Plant-Based Bioactive Peptides
Antioxidant peptides isolated from a soybean protein hydrolysate is very important and there have been many studies about it. Triple peptides from soy bean containing two Tyr residues are stronger because they contain two His residues to inhibit linoleic acid peroxidation, and also a high antioxidant activity if the peptide contains Trp amino acid or Tyr tripeptide at the C-terminal (Saito et al. 2003). In 1996 a peptide from soybean has found. After it was designed new peptides were based on this peptide: Leu-Leu-Pro-His-His. In comparison, among the tested peptides Pro-Her-Her was found the most antioxidative sequence. So, the antioxidant activity is associated with histidine and proline amino acids (Chen et al. 1996). In a study, three separate enzymes were used and have demonstrated that the ultrafiltration membrane fractions and the soy protein hydrolysates may hinder lipid peroxidation in cooked minced meat (Zhang, Li, and Zhou 2010). Additionally, in this study results with peptide (Leu-Met-Trp) revealed that the low molecular weight of peptide sequences had a greater effect on peroxyl radical scavengers compared with higher molecular weight peptide sequences (Aluko 2015). In another study, it is found that a peptide (Ala-Arg-Glu-Glu-Thr-Val-Val-Pro-Gly) isolated from wholewheat products operates a protective role in vascular smooth muscle cells on high glucose-induced oxidative stress and may have a potential therapeutic effect (Chen et al. 2017).
Antioxidant peptides are also isolated from hydrolysates of walnut flour proteins. There are six important peptides (Val-Arg-Asn, Asn-Pro-Ala-Asn, Ala-His-Ser-Val- Gly-Pro, Ser-Ser-Glu, Thr-Tyr, and Ser-Gly-Gly-Tyr) and those were found to have more antioxidant potential than other peptides of walnut (Feng et al. 2018).
In another study, peptides that have antioxidative properties from millet were identified using trypsin enzyme and the peptides showed a high antioxidant activity when tested by different free radicals (Agrawal, Joshi, and Gupta 2016).
Cereal peptides and hydrolyzed proteins have been found to exhibit oxidative stress-reducing effects in experiments (in chemical-based analyzes, cell cultures, animal models, and food systems) (Esfandi, Walters, and Tsopmo 2019).
The antioxidant peptide is reported to be purified from chickpea (Cicer arietium L.) protein hydrolysates. The amino acid sequence of this purified peptide is Asn- Arg-Tyr-His-Glu and amino acids to each other were determined as 1: 1: 1: 1: 1. This antioxidant peptide has been found to effectively inhibit DPPH, superoxide, and hydroxyl free radicals from free radical sources. It is reported that the peptide has Cu + 2 and Fe + 2 chelate activities also inhibit autooxidation of linoleic acid (Zhang et al. 2011).
A protein isolate from beans (Phaseolus vulgaris L.) and a purified protein product (phaseolin) were digested with pepsin and pancreatin and then the antioxidant activities were tested from the protein hydrolysates (Carrasco-Castilla et al. 2012).
The yellow eld pea seed hydrolysate has been shown to be an important contributor to the peptide antioxidant properties of hydrophobicity and net charge with a series of trials on thermolysin digestion including column chromatography divisions. First, pea protein hydrolysate was divided into fractions (F1-F5), which differ in the total content of hydrophobic amino acids by reverse phase high performance liquid chromatography (HPLC). (Pownall, Udenigwe, and Aluko 2010).
Spirulina platensis is the only blue-green algae that is grown commercially for food use. It is a good food source due to its high protein content and natural biochelate vitamins. A mixture of these two sources rich in protein was found to be successful in preventing liver damage induced by CC14 (hepatotoxin) in an in vivo study (Gad et al. 2011).
Also, with assay on shrimp peptides Gin and Lys amino acids are also known as potential antioxidants (Wu et al. 2019).
Alfalfa leaf: Due to its high protein content and nutritional value, the Food and Agriculture Organization recommended it for human consumption as a potential protein source. Mice fed with the proteins of these leaves were observed to have an increase in GSH-Px and SOD enzymes and a decrease in the concentration of malonaldehyde (MDA). In the leaf, albumin was found to be the dominant protein, while gluten and globin were found in small amounts. It is found that cloverleaf peptides have a good antioxidant activity (Xie et al. 2008). In a study they have found that hydrolysate of carrot seed protein peptides can be promising oxidative damage scavengers in food. They have antioxidant activities (Ye et al. 2018). In another study, peptides were produced from pollen using the alcalase enzyme. It was purified by size-exclusion chromatography after enzymatic hydrolysis. Reverse-phase HPLC was used to lyse the antioxidant activity of pollen-derived peptides. The DPPH radical removal activity of the fractions obtained was 66.61% (Maqsoudlou et al. 2018) (Table 12.1).