Combined effects of irradiation and the use of natural antioxidants on the shelf-life stability of overwrapped minced beef

Five batches of aerobically packaged minced beef from Friesian cattle were irradiated at 0, 1, 2, 3 or 4 kGy using a 60Co irradiation source. The five batches were as follows: non-supplemented (C), dietary alpha-tocopheryl acetate supplemented (S), alpha-tocopheryl acetate supplemented with water soluble rosemary extract added after mincing (Rw), alpha-tocopheryl acetate supplemented with oil soluble rosemary extract added after mincing (Ro) and alpha-tocopheryl acetate supplemented with water and oil soluble rosemary extracts added after mincing (R). Incorporation of antioxidants resulted in better retention of colour. Irradiation at 4 kGy increased Hunter 'a' values up to day 4 with alpha-tocopheryl acetate supplementation and up to day 6 when rosemary extracts were added. Irradiation at 4 kGy increased Hunter 'b' values on days 4, 6 and 8 in the control samples. Antioxidants decreased metmyoglobin values on day 0 and day 2 for non-irradiated (0 kGy) samples and for the entire display period for irradiated samples. Antioxidants increased the oxymyoglobin values up to day 4 for the 1, 2 and 3 kGy beef samples and over the entire display period for the 4 kGy samples. TBARS values for each treatment group increased with increasing irradiation dose. alpha-Tocopheryl acetate supplemented samples had lower TBARS values than control samples at all irradiation doses. The levels of alpha-tocopherol in samples on day 0 decreased with increasing irradiation dose for the (C) and (S) samples. However, levels of alpha-tocopherol in samples on day 0 increased with increasing irradiation dose for Ro, Rw and R samples. All antioxidant treatments were effective at inhibiting lipid peroxidation even at the highest irradiation dose applied. Irradiation caused a significant reduction in the polyunsaturated fatty acid (PUFA) content, mainly in C18:2 after storage at 40 degrees C under fluorescent light for 8 days.