Abstract: To optimize the ultrasound⁃assisted enzymatic extraction process of selenium proteins from selenium⁃enriched Lentinula edodes and systematically evaluate their nutritional quality and antioxidant activity，single⁃factor experiments were carried out using protein extraction rate and total selenium extraction rate as response indicators to determine the parameter range. The Box⁃Behnken response surface methodology was then adopted to establish a regression model for extraction process optimization.Subsequently，the optimized process was applied to four groups of Lentinula edodes raw materials with different total selenium contents（S0：0.3±0. 0 mg/kg；S1：9.8±0.4 mg/kg；S2：20.0±0.9 mg/kg；S3：99. 6±1. 1 mg/kg）. The selenium speciation，amino acid compositions and in vitro antioxidant capacity of selenium protein extracts obtained from different raw materials were compared and analyzed.The results of process optimization showed that the optimal conditions were as follows：alkaline cellulase addition amount of 0.6%（mass ratio），solid⁃liquid ratio of 1∶25（g/mL），pH value of 9.0，enzymolysis temperature of 48 ℃，ultrasonic power of 300 W，and ultrasonic time of 54 min. Under these conditions，the protein extraction rate predicted by the model could reach 50. 02%. Selenium speciation analysis indicated that selenoamino acids accounted for up to 86.6% of the total selenium in the selenium protein extract of S3，with selenocysteine as the predominant existing form. Amino acid nutritional evaluation revealed that the S3 selenium protein extract exhibited superior values in the ratio of essential amino acids to total amino acids（40.32%），methionine ratio coefficient（0.47） and amino acid ratio coefficient
score（75.28） compared to those of S0. In vitro antioxidant tests verified that the selenium protein extract of S3 exhibited strong scavenging capacities against 1，1⁃diphenyl⁃2⁃picrylhydrazyl（DPPH）radicals and hydroxyl radicals，accompanied by favorable ferric⁃reducing power. In conclusion，selenium proteins from high⁃selenium Lentinula edodes prepared by ultrasound⁃assisted enzymatic extraction possess a proportionally balanced amino acid composition，a high proportion of selenoamino acids and excellent antioxidant activity，and have the potential to serve as a novel fungal⁃derived organic selenium nutritional supplement.

Key words: Selenium protein, Selenium?enriched Lentinula edodes, Ultrasound?assisted enzymatic extraction, Amino acid nutritional evaluation, Selenium speciation, Antioxidant activity