Peptides derived from food sources: Antioxidative activities and interactions with model lipid membranes
Introduction
Oxidative stress is associated with increased production of oxidising species and/or decreased effectiveness of antioxidant defences, and it can arise through various biochemical reactions (Carocho & Ferreira, 2013). This stress is governed by free radicals, atoms, molecules and ions that are highly active and prone to interactions with other molecules, due to their unpaired electrons (Ak & Gülçin, 2008). Substances that delay, prevent or inhibit oxidative damage of targeted molecules at low concentrations are defined as antioxidants (Gas Halliwell, 1990). The well-known naturally occurring antioxidants include vitamins C and E, glutathione (GSH) and the enzymes superoxide dismutase and catalase. Many new antioxidants with phenolic structures have been identified in plant extracts, or have been produced by chemical synthesis.
Special attention has been paid to biologically active peptides that can be obtained from protein molecules in foods through enzymatic degradation (Korhonen & Pihlanto, 2003). The most studied food source for bioactive peptides is milk, although along with many others, such as eggs, meat, soy, corn, chickpea, whey, sweet potato and even fish waste (Bouglé & Bouhallab, 2017). Less attention has been paid to grain, like millet, which is used in rural areas, and has been shown to be nutritional and an active peptide source (Kumar et al., 2016, Agrawal et al., 2018).
Bioactive peptides have a wide range of different activities, with most being antioxidative and antimicrobial (Hartmann & Meisel, 2007). Recently, antioxidative peptides have also been found in processed food, like ham (Gallego, Mora, & Toldrá, 2018). Peptides with antioxidative activities against lipid oxidation are of particular interest to the fish product industry, and especially fish oil, which undergoes rapid oxidation (Hu & Jacobsen, 2016). Antioxidative peptides might be candidates for the design of active food matrices, as active agents incorporated into biopolymers (Dehghani, Hosseini, & Regenstein, 2018).
Bioactive peptides with antimicrobial activities can inhibit bacteria by interfering with different biological processes. Indeed, antimicrobial peptides might be even more potent then antibiotics (Khan, Pirzadeh, Förster, Shityakov, & Shariati, 2018). They can affect bacteria by interactions with their inner macromolecules (Shah, Hsiao, Ho, & Chen, 2016) or by making pores in the bacteria membrane. As bacterial strains can adapt and change their biological pathways, and in this way develop resistance, peptides that can attach to the bacterial membrane and form pores or disrupt the bacteria cell transport are of special interest. Antimicrobial peptides usually have charged and hydrophobic residues (Galdiero et al., 2013).
Recently, peptides with antioxidative and antimicrobial activities have been used in the formulation of different food packaging and for coating technologies, by incorporating them into an active coating polymer or coating emulsion (Angiolillo et al., 2016, Galus and Kadzińska, 2015). The main goal of the food package/coating is to preserve the food composition intact, and to prevent protein and lipid oxidation or microbiological decomposition.
In the present study, we investigated seven known peptides from different sources (Table 1) and one designed by in-silico techniques, to determine the most active peptides with the strongest antioxidative and antimicrobial activities, and to determine which amino-acid residues are crucial for their mode(s) of action. Additionally, we studied the interactions of peptides with model lipid membranes. The peptide kinetics towards reactive oxidative species (ROS), their antimicrobial activities, and their interactions with model lipid membranes were studied using a combination of different antioxidative and antimicrobial assays, fluorescence emission spectrometry, and differential scanning calorimetry (DSC).
Section snippets
Materials
1,1-Diphenyl-2-picrylhydrazyl (DPPH), Triton X-100, GSH, Trolox reagents, and the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and N,N,N-trimethyl-4-(6-phenyl-1,3,5-hexatrien-1-yl)phenylammonium p-toluenesulfonate (TMA-DPH) were from Sigma Chemicals (St. Louis, MO, USA). The fluorescent label 4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid (BODIPY 581/591C11) was from Invitrogen Molecular Probes (USA). Egg phosphatidylcholine (PtdCho),
Peptides
In this study, we used seven known peptides (P#1-P#7) that originated from the different parent proteins listed in Table 1, and one peptide obtained based on in-silico hydrolysis by endopeptidase of whey protein lactalbumin (P#8). Peptide P#1 (Pro-Glu-Leu) originated from milk casein, and was obtained after 20 h of enzymatic hydrolysis by pepsin at 37 °C (Suetsuna, Ikeda, & Ochi, 2000). The short P#1 that included proline was chosen due to its known antioxidative activity. P#2 (Leu-Gln-Lys-Trp)
Conclusions
This study was conducted to evaluate any changes in the antioxidative and antimicrobial activities, and the interactions with model lipid membranes, for eight active peptides. The data summarized in Table 2 revealed some antioxidative properties of these active peptides towards different oxidants: superoxide radicals, metal ions, DPPH and lipid radicals. These depended on many properties, such as peptide size, polarity and amino-acid composition.
Here, we have shown that the four main aspects of
Acknowledgements
The authors thank the Slovene Human Resources Development and Scholarship Fund No. 11011-55/2013 (A.G.), and the Slovenian Research Agency, for financial support through the programme P4-0121 (N.P.U).
Declarations of interest
None.
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