Studies On The Antioxidant Peptides Prepared From Two Species Of Shellfish

Scallop (Patinopecten yessoensis) and abalone (Haliotis Discus Hannai Ino) were hydro lyzed by using protease to produce antioxidant peptides.Scallop adductor muscle and abalone foot muscle were hydro lyzed by five proteases including neutral protease (Nep), alcalase (Ale), papain (Pap), pepsin (Pep), and trypsin (Try), respectively. Based on an overall consideration of the activities, yield of peptide (TCAI) and reaction conditions of the proteases, Pap and Nep were selected as the tool enzymes in this study to hydrolyze scallop adductor muscle and abalone foot muscle, respectively.The hydrolysis of scallop adductor muscle with Pap and abalone foot muscle with Nep were optimized for manimal degree of hydrolysis (DH) using single-factor experiment. The optimum conditions for the production of the hydrolysates derived from scallop adductor muscle (HSAMs) are listed as below:the hydrolytic temperature of 50℉, pH of 7.0, enzyme-to-substrate ratio of 3500 U/g, the substrate concentration of 8.0%, and hydrolytic time of 3 h. Under this condition, the values of DH and TCAI are 28.77% and 58.88%, respectively. The optimum conditions for the production of the hydrolysates derived from abalone foot muscle (HAFMs) are listed as below:the hydrolytic temperature of 50℃, pH of 7.0, enzyme-to-substrate ratio of 2500 U/g, the substrate concentration of 4.0%, and hydrolytic time of 4 h. Under this condition, the values of DH and TCAI are 27.06%,57.50%, respectively.The peptides prepared with different hydrolytic time were assayed for their antioxidant activities using four in vitro systems, including the scavenging activity on DPPH radical, reducing power, scavenging effect on hydroxyl radical and ferrous chelating activity. Results showed that the antioxidant activities for HSAMs increased quickly during the initial stage and reached the highest level after 25 or 30 min of incubation; thereafter the activities decreased gradually. At 25 min of incubation, HSAMs exhibited the highest DPPH radical scavenging capacity (IC50=10.27 mg/mL), hydroxyl radical scavenging activity (IC50=13.76 mg/mL) and ferrous chelating activity (IC50=0.40 mg/mL). After 30 min of incubation, the reducing power (AC0.5=11.60 mg/mL) of HSAMs reached the highest level. For HAFMs, the antioxidant activities increased with the incubation time during the whole hydrolysis process. After 180 min of incubation, the IC50 or AC0.5 of DPPH radical scavenging capacity, hydroxyl radical scavenging activity, ferrous chelating activity and reducing power were 14.83 mg/mL, 10.77 mg/mL,0.48 mg/mL and 10.93 mg/mL, respectively.To reveal the reasons for changes of antioxidant activities of HSAMs and HAFMs with hydrolysis time, the molecular weight (MW) distribution, free amino acids levels and total amino acid compositions of HSAMs and HAFMs were studied. For the two hydrolysates, hydrolysis with different time did not appreciably change the mole percent of most amino acids indicating that amino acid composition was not the main reason for variations of antioxidant activities. At the initial stage of hydrolysis, HSAMs contained more low MW peptides than HAFMs, which maybe contribute to the higher antioxidant activities of HSAMs. With the increase in incubation time, the relative content of the fraction below 0.5 kDa (include free amino acids) of HSAMs increased obviously indicationg that the hydrolysis became too extensive. This could be the reason for the decrease in antioxidant activities. As for HAFMs, the relative content of fractions above 10 kDa decreased primarily. At the end of hydrolysis, the relative content of fraction below 0.5 kDa was still low, it indicated that the hydrolysis was not excessive. This could be the reason for the increase in antioxidant activities of HAFMs during the whole hydrolysis process.