Protection of blue color in a spirulina derived phycocyanin extract from proteolytic and thermal degradation via complexation with beet-pectin

Abstract

The focus of the presented work was on improvement of spirulina based phycocyanin (PhyC) extracts as a potential natural blue colorant by enhancement of color stability via polysaccharide complexation. Beet pectin (β-pectin), guar gum and soluble soy polysaccharides (SSPS) were assessed for their ability to protect the color of a commercial phycocyanin (PhyC) extract from thermal and proteolytic degradation. Both the beet pectin and guar gum studied formed stable and homogenous solutions with the PhyC extract; SSPS did not. Color change was assessed throughout by measurement of L, a, and b color space values (Hunter, 1948) before and after thermal or proteolytic treatment. Beet pectin improved color stability, over PhyC alone, with respect to heating at 65 °C (20 min) and proteolysis by Alcalase 2.4L, papain and bromelain. For these treatments beet pectin reduced color change values (ΔEab) from 13.0 ± 0.1 to 6.2 ± 0.4 following thermal treatment and from 12.7 ± 0.2 to 5.9 ± 0.7, 19.6 ± 1.3 to 12.5 ± 0.8, and 10.8 ± 0.4 to 4.6 ± 0.6 for the Alcalase, papain and bromelain treatments, respectively. Intrinsic fluorescence (excitation at 285 nm, emission at 325 nm) of beet pectin complexed PhyC indicates an increased presence of exposed tryptophan residues compared to PhyC alone. Furthermore, measured zeta-potentials following complex heating generally diverged to slightly more negative values for PhyC-beet pectin complexes at elevated temperatures compared to PhyC alone, suggesting that maintenance of a negatively charged environment may be important to pigment color stability in PhyC complexes.