Method of preparing sturgeon skin gelatin and sturgeon skin gelatin film with antioxidant activity

A method of producing a sturgeon skin gelatin with antioxidant activity comprising the following steps:

• 1) drying the sturgeon skin naturally, placing the sturgeon skin in water;
• a weight ratio of sturgeon skin and water being 1:10-15, soaking sturgeon skin in distilled water at 4° C. for 24 hours, and sonicating the sturgeon skin for 2 hours to let the sturgeon skin swell up;
• 2) cutting the sturgeon skin of step 1) into pieces, soaking the sturgeon skin in a NaOH solution at 2-6° C. for 3-5 hours, washing the sturgeon skin to neutral, and soaking the sturgeon skin in an HCl solution at 2-6° C. for 3-5 hours;
• 3) washing the sturgeon skin of step 2) to neutral, placing the sturgeon skin in an extraction solution for extracting sturgeon skin protein, the extraction solution being a two-phase aqueous solution and including PEG4000, Na2SO4, and KCl, and collecting a top phase layer of the extraction solution, the extraction solution including 10-12% of PEG4000, 14-16% of Na2SO4, and 1% of KCl;
• and
• 4) heating the top phase layer of step 3) with a water bath at 50-70° C. for 5-9 hours, filtering the top phase layer to obtain a first filtrate and a filter cake, placing the filter cake in water to obtain a filter cake solution, heating the filer cake solution with the water bath at 60-80° C. for 3-6 hours, filtering filter cake solution to obtain a second filtrate, combining the first filtrate and second filtrate and centrifuging combined filtrate, collecting a supernatant after centrifugation, and lyophilizing the supernatant to obtain the sturgeon skin gelatin.