**Contents**


## **About the Editors**

#### **Lourdes Amigo Garrido** (PhD)

Lourdes is a research professor at the Institute of Food Science Research (CIAL, CSIC-UAM), Madrid, Spain. She was director of the Institute of Industrial Fermentations (CSIC) (February 2002–July 2010), director of the Centre of Organic Chemistry "Manuel Lora-Tamayo" (June 2002–June 2004), and coordinator of the director's permanent commission of CSIC (September 2006–July 2010). She has participated in 66 different R+ D projects and published 120 research papers in journals and 9 book chapters. Prof. Amigo has presented 22 invited lectures and 106 oral communications and posters in international and national symposia. She is co-author of four patents. She has supervised 8 PhD theses and 12 master's theses. She is a teacher in different graduate and post-graduate specialization courses for graduates, technicians, and master's students in Spain and South America. She is a supervisor of graduate students and technical personnel. She is also a reviewer of 35 SCI journals and a research projects evaluator.

#### **Blanca Hern´andez Ledesma** (PhD)

Blanca Hernandez Ledesma has been working at the Institute of Industrial Fermentations (CSIC, ´ January 1999–December 2006), the Univ. of California at Berkeley (January 2007–November 2009), and the Institute of Food Science Research (CSIC-UAM, January 2010-current). Her research career has been focused on the study of the biological activity of food proteins/peptides, investigating their modifications during gastrointestinal digestion, their bioavailability, and their mechanisms of action, and developing processes to produce ingredients with improved techno-functional and organoleptic properties. She is author of 85 JCR articles and 38 book chapters (h-index 37). Her results have been presented in 64 International and 24 National Symposia. She is co-inventor of three patents. She has supervised 4 PhD theses and 17 master's theses. She has participated in 30 R+D Projects, and 3 contracts within the industry. She is member of the editorial committees of four books and nine journals, participating as guest editor of six Special Issues.

## *Editorial* **Introduction to the Special Issue: New Advances in the Research of Antioxidant Food Peptides**

#### **Lourdes Amigo and Blanca Hernández-Ledesma \***

Institute of Food Science Research (CIAL, CSIC-UAM, CEI UAM + CSIC), Nicolás Cabrera 9, 28049 Madrid, Spain; lourdes.amigo@csic.es

**\*** Correspondence: b.hernandez@csic.es; Tel.: +34-91-0017970

Received: 1 December 2020; Accepted: 4 December 2020; Published: 7 December 2020

During cell metabolism, oxygen is partially reduced to reactive oxygen species (ROS) that play a physiological role in cellular processes, including proliferation, cell cycle and death, and signal transduction. However, ROS are responsible for attacking cell nucleophilic centers, causing lipid peroxidation, protein oxidation, and genetic alterations, including DNA damage, mutations, epigenetic changes, and genomic instability. Fortunately, the human body is equipped with an effective defense system to neutralize the toxicity of ROS. However, an imbalance provoked by either an over-production of ROS or a defect in the cellular defense system results in a state known as oxidative stress. This status and its subsequent damages to vital cellular components have been associated with numerous severe chronic disorders, such as cardiovascular and neurodegenerative diseases, diabetes, metabolic syndrome, intestinal inflammatory diseases, and cancer. In addition, oxidation reactions are responsible for food deterioration during processing and storage. In spite of their remarkable effectiveness, the endogenous antioxidant systems are not sufficient and humans are dependent on dietary antioxidants to maintain ROS concentrations at low levels. A number of natural antioxidants have been revealed as potential preventative/therapeutic agents against oxidative stress. Among them, peptides from animal and vegetal food sources have attracted attention because of the plentiful evidence of their in vitro antioxidant properties. In addition to their potential as safer alternatives to synthetic antioxidants used to prevent oxidative reactions in foods, antioxidant peptides can also act by reducing the risk of numerous oxidative stress-associated diseases. Furthermore, peptides can act synergistically with non-peptide antioxidants, enhancing their protective effect.

