Abstract
Purpose: To evaluate protein hydrolysates and membrane ultrafiltration fractions of blue-spotted stingray for metal chelating and radical scavenging activities, as well as protection against oxidative protein damage. Methods: Stingray protein isolates were hydrolysed with alcalase, papain and trypsin for 3 h. Alcalase hydrolysate was fractionated by membrane ultrafiltration to yield 10 kDa fractions. Peptide contents, iron and copper chelating activity, 2, 2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and hydroxyl radical scavenging activities, and protection against oxidative protein damage were evaluated. Results: Three-hour alcalase hydrolysate (3AH) had the highest peptide content and the lowest half maximal effective concentration (EC50) for ABTS radical scavenging (793.9 µg/mL), hydroxyl radical scavenging (6.93 mg/mL), iron chelating (116.4 µg/mL) and copper chelating activity (2136.9 µg/mL) among the hydrolysates. Among the fractions of 3AH, 10 kDa fraction showed the best copper chelating activity. The < 3 kDa and 3 - 10 kDa fractions had similar levels of hydroxyl radical scavenging activity to reduced glutathione. The protective effects of 3AH and < 3 kDa fraction against oxidative protein damage were comparable to that of reduced glutathione. Conclusion: Alcalase is the best protease for producing hydrolysates with metal chelating and antioxidant activities from stingray proteins. Alcalase hydrolysate, specifically its < 3 kDa fraction, has potential for future applications in antioxidant therapy and health food formulation.
Highlights
In recent years, the antioxidant potential of protein hydrolysates derived from edible fishes and other animal sources has generated great interests among researchers [1,2,3]
For ABTS radical scavenging activities, the EC50 of 3AH was the lowest among all hydrolysates, it was 16-fold higher compared with reduced glutathione
For the ultrafiltration fractions prepared from 3AH (Fig 1B), we found the < 3 kDa and 3 - 10 kDa fractions to have similar hydroxyl radical scavenging activities, both being higher compared with the > 10 kDa fraction
Summary
The antioxidant potential of protein hydrolysates derived from edible fishes and other animal sources has generated great interests among researchers [1,2,3]. Animal and microbial origins, such as papain, trypsin, chymotrypsin, neutrase, and alcalase, have been used in the production of antioxidative fish protein hydrolysates (FPH) [2,3]. The potential applications of FPH, including their use as antioxidants to extend the shelf-life of meat products as well as their health-promoting and disease-preventive effects, have been discussed in recent reviews [2,3]. Very little attention was given to the antioxidant potential of protein hydrolysates prepared from edible, cartilaginous marine fishes, such as stingrays
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