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

The digestive fermentation characteristics of κ-carrageenan with different molecular weights and its acetylated derivatives were investigated through the changing rules of intestinal flora and metabolites. The results showed that κ-carrageenan with different molecular weights and its acetylated derivatives did not digested in the oralgastric-small intestinal digestion process but could be fermented by colonic intestinal flora, and was mainly degraded in the ascending colon stage. The lower molecular weight κ-carrageenan was more likely to increase the abundance of Proteobacteria and Enterobacteriaceae, decreased colonic acetic acid production at 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 Lactobacillus and Bifidobacterium, as well as greatly increased the contents of acetic acid. Moreover, the increased acetic acid production was involved in the up-regulation of acetylated κ-carrageenan on the expression acetylcoenzyme A, acetate kinase, and formate dehydrogenase through the Wood-Ljungdahl pathway. The results indicated that acetylation modification can ameliorate the potential intestinal dysbiosis caused by κ-carrageenan especially with low-molecularweight by increasing beneficial gut microbiota e.g., Lactobacillus and acetic acid metabolism, which can provide precise molecular evidence for the functional optimization of κ-carrageenan and its application in intestinal health.