Antioxidants are vital substances which possess the ability to protect the body from damage caused by free radical-induced oxidative stress. A variety of free radical scavenging antioxidants exist within the body which many of them are derived from dietary sources like fruits, vegetables and teas.This article describes a test method for screening the antioxidant activity of 60 Iranian plants of Iran by linoleic acid peroxidation test using 1, 3-diethyl-2-thiobarbituric acid as the reagent. Some plants including Achillea wilhelmsii, Berberis crataegina, Buxus hyrcana, Chrysanthemum cinerariaefolium, Colutea persica, Hyoscyamus niger, Mentha pulegium, Nerium oleander, Pteropyrum aucheri, Rhus coriaria, Rosa canina, Scutellaria pinnatifida, Thymus pubescens, Verbascum alceoides and Ziziphora clinopodioides subsp. rigida showed antioxidant activity (0.41<IC50<1.64 mg) comparable to α-tocopherol (IC50=0.60 mg), which was used as the positive control.

The antioxidant activity of the melia azedarach was investigated in rats with ethanol-induced erythrocyte damage. Chronic administration of ethanol (20% w/v, 2 g/kg.p.o., daily for four weeks) increased the level of lipid peroxidation (LPO), decreased the activity of superoxide dismutase (SOD) and catalase and reduced the content of glutathione (GSH). The concurrent treatment of ethanol-administered rats with melia azedarach (500mg/kg, p.o.) prevented the ethanol-induced changes and the effect was compared with combination of vitamin E and C. It can, therefore, be suggested that the leaves of melia azedarach posses an erythrocyte protective activity against drug-induced oxidative stress.

This study aimed to evaluate the effect of enzymatic hydrolysis of Spirulina protein on the solubility, emulsifying activity index (EAI), emulsion stability index (ESI), and DPPH and ABTS radical scavenging activity of extracted peptides. The molecular weight of spirulina protein was determined using the SDS-Page technique. The extracted protein was hydrolyzed by alcalase enzyme and the degree of hydrolysis (DH%) was determined after 2-12 h. Functional properties and antioxidant activities of extracted protein and hydrolyzed proteins were evaluated. The concentration of extracted protein was 108 mg/L and the protein content of Spirulina was 54% (w/w). Most of the protein bands were in the molecular weight range of 15 to 20 kDa, and the DH reached from 4.2 ± 2.1% to 14 ± 1% after 10 h of enzymatic hydrolysis. The lowest solubility was recorded for the extracted protein at pH of 4, and the highest was related to the 14% hydrolyzed protein at pH of 8. Moreover, the extracted protein had higher EAI and ESI than hydrolyzed proteins, and the effect of pH was more evident on the EAI of hydrolyzed proteins compared to ESI. The present study showed that the antioxidant activity of the protein increased with increasing degree of hydrolysis and its concentration. Moreover, the protein with a DH of 14% in all concentrations had the highest inhibition. This work presented that the current method used for extraction and enzymatic hydrolysis of spirulina protein led to the production of peptides that have desirable properties for use in the food industry.