Degradation of food-grade λ-carrageenan by human gut microbiota: Potential adverse effect

Carrageenans (CGN) are large linear sulfated polysaccharides extracted from seaweeds and have been widely applied in the food industry as a emulsifier, stabilizer and thicker. However, there is a controversy over CGN safety as the field is re-evaluating if CGN can be degraded in vivo, especially the potential degradation by gut microbiota. To resolve this controversy, selected culture medium with food grade CGN as the sole carbon source was used to screen CGN-degrading bacteria (from human fecal samples) under anerobic circumstance. Our results showed the degradation of food grade CGN by purified bacteria colony, as indicated by the significant decrease of pH and total carbohydrate, and the increase of SCFA. Thin layer chromatography and HPLC data suggested the presence of degrade-CGN in culture medium. Moreover, the bacteria was identified as Bacteroides xylanisolvens, via 16s rDNA sequencing and whole genome sequencing. Furthermore, cell culture study suggested the proinflammatory effect of degrade-CGN, as the fermentation supernatants promoted the production of nitric oxide and the pro-inflammatory cytokines. In summary, food-grade CGN can be broken down into degrade-CGN by gut microbiota, e.g. Bacteroides xylanisolvens, and its potential risks to human health are deserved further investigation.