Morchella esculenta polysaccharides (MEP) have attracted extensive attention due to their notable biological activities.However, their high molecular weight results in poor water solubility, high viscosity, and low bioavailability, which severely restrict their application potential in the fields of functional foods and biomedicine.This study aimed to investigate the effects of ultrasonic degradation process, a green physical modification technique, on the physicochemical properties and antioxidant activity of MEP.Response surface methodology was used to optimize the ultrasonic degradation process.High-performance gel permeation chromatography (HPGPC), Fourier transform infrared (FTIR) spectroscopy, Congo red test, X-ray diffraction (XRD) and scanning electron microscope (SEM) were employed to systematically characterize the molecular weight, monosaccharide composition, functional groups, chain conformation, crystallinity, and micro-morphology of the polysaccharides before and after degradation (MEP and UMEP).In addition, the antioxidant activity was evaluated by measuring the DPPH radical, ABTS cation radical, and hydroxyl radical scavenging capacities.The optimal degradation conditions obtained by response surface optimization were as follows:solution concentration of 3 mg/mL, ultrasonic power of 200 W, and treatment time of 70 min.Under these conditions, the measured average molecular weight of UMEP was (2 453.00±4.38) kDa, with a relative error of only 1.30% compared with the model-predicted value (2 421.52 kDa).Structural analysis showed that the molecular weight of polysaccharides decreased significantly after ultrasonic treatment, and the micromorphology changed from dense and smooth to porous and fragmented, while no obvious changes were observed in the monosaccharide composition or basic functional groups.The Congo red test revealed that the triple-helix structure was dissociated, whereas the iodine-potassium iodide reaction confirmed that the branched structure was still retained.The evaluation of antioxidant activity showed that the scavenging capacities of UMEP against DPPH radical, ABTS cation radical, and hydroxyl radical were significantly superior to those of untreated MEP, exhibiting a concentration-dependent effect.In conclusion, ultrasonic degradation is an efficient and green physical modification method that can enhance the antioxidant activity of MEP by reducing their molecular weight and changing their advanced structure on the premise of maintaining the basic chemical structure of polysaccharides.
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