This Special Issue of the *Foods* journal includes seven outstanding papers describing examples of the most recent advances in the antioxidant peptide research. It begins with a group of papers describing the antioxidant potential of vegetal food-derived hydrolyzates and peptides. The review of Olivares-Galván et al. [1] summarized the existing evidence on antioxidant peptides released from fruit residues, focusing on the current techniques used in their extraction, purification, fractionation, and identification, the strategies followed to allow the peptides' release from source protein, as well as the assays used to determine their antioxidant activity. Two research articles described the potential of two vegetal proteins as sources of antioxidant peptides. Thus, the study of Kusumah et al. [2] aimed at identifying the mung bean (Vigna radiata) albumin sequences with antioxidant capacity by both in silico and in vitro assays. The hydrolysates produced by thermolysin showed high antioxidant potential in terms of ferrous ion chelating and ORAC values because of the high hydrophobicity and low molecular mass of the released peptides. In the study of Esfandi et al. [3], hydrolyzates from oat bran protein with Alcalase®, Flavourzyme®, papain or Protamex® showed the ability to protect hepatic HepG2 cells against oxidative damage by reducing ROS levels and caspase-3 activity, and increased glutathione concentration and antioxidant enzymes activity.

The following articles focused on animal protein sources of antioxidant peptides. First, the review of Gilmartin et al. [4] described the potential role exerted by whey protein, hydrolyzates or peptides in the modulation of sarcopenic biomarkers in myoblast cell lines, and in aged rodents and humans. The human intervention trials have shown that a daily dietary supplementation of 35 g of whey is likely to improve sarcopenic biomarkers, improving muscle mTOR signaling in the elderly, although exercise appears to have the greatest benefit for old muscle. Kleekayai et al. [5] hydrolyzed bovine whey protein concentrate with DebitraseTM and FlavorProTM under pH-stat and non pH-controlled conditions, evaluating the impact of hydrolysis conditions on the physicochemical and antioxidant activities of the released hydrolyzates. These authors demonstrated that hydrolyzates generated under pH-stat conditions displayed higher radical scavenging activities than those shown by non-pH-controlled conditions. Moreover, a more pronounced impact of conditions in the biochemical assays compared to the cellular antioxidant assay was observed. In the study of Amigo et al. [6], an integrated approach combining in silico and in vitro assays was used, confirming the multifunctionality of milk and meat protein-derived peptides that were similar to or shared amino acids with previously described opioid peptides. Fifteen of twenty-seven assayed peptides were found to exert two or more activities, with angiotensin-converting enzyme (ACE) inhibitory, antioxidant, and opioid being the most commonly found. Four fragments, RYLGYLE, YLGYLE, YFYPEL, and YPWT, demonstrated ACE-inhibitory and antioxidant activities, and also protected Caco-2 and macrophage RAW264.7 cells against chemical-induced oxidative damage. Finally, the review of Benedé and Molina [7] summarized the current knowledge on the antioxidant activity of chicken egg proteins and their derived peptides. The main process for obtaining these bioactive peptides from their source proteins is enzymatic hydrolysis using enzymes and/or processing technologies, such as heating, sonication or a high-intensity-pulsed electric field. Different in vitro assays have been used to evaluate the mechanisms of action of egg bioactive peptides, the in vivo effects of which have been confirmed by both cell culture assays and animal models.

**Author Contributions:** Writing—original draft preparation, L.A., and B.H.-L.; writing-review and editing, L.A., and B.H.-L.; funding acquisition, L.A., and B.H.-L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by project AGL2015-66886-R from the Spanish Ministry of Science and Innovation (MICIU) and PID2019-104218RB-I00 (CSIC).

**Acknowledgments:** We wish to thank the invited authors for their interesting and insightful contributions.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


7. Benedé, S.; Molina, E. Chicken Egg Proteins and Derived Peptides with Antioxidant Properties. *Foods* **2020**, *9*, 735. [CrossRef] [PubMed]

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