Improving stability of phycocyanin under acidic conditions by surface patch binding induced complexation with gelatin

Phycocyanin is a well-known natural colorant with a blue hue, utilized extensively in food and beverage applications. However, phycocyanin displays poor colloidal stability and precipitates from solution under acidic conditions, resulting in loss of blue color. In this study, gelatin (0.1%-1.0%w/v) was used to protect the colloidal and color stability of phycocyanin while also enhancing its antioxidant activity. Zeta-potential, particle size, and SEM results indicated that suitable concentrations of gelatin could form complexes with phycocyanin. This was induced by surface patch binding (SPB), making phycocyanin more electrostatically repulsive to overcome protein aggregation. Free radical scavenging experiments showed that phycocyanin-gelatin binding promoted the antioxidant activity of phycocyanin. UV–vis absorption, fluorescence spectra, and Fourier transform infrared spectroscopy results showed that gelatin could stabilizing the tertiary structure of phycocyanin and the tetrapyrrole chromophore through hydrophobic interactions and hydrogen bonds formation. Circular dichroism further revealed that gelatin could preserve the native secondary structure of phycocyanin, particularly the α-helix, thereby stabilizing the chromophore and protecting the blue color. This study showed that gelatin has a beneficial role in recovering acidified phycocyanin structure and color, facilitating the potential application of phycocyanin in foods and beverages as a natural pigment.