Study On Preparation Of Tree Peony Seed Protein Hydrolysate And Its Antioxidant Activity

Tree peony?Paeonia suffruticosa Andr.?seed protein?TPSP?are considered to have a huge potential in nutraceutical industry due to its desirable amino acid content and potentially useful functional characteristics.Thus,the effect of different proteases on the physicochemical properties and antioxidant activity of different hydrolysates were investigated in this paper.After that,based on the better antioxidant activity of alcalase hydrolysates,polypeptide fractions with different molecular weight ranges were obtained by ultrafiltration.The structure characteristics,antioxidant activity and the protective effects on H₂O₂induced oxidative damage in Hep G2 cells of ultrafiltration fractions were studied.The results of the experiment are as follows.?1?The effects of different proteases hydrolysis on the physicochemical properties of TPSP hydrolysates were studied.The results showed that alcalase hydrolyzed TPSP more easily when compared with other proteases.The alcalase hydrolysates had a lower average particle size?231.33±36 nm?and molecular weight?<13 kDa?.The intrinsic fluorescence spectra showed that the?_maxof TPSP hydrolysates had a marked redshift,indicating that the spatial structure of TPSP hydrolysates was opened with a small amount of aromatic amino acids?AAA?exposed.The hydrolysis of five proteases significantly changed the secondary structure of TPSP,especially the?-helix structure,which decreased from 15.01±0.36%to 5.72±0.69%to 7.94±0.34%,making the ordered structure of TPSP more flexible and loose.The contents of free amino acids indicated that the five proteases mainly hydrolyzed the peptide bonds between hydrophobic amino acids and AAA,such as Phe and Tyr,in the TPSP,reducing the surface hydrophobicity of TPSP hydrolysates and forming the conformation of hydrophilic groups exposed to the outside,thus improving the dispersity of TPSP in water.?2?The amino acid composition,functional characteristics and antioxidant activity of TPSP hydrolysates obtained by five proteases hydrolysis were studied.The amino acid composition showed that the EAA?22.96-28.06%?contents of five TPSP hydrolysates were equal to or higher than that of TPSP?20.95%?,which indicated that TPSP and its hydrolysates had higher nutritional value.Secondly,TPSP hydrolysates were rich in Glu and Asp?NCAA?,which accounted for about 25.52-28.96%of the total amino acids.The hydrolysis of five proteases could improve the solubility of TPSP,which might be related to the hydrophilic structure of these hydrolysates,especially papain and alcalase hydrolysates.However,the surface properties such as foaming and emulsifying properties of TPSP decreased after the hydrolysis of five proteases.Besdes,alcalase hydrolysates had better antioxidant activity,including free radical scavenging ability,chelating metal ions and reducing power among the five TPSP hydrolysates.?3?The five fractions of>30 kDa,10-30 kDa,5-10 kDa,3-5 kDa and<3 kDa were obtained by ultrafiltration.The structural characteristics,chemical antioxidant activity and functional characteristics of these five fractions were studied.The results showed that the fraction>30 kDa retained the secondary structural characteristics of TPSP and had high content of AAA.Therefore,the structural characteristics of the fraction>30 kDa endowed it with high emulsifying activity and better free radical?DPPH and ABTS?scavenging abilities as well as inhibition of?-carotene bleaching.However,the fractions<3 kDa and 10-30 kDa had the better ability to chelate Fe²⁺,which might be related to the higher contents of NCAA in their components.But except for the fraction>30 kDa),other fractions had a good foaming ability?105.26-140.63%?.?4?The protective effects of different ultrafiltration fractions of alcalase hydrolysate on oxidative damage of H₂O₂induced Hep G2 cells were studied.The different ultrafiltration components of TPSPH could stimulate the growth of Hep G2cells at low concentrations but inhibit their growth at high concentrations.Neither promoted nor inhibited Hep G2 cells growth in the concentration range 0.07-1.0mg/m L.The MTT method was used to establish the H₂O₂-induced Hep G2 cell oxidative damage model with a concentration of 500?M and an induction time of 24h.The different ultrafiltration fractions of TPSPH could protect the integrity of Hep G2 cell membrane from H₂O₂damage,and increase the activity of antioxidant enzymes?SOD and CAT?of Hep G2 cell and reduce the ROS content,thus achieving the protective effect on H₂O₂induced oxidative damage,and the fraction 5-10 kDa had the strongest protective effect.