Title : Exploring the influence of amino acid composition and size on antioxidant and antimicrobial functions of plant derived peptides
Abstract:
Plant-Derived Peptides (PDP) have recently become scientifically popular for being natural bioactive compounds encompassing strong antioxidant and antimicrobial properties. PDPs are small fragments of protein that can be extracted from cereals, legumes, oilseeds, and other plant sources through different techniques, especially enzymatic hydrolysis or fermentation. Several factors influence their activity, but the recent research favours that amino acid composition and molecular size are the most important markers enhancing the biological activity. Furthermore, hydrophobic residues enriched peptides such as leucine, valine, alanine and methionine strongly inhibit lipid oxidation because of their affinity for hydrophobic environments. On the other hand, aromatic amino acids, including tyrosine, tryptophan, and phenylalanine, intensify radical scavenging performance. Their structure stabilizes free radicals via donation of electrons and thus strong performance is seen in 2,2-Diphenyl-1-picrylhydrazyl (DPPH) , 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and reported IC₅₀ values ranging from 0.12 to 1.5 mg/mL in DPPH and ABTS assays, with lower IC₅₀ values predominantly observed in fractions enriched with hydrophobic and aromatic residues. Additionally, Oxygen Radical Absorbance Capacity (ORAC) and hydroxyl radical assays also showed improved results. Peptides that have hydrophobic ends at N terminal and aromatic ends at the C-terminal tend to have higher antioxidant activity. This shows that sequence arrangement leads to efficient transfer of electrons. Positioning of amino acids in a chain also influences the activity, electron transfer ability, and overall stability compared to a randomly arranged sequence.
Moreover, researchers concluded that amino acid composition also influences the antimicrobial activity. For instance, Peptides rich in positively charged amino acids, >+3 such as arginine and lysine, proved to have a stronger antibacterial effect. This result depicts that these positively charged residues interact with negatively charged membranes of the microbes via electrostatic attraction, and it leads to microbial cell death by creating pores and disrupting membrane integrity. Peptides with a net positive charge show more effective response against bacterial activity, especially for food-borne pathogens, however it does not always show a higher antioxidant activity. This highlights the fact that there must be a balanced amino acid distribution to support antimicrobial functionality.
The second important determinant is molecular size. Evidence shows that low molecular weight peptide specially <3kDA performs superior in terms of having antioxidant and antimicrobial activities, while peptides in the 500-1000 DA range produced the highest values in radical scavenging activity and ORAC. similarly, high molecular weight peptides >3kDA showed reduced radical scavenging activity and weak bacterial inhibition more likely due to reduced mobility and steric hinderance. Thus, this shows that smaller peptides have more accessibility to interact with reactive species.
Collectively, these findings demonstrate that amino acid composition and molecular size work in conjunction in evaluating the efficacy of plant derived peptides. Antioxidant performance is enhanced by hydrophobic and aromatic residues while cationic residues enhance antimicrobial action and appropriate molecular weights improve functional efficacy. Focusing on these two major characteristics helps design a strategy to design affective plant derived peptides which ultimately helps in developing plant based functional ingredients for food preservation and nutraceuticals agents.
