Structural changes of complexes from Arthrospira platensis protein and pectin influenced by degree of esterification and pH

The complexes of phycocyanin and pectin have received attention as a solution for stabilizing the rare, naturally blue-occurring pigment. Challenging are acidic conditions, in which the phycobiliprotein is at risk of denaturation. Structural features of these complexes are key to their colloidal stability, and understanding their formation is essential to prevent precipitation. However, effects of pH and polysaccharide properties on the size and structure of these complexes remain poorly understood. This study explores the interaction between phycocyanin and pectins with varying degrees of esterification (8.9–60%) at pH 3–6, using a 1:2 mixing ratio. Analyses included high-pressure size exclusion chromatography (HPSEC), dynamic and static light scattering (DLS, SLS), microscopy, and rheological voluminosity measurements. Confocal laser scanning microscopy revealed that pectin forms a sheath around the phycocyanin-rich core. At acidic pH, low-DE pectin promotes aggregation through pectin bridging, forming large (>10 μm), dense complexes (54.19 mL g −1 ) caused by reduced steric hindrance and minimal electrostatic repulsion. In contrast, high-DE pectin forms smaller (<1 μm) and less dense complexes (145.10 mL g⁻ 1 ), attributed to a predominance of associative forces over repulsive interactions. High-DE pectin appears to be especially effective in preventing precipitation at acidic pH, forming compact yet voluminous complexes that remain soluble. Overall, this study provides novel insights into the structural formation and evaluation of phycocyanin:pectin complexes. By outlining strategies for tailoring complexes over a wide pH range and by varying the type of pectin it is relevant to food and beverage applications, with potential extensions to the pharmaceutical and cosmetic industries. • Structue of phycocyanin:pectin (PC:P) complexes was analyzed at pH 3–6 & DE 8.9–60. • LMP promoted aggregation at acidic pH by reduced steric hindrance & pectin bridging. • HMP formed smaller complexes remaining soluble at low pH due to a high voluminosity. • Staining the hydrocolloids revealed that a pectin sheath covers a PC-rich core. • Insights into stabilizing proteins for food, pharmaceutical & cosmetic applications.