In recent years, more and more studies have described the antioxidant capacity of plant protein-derived peptides. Plant proteins are considered a new source of antioxidant peptides that can not only save energy, but also enhance the treatment of oxidation-related diseases, delay the oxidation of food, and thus improve the quality of life. Despite an increasing number of reports on the preparation, structure, and activity of antioxidant peptides, and the commercialization of some antioxidant peptides, a systematic review and evaluation of plant protein-derived antioxidant peptides is still lacking. This article summarizes the latest advances in plant protein-derived antioxidant peptides, including (1) the preparation, purification, identification, and application of plant protein-derived antioxidant peptides by enzymatic hydrolysis; (2) Influencing factors, evaluation methods, and mechanism of antioxidant protein hydrolysates or peptides.
Traditional purification and identification methods of antioxidant peptides are expensive and time-consuming. To solve this problem, researchers have conducted extensive exploration and research on computer-aided mathematical models (molecular docking, QSAR studies, etc.), bioinformatics tools, and real-time updated protein databases. In addition, the authors of the reviews believe that future research should focus on the large-scale commercial production of plant protein-derived antioxidant peptides, comprehensive studies on the structure-activity relationship of antioxidant peptides, an in-depth understanding of antioxidant mechanisms, and confirmation of their health benefits in vivo.
Antioxidant peptides are specific protein fragments possessing antioxidant activity and antioxidant peptides derived from plant protein are called plant protein-derived antioxidant peptides. With increasing consumer demand for high nutritional and functional proteins, researchers are shifting their focus from traditional raw proteins to plant-based proteins. In particular, natural antioxidant peptides derived from plant proteins have attracted worldwide attention due to their advantages of environmental protection, sustainability, low cost, and non-toxic side effects.
The effective prevention of oxidative stress and food oxidation of antioxidant peptides attracted researchers to evaluate their antioxidant capacity. At present, there are three methods to evaluate the antioxidant capacity of peptides: chemical method, cell biology method in vitro, and animal experiment in vivo. The potential mechanisms of antioxidant peptides are as follows: (1) direct scavenging of reactive oxygen species; (2) chelated metal ions; (3) Inhibition of lipid peroxidation; (4) Activate the body’s antioxidant defense system.
From the point of view of sustainable development and utilization of biological resources, protein resources in the by-products or wastes produced during plant processing have great potential to produce bioactive peptides. The rational development and utilization of plant processing by-products or wastes are beneficial to improve the nutritional utilization value of wastes, save energy and protect the environment. In particular, wheat gluten, wheat germ, rapeseed, watermelon seed, corn gluten, rice bran, oat bran, palm kernel cake, and wine-making grains have been used to produce antioxidant peptides.
Plant proteases (animal proteases, plant proteases, and microbial proteases) are hydrolyzed first to form proteolysis, followed by further purification, membrane separation, electrophoresis, chromatography (gel permeation chromatography (GPC), ion exchange chromatography (IEC), reversed-phase high-performance liquid chromatography (RP-HPLC), etc.) to obtain antioxidant peptides. The obtained antioxidant peptides were identified by mass spectrometry or mass spectrometry/mass spectrometry, and their antioxidant activities were evaluated by in vitro and in vivo experiments. At present, the main preparation methods for peptides are chemical extraction, fermentation, synthesis, and enzymolysis.
The enzymolysis product of proteins is a mixture consisting of partially unhydrolyzed proteins, peptides with different chain lengths, hydrophobicity and net charge, and free amino acids. To evaluate the structure and activity of antioxidant peptides more accurately, it is necessary to develop suitable purification methods. At present, the main separation and purification technologies of peptides include chromatography (GPC, IEC, RP-HPLC), membrane separation, and a combination of these technologies. Identification of protein hydrolysates is usually accomplished by mass spectrometry, mass spectrometry/mass spectrometry, and bioinformatics techniques.
After a series of isolation and purification schemes, the peptide structure needs to be identified. DNA translation, mass spectrometry, and peptide sequencing are commonly used to identify peptides. It is worth noting that mass spectrometry has been widely used in the identification of peptide sequences because of its high efficiency, sensitivity, and good reproducibility. In addition, several online databases have become popular for researching antioxidant peptides. Table 2 summarizes the main bioinformatics analysis tools.
It is important to summarize the properties and activities of plant-derived antioxidant peptides as comprehensively as possible for guiding and predicting the relationship between the structure and function of plant-derived antioxidant peptides. The activity of antioxidant peptides is mainly affected by amino acid composition, sequence, and molecular weight.
QSAR is a mathematical model to establish quantitative dependence between the structure-activity relationships of a series of compounds. QSAR is used to evaluate the correlation between the molecular structure and activity of antioxidant peptides, which provides a good theoretical basis for the prediction, isolation, and purification of peptide activity and elucidation of molecular mechanism.
As mentioned earlier, proteins derived from plant products can be used to produce antioxidant peptides. On this basis, the research progress of plant-derived antioxidant peptides was reviewed in this paper. The molecular mechanism of these peptides at the level of the whole gene will be verified with the advancement of science and technology in the future and the continuous investment in the research of these peptides in vivo. In addition, the preparation of nanoparticles and microcapsules of antioxidant peptides and their synergies with other active ingredients are also the focus of future research. Future research and industrial cooperation will help achieve the long-term goal of commercializing plant antioxidant peptides.
]]>Cytokines are an important group of proteins realizing intercellular communications among cells of the same tissue (paracrine) or of different tissues (endocrine). Such communications are essential for the correct synchronized reactions of the cells of different tissues. In the literature different designations are used to denote these factors: lymphokines, monokines, interleukins, and growth factors, which are now unified under the common name cytokines. The main cytokines include interleukins 1 to 18 (IL-1 to IL-18); interferons α, β, and γ (IFNα, IFNβ, and IFNγ, respectively); tumor necrosis factorsα and β (TNFα and TNFβ); colony-stimulating factors — granulocyte, macrophage, and granulocyte-macrophage (CSF-G, CSF-M, CSF-GM, respectively); basic and acid fibroblast growth factors (aFGF and bFGF); and others.
There are two types of human interferons, type I and type II, and interferon-like cytokines. Type I human interferons consist of six classes: IFN-α, IFN-β, IFN-ε, IFN-κ, IFN-ω, and IFN-ν. However, a large number of type I interferons are found in other animal species. Type II interferon consists only of IFN-γ. In addition, three related human interferon-like cytokines have been reported: IL-28A, IL-28B, and IL-29. There is only one IFN-β, IFN-ε, IFN-κ, IFN-ω, and IFN-ν, but the IFN-α proteins consist of twelve individual proteins.
Differences between IFNγ and IFNα/β
The main differences between IFNγ (type II) and IFNα/β (type I) are summarized as follows:
The different receptors and the differences in the metabolic signaling pathways open avenues for a combined clinical use of IFNγ and IFNβ or IFNγ and IFNα. In the latter case, the possible effect of IFNγ on the IFNα receptor has to be taken into consideration. This effect seems to depend on the cellular type. In the neuroblastoma cell line T98G, IFNγ suppresses the binding of IFNα to its receptor, possibly by affecting its dissociation constant (Kd). In other tumor cell lines (melanoma HMV-1, kidney carcinoma ACHN, Daudi lymphoma), IFNγ induces the receptors of IFNα but only under the condition that IFNγ preceded the treatment with IFNα.
The Principal Properties of Interferon
Interferon possesses certain characteristic properties which distinguish it from other virus inhibitors. These include:
Besides these properties, interferon also possesses others which characterize it as a protein of low molecular weight with particular physicochemical properties. Details of the various properties of interferon are given below.
Physicochemical Properties
Interferon is a protein of low molecular weight. Its molecule contains the following components: tyrosine 2.3%, tryptophan 2.6%, arginine 7.2%, lysine 11.1%. It does not contain nucleic acids and only traces of carbohydrate are present. Interferon has a slightly acid reaction and contains disulfide bridges. The number of polypeptide chains has not been established. However, the reaction of this protein is alkaline and the isoelectric point is close to pH 6.9-7.1 or 7.2-7.8.
Species Specificity
One of the most important properties of interferon is its well-marked species specificity. This property of interferon was first described by Tyrrell. In his experiments the inhibitors obtained in the chorioallantoic membranes of the chick embryo and in cultures of calf kidney cells possessed antiviral activity only in homologous cells. Isaacs and Westwood also showed that vaccinal lesions in the rabbit’s skin were actively inhibited by interferon produced in cultures of rabbit cells, whereas chick interferon gave a very weak effect in such cases. The opposite effect was obtained in experiments on chick embryos, i.e., only chick and not rabbit interferon was active. Later the marked species specificity of interferon was confirmed by most investigations.
Antigenic Properties
The weakness of the antigenic properties of interferon is confirmed by the results obtained by Falcoff and co-workers, who found that repeated intravenous injections of human leukocytic interferon into adults and children were not accompanied by the formation of any detectable quantities of antibodies. No antibodies could be detected even in a child aged 6 years who received 3620 ml of leukocytic interferon intravenously over a period of 400 days.
Solov’ev, V. (2012). Interferon: Theory and Applications. Springer Science & Business Media.
Tsanev, R. G., & Ivanov, I. (2001). Immune interferon: properties and clinical applications. CRC Press.
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