Red algae store carbon as floridean starch, a cytosolic branched α-linked glucose polymer (Fig. 1). As an intermediate between amylopectin and glycogen—often described as “semi-amylopectin” [1, 2]. The term floridean starch originates from the red algal class Florideophyceae, where this storage glucan is abundant, though it also occurs in glaucophytes and other rhodophytes as a primary sink for carbon fixation. In species such as Furcellaria lumbricalis, floridean starch accumulates in discrete cytoplasmic granules and can occupy a substantial proportion of the cell volume, distinguishing it structurally and spatially from the plastid-based starch of green plants [1, 2].

Floridean starch can account for up to 20% of the algal dry weight, and during carrageenan extraction it is commonly removed to prevent interference with the gelling performance of the sulfated galactans [3]. In this study, floridean starch isolated from F. lumbricalis using aqueous extraction is compared to crude extracts, purified furcellaran (β/κ-carrageenan), and their reconstructed blends. We evaluated the specific influence of floridean starch on carrageenan gelation behaviour and mechanical properties.

Floridean starch properties are characterized using spectrophotometric analysis of the starch–iodine complex and differential scanning calorimetry (DSC). The degree of branching was assessed by ¹H-NMR to quantify the relative proportions of α-1,4 and α-1,6 linkages, the monosaccharide composition was determined using HPAEC-PAD and the molecular weights by HPLC-SEC.

[1] S. Yu, A. Blennow, M. Bojko, F. Madsen, C.E. Olsen, S.B. Engelsen, Physico-chemical Characterization of Floridean Starch of Red Algae, Starch - Stärke, 54 (2002) 66-74.

[2] S. Yu, Enzymes of floridean starch and floridoside degradation in red alge: purification, characterization and physiological studies, Faculty of Science, Uppsala University, Uppsala, 1992.

[3] H. Srivastava, B. Bisht, J. James, R.K. Malhotra, A. Kurbatova, A. Dabral, S. Upadhyay, V. Kumar, Advanced extraction technologies and functional applications of algal polysaccharides in modern food systems, Discover Food, 5 (2025) 272.