Abstract
For utilizing the largest source of marine proteins, Antarctic krill (Euphausia superba) proteins were defatted and hydrolyzed separately using pepsin, alcalase, papain, trypsin, and netrase, and alcalase hydrolysate (EPAH) showed the highest DPPH radical (DPPH·) and hydroxyl radical (HO·) scavenging activity among five hydrolysates. Using ultrafiltration and chromatography methods, fifteen antioxidant peptides were purified from EPAH and identified as Asn-Gln-Met (NQM), Trp-Phe-Pro-Met (WFPM), Gln-Asn-Pro-Thr (QNPT), Tyr-Met-Asn-Phe (YMNF), Ser-Gly-Pro-Ala (SGPA), Ser-Leu-Pro-Tyr (SLPY), Gln-Tyr-Pro-Pro-Met-Gln-Tyr (QYPPMQY), Glu-Tyr-Glu-Ala (EYEA), Asn-Trp-Asp-Asp-Met-Arg-Ile-Val-Ala-Val (NWDDMRIVAV), Trp-Asp-Asp-Met-Glu-Arg-Leu-Val-Met-Ile (WDDMERLVMI), Asn-Trp-Asp-Asp-Met-Glu-Pro-Ser-Phe (NWD-DMEPSF), Asn-Gly-Pro-Asp-Pro-Arg-Pro-Ser-Gln-Gln (NGPDPRPSQQ), Ala-Phe-Leu-Trp-Asn (AFLWA), Asn-Val-Pro-Asp-Met (NVPDM), and Thr-Phe-Pro-Ile-Tyr-Asp-Tyr-Pro-Gln (TFPIYDPQ), respectively, using a protein sequencer and ESI/MS. Among fifteen antioxidant peptides, SLPY, QYPPMQY and EYEA showed the highest scavenging activities on DPPH· (EC50 values of 1.18 ± 0.036, 1.547 ± 0.150, and 1.372 ± 0.274 mg/mL, respectively), HO· (EC50 values of 0.826 ± 0.027, 1.022 ± 0.058, and 0.946 ± 0.011 mg/mL, respectively), and superoxide anion radical (EC50 values of 0.789 ± 0.079, 0.913 ± 0.007, and 0.793 ± 0.056 mg/mL, respectively). Moreover, SLPY, QYPPMQY and EYEA showed strong reducing power, protective capability against H2O2-damaged plasmid DNA, and lipid peroxidation inhibition ability. Furthermore, SLPY, QYPPMQY, and EYEA had high stability under temperatures lower than 80 °C, pH values ranged from 6–8, and simulated GI digestion for 180 min. The results showed that fifteen antioxidant peptides from alcalase hydrolysate of Antarctic krill proteins, especially SLPY, QYPPMQY and EYEA, might serve as effective antioxidant agents applied in food and health products.
Highlights
Defatted Antarctic krill powder was separately hydrolyzed with alcalase, trypsin, neutrase, pepsin, and papain, and the radical scavenging activity of five protein hydrolysates is
0.51 mg/mL for EDIVCW, MEPVW, and YWDAW, respectively) [22], scales of croceine croaker (0.675 and 0.283 mg/mL for GPAGPAG and GFPSG, respectively) [36], and miiuy croaker swim bladders (0.51 ± 0.03 and 0.78 ± 0.05 mg/mL for FPYLRH and GIEWA, respectively) [39]. These results indicated that the antioxidant peptides of ESP1, ESP4, ESP6, ESP7, and ESP8 had strong ability to inhibit DPPH· reaction
The purification, identification, activity evaluation and stability of antioxidant peptides from alcalase hydrolysate of Antarctic krill (E. superba) proteins were systematically studied, and fifteen antioxidant peptides were purified from alcalase hydrolysate and identified as NQM, WFPM, QNPT, YMNF, SGPA, SLPY, QYPPMQY, EYEA, NWDDMRIVAV, WDDMERLVMI, NWDDMEPSF, NGPDPRPSQQ, AFLWA, NVPDM, and TFPIYDPQ, respectively
Summary
Among the most studied bioactive peptides, antioxidant peptides derived from marine living resources and their processing by-products, such as yellowfin tuna (Thunnus albacares) skin [20], monkfish muscle [21,22], red tilapia (Oreochromis sp.) scale [23], miiuy croaker swim bladder [24], Skipjack tuna bone and head [25,26], and mackerel muscle [13], exhibit excellent capacity for inhibiting lipid peroxidation and scavenging reactive oxide species (ROS). EDIVCW and YWDAW showed positive protective function on H2 O2 -damaged HepG2 through increasing the activity of antioxidant enzymes (superoxide dismutase and glutathione peroxidase) and decreasing the contents of ROS and malondialdehyde (MDA) [22]. EDYGA from soft-shelled turtles was confirmed as the most potent ARE-luciferase inducer because it could increase the
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