Preparation, separation and antioxidant properties of hydrolysates derived from Grifola frondosa protein

In order to take full advantage of Grifola frondosa resources, the protein (GFP) was extracted from G. frondosa fruiting body and digested using six different proteases (papain, neutrase, alcalase, trypsin, pepsin, and Protamex) to produce the antioxidative hydrolysates. The trypsin hydrolysate prepared at 1.5 h possessed the strongest antioxidant potential among different hydrolysates, which was separated into four major fractions by ultrafiltration membranes with different molecular weight cut-off (MWCO), that are GFHT-1 (Mw > 10 kDa), GFHT-2 (Mw = 5-10 kDa), GFHT-3 (Mw = 3-5 kDa), and GFHT-4 (Mw < 3 kDa). In succession, the in vitro antioxidant activities of the four fractions were further evaluated, including the scavenging effect on DPPH, ferrous ion chelating effect, reducing power, and ability to inhibit the autoxidation of linoleic acid. The results demonstrated that all fractions are effective antioxidants and comparably GFHT-4 has the highest antioxidant activity. Then GFHT-4 was separated to two major peptide fractions by gel filtration chromatography, and the two fractions were located at 2,385 Da (F-1) and 1,138 Da (F-2), respectively.