Abstract
DPPH• scavenging peptides (<3kDa) from underutilized Dunaliella salina protein were obtained by the following successive treatment, i.e., ultrasound extraction, simulated in vitro gastrointestinal digestion hydrolyzation, and membrane ultrafiltration classification. The optimal condition for ultrasound-assisted extraction was an ultrasound wave with 800 W of power treating a mixture of 60 mL of 1.0 mol L−1 NaOH and 2 g algae powder for 15 min. A high correlation (r=0.8146) between DPPH• scavenging activity and yield of the intact peptides showed their antioxidant capacity. Simulated in vitro digestion assay resulted in excellent DPPH• scavenging activity of the total peptide, amounting to (86.5 ± 10.1)%, comparing with the nondigestion samples at (46.8 ± 6.5)%. After fractionation, the 500-1000 Da fraction exhibited the highest DPPH• scavenging activity (81.2 ± 4.0)%, increasing 1.5 times due to digestion. Then, the 500-1000 Da fraction was analyzed by RPLC-Q Exactive HF mass spectrometer, and 4 novel peptides, i.e., Ile-Leu-Thr-Lys-Ala-Ala-Ile-Glu-Gly-Lys, Ile-Ile-Tyr-Phe-Gln-Gly-Lys, Asn-Asp-Pro-Ser-Thr-Val-Lys, and Thr-Val-Arg-Pro-Pro-Gln-Arg, were identified. From these amino acid sequences, hydrophobic residues accounted for 56%, which indicated their high antioxidant property. The results indicated that underutilized protein of Dunaliella salina could be a potential source of antioxidative peptides through simulated in vitro gastrointestinal digestion.
Highlights
It was recognized that the growing chronic diseases linked to the key biological molecules such as DNA, protein, and lipid were disposed by the excess reactive oxygen and free radicals species in the body due to variation of life style and environment problem [1,2,3,4]
According to many epidemiological and empirical studies, bioactive peptides derived from various protein sources have showed great potential to scavenge the free radicals, and the highest activity was observed at fractions with molecular weight less than 3 kDa [7,8,9,10]
The results suggest that ultrasound wave could accelerate the establishment of an equilibrium for dissolution of the peptide with DPPH∙ scavenging activity among algae cell and the extraction solvent in a short time, even at 5 min, which is huge advantage as an extract projection for bioactive compounds compared to the conventional solvent extraction
Summary
It was recognized that the growing chronic diseases linked to the key biological molecules such as DNA, protein, and lipid were disposed by the excess reactive oxygen and free radicals species in the body due to variation of life style and environment problem [1,2,3,4]. According to many epidemiological and empirical studies, bioactive peptides derived from various protein sources have showed great potential to scavenge the free radicals, and the highest activity was observed at fractions with molecular weight less than 3 kDa [7,8,9,10]. The characteristics of peptides with antioxidant activity less than 3 kDa have been paid increasing attention of researchers in relative field. Dunaliella salina, as a unique unicellular microalgae, is rich in good proteins and can survive in various salt concentrations (0.2%-35%) and light intensity conditions. Some researchers have confirmed that, due to salt stress and flagellar disassembly, peroxiredoxin mRNA and protein expression significantly increased in Dunaliella salina cells [20,21,22], while salt stress has been found to contribute
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