Linum usitatissimum, commonly known as flaxseed or linseed, is a flowering plant that originated in the Middle East. One of the oldest crops known to man, it has been cultivated since the beginning of civilization. Today, flaxseed is considered a superfood and is known for its abundance of macro- and micronutrients, such as fiber, protein and heart-healthy omega-3 fatty acids.
Thanks to its high protein content, flaxseed is also a great source of antioxidant peptides. These short but useful protein fragments typically consist of two to 20 amino acids and are gradually being accepted as natural food ingredients. Because of their ability to donate electrons, scavenge free radicals and chelate metals, antioxidant peptides present a promising solution for reducing oxidative stress and controlling the oxidation of lipids in food and cosmetic products.
Oxidative stress is a phenomenon caused by an imbalance between the generation of free radicals and the production of antioxidants inside the body. This event is known to trigger inflammation, which is linked to the development of chronic diseases. On the other hand, lipid oxidation not only causes the formation of unhealthy compounds in foods and cosmetic products, but it also negatively impacts their sensory properties and reduces their shelf life.
In a recent study, researchers from New Zealand and Canada analyzed storage proteins from mature flaxseed in hopes of discovering new antioxidant peptides that can be used to preserve the quality of foods and cosmetics. They chose flaxseed because of its nutritionally desirable amino acid profile, reputation as a high-value superfood and the reported antioxidant capacity of its protein hydrolysis products. The researchers reported their findings in an article published in the journal Food Science and Human Wellness.
Identification of antioxidant peptides in flaxseed for use in foods and cosmetics
In recent years, consumer preference for natural ingredients not only in foods but also in cosmetics has increased tremendously. The discovery of antioxidant peptides and their ability to protect against oxidation has made them desirable natural additives to functional foods, nutraceuticals and a variety of personal care products. (Related: Summer savory essential oil can be used to extend the shelf life of food products.)
Like other bioactive peptides, antioxidant peptides are inactive in their natural form. They need to be first released from proteins before they can perform their functions. Fortunately, proteolytic enzymes, or proteases, that can excise these peptides from whole protein sequences abound in nature. This means that countless protein-protease combinations can be made and used to produce different bioactive peptides.
For their study, the researchers identified antioxidant peptides encrypted in the protein sequences of flaxseed with the help of a bioinformatic tools. Using the BIOPEP database of sensory peptides and amino acids, they also assessed the ability of nine proteases from digestive, plant and microbial sources to excise known antioxidant peptides from 23 mature flaxseed storage proteins.
The researchers identified several protein families, including globulins and oleosins, which are the predominant proteins in flaxseed, and a small amount of conlinin. Globulins are the most common group of storage proteins in plants while oleosins are involved in the biosynthesis and mobilization of lipids during seed maturation and germination. Conlinin is a major storage protein found in flaxseed gum.
From these families, the researchers identified a total of 253 different antioxidant peptides. Enzymatic hydrolysis released more peptides from globulins than from oleosins and conlinin. The researchers found that among the plant proteases they tested, papain from papaya, ficin from a tropical fig tree and bromelain from pineapples were the most effective at releasing antioxidant peptides from flaxseed proteins.
Toxicity analysis showed that none of the peptides released from flaxseed proteins were toxic. Most of them owed their antioxidant properties to their abundance of antioxidant amino acid residues (e.g., glutamic acid and histidine). In addition, the peptides exhibited amphipathic properties, which meant they have water-loving (hydrophilic) and water-repellent (hydrophobic) parts, and had low Boman indices, which suggests they’re unlikely to interact with other proteins.
Based on these findings, the researchers concluded that flaxseed proteins are excellent sources of antioxidant peptides that can be used to combat oxidative stress in biological systems and prevent lipid oxidation in foods and cosmetics.