahl pathway, with the up-regulated expression of acetyl-coenzyme A, acetate kinase, and formate dehydrogenase. The results indicated that acetylation modification can ameliorate the potential intestinal dysbiosis caused by κ-carrageenan, especially low-molecular-weight κ-carrageenan, by increasing the beneficial gut microbiota <i>e.g.</i>, <i>Lactobacillus</i> and acetic acid metabolism, which can provide precise molecular evidence for the functional optimization of κ-carrageenan and its application in intestinal health.