www.ijapbc.com IJAPBC – Vol. 5(1), Jan - Mar, 2016 ISSN: 2277 - 4688 1 INTERNATIONAL JOURNAL OF ADVANCES IN PHARMACY, BIOLOGY AND CHEMISTRY Research Article ABSTRACT Gamma radiation induced variation in free radical scavenging capacity of maize flour was optimized by response surface methodology. Central composite design was constructed at three levels of each of particle size, in terms of mesh number (40, 60 and 80 meshes), and gamma radiation dose (25, 50 and 75 kGy). A significant increase (p<0.05) in IC 50 value for 2, 2-Diphenyl-1-picrylhydrazyl radical scavenging capacity (DPPH RSC) and hydroxyl radical scavenging capacity (HRSC) was observed in response to an increase in gamma radiation dose. Increase in mesh No. (decrease in particle size) resulted in a significant increase in IC 50 for DPPH RSC and decrease in IC 50 for HRSC. Increase in IC 50 value indicates a decrease in free radical scavenging activity and vice versa. Optimum levels of radiation dose to achieve minimum value of IC 50 for DPPH RSC and HRSC were found to be 25 and 37 kGy respectively. Optimum level of mesh number No. to achieve minimum levels of IC 50 for DPPH RSC and HRSC were found to be 60 and 70 meshes respectively. Key words: Central composite design, Free radical scavenging capacity, Gamma irradiation, Maize flour, Particle size, Response surface methodology, Zia mays L. INTRODUCTION Free radicals are reactive oxygen and nitrogen species which may lead to protein denaturation, lipid per- oxidation, DNA lesions and finally diseased conditions if not captured effectively 1, 2 . Antioxidants are a unique class of substances that are able to protect the biomolecules from oxidative damage caused by endogenous free radicals such as superoxide and hydroxyl radicals produced during various metabolic processes 3-5 . The antioxidants perform their action by trapping the free radicals, reducing the metal ions and preventing the initiation of free radical chain, hydrogen abstraction and peroxide decomposition 3 . A large number of natural compounds such as ascorbic acid, tocopherols, phenolic acids, flavonoids, anthocyanins, proanthocyanidins and other phytochemical compounds present in food materials have been reported to possess antioxidant properties due to the presence of hydrogen donating groups in their chemical structures 6, 7 . Foods rich in antioxidant compounds have been proved to be effective in decreasing risk of cardiovascular mortality, destruction of cancer cells and preventing the oxidative lung damage 8-10 . Maize, botanically known as Zia mays L., is widely used as a source of starch, protein, vitamins and minerals in various food supplementations all over the world. It possesses great medicinal importance due to the presence of considerable amounts of naturally occurring antioxidant compounds including ß-carotene, tochopherls, phenolic acids, flavonoids and anthocyanins 11, 12 . Effect of High Dose Gamma Radiation on Free Radical Scavenging Capacity of Maize ( Zea mays L.) Flour at Various Levels of Particle Size Haq Nawaz 1 * , Muhammad Aslam Shad 1 , Tanzila Rehman 2 and Ayesha Ramzan 2 . 1 Department of Biochemistry, Bahauddin Zakariya University, Multan, Pakistan - 60800. 2 Institute of Chemical Sciences, Bahauddin Zakariya University, Multan, Pakistan - 60800.