Effects of origin and harvest period on characterisation, structure and antioxidant activity of polysaccharides derived from Porphyra haitanensis

Summary In the present study, the influences of different origins and harvest periods on the characterisation, structure and antioxidant activity of Porphyra haitanensis polysaccharides (PHPs) were investigated. PHPR03 obtained from the third harvest period (late December) in Raoping possessed the highest content of sulphate group (14.70%), the lowest viscosity (434.34 mL·g −1 ) and exhibited better antioxidant activity. FTIR spectrum confirmed that PHPs obtained in different origins and harvest periods had similar functional groups (O—H, C—H and C—O group). Thermal gravimetric analysis suggested that PHPR03 has good thermal stability until 182 °C. PHPR03 microstructure was detected using scanning electron microscopy, and it was mainly irregular flocs. Atomic force microscope data showed that its diameter and height ranged from 1.32 to 1.99 μm and 14.16 to 34.92 nm, respectively. X‐ray diffraction and Congo red experiments indicated that PHPR03 belongs to amorphous material with weak rigidity and exists in the form of random coils in an aqueous solution. PHPR03 resulted in a decrease of thiobarbituric acid‐reactive substances value of ground pork. This study provides the theoretical basis for rational utilisation and further applications in the food industry of PHPs.