Antioxidant Activity of Food-derived Peptides
The presence of antioxidants in foods facilitates improving the organoleptic characteristics and extending the shelf-life of the foods. Lipid oxidation as one of the major deteriorating factors can be inhibited by the activities of antioxidants. Regular ingestion of antioxidant-content foods help reduce the risk of cancers and cardiovascular diseases by protecting the body against chemically reactive molecules namely reactive oxygen species (ROS) which are the causative factors of oxidative damage of proteins, lipids and DNA.
Application of natural antioxidants or antioxidant synergists (e.g. peptides) derived from foods is believed to be a safer alternative to the use of synthetic antioxidants. This is primarily due to the potential health hazards of synthetic antioxidants which necessitate the strict legal compliance on the quantities used in the food products.
There is an increasing trend towards researching on efficient strategies to purify and isolate natural peptides and investigating their potential for antioxidant activities. The antioxidant ability of the isolated peptides (to scavenge free radicals, inhibit ROS and to suppress lipid oxidation) can be determined by means of some analytical methods.
The liberation of peptides from food sources is generally based on enzymatic hydrolysis of protein substrates to generate protein hydolysates which are then subjected to the separating stage such as ultra-filtration to obtain size-sorted fractions of peptides. The peptide fractions are subsequently purified by means of methods such as gel permeation chromatography or by reversed-phase high- performance liquid chromatography (RP-HPLC). The purified peptide fractions are individually detected by the combination of protein sequencing and mass spectrometry methods.
Mackerel and tuna are good sources of proteins containing antioxidant peptides. It has been reported that the released peptides from hydrolysed proteins of mackerel (using Protease N) display antioxidant and antiradical activities as it was observed that the generated peptides were able to inhibit auto-oxidation of linoleic acid and scavenge diphenyl-l-picrylhydrazyl (DPPH) radical. Fish proteins hydrolysed with Protease A, Protease N, Neutrase and Flavourzyme have been found to be highly effective in scavenging ROS and reducing ferric ions.