Abstract
Actinopyga lecanora, a type of sea cucumber commonly known as stone fish with relatively high protein content, was explored as raw material for bioactive peptides production. Six proteolytic enzymes, namely alcalase, papain, pepsin, trypsin, bromelain and flavourzyme were used to hydrolyze A. lecanora at different times and their respective degrees of hydrolysis (DH) were calculated. Subsequently, antibacterial activity of the A. lecanora hydrolysates, against some common pathogenic Gram positive bacteria (Bacillus subtilis and Staphylococcus aureus) and Gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas sp.) were evaluated. Papain hydrolysis showed the highest DH value (89.44%), followed by alcalase hydrolysis (83.35%). Bromelain hydrolysate after one and seven hours of hydrolysis exhibited the highest antibacterial activities against Pseudomonas sp., P. aeruginosa and E. coli at 51.85%, 30.07% and 30.45%, respectively compared to the other hydrolysates. Protein hydrolysate generated by papain after 8 h hydrolysis showed maximum antibacterial activity against S. aureus at 20.19%. The potent hydrolysates were further fractionated using RP-HPLC and antibacterial activity of the collected fractions from each hydrolysate were evaluated, wherein among them only three fractions from the bromelain hydrolysates exhibited inhibitory activities against Pseudomonas sp., P. aeruginosa and E. coli at 24%, 25.5% and 27.1%, respectively and one fraction of papain hydrolysate showed antibacterial activity of 33.1% against S. aureus. The evaluation of the relationship between DH and antibacterial activities of papain and bromelain hydrolysates revealed a meaningful correlation of four and six order functions.
Highlights
The demands for natural antimicrobial compounds that are effective and non-toxic with less environmental risk has greatly increased due to the rising bacterial resistance against the synthetic antimicrobial agents and limitation on the use of synthetic preservatives in food systems
Pseudomonas sp. and E. coli (Figure 7a,d) but peptides with low hydrophobicity had strong effect on Pseudomonas aeruginosa and S. aureus (Figure 7b,c). These findings demonstrated that antibacterial activity of A. lecanora protein hydrolysates were not correlated only to the size, molecular weight and degree of hydrolysis, and hydrophobicity of peptides that could be attributed by the presence of hydrophobic amino acids such as leucine, isoleucine and phenylalanine [40]
This study demonstrated that due to its relatively high protein content, A. lecanora can be used as a raw material for the generation of bioactive peptides
Summary
The demands for natural antimicrobial compounds that are effective and non-toxic with less environmental risk has greatly increased due to the rising bacterial resistance against the synthetic antimicrobial agents and limitation on the use of synthetic preservatives in food systems. Apart from antimicrobial activity, bioactive peptides are known to exhibit other functional properties such as antihypertensive, immunomodulating, anti-thrombotic, antioxidative, anticancer, and antithrombotic [2]. These bioactive peptides are liberated through hydrolysis from the parent protein structure where they are inactive [3,4]. Most of them are linear with a potential to form amphipathic α-helical or β-sheet structures. In spite of these variations, they kill bacteria through similar mechanisms such as membrane disruption, metabolism interference and interacting with intracellular compounds [6]
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