Abstract
For full use of fish by-products, scale gelatin (TG) and antioxidant peptides (APs) of skipjack tuna (Katsuwonus pelamis) were prepared, and their properties were characterized using an amino acid analyzer, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier transform infrared spectroscopy (FTIR), electrospray ionization mass spectrometers (ESI-MS), and radical scavenging assays. The results indicate that TG with a yield of 3.46 ± 0.27% contained Gly (327.9 ± 5.2 residues/1000 residues) as the major amino acid and its imino acid content was 196.1 residues/1000 residues. The structure of TG was more unstable than that of type I collagen from scales of skipjack tuna (TC) and TG was more suitable for preparation of hydrolysate by protease than mammalian gelatins. Therefore, TG was separately hydrolyzed under five proteases (pepsin, papain, trypsin, neutrase, and alcalase) and ten APs (TGP1–TGP10) were isolated from the alcalase-hydrolysate. Among them, TGP5, TGP7, and TGP9 with high antioxidant activity were identified as His-Gly-Pro-Hyp-Gly-Glu (TGP5), Asp-Gly-Pro-Lys-Gly-His (TGP7) and Met-Leu-Gly-Pro-Phe-Gly-Pro-Ser (TGP9), respectively. Furthermore, TGP5, TGP7, and TGP9 exhibited a high radical scavenging capability on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical (EC50 values of 1.34, 0.54, and 0.67 mg/mL, respectively), hydroxyl radical (EC50 values of 1.03, 0.41, and 0.74 mg/mL, respectively), and superoxide anion radical (EC50 values of 1.19, 0.71, and 1.59 mg/mL, respectively). These results suggest that three APs (TGP5, TGP7, and TGP9), especially TGP7, have a strong antioxidant activity and could act as potential antioxidant ingredients applied in functional products.
Highlights
Gelatin is a denatured form of collagen and traditionally extracted by processing by-products of land mammals, such as beef bones, bovine hides, and pig skins [1,2,3]
molecular weight (MW) below was noticeable in the results indicate thatApartial helical fragments structure and peptide bonds of
Fourier Transform Infrared Spectroscopy (FTIR) spectra spectra of of the scale gelatin (TG), TG, we found that the structure of was more unstable than should be suitable we found that the structure of TG was more unstable than Type I collagen (TC)
Summary
Gelatin is a denatured form of collagen and traditionally extracted by processing by-products of land mammals, such as beef bones, bovine hides, and pig skins [1,2,3]. According to the acid and alkali preparation processes, the produced gelatins were divided into type A and type B, with a. Mar. Drugs 2019, 17, 565; doi:10.3390/md17100565 www.mdpi.com/journal/marinedrugs. Mar. Drugs 2019, 17, 565 molecular weight (MW) ranging from 80 to 250 kDa [3,4]. Religious sentiments and the anxiety of consumers on the safety of mammalian gelatins have led to producers needing to find new alternative sources of mammalian gelatins [1,7]. Gelatins derived from fish by-products are considered to be a promising alternative to mammalian gelatins due to their production, safety, and non-religious conflict [4,8]
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