Commercially available carrageenans show broad variation in their structure, composition, and functionality

Carrageenans are polysaccharides from red algae which are widely used as food additives and in other applications. Their structure is often described by different disaccharide repeating units, although it was already demonstrated that reality is more complex. In many studies, commercial carrageenans were used to establish structure function relationships, but a detailed structural and compositional analysis was rarely conducted. Therefore, the aim of our study was to characterize commercial carrageenans with different specifications from different manufacturers. Furthermore, partial enzymatic hydrolysis and rheology were used to gain detailed insights into the structure and functionality of selected samples. Our results demonstrate that significant structural variation can be observed for commercial carrageenans. The samples contained different cations and the carrageenan type specified by the manufacturer did not always represent the structure of the corresponding polysaccharides. This was especially true for λ-carrageenans: Of the six commercial samples analyzed, none contained structural elements from the λ-type. Instead, the corresponding carrageenans contained κ-, ι- and ν-units. Mixtures of κ- and ι-units were also observed for a ι-carrageenan and unspecified carrageenans. By using partial enzymatic hydrolysis in combination with HPLC-MS and HPSEC-RI, it was possible to demonstrate the presence of different hybrid carrageenans. In addition, the rheological analysis of the commercial carrageenan samples showed clear differences in the gelling properties upon calcium addition which could influence their behavior in different applications. Our results demonstrate that commercial carrageenan samples should be analyzed for their structure and composition before they are used for the investigation of structure function relationships.