Potassium sulphate

In this study, ethanol and hydrochloric acid (HCl) were purchased from Aladdin Biochemical Technology Co., (Shanghai, China). The guarantee reagents of copper sulphate, potassium sulphate, sulfuric acid, boric acid were purchased from Sinopharm Chemical Reagent Co., LTD., China. Standards for the determination of amino acids: aspartic acid (Asp), threonine (Thr), serine (Ser), glutamic acid (Glu), glycine (Gly), alanine (Ala), valine (Val), methionine (Met), isoleucine (Ile), leucine (Leu), tyrosine (Tyr), phenylalanine (Phe), lysine (Lys), histidine (His), arginine (Arg), proline (Pro), cysteine (Cys) and tryptophan (Trp) were all purchased from Anpu Experimental Technology Co., (Shanghai, China). Standards for the determination of fatty acids were purchased from Sigma co., United States. Protease, trehalase and lipase kits were all purchased from Qingdao Sci-tech Innovation Quality Testing Co., LTD. (Qingdao, China). DNA kits and Polymerase chain reaction (PCR) amplicons kits for intestinal contents samples were purchased from Omega Bio-Tek Co. (Norcross, GA, United States) and Invitrogen Co., (Carlsbad, CA, United States), respectively.

Antarctic krill was provided by the Liaoning Province Dalian Ocean Fishery Group Corporation, and stored at −70°C in a refrigerator. The Antarctic krill biomass was composed of total amounts of proteins (13.95 ± 1.24%), EPA (12.47 ± 1.69%), DHA (8.62 ± 1.28%), oils (2.87 ± 1.43%), and flavonoids (0.004 ± 0.002%) w/w, respectively. The total amount of EPA and DHA in oil was determined according to Zeb et al. [24 ], while the total oil according to Bligh & Dyer's [25 (link)]. The total amount of protein was analyzed using Kjeldahl method (GB5009.5‐85). The total flavonoid was determined by a modified method according to Zeb et al. [24 ]. Each experiment was repeated until the highest yield was achieved. Standard chemicals such as EPA, DHA, heptadecanoic acid, quercetin, and bovine serum albumin (BSA) were purchased from Sigma‐Aldrich (purity greater than 99%). Sodium hydroxide, fluoride, hydrogen peroxide, sodium carbonate, ammonium citrate, ammonium sulphate, sodium sulphate, sodium citrate, potassium sulphate, and all solvents were purchased from Sinopharm Chemical Reagent Co., Ltd. All other chemicals were of analytical grade. At the same time, deionized water was used for solution preparation.

Alcalase (2.4 AU/g) was obtained from Novozymes Biotech (Copenhagen, Denmark). Papain (8 × 10⁵ U/g), neutral protease (6 × 10⁴ U/g) and Flavourzyme (1.5 × 10⁴ U/g) were obtained from Beijing Solarbio Technology Co., Ltd. (Beijing, China). 2.2-diphenyl-1-picrylhydrazyl (DPPH) and N, N, N’, N’-tetramethylethylenediamine (TEMED) was obtained from Sigma-Aldrich (St. Louis, MO, USA). Copper sulphate, potassium sulphate, boracic acid, sulfuric acid, acrylamide, methylene diacrylamide, tris-(hydroxymethyl)-aminomethane (Tris), and lauryl sodium sulfate (SDS) were obtained from Sinopharm Chemical Reagents Co., Ltd. (Shanghai, China). Protein molecular weight marker (Low) was obtained from Takara Bio (Dalian) Co., Ltd. (Dalian, China). Coomassie brilliant blue R250, Coomassie brilliant blue G250, methyl red, methylene blue, ammonium persulfate and methanal and sodium hydroxide were obtained from Aladdin Reagent Co., Ltd. (Shanghai, China). All other chemicals used were of analytical grade.