Improvement of blue color and structural stability of phycocyanin by forming soluble complexes with algae oligosaccharides

Phycocyanin (PC) is a natural blue pigment whose application in foods is currently limited due to its poor color stability. The impact of oligosaccharides (OS) on PC's color and structural stability was therefore investigated because they may enhance color stability without greatly increasing viscosity as caused by polysaccharides . Three main algae-derived oligosaccharides were obtained by hydrolysis of agar, carrageenan , and alginate. The optimum mass ratio of OS-to-PC required to form complexes was 5:1. The carrageenan oligosaccharide exhibited the highest complexation degree with PC (31.20%), attributed to sulfate and hydroxyl groups that bind strongly to the protein surface through electrostatic and hydrogen bonding interactions. The complexes formed by this OS had the highest hydrophilicity (fluorometry), wrapping effect (X-ray diffraction analysis), and particle compactness (scanning electron microscopy). The stoichiometric ratio between the PC hexamer and carrageenan oligosaccharide was ∼62, higher than those obtained with agar and two alginate oligosaccharides (isothermal titration calorimetry). Excess agar and carrageenan oligosaccharides bound to the complexes, whereas excess alginate oligosaccharides did not (differential scanning calorimetry). Physical-, light-, heat-, and storage-stability evaluations showed that carrageenan oligosaccharide provided the greatest protection to PC's blue color, mainly attributed to their ability to stabilize PC's structure. • Algae oligosaccharides were upcycled from phycocyanin's by-products to its stabilizers. • Algae oligosaccharides stabilized phycocyanin without significantly increasing viscosity. • Carrageenan oligosaccharide imparted the highest stability to phycocyanin. • Excess agar and carrageenan oligosaccharides stacked on their phycocyanin complexes. • Excess alginate oligosaccharides stayed free from their phycocyanin complexes.