Rheological Behavior, Textural Properties, and Antioxidant Activity of Porphyra yezoensis Polysaccharide

Porphyra yezoensis has attracted much attention due to its gelling properties and bioactivity. In this study, the chemical structure of Porphyra yezoensis polysaccharides (PYPSs) was characterized, and the effects of concentration, temperature, pH, and calcium ion (Ca²⁺) addition on the rheological properties of PYPS were systematically investigated. Chemical composition analysis indicated that PYPS primarily contained galactose (89.76%) and sulfate (15.57%). Rheological tests demonstrated that PYPS exhibited typical pseudoplastic properties, with apparent viscosity increasing with an increasing concentration. Temperature elevation from 30 °C to 90 °C weakened the intermolecular forces and reduced the apparent viscosity, whereas neutral pH (7.0) provided an optimal electrostatic equilibrium to maintain the highest viscosity. Ca²⁺ could modulate the interactions between PYPS molecules and affect the formation of the gel network structure. When the Ca²⁺ concentration reached the optimal value of 6 mM, the calcium bridges formed between Ca²⁺ and PYPS molecules not only enhanced the rheological behavior and textural properties but also formed a smooth and well-ordered network structure, achieving the highest value of fractal dimension (D_f = 2.9600), though excessive Ca²⁺ disrupted this well-ordered structure. Furthermore, PYPS possessed significant scavenging ability against DPPH, ABTS, and HO• radicals, demonstrating its potential application as a natural antioxidant in functional foods